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Breeding objectives for beef cattle in Ireland
a ,
*
b c d eP.R. Amer
, G. Simm , M.G. Keane , M.G. Diskin , B.W. Wickham
a
AgResearch Invermay, Private Bag 50034, Mosgiel, New Zealand
b
Animal Biology Division, SAC, West Mains Road, Edinburgh EH9 3JG, UK
c
Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland
d
Teagasc, Athenry Research Centre, Athenry, Co. Galway, Ireland
e
Irish Cattle Breeding Federation Society Ltd., Bandon, Co. Cork, Ireland
Received 8 October 1999; received in revised form 26 April 2000; accepted 7 May 2000
Abstract
Breeding objectives for beef cattle in Ireland were derived and used to define selection sub-indexes. The intention of the sub-indexes was to simplify selection decisions by commercial bull and semen buyers for situations where all of the resulting progeny are slaughtered, or when some female progeny are kept as replacement breeding cows. Separate sets of economic values for calving ease and gestation length are proposed for use in separate calving sub-indexes depending on whether dairy cows or beef cows are to be mated. Proposed economic values for calf quality, growth, calving and reproduction sub-indexes were assumed to be independent of the breed of cow to be mated. It was also recommended that separate total indexes for dairy cow and beef cow matings be constructed as simple linear functions of the sub-indexes. 2001 Elsevier Science B.V. All rights reserved.
Keywords: Beef cattle; Selection index; Terminal sire; Reproduction
1. Introduction omic values are needed for each trait in the breeding
objective to ensure that selection emphasis is propor-Clearly defined breeding objectives are vital for tional to the economic importance of each of these effective genetic improvement of all livestock traits. Having a clear breeding objective is also an species. Since they were first proposed for animals important prerequisite to the development of cost by Hazel (1943), multiple-trait selection indexes effective breeding strategies, and to the identification have become the method of choice for maximising of a set of traits making up the selection criteria genetic gain in a chosen breeding objective. These which contribute to accurate prediction of traits indexes simplify comparisons of animals based on affecting commercial profitability.
estimated breeding values for individual traits. Econ- The organisational structure for beef performance recording, data capture and breeding programmes in Ireland is in the process of change (Keane and
*Corresponding author. Tel.: 164-3-4893-809; fax: 1
64-3-Diskin, 1996). Some time has elapsed since breeding
4893-739.
E-mail address: [email protected] (P.R. Amer). objectives for Irish beef cattle have been evaluated in
detail (Cunningham, 1974; Barlow, 1982; Barlow breed parent in these herd types are shown in Table and Cunningham, 1984). Thus, it is timely for a 1. These breeding objective traits are divided into reassessment of the breeding objective for Irish beef five groups, with some repetition for traits included cattle. in the reproduction group. This repetition facilitates a The primary objective of this paper was to outline more simple combination of a reproduction sub-the approaches taken in sub-the development of a index with sub-indexes for the other groups. Where breeding objective for Irish beef cattle. The sec- economic values vary across mating (terminal sire ondary objective was to explore the potential mag- versus sire to breed female replacements) and pro-nitude of variation in economic values when calcu- duction (beef breed matings to dairy versus beef lated for some alternative breeds and production cows) systems, sub-indexes can be presented to systems. This largely involved the use of published index users to allow flexibility in selection emphasis methodology and models, adapted to be relevant to across relevant groups of traits. Sub-indexes are Irish beef cattle production, although in some in- computed by setting economic values for all breed-stances, new models and approaches were used, and ing objective traits not in the sub-index of interest to these are also described here. zero (Amer et al., 1998a).
Traits expressed by calves prior to or at weaning are assumed to have both direct and maternal
2. Materials and methods breeding values estimated for them. While economic values are typically the same for direct and maternal 2.1. Breeding perspective effects on the same trait, the number and timing of their expression is different across different classes In this study we take farm profit as the perspective of selection candidates and so both effects are from which the benefits of selective breeding are included in Table 1.
defined. The number of animals per farm is assumed Cow mature weight takes three forms in the to be the long run constraint on farm size, as reproduction index. Cow mature weight influences opposed to the feed resources available, or the feed requirements for replacement heifers, mainte-absolute level of beef output. There are currently no nance requirements for mature cows (neither in-limits to beef output per farm, rather, there is an cluded in the breeding objective as feed intake traits increased tendency for support systems to be linked in their own right), and also cull cow slaughter to extensive management practices such that stocking values. It was not appropriate to combine these into a rates are constrained below the economic optima single economic value because they have differential which would apply in the absence of such support rates and timing of expression which are accounted systems. Allowances for projected changes in beef for by using discounted gene flow coefficients. prices and the carcase payment system were also
made to increase the relevance of the breeding
2.3. Economic values of feed intake and weaning objective to the time when genetic improvements are
weight
expressed in commercial animals. Calving is typical-ly in spring time in Ireland, with steers finished at 24
(Em-Table 1
Outline of breeding objective structure including traits, abbreviations and expressions coefficients by breeding objective trait group Breeding objective Breeding objective trait Abbreviation Context Expressions coefficient
trait group a
Terminal sire Sire breeding
b,c
replacement females
Growth Weaning weight direct WWd Beef X K?X
TB TB
d
Feed intake summer FIS Beef, dairy X K?X
TS TS
d
Feed intake winter FIW Beef, dairy X K?X
TS TS
Carcase weight CW Beef, dairy X K?X
TS TS
Mortality MT Beef, dairy X K?X
TB TB
Weaned calf Weaning weight direct WWd Beef X K?X
TB TB
Calf quality CQ Beef X K?X
TB TB
Calving Calving ease direct CEd Beef, dairy X K?X
TB TB
Gestation length direct GLd Beef, dairy X K?X
TB TB
Carcase Carcase fat score CFS Beef, dairy X K?X
TS TS
Carcase conformation score CCS Beef, dairy X K?X
TS TS
Reproduction Reproductive success RS Beef, dairy – (12K )?X
RA
XTBand XTS are numbers of discounted expressions of a sires genes at birth and slaughter, respectively, per calf born.
b
XRA, XRW, XRHand XRCare numbers of discounted expressions of a sires genes in his daughters at annual calvings, weaning of their calves, replacement heifer age and at culling, respectively, per female calf born which is destined to become a replacement.
c
K is the average proportion of a bulls progeny not destined to be replacements and is calculated as 121 / 2P where P is the proportion of a sires daughters which become replacement heifers.
d
Feed intake aggregated assuming two summers and two winters for summer and winter feed intake, respectively.
e
In the reproduction sub-index, the effect of gestation length on the barren cow rate is omitted to avoid double counting of effects on reproductive success.
mans, 1994) using EE values for foods presented by sexes showed only trivial effects on the economic Amer and Emmans (1998). value of winter feed intake.
It was assumed that baled and wrapped silage Summer feed costs were calculated accounting for costs Irish pounds (IP)13.63 per tonne (wet basis) annual, per hectare, variable costs of fencing (IP23), and that per animal feeding costs are independent of weed control (IP10), fertiliser (IP120) and provision the volume of feed fed on average to each animal of drinking water (IP20). Opportunity cost of land (Anonymous, 1998). After allowance for projected was excluded from the calculations, because of the reductions in future feed prices, weaner concentrates increasing importance of support payments linked to and feed barley were assumed to cost IP119 and upper limits on stocking rates which are applied on a IP110 per tonne (wet basis), respectively (Anony- per head, rather than on a per unit of feed intake, mous, 1998). Calculations allowing for differences in basis.
gained prior to weaning is achieved using relatively result in economic values which are highly depen-cheap summer pasture feed, which would otherwise dent on the mean carcase characteristics of the group have to be made up using more expensive feeds in of commercial animals at the time when they are the first winter. In this way, benefits of increased slaughtered. Amer et al. (1998b) have shown that weaning weight are calculated independently of any substantial variation can be expected in carcase trait benefits from calves heavier at weaning having economic values across breeds, sexes and finishing higher slaughter weights, and the potential for double systems for commercial calves.
counting is avoided. It was calculated that approxi- There are currently only very limited price dif-mately 16 units of EE would be saved in the first ferentials in Ireland even though carcases are in-winter for every 1 kg of additional weaning weight dependently graded according to European Union using the model of Amer and Emmans (1998). standards. This is in marked contrast to the consider-able variation in value of carcases of different grades 2.4. Economic values of growth traits at market prices to processors, although these price signals are partially distorted by non-discriminatory The economic value for carcase weight at a export subsidies for carcases and meat going to non constant age was calculated directly from the carcase European Union destinations.
price schedule (IP1.78 per kg carcase weight), Despite these problems, efforts are under way to ignoring feed costs, which are accounted for else- ensure that a carcase pricing system reflecting ulti-where in the breeding objective. Allowance was mate consumer value does become implemented in made for an expected reduction in the beef price to the near future. Industry representatives and sci-85% of 1998 levels due to modifications to the entists have established a payment schedule which is Common Agricultural Policy in the European Union. expected to form the basis of a future carcase pricing
system and this was used in the current analysis. 2.5. Economic value of mortality Proposed price differentials for standard European
Union carcase grades are shown in Table 2. For the For beef cross calves from the dairy herd, the purpose of deriving economic values, carcase con-economic value of mortality (trait of calves) was formation and carcase fat scores were transformed to taken as the opportunity cost of lost revenue from linear, 15-point, scales (Kempster et al., 1986). not being able to sell the calf at weaning after an Multivariate distributions of carcases are specified by allowance for saved feed costs from 1 week of age breed type and sex according to parameters in Table until weaning. Weaned calf prices were assumed to 3. Fifty thousand carcases were simulated for each be IP100 and 64 per 100 kg for steers and heifers, set of parameters, and the average price for the respectively. A deduction of IP54 was made for milk
replacer and weaner ration costs (Anonymous, 1998). Table 2
It was assumed that mortality in calves from beef Price differentials for standard European Union carcase grades as
a
proposed for use in Ireland
cows occurred around birth and that the calf could be
replaced with a Friesian calf. From Anonymous EU carcase grades Price differential
(1998), it was also assumed that the Friesian calf (p / kg CW)
would cost IP120 and that revenue at weaning would U2, U3 118
be reduced by IP15 per 100 kg. Assuming equal U4L 115
U4H 113
proportions of steer and heifer calves which would
U5, R2, R3 17
have achieved 260 and 235 kg by autumn means the
R4L 14
average opportunity cost of a dead calf is IP157.
O3 0
O4L 22
2.6. Economic values of carcase quality traits R5, O4H 24
O5, P2, P3, P4L, P4H, P5 211
a
Economic values for carcase traits derived using U, R, O, P range from good conformation to poor
Table 3
a
Base carcase weights, carcase conformation scores and carcase fat scores for groups of slaughtered steers by breed type used to simulate
b,c,d
slaughter groups and derived percentages of each group to total male and female calves slaughtered
Sire breed type Dam breed type Carcase weight Carcase conformation Carcase fat Males Females (kg) (15-point scale) (15-point scale) (%) (%)
Traditional Holstein–Friesian 320 9.4 9.9 7 0
Traditional Traditional 320 10.8 12.6 11 12
Traditional Small continental 320 11.2 10.4 3 3
Traditional Large continental 330 11.2 9.0 3 3
Traditional Dairy cross 320 10.1 11.4 11 12
Small continental Holstein–Friesian 320 9.8 7.7 2 0
Small continental Traditional 320 11.2 10.4 7 8
Small continental Small continental 320 12.2 8.2 5 5
Small continental Large continental 330 12.2 7.5 1 1
Small continental Dairy cross 320 10.5 9.2 11 12
Large continental Holstein–Friesian 330 9.8 7.0 3 0
Large continental Traditional 330 11.2 9.7 11 13
Large continental Small continental 330 12.2 7.5 4 4
Large continental Large continental 350 12.2 6.7 4 4
Large continental Dairy cross 330 10.5 8.5 18 21
a
Adjustments to carcase weights (270 and220), carcase conformation scores (20.6 and11.3), and carcase fat scores (0 and 21.5)
were made to simulate groups of heifers and bulls, respectively.
b
Phenotypic standard deviations for carcase conformation and carcase fat were assumed to be 2.5, with a correlation between the two variables of 0.4.
c
Sources: Keane, 1994; Keane and Diskin, 1996; Keane and More O’Ferrall, 1992; Keane et al., 1989; More O’Ferrall and Keane, 1990.
d
Carcase conformation and carcase fat scores transferred to a 15-point scale based on Kempster et al., 1986.
carcases computed from the simulations. Economic theoretical grounds, the importance of seasonal feed values for carcase conformation and carcase fat at a availability and management of animals to maximise constant age (by breed type and sex) were computed receipt of direct support payments in determining by re-simulating carcases adjusted upwards by 1 unit slaughter decisions do support such an assumption. for each, respectively, and taking the change in the Furthermore, results of Amer et al. (1998b) under a average carcase price as the economic value ex- similar carcase grading system suggest that this pressed per unit on the 15-point scales. Economic assumption may only have trivial impact on the values were also calculated in a similar way for two economic values.
alternative scenarios. The first scenario considers a
situation where changes to either carcase grading or 2.7. Economic value of reproductive success direct subsidies result in animals being slaughtered at
lighter carcass weights (e.g., 300 kg for steers, A critical cost when deriving economic values for irrespective of breed type) on average than they are reproductive traits is that of a barren cow. The cost currently. The second scenario assumes that heifers of a barren cow can be used directly as an economic and steers are slaughtered at a mean carcase fat score value for reproductive rate. Alternatively, it can be of 7 points. used indirectly in more complex reproductive and All animal traits at slaughter, other than the one breeding models which assign economic values to changed genetically, are implicitly assumed to be component factors such as conception rates, length constant. This implies that a genetic change in of the post-partum anoestrous interval and gestation carcase fat or carcase conformation will not cause a length which contribute to reproductive failure complementary change in any management variable. (Amer et al., 1996).
assuming that barren cows are culled following a shorter gestation length results in a longer effective pregnancy diagnosis and replaced in the breeding breeding season and less barren cows (Amer et al., herd with an in-calf heifer. It is important to recog- 1996). However, because the barren cow rate is nise that there is not a one-to-one relationship already taken into account in the reproduction index between the level of culling due to reproductive (reproductive success), this component was only failure and the number of in-calf heifer replacements included in the computation of the economic value required in the herd. This is because older cows for the terminal sire index. The model of Amer et al. culled for reproductive failure have only a limited (1996) was adapted to Irish beef and dairy cow herds remaining life span in the herd and would have had based on assumptions in Table 4. Parameter sets to be replaced in due course anyway. corresponding to base herds, favourable herds where The costs of replacement heifers were derived as biological parameters are favourable but the length opportunity costs from not being able to sell equiva- of the mating period is shortened, and unfavourable lent beef animals with an addition of IP40 to cover herds where biological parameters are unfavourable breeding expenses. Average cull cow values were (long mating period) were considered (Table 4). also calculated based on assumed prices for cows of Changes in the proportion of the herd barren over each age and the proportion of cows in the herd of five alternative gestation lengths (range from base that age. Thus, the cost of a barren cow was taken as value minus 2 days to base value plus 2 days) were the weighted average reduction in cost of replace- evaluated for each scenario. The linear regressions of ments minus the weighted average net revenue from the proportion barren on gestation length multiplied cull cow sales given a 1% improvement in reproduc- by the cost of a barren cow (see above) for the base tive success. dairy and base beef parameter sets were taken as the
economic values for gestation length.
2.8. Economic value of gestation length The second component of the economic value of gestation length accounts for the longer summer Economic values for gestation length were calcu- growing season for calves born earlier in the spring. lated assuming two components to the overall bene- The value of this component was quantified as the fit. The first component is based on the rationale that average pre-weaning growth rate (kg per day)
mul-Table 4
Assumptions used to calculate economic values for gestation length (GL) – reproductive component
Parameter Dairy Beef
Base Favourable Unfavourable Base Favourable Unfavourable
Mating period (days) 100 85 110 115 90 125
Post partum interval mean (days) 45 45 55 55 50 60
Post partum interval S.D. (days) 5.75 5.75 5.75 5.75 5.75 5.75
Conception rate first oestrous 0.4 0.4 0.4 0.45 0.45 0.45
Conception rate subsequent 0.55 0.6 0.5 0.6 0.65 0.55
Oestrous cycle (days) 21 21 21 21 21 21
Gestation length mean (days) 283 280 286 286 283 289
Gestation length S.D. (days) 5 5 5 5 5 5
a
Percent barren GL22 days 3.18 3.05 5.89 2.41 1.98 5.25
a
Percent barren GL21 day 3.26 3.10 6.25 2.60 2.10 5.69
a
Percent barren 3.34 3.16 6.65 2.81 2.16 6.40
a
Percent barren GL11 day 3.51 3.23 7.11 3.07 2.30 6.92
a
Percent barren GL12 days 3.61 3.37 7.61 3.36 2.38 7.79
Regression % barren per GL day 0.11% 0.08% 0.43% 0.24% 0.10% 0.63%
a
tiplied by the economic value for weaning weight. A severe assistance, (4) veterinary assistance and (5) constant pre-weaning growth rate of 1 kg per day caesarean section. Calculation of total costs for each was assumed for all dairy and beef production calving type in excess of those of a ‘‘no assistance’’ systems. calving for calving categories (2) to (5),
respective-ly, are shown in Table 5.
2.9. Economic value of calving ease Probabilities of assistance types are calculated within sex of calf by age of dam (first, second and For the purpose of the breeding objective, the greater than second parity) combinations. Threshold economic value of calving ease was defined here on differences were used which were derived from the an underlying liability scale with animals, within a international literature and which are also consistent sex and age of dam sub-class, assumed to have with incidences of calving difficulty in the UK phenotypic values distributed on a standard normal reported by Allen (1988) and McGuirk et al. distribution (Meijering, 1980). Such an approach is (1998a). Percentages of specific assistance types fully compatible with a genetic evaluation system for were computed assuming threshold differences of calving ease using a threshold model. There are 0.6, 0.3 and 0.3 between slight assistance, severe many advantages of such an approach (McGuirk et assistance, veterinary assistance and caesarean
sec-al., 1998b). tion sequentially.
The category of calving assistance required by an Following Meijering (1980), let p(u) denote i51
i
animal depends on where its phenotypic value lies, to t probabilities of a normally distributed calving on the underlying scale, relative to thresholds which liability falling within a pair of thresholds T andi
partition this scale into calving assistance categories. Ti11 given a sub-population mean u, and let ai
Following Amer et al. (1998a), the categories consid- denote calving costs associated with calving ered were (1) no assistance, (2) slight assistance, (3) liabilities between T and Ti i11. The average cost of a
Table 5
Calculation of costs for calving assistance categories
Caesarean section Veterinary assistance Severe assistance Slight assistance
Stockman hours 3 3 4 1
a
Cost per hour (IP) 7 7 7 7
Veterinary cost (IP) 120 30 0 0
Probability of dead calf 0.25 0.10 0.05 0
b
Cost of dead calf 210 210 210 210
Probability of a dead cow 0.05 0 0 0
c
Cost of a dead cow – dairy 359 359 359 359
c
Cost of a dead cow – beef 409 409 409 409
Reduction in reproductive success 0.35 0.25 0.15 0.05
d
Barren cow cost – dairy 134 134 134 134
d
Barren cow cost – beef 149 149 149 149
Lost milk production litres 600 300 300 100
e
Cost of milk (IP/ litre) 0.13 0.13 0.13 0.13
Total cost for dairy cow 336.35 183.50 97.60 26.70
Total cost for beef cow 266.10 109.25 71.35 35.45
a
Based on statutory minimum of IP3.91 per hour (Anonymous, 1998) but revised upwards to account for overtime rates, requirement for experienced stockman and / or opportunity cost of owner operators time.
b
Based on Anonymous (1998).
c
Based on the expected cost of a replacement per infertile animal.
d
Based on the expected cost of a replacement minus the cull value per infertile animal.
e
calving (SC) in a sub-population with mean liability 1.7 (McGuirk et al., 1998b) and that calves are of u is calculated as equally distributed across categories. A mean weaned calf price function was first derived
assum-t
ing an underlying normal distribution for calf quality SC(u)5
O
a p(u)i i
i51 score with an IP0.25 / kg liveweight premium for each successive increase in calf quality score and a By setting a to zero, the proportion of unassisted1
mean liveweight of 240 kg (equates to IP60 per calf). calvings is ignored, and so this equation gives
The economic value was then computed as the average expected costs in excess of those from an
marginal change in mean weaned calf price per unit unassisted calving.
change in mean calf quality score using numerical If we treat cows of different age groups carrying
differentiation. calves of different sex as sub-populations, average
expected calving costs for the total population can be
2.11. Economic values of cow mature weight traits calculated as
6
Changing cow mature weight is expected to result EC(u)5
O
SC(u )qj j in changes to feed requirements for replacement j51
heifers (growth and maintenance) and cow feed where u is the mean of sub-population j and q is thej j requirements for maintenance. Feed requirement proportion of animals in the total population which prediction equations based on the inter-species come from sub-population j defined according to six growth model of Emmans (1988) were used to age of dam by sex of calf combinations. For dairy predict the size of these changes. Mature weight is a cows, the proportions q were assumed to be 0.33, primary driving variable in the model.
0.25 and 0.42 for heifers, first calving and older Heifers were assumed to be fed pasture in the dams, respectively. Corresponding proportions for summer and a silage / barley or concentrate diet in beef cows were assumed to be 0.2, 0.18 and 0.62. A their first two winters at a rate assuming that they calf sex ratio of 1:1 was also assumed. had to reach 85% of mature weight at first calving in The economic value, EV(u) of a unit change in order to maintain optimal economic performance. calving difficulty on the underlying normal scale for Effective energy contents and prices of summer and a population is calculated as the partial derivative of winter feeds were assumed to be equivalent to those the equation for expected calving costs. Because of used for finishing heifers. Calving was assumed to be the complexity of the equation, the partial derivative at the beginning of spring turnout. The economic was taken numerically, rather than algebraically. value for the mature weight effects on replacement Finally, the values of u for which economic values heifer feed requirements was calculated as the in-were derived for the selection indexes in-were obtained crease in feed costs for growth and maintenance by back-solving to obtain proportions of an average from birth to two years of age and for growth only herd of cows requiring any assistance which corre- from 2 to 3 years of age with a 1 kg increase in spond to proportions observed in practice. The mature weight. Additional maintenance requirements proportions were taken as 0.08 for herds with from 2 to 3 years of age are assumed to be accounted medium to small beef cows, 0.06 for herds with large for in the cow maintenance economic value ex-beef cows, 0.20 for dairy herds mated to a large pressed annually by cows of 2 years of age and continental breed, 0.18 for dairy herds mated to a older. Feed costs were discounted to their present small continental breed and 0.12 for dairy herds value equivalents at 2 years of age assuming all mated to a traditional beef breed. expense is incurred prior to the season in which it is
to be fed.
The cow maintenance economic value was calcu-2.10. Economic value of calf quality
lated as the change in daily cow maintenance requirements (EE units) with a 1 kg change in The economic value of calf quality scored as 1 for
mature weight multiplied by 155 and 210 days of poor, 2 for average and 3 for excellent was
were assumed to be fed pasture in summer and a here is adapted from Everett (1975) and Van Vleck silage diet costing IP0.0068 per EE unit in winter. and Everett (1976) who addressed the value of The price differential for cull cows based on genetically superior semen in dairy cattle. Amer weight was used as the economic value for cull value (1999) has also applied the methodology (with as influenced by mature weight. The 1997 price of modification) to sheep. It is assumed that individual IP148.30 per 100 kg carcase weight was multiplied estimated breeding values (not EPDs or estimated by 0.85 to account for projected beef price reduc- progeny differences) are used for individual traits, tions and adjusted to a live weight equivalent but that indexes are expressed as the contribution of assuming a killing out proportion of 0.5. a parent to the profitability of each progeny born. The equations used to calculate the discounted 2.12. Aggregation of economic values genetic expressions are in Appendix A.
It is impractical to have a separate selection index
for each breed type and sex of calf combination. For 3. Results
example, a single bull is expected to produce calves
of both sexes and is likely to be mated to more than 3.1. Feed intake and weaning weight one cow breed type. Full aggregation of the
econ-omic values for use in a single industry index is Economic values for FIW were robust to different possible, but must take account of the distribution of steer and heifer production systems. They were also sexes and breed types of slaughtered animals. Index- robust across breed types where from 15 to 20% of es containing economic values with intermediate total winter EE intake is supplied from concentrate levels of aggregation can also be derived to suit or barley. Base values were calculated to be 0.008 specific applications, for example, for beef bulls (of and 0.0025 IP per EE feed intake unit for winter and any breed type) mated to dairy cows. summer, respectively. For intensively finished bulls An intermediate level of aggregation was achieved assumed to be fed a diet with 60% of EE supplied here by building a demographic model of slaughtered from concentrate, the cost per unit of EE was cattle in Ireland. The model was driven by numbers IP0.011.
of beef breed inseminations by AI centres in Ireland Under the assumption that 1 kg extra weaning along with percentages of total inseminations to beef weight results in a reduction by 16 units of EE and dairy cows. Slaughtered animals (excluding cull requirements in the first winter, the economic value cows) sired by natural mating in both dairy and beef for weaning weight in heifers and steers was IP0.09 herds were back calculated using the population sizes per kg.
of dairy and beef cows, assuming that 80% of these
animals calve each year. It was also assumed that 3.2. Mortality and carcase weight most surplus heifers from dairy cows were sired by
beef breeds and consequently used as replacements The economic value for calf mortality was IP2
in the beef herd. Bulls were ignored in the aggrega- 1.51 in beef cross dairy calves and IP21.57 in beef
tion steps as there are currently very few slaughtered calves for each percent increase in mortality. For in Ireland. The derived proportions of heifers and carcase weight, the economic value was IP1.51 per steers slaughtered by sire and dam breed type are kg increase with no account taken for differences in presented in Table 3. carcase quality for different breeds because the
effects on resulting indices would be trivial. 2.13. Discounted genetic expressions
3.3. Carcase quality Application of beef selection indices outlined in
Table 6
Carcase trait economic values aggregated over heifers and steers resulting from matings with weighted proportions of beef and dairy cows (aggregate) and resulting from matings with dairy cows only (dairy cross), ranges for steers, and weighted average deviations to economic values for bulls and heifers
a b
Base scenario Reduction in CW Reduction in fatness Carcase conformation
c
Aggregate EV (IP/ unit) 5.1 5.5 5.0
c
Dairy cross EV (IP/ unit) 7.1 7.4 6.1
Range for steers (IP/ unit) 2.8 to 7.6 3.0 to 7.6 2.3 to 7.6
Heifer deviation (IP/ unit) 20.4 10.4 10.5
Bull deviation (IP/ unit) 22.2 21.7 21.4
Carcase fat
c
Aggregate EV (IP/ unit) 24.0 24.1 22.0
c
Dairy cross EV (IP/ unit) 24.5 24.3 22.2
Range for steers (IP/ unit) 22.7 to 25.0 21.7 to25.0 20.9 to23.8
Heifer deviation (IP/ unit) 11.2 10.5 10.3
Bull deviation (IP/ unit) 10.7 10.1 11.0
a
Mean carcase weights (CWs) reduced to 320, 300 and 340 kg for steers, heifers and bulls, respectively. Carcase conformation and carcase fat were reduced by20.015 and20.025 points per kg for every 1 kg reduction in carcase weight (relative to values in Table 4).
b
Mean carcase fat reduced to 7, 7 and 5.5 points for steers, heifers and bulls, respectively. Carcase weight and conformation were also adjusted using the constants specified in footnote a.
c
EV denotes economic value.
ignored in the aggregation steps as there are current- dairy cows were IP149.11 and 134.45, respectively. ly very few slaughtered in Ireland. These costs are relevant as components for economic Table 6 shows the overall aggregate economic values of reproductive success, gestation length and values along with the range observed within steers, calving ease. The differences in costs of replacement and the weighted average effects of sex (heifer or heifers and cull cow revenues expressed for a 1% bull relative to steers) on carcase conformation and change gave economic values for reproductive suc-carcase fat economic values for current, and two cess of IP1.49 and 1.34 for beef and dairy cow alternative scenarios. Both the reduced average car- matings, respectively. The economic value for re-case weight, and reduced average fat score scenarios productive success in dairy cows is only relevant to resulted in a small increase in the economic value for the breeding objective of a beef breed when it is carcase conformation (Table 6). However, when affected by the fertility of the beef bull.
animals were assumed to be much leaner at slaughter Mature weight economic values linked to feed than in the base situation, the negative economic requirements showed a modest dependency on the value for carcase fat score was almost halved. expected mature weight to be achieved by the Aggregate economic values encompassing all mat- replacement heifer resulting from a specific mating. ings to dairy cows are also shown in Table 6. For example, the economic value of mature weight Economic values for carcase conformation and car- for heifer feed requirements ranged from IP0.242 to case fat are higher and similar, respectively, for the 0.230 (per heifer) and for cow maintenance ranged dairy situation relative to the overall aggregate. from IP0.103 to 0.093 (per year) for expected mature
weights of 450 and 650 kg, respectively.
3.4. Reproductive traits The economic value of cull cow value as in-fluenced by mature weight was IP2.52 per kg of Tables 7 and 8 show changes in replacement liveweight at slaughter.
Table 7
a
Changes in replacement requirements and cull cow revenues from an improvement in fertility of beef cows of all ages Age of cow Base level Effects per barren cow
(years)
Survival rate Herd proportion Extra replacements Savings Reduced cull cow revenue
b c
(IP) (IP)
2 0.95 0.195 1.000 105.30 66.89
3 0.94 0.183 0.902 89.14 56.62
4 0.93 0.170 0.758 69.58 44.20
5 0.88 0.150 0.661 53.54 34.01
6 0.83 0.124 0.564 37.77 23.99
7 0.70 0.087 0.562 26.40 16.77
8 0.60 0.052 0.570 16.01 10.17
9 0.50 0.026 0.587 8.24 5.23
10 0.50 0.013 0.394 2.77 1.76
Totals 1.000 408.74 259.63
a
Assuming that improving fertility by 1% at each age increases cow survival by 1% at each age and that the cost of a replacement beef heifer is IP540 (opportunity cost of an 18 month old heifer in good condition plus breeding expenses of IP40 and IP40 for additional feed and management expenses).
b
Savings from reduced replacements calculated as the herd proportion multiplied by the replacements per barren cow for each age group multiplied by the cost of a replacement heifer. The total at the bottom of the column gives the savings per average cow.
c
Costs from reduced cull beef cow revenue calculated as the herd proportion multiplied by the cull cow value for each age group.
Table 8
a
Changes in replacement requirements and cull cow revenues from an improvement in fertility of dairy cows of all ages Age of cow Base level Effects per barren cow
(years)
Survival rate Herd proportion Extra replacements Savings Reduced cull cow revenue
b c
(IP) (IP)
2 0.85 0.33 1.000 93.60 58.50
3 0.75 0.25 1.179 103.56 64.73
4 0.75 0.18 0.997 81.36 50.85
5 0.75 0.14 0.755 54.36 33.98
6 0.75 0.11 0.431 25.65 16.03
Totals 1.00 358.53 224.08
a
Assuming that improving fertility by 1% at each age increases cow survival by 1% at each age and that the cost of a replacement dairy heifer is IP440 (opportunity cost of a 2 year old dairy cross heifer sold for beef, plus breeding expenses of IP40).
b
Savings from reduced replacements calculated as the herd proportion multiplied by the replacements per barren cow for each age group multiplied by the cost of a replacement heifer. The total at the bottom of the column gives the savings per average cow.
c
Costs from reduced cull dairy cow revenue calculated as the herd proportion multiplied by the cull cow value for each age group.
additional allowance for being 1 kg heavier at 3.5. Calving ease weaning of IP20.08 was also accounted for giving
economic values for gestation length in the calving Separate economic values for calving ease in dairy sub-indexes of 20.24 and 20.45 with dairy and and beef herds (beef breed sires) are shown in Fig. 1.
3.7. Discounted genetic expressions
Table 9 shows values derived for discounted genetic expressions coefficients. Expressions at slaughter are lower than expressions at birth because not all calves survived, and because of discounted effects over 2.5 years. Discounted expressions by replacement females at later ages (i.e., as cows) are higher because of multiple calvings per lifetime.
4. Discussion
Fig. 1. Economic values for calving ease in dairy and beef cow herds with different incidences of assistance required (A, T, SC
4.1. General
and LC correspond to average, traditional, small continental and large continental sire breed types, respectively).
The economic values derived here provide a useful basis from which economic comparisons of selection candidates, breeding strategies and breeding industry large continental beef breed sires, respectively. The structures can be made. However, it is not just the economic value for calving ease in beef cow herds economic values in the breeding objective which will based on an overall incidence of 8% of calvings determine the rate and direction of genetic change. assisted was IP7.25 per liability unit per calving. Breeding objectives constitute the ‘‘demand side’’ of genetic improvement, in other words, how much a 3.6. Calf quality score genetic improvement in a specific trait would be worth paying for. The ‘‘supply side’’ of genetic The economic value of calf quality score was improvement, which involves trait recording, selec-calculated to be IP25.44 per unit change in the score. tion strategies and mating systems, also needs to be Relaxation of the assumption that equal probabilities taken into consideration for beef cattle breeding in of calves fall in each quality grade resulted in a Ireland. Integration of ‘‘supply side’’ with ‘‘demand modest reduction in the economic value. However, side’’ genetic improvement issues has been under-the economic value was greater than IP20 per unit taken in a parallel study to this one.
for situations where the percentage of high quality
calves ranged between 12 and 65%. 4.2. Definition of sub-indexes and indexes
Sub-indexes for growth, calving, weaned calf, carcase and reproduction trait groups have been
Table 9 proposed (Table 1) as a way of providing
infor-Numbers of discounted genetic expressions of a sires genes for
mation to complement total index scores for
alter-traits expressed at different life cycle stages (per calf born)
native production system situations. Because the
Coefficient Abbreviation Value economic importance of calving ease was found to
Terminal differ substantially with dairy versus beef cow
Birth XTB 0.50 matings (Fig. 1), it is also proposed that the calving
Slaughter XTS 0.39 sub-index should be further differentiated to be
specific for dairy versus beef cow matings, with
Replacements
separate sets of economic values. For the other
sub-Annual cow XRA 2.75
Annual cow by weaned calf XRW 2.50 indexes, economic values can be assumed to be the
Table 10
a
Calculations of economic weights (multiplied by the trait genetic standard deviation , sG) for breeding objective traits in sub-indexes (IP/ calf born)
b c d
Sub-index(SI) DGE EV s EW
G
Breeding objective trait (per calf) (IP/ unit) IP/(s ?calf)
G
Dairy calving(DCSI)
Gestation length (days) 0.5 20.27 3.20 20.43
Calving ease (liability units) 0.5 29.81 0.44 6.56
Beef calving(BCSI)
Gestation length (days) 0.5 20.50 3.20 20.80
Calving ease (liability units) 0.5 10.48 0.44 2.31
Weaned calf( WCSI)
Weaning weight (kg) 0.43 1.09 9.0 4.22
Calf quality (quality score units) 0.43 25.44 1.0 10.94
Production(PSI)
Weaning weight (kg) 0.43 0.09 9.0 0.35
Feed intake summer (EE units) 0.39 20.0025 141 20.14
Feed intake winter (EE units) 0.39 20.008 141 20.44
Carcase weight (kg) 0.39 1.51 12.5 7.36
Carcase fat score (points) 0.39 24.00 0.72 21.12
Carcase conformation score (points) 0.39 5.10 1.05 2.09
Reproduction(RSI)
Reproductive success (%) 2.75 1.49 2.85 11.67
Calving ease direct (liability units) 3.25 6.50 0.44 9.30
Calving ease maternal (liability units) 5.50 6.50 0.47 16.80
Weaning weight direct (kg) 3.00 0.09 9.0 2.43
Weaning weight maternal (kg) 5.00 0.09 8.77 3.95
Mature weight annual (kg) 2.75 20.10 32.0 28.80
Mature weight heifer (kg) 0.72 20.235 32.0 25.41
Mature weight cull (kg) 0.38 0.69 32.0 8.39
e
Gestation length (R) direct (days) 3.25 20.08 3.20 20.83
e
Gestation length (R) maternal (days) 5.50 20.08 1.40 20.62
a
Genetic standard deviations for direct traits in the calving, weaned calf and production sub-indexes were based on a literature review of parameters for temperate beef breeds (J. Roden, personal communication). Maternal trait genetic standard deviations were derived assuming
2
maternal variance proportions (m ) of 0.22 for calving ease, 0.07 for gestation length, and 0.22 for weaning weight.. For reproduction traits, the genetic standard deviation of reproductive success was based on a binomial distribution with incidence of reproductive failure of 10% and heritability of 0.1, and for mature weight assuming a mean of 500 kg, C.V. of 10% and a heritability of 0.4.
b
DGE are discounted genetic expressions taken from Table 9.
c
EV are economic values which do not account for discounted genetic expressions and are expressed per trait unit.
d
EW are economic weights which account for discounted genetic expressions and are expressed per genetic standard deviation per calf born.
e
Economic values for gestation length in the reproduction sub-index ignore the advantage of a longer effective breeding season with a shortened gestation length. This avoids double counting of reproductive success.
expres-sions contain two components, one component for based on visual conformation. The farmer could the replacement female’s own performance as a calf, narrow down the available choice of bulls by first and an additional component for the performance of selecting those ranking highly for the total beef descendants as calves (see Table 1). index. From within the remaining list, any bulls In addition to calculation and presentation of the ranking poorly for the calving index could be sub-indexes to relevant sectors of the Irish cattle eliminated because of greater risk of difficult calving industry, we propose that two total indexes also be in a heifer, relative to a mature cow. Similarly, any used. The total dairy beef index (TDBI) is for dairy bulls ranking poorly for the weaned calf or reproduc-farmers buying a beef bull, and represents the tion sub-indexes could also be eliminated. The fact expected economic merit of progeny over all aspects that each index and sub-index has the same units of beef production. It should be calculated as fol- (i.e., currency units), simplifies their comparison. lows: There are also considerably less indexes and sub-indexes than the potential number of recorded traits, TDBI5K?(DCSI1PSI)1(12K )?RSI
and the confusion created when some recorded traits are both positively and negatively related to contrast-where K, the average proportion of a bulls progeny ing aspects of animal performance is circumvented. not destined to be replacements is 0.75, while DCSI,
PSI and RSI are the dairy calving, production and 4.3. Comparisons with other studies reproduction sub-indexes as described in the
previ-ous section. Phocas et al. (1998) compared results from a The total beef index (TBI) is for beef farmers range of international studies on beef breeding purchasing a bull to mate to their beef cows. objectives and concluded that when expressed on a Calculation of the TBI is as follows: per phenotypic standard deviation basis, absolute
values for trait group economic values decrease 1
]
S
D
TBI5K? BCSI1 [PSI1WCSI] 1(12K)?RSI across reproduction, growth and carcase trait groups.
2
When expressed on a per phenotypic standard devia-tion basis, results of this study (Table 10) are where K50.75 as above and BCSI and WCSI are the
consistent with their general conclusion. Economic beef cow calving and weaned calf sub-indexes,
values favouring reduced carcass fatness reported by respectively.
van der Werf et al. (1998) for dual purpose cattle in It was assumed that only beef calves with no dairy
the Netherlands and Amer et al. (1998b) for beef breeding would be eligible for the special premiums
cattle in the UK were minimal relative to those available for high quality calves destined for live
favouring improved carcass conformation score. This export so that WCSI is not a component of the
study found modest economic values favouring TDBI. Furthermore, it was arbitrarily assumed that
reduced carcass fat reflecting quite high mean levels 50% of beef calves from beef cows would be
of carcass fatness in Ireland relative to other coun-slaughtered in Ireland, and that for these calves, the
tries in Europe, and consequently, a desire to reduce production sub-index would be more relevant than
carcass fatness levels by beef processors. As found the weaned calf sub-index. These assumptions can be
in this study, significant positive economic values for readily modified as better information on future
carcass conformation relative to growth rate traits markets and production systems becomes available.
have consistently been reported for other European As an example of the application of indexes and
countries (Phocas et al., 1998; van der Werf et al., sub-indexes, consider a beef farmer choosing semen
1998; Amer et al., 1998b). from a number of bulls of a single breed to
insemi-Koots and Gibson (1998) derived economic values nate a suckler beef heifer. If a female calf is born,
for a range of genotypes, production systems and the farmer intends to retain the calf as a replacement
marketing circumstances and in some situations, heifer, whereas a male calf would be sold at weaning
found substantial variation in economic values. into a market where significant premiums can be
economic values for purebred Limousin cattle across good conformation calves for export, and / or for the five major beef production systems in France. mating primarily to heifers, the sub-indexes provide Moderate to large variation in economic values for a relatively straight forward means of adjusting calving ease (Amer et al., 1998a), reproduction traits selection emphasis accordingly. The breeding objec-(Amer et al., 1996) and carcase quality traits objec-(Amer tive can also be used when comparing alternative et al., 1998b) has been observed for UK beef breeding strategies and breeding industry structures. production systems. The present study has shown
substantial variation in economic values for calving
ease, and to a lesser extent carcase traits and Acknowledgements
reproductive success, across breed types and
pro-duction systems. In particular, the difference in the Financial support for this study was provided by economic values for calving ease depending on the Irish Cattle Breeding Federation Society Ltd. whether beef bulls are mated to dairy versus beef through EU structural funds. We are also grateful to cows was found to be substantial. This is as ex- Chris Morris and Neville Jopson for comments on a pected, but does not appear to have been previously draft manuscript, and would like to thank the many shown in a formal way. members of the Irish beef industry and Irish research Phocas et al. (1998) advocate using a weighted organisations, who provided input to this study. average of specific production system economic S.A.C. receives financial support from the Scottish values to obtain a unique set for the Limousin breed. Executive Rural Affairs Department.
In contrast, Koots and Gibson (1998) tentatively advocate a customised index approach, depending on
the robustness of indexes constructed in part using Appendix A the breeding objective, but which also depend on the
choice and characteristics of the selection criteria. A A.1.. Survival parameters for discounted genetic premise of this study was that specific customised expressions
indexes would not be feasible for Ireland, where Let s be an n by 1 vector of probabilities of a cow large numbers of quite small cattle farms with mixed surviving and calving from age group i21 to age
breed types make up the commercial herd. The group i for i51 to n, where n is the highest cow age
sub-index approach described here is an extension of (in years) considered possible. Also let p be an n by the two sub-indexes proposed for terminal sires by 1 vector of numbers of calves reaching slaughter age Amer et al. (1998a). Sub-indexes provide a com- or reproductive age born per cow calving in age promise between the situation of having a single group i. Note that elements p and s should have1 1 industry objective and the alternative of calculating values of zero. Values used for elements in s were specific indexes for individual breeders, and also 0.95, 0.94, 0.93, 0.88, 0.83, 0.7, 0.6, 0.5 and 0.5 for potentially for specific bull and semen buyers. cow ages from 2 to 10 years of age, respectively. Values in p were 0.9 for cows ages from 2 to 6 years, 4.4. Implications 0.85 for cow ages from 7 to 9 years and 0.8 for 10
year old cows.
Breeding objectives in the form of six sub-indexes Now let c be a cull for age threshold (c#n), in
and two total indexes are proposed to summarise other words, all cows above the age of c, are culled, breeding value information so as to simplify selec- irrespective of their potential future survival. A tion decisions of commercial dairy and beef cattle vector (a) of probabilities of a cow surviving to and herd owners purchasing beef breed bulls. The two calving at age i, given that it was alive at age 1, can total indexes can be used for typical dairy and beef now be calculated where
cow farming situations where average proportions of i
female progeny are retained as replacement females.
P
s , i52 to cj
a 5 j52
i
For more specific farming systems, such as when
5
for i51 to n. The probability of a cow dying or accumulated over generations are therefore
calcu-being culled at i years of age, d , can be calculatedi lated as
as m
Matrices D, G and H can now be used to multiply 0 otherwise
first expressions to the multiple expression of genes
A.2. Self replacing females for each cow over it’s expected life span. Also, let q Let D be an h by h transition matrix with columns be a vector (dimension h) of discount coefficients of survival probabilities lagged by one row for each with elements defined as
new birth year where h is the planning horizon in 1 i21 years from birth of the self replacing female. The q 5
S D
]]i 11r
(i, j )th element of D is specified as
so that the discount coefficient is 1 at birth of the
a for j,i21 and i2j#c
i2j
heifer replacement. The number of genetic
expres-D 5
H
i, j
0, otherwise sions for a trait expressed annually by a self replac-ing cow is therefore calculated as
Similar matrices for cull cow, G, and replacement
heifer, H, expressions, respectively, are calculated as 1
] 9
X 5 ?g D9q
follows; RA 2 sum
d for j,i21 and i2j#c
i2j
The discounted numbers of end of cow life
G 5
H
i, j
0, otherwise expressions (X ), heifer replacement expressions RC
(XRH) and calf at weaning expressions (XRW) for a and
self replacing female are calculated as 1 for i115j
Vectors containing increments of gene flows (g )k 1
can be calculated for each generation k as X 5]?g9 H9q
cows genetic contribution to her progeny and where f where v is the number of calves reaching slaughter
is the number of heifers required as replacements (at age or sold per cow calving and s (0.98) is calf 2
first reproductive age) per cow calving per year. survival from weaning to slaughter or replacement
21
Under the assumption of a constant herd age struc- age. Note that v5a9p?(19a) where vectors a, p
ture, f can be calculated as the proportion of 2 year and 1 are all of dimension n and all elements of 1 are old cows relative to all cows calving as follows ones.
1
]]
f5 c
A.3.. Terminal sires
O
ai The number of expressions of a terminal sire’s i51genes in slaughtered calves is also required. The discounted numbers of expressions of the terminal Rows of each g vector correspond to the year ofk
sire’s genes in calves at birth (X ) and in slaug-expression of the genes so that each gk is of MTL
Emmans, G.C., 1994. Effective energy: a concept of energy
1 utilization applied across species. Br. J. Nutr. 71, 801–821.
]
X 5
TB 2
Everett, R.W., 1975. Income over investment in semen. J. Dairy Sci. 58, 1717–1722.
and Hazel, L.N., 1943. The genetic basis for constructing selection
indexes. Genetics (USA) 28, 476–490. sa
1 1
Keane, M.G., Diskin, M.G., 1996. Exploitation of the genetic
]
S D
]]X 5 ?s s ?
TS 2 1 2 11r
potential of the national herd for beef production. Irish Grassland Anim. Prod. Assoc. J. 30, 218–230.
where s (50.94) is survival from birth to weaning,
1 Keane, M.G., More O’Ferrall, G.J., 1992. Comparison of Friesian,
r (50.07) is the discount rate and sa (52) is the age
Canadian Hereford3Friesian and Simmental3Friesian steers
of animals at slaughter. for growth and carcase composition. Anim. Prod. 55, 377–387. Keane, M.G., More O’Ferrall, G.J., Connolly, J., 1989. Growth and carcase composition of Friesian, Limousin3Friesian and Blonde D’Aquitane3Friesian steers. Anim. Prod. 48, 353–365.
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