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Review article
Impact of recent research on energy feeding systems for dairy
cattle
1
*
R.E. Agnew , T. Yan
a
The Agricultural Research Institute of Northern Ireland, Hillsborough, Co. Down, Northern Ireland BT26, UK
Received 27 July 1999; received in revised form 14 December 1999; accepted 11 January 2000
Abstract
A considerable volume of research in the energy metabolism of dairy cows has been undertaken over the last 2 decades. The purpose of the present review is to reflect on the impact of these studies on the UK metabolisable energy (ME) system, and other net energy (NE) systems, and validate these systems using published calorimetric data. The NE requirement for maintenance (NE ) in the UK ME system is based on the fasting metabolism of cattle, while in other NE systems the NEm m
was obtained from regression techniques. The NEm values currently used in Europe and North America, which were developed from the data published 30 years ago, have been demonstrated, in recent studies, to be lower than for present dairy cattle. Maintenance metabolic rate can increase with increasing dietary fibre concentration, possibly being due to increasing gut mass and metabolic activity in organs. Grazing cattle require more time and greater physical efforts for eating the same amount of feed as housed animals and thus require extra energy for grazing activity. The NEmof cattle may be a function of body protein mass, rather than total liveweight of the animal. The efficiency of utilisation of ME for lactation (k ) can bel
derived from regression techniques or calculated by relating milk energy output and energy balance to ME available for production. Dietary fibre concentration has little effect on k , although it can influence the composition of volatile fatty acidsl
produced in the rumen and consequently shift milk composition and energy partition between milk and body tissue. There is no evidence to show an effect of cow genetic merit on k , but high genetic merit cows have the ability to partition morel
energy into milk than medium or low genetic merit cows. The k has been shown to be higher than the efficiency ofl utilisation of ME for tissue retention (k ) for dry cows, but ME was utilised with similar efficiency for milk production andg
concomitant tissue retention. The energy value per unit of liveweight gain or loss should not be fixed as it depends on gut fill and composition of fat, protein and water in the gained or mobilised liveweight. The energy value per mobilised liveweight can also differ with stage of lactation. The above effects are important for dairy cattle feeding and should therefore be incorporated in the future revision of an energy feeding system. The current energy feeding systems used in Australia, the Netherlands, UK and USA have also been validated using calorimetric data of lactating dairy cows published since 1976.
2000 Elsevier Science B.V. All rights reserved.
Keywords: Dairy cow; Energy system; Maintenance; Efficiency; Validation
*Corresponding author.
E-mail address: t.yan@qub.ac.uk (T. Yan).
1
Also a member of staff of the Department of Agriculture for Northern Ireland and The Queen’s University of Ireland.
1. Introduction liveweight change and energy value per unit of liveweight change.
The UK metabolisable energy (ME) feeding sys-tem, developed by Blaxter (1962), was first proposed for use in the UK in 1965 by the Agricultural
2. Energy requirement for maintenance
Research Council (ARC, 1965). This system was designed to overcome the deficiencies of the starch
2.1. Methods of estimating energy requirement for equivalent (SE) system (a net energy (NE) system)
maintenance
which was then used in the UK. The SE system assumed a simple ratio of NE values of feeds for
The NE requirement for maintenance (NE ) in
maintenance, fattening and lactation and also took no m
energy feeding systems presently used in Europe and account of the effect of feeding level on NE
con-North America was derived from calorimetric data. centration of a feed. Using the proposals put forward
In the UK ME system the NE was based on fasting
by ARC (1965), a simplified ME system was m
metabolism data (fasting heat production (FHP) plus recommended to be adopted in UK by the Ministry
fasting urinary energy output) from beef steers and of Agriculture, Fisheries and Food (MAFF, 1975).
dry non-pregnant dairy cows after a prolonged period The original ME system (ARC, 1965) was later
of restricted feeding (usually at maintenance level). substantially revised by ARC (1980) and further
Using this approach ARC (1980) reported a curvi-modified by Agricultural and Food Research Council
linear relationship between fasting metabolism (FM) (AFRC, 1990) and a new working version was
0.67
and liveweight (LW) (FM50.53?(LW/ 1.08) ) published in 1993 (AFRC, 1993). At the same time a
from a review of eight sets of data. This relationship, number of NE systems have been developed in
plus an activity allowance (0.0091?LW), is taken as Europe (Van Es, 1978; Institut National de
Re-NE for use at present in UK (AFRC, 1990). This cherche Agronomique (INRA, 1978) and Northern m
approach would suggest a fasting metabolism of America (National Research Council (NRC, 1978).
around 0.30 (or NE of 0.35 if an activity allowance There is no difference in principle between the m
0.75
is included) MJ / kg for an adult dairy cow. The ME and NE systems, with both systems recognising
ME requirement for maintenance (ME ) is
calcu-that the energy requirement of cattle is the sum of m
lated as NE divided by the efficiency of utilisation their energy requirements for maintenance, product- m
of ME for maintenance (k ,50.35?ME / GE10.503)
ion (milk and liveweight gain) and foetal growth. m
(AFRC, 1990). Alternatively, the NE can be
esti-The only difference between them is where the m
mated using regression techniques relating ME in-energetic efficiencies are embodied within the
calcu-take to milk energy output, adjusted to zero energy lation. In the ME system the energetic efficiencies
balance, with dairy cows offered diets at production are used for ration formulation and the prediction of
levels. Using this approach, Moe et al. (1972) and animal performance, while in the NE system the
Van Es (1975) reported NE values of 0.305 and
efficiencies are included as part of the energy m
0.75
evaluation of feeds. 0.293 MJ / kg , respectively from large sets of
Over the last 2 decades a considerable volume of calorimetric data. The former value is used to form research in the energy metabolism of dairy cows has the American NE system, with an activity allowance been undertaken. These studies have highlighted a of proportionately 0.10 being added (NRC, 1988). number of concerns over current energy feeding The latter value is adopted in the European NE systems. The purpose of the present review is to systems used in the Netherlands, France, Germany reflect on the impact of these studies on the UK ME and Switzerland. No activity allowance is adopted in system, and other NE systems, and validate these the Netherlands (Van Es, 1978), while an activity systems using published calorimetric data. The areas allowance of proportionately 0.10 is added for loose which will be addressed in the present review housed cows in France (INRA, 1989).
include the energy requirement for maintenance, The NEm in the UK ME system is a curvilinear
0.75
increasing liveweight (age) of cattle. This is because al., 1999). This type of infusion can also result in a the metabolic rate can be higher for growing than lower heat production than FHP (Chowdhury, 1992). adult cattle (ARC, 1965) and light adult animals However, the maintenance metabolic rate obtained
0.75
generally have a greater proportion of internal organs by fasting metabolism (0.30 MJ / kg ) (ARC, over total liveweight than heavy adult ones (NRC, 1980) is similar to that derived from regression
0.75
1988). The internal organs produce much higher heat techniques (0.305 or 0.293 MJ / kg ) (Moe et al., than muscle per unit weight. In contrast, the NEmfor 1972; Van Es, 1975). It thus seems unlikely that the
0.75
cattle is constant per kg in the NE systems used detriment of fasting to animal health influences in Europe and North America. In these systems the greatly the heat production.
NEmvalues were derived from data on mature dairy
cows. It is therefore likely that these latter systems 2.2. Recent research on energy requirement for may theoretically underestimate the energy require- maintenance
ments of young cattle.
The use of fasting metabolism data to determine The NEm values currently used in Europe and NE may have limitations. It has been suggested thatm North America were developed from data published fasting after a long period of restricted nutrition can 30 years ago. However, a recent study reported by result in deamination of amino acids from tissue Birnie (1999) revealed a FHP value of 0.39 MJ /
0.75
protein for the supply of essential glucose (Chow- kg for dry, non-pregnant dairy cows fed at dhury and Ørskov, 1994). This can induce a range of maintenance level prior to measurement of FHP. metabolic disorders in the animal, such as hypo- Assuming a fasting urinary energy output of 0.05 of glycaemia, hyperlipidaemia, hyperketonaemia and FHP (Van Es, 1972), the derived fasting metabolism hypoinsulinaemia. The deamination caused by fast- is proportionately 0.36 higher than that adopted in ing can however be reduced, as evidence of a lower current energy systems (Van Es, 1978; NRC, 1988; N output in urine, after infusing a small amount of INRA, 1989; AFRC, 1990). Similar higher FHP volatile fatty acids (VFAs) or glucose with or values were also reported by Yan et al. (1997b) and without casein (Ku Vera et al., 1987, 1989; Ørskov et Birnie (1999) when dairy cows were offered,
respec-Table 1
Fasting heat production of steers and dairy cows offered dried forage-based diets published since 1985
Reference Feeding Live weight Forage Fasting HP
0.75
level (kg) proportion (MJ / kg )
Beef and dairy steers
Birkelo et al. (1991) 1.2?Maintenance 344 0.40 0.357
2.7?Maintenance 344 0.40 0.383
Hotovy et al. (1991) Near maintenance 373 0.55 0.337
Carstens et al. (1989) Maintenance 236 0.40 0.350
Maintenance 372 0.55 0.331
Gill et al. (1989) Near maintenance 210 1.00 0.353
Smith and Mollison (1985) Near ad libitum 200 0.15 0.398
Near ad libitum 200 0.30 0.389
Dairy cows
Birnie (1999) Maintenance 571 1.00 0.408
Maintenance 557 0.14 0.382
2?Maintenance 614 1.00 0.414
2?Maintenance 613 0.14 0.410
Yan et al. (1997b) Near ad libitum 501 1.00 0.454
Table 2
Summary of the ME requirement for maintenance (ME ) and the efficiency of ME utilisation for lactation (k ) by lactating dairy cattle,m l
calculated by a range of authors using regression techniques and pooled calorimetric data
Reference Cow Forage Method MEm kl
0.75
no. (MJ / kg )
Moe et al. (1970) 350 Lucerne / grass hay Multiple 0.51 0.64
Van Es et al. (1970) 198 Hay / silage Linear 0.49 0.62
Van Es (1975) 1148 A range of forages Linear 0.49 0.60
Unsworth et al. (1994) 108 Grass / silage Linear 0.64 0.67
Hayasaka et al., 1995 53 Hay / silage Linear 0.59 0.64
Yan et al. (1997a) 221 Grass silage Linear / multiple 0.67 0.65
Present study .1500 A range of forages Linear / multiple 0.62 0.66
Mean 0.57 0.64
S.D. 0.075 0.024
tively diets at near ad libitum and at twice mainte- MEI50.664( 0.0471 )MW11.452( 0.0755 )El
nance levels prior to fasting (Table 1). FHP data 2
11.079( 0.1200 )E Rg 50.92 (2) published using studies with beef and dairy steers
since 1985, as presented in Table 1, are in accord
where E , E , MEI and MW are, respectively milk with the above dairy cow results. The mean derived l g
energy output, energy balance, ME intake and meta-fasting metabolism, when assuming a meta-fasting urinary
0.75
bolic liveweight (kg ); E 5E 1E for positive
energy output of 0.05 of FHP (Van Es, 1972), is l( 0 ) l g
E or 5E 20.84?E for negative E . The units for
proportionately 0.19 higher than that proposed by g l g g
0.75
Eqs. (1) and (2) are, respectively MJ / kg and ARC (1980).
MJ / day. The values in brackets are standard errors. The MEm values derived from regression
tech-The mean ME derived from these two equations is niques have also been reported to be higher in recent m
0.75
studies. The MEm values obtained in 6 studies are 0.62 MJ / kg , a value which is proportionately presented in Table 2. The mean MEm value derived 0.27 higher than that derived from Van Es (1975), or in recent studies (Unsworth et al., 1994; Hayasaka et calculated from AFRC (1990).
al., 1995; Yan et al., 1997a) is proportionately 0.28 higher than that reported over 20 years ago (Moe et al., 1970; Van Es et al., 1970; Van Es, 1975). As Van Es (1975) used a total of 1148 data from across the world, the NEm derived from his study is thus adopted in a number of European NE systems. The present authors have reviewed calorimetric studies with lactating dairy cows published since 1976. A total of 42 studies (more than 1500 individual animal data) were selected, in which the liveweights of the animals and the energy intake and outputs were available (for references see appendix). The ex-perimental mean data from these 42 studies were used to examine the relationship between ME intake and energy outputs. The linear (Fig. 1) and multiple regression equations obtained are:
2 Fig. 1. Relationship between ME intake and milk energy output
El( 0 )50.637( 0.0358 )MEI20.371( 0.0557 )R adjusted to zero energy balance using calorimetric data of dairy
cows published since 1976 (experimental means, n542).
The higher MEm may reflect differences in both feed intake, total heat production (MJ / day) was the diet and the cow now used, particularly the found to be similar between fat and lean rats at a considerable improvement in cow genetic merit similar body lean mass although total liveweight of during the last two decades (Coffey, 1992). The fat rats was heavier (Ramsey et al., 1998). The latter has led to an increase in milk yield of estimated MEm reported by Pullar and Webster approximately 62 kg / lactation per year (Agnew et (1977) in Zucker rats and by Toutain et al. (1977) in al., 1998). Indeed, high producing dairy cows were sheep also showed no significantly difference in
0.75
found 30 years ago by Flatt et al. (1969b) to require MEm (MJ / kg ) when related to protein mass, but proportionately 0.20 more ME for maintenance than was higher with lean than fat animals when related to cows producing moderate yield, as reported at the total liveweight.
same time by Moe et al. (1970) and Van Es et al. A series of fasting studies, in dry and non-preg-(1970). The higher MEm obtained in the recent nant Holstein–Friesian cows, carried out recently at studies may be attributable to a higher proportion of this Institute would support the above results. Cattle liveweight as body protein mass. This is evidenced were fattened from condition scores (CS) (Mul-in that high genetic merit cows had a lower backfat vanny, 1977) below 2.0 to over 4.5, or restricted thickness at a similar liveweight to medium and low feeding to reverse CS change. While FHP (MJ /
0.75
genetic merit animals (Ferris et al., 1999a), and a kg ) was significantly higher for cattle with low higher estimated lipid-free empty body weight as a than high CS, the former animals required a similar proportion of empty liveweight (Veerkamp et al., amount of estimated ME for maintenance (MJ / day) 1994). The MEm has been reported to be a function although they had a much heavier weight (Birnie,
0.75
of body protein mass (discussed later). On the other 1999). A regression of FHP (MJ / kg ) against CS
2
hand, high genetic merit cows obviously require (from 1.0 to 5.0) (R 50.83, n528) indicated that
0.75
greater nutrient intakes and this could stimulate the FHP was 0.483 MJ / kg at CS of 1.0 and an activity of internal organs with greater digestive increase of CS by 1.0 would reduce FHP by 0.029
0.75
load, cardiac output and blood flow required to MJ / kg .
digest, absorb and deliver nutrients to the mammary The above findings support the view of Oldham gland and a greater oxygen consumption (Reynolds, and Emmans (1990) that the major part of the energy 1996). These activities in return can enlarge the cost associated with tissue ‘maintenance’ results internal organ size. Liver and other internal organs from the continual process of synthesis, degradation can produce much more heat (MJ / kg) than that of and replacement of those parts of body tissues which muscle (Baldwin et al., 1985; Johnson et al., 1990). ‘turnover’. This is particularly the case with body protein for which the process of ‘turnover’ is sub-2.3. Factors affecting the energy requirement for stantial, although variable (Reeds, 1989). It has been
maintenance suggested that fat tissue does not ‘turnover’ at all in
animals fed regularly, although there does appear to 2.3.1. Body condition ( fat vs. lean) be an extent of fatty acid turnover which is obligat-In all currently used energy systems the energy ory and which might be presumed to represent a requirement for maintenance is related to the degree of turnover of body fat (Oldham and Em-liveweight of animals. However, there has been mans, 1990). The energy cost of maintaining body increasing evidence to suggest that maintenance protein would, however, be expected (on stoichio-metabolic rate depends on body lean mass, rather metric grounds) to exceed that of fat even if their than whole liveweight. For example, Noblet et al. rates of turnover were similar. Against this back-(1998) reported a significantly lower FHP per unit of ground it is biologically unreasonable to expect liveweight in fat than lean pigs of different breeds. maintenance to be directly related to scaled While this finding could partially be due to breed liveweight when the composition of the body may differences, a similar result has been obtained be- vary.
techniques can be used to indirectly predict body fat expensive process (four phosphate bonds required and protein masses. For example, the ultrasonic per molecule urea synthesis) (Martin and Blaxter, scanning technique can be used to measure the back 1965).
fat thickness of an animal (Ferris et al., 1999a). The Dietary fibre concentration can also influence k ,m
prediction of body protein mass can also be derived because kmis predicted from energy metabolisability from slaughter techniques. Fat-free mass of dairy in the UK ME system. Increasing fibre concen-cows was reported to be similar during the dry trations in diets can reduce energy metabolisability period, early and late lactation stages (Andrew et al., by reducing energy digestibility (Flatt et al., 1969b; 1994). Protein mass of cattle is curvilinearly related Beever et al., 1988) and increasing methane energy to their liveweight and liveweight is the best single output as a proportion of total DE intake (Yan et al., predictor of body protein mass (Wright and Russel, 1999). The effects of dietary fibre fraction on 1984). Gibb and Ivings (1993) reported a linear maintenance metabolic rate and kmcan thus result in relationship between body protein mass (P) and a higher MEm for a high compared to a low fibre liveweight (LW) for Holstein–Friesian cows (P5 diet. This has been demonstrated in a number of 0.0997 LW122.37), but cow body condition is not studies with lactating dairy cows (Flatt et al., 1969b; considered in this equation. Tyrrell and Moe, 1972; Yan et al., 1997a) and with beef cattle (Beever et al., 1988; Reynolds et al., 2.3.2. Dietary concentration of fibre fraction 1991a).
All currently used energy systems for cattle
as-sume that dietary fibre concentration has no effect on 2.3.3. Grazing activity
1990). The increase in NEm cost for grazing would For individual calorimetric studies, k has oftenl
be greater (0.30–0.40) under extensive grazing con- been determined by assuming a MEmvalue which is ditions, since the animals would spend more time deducted from ME intake to provide the ME avail-eating and walking (Langlands et al., 1963). In able for production (ME ), and then relating this top
addition, lactating dairy cows grazing on pasture are adjusted milk energy output (El( 0 ), kl5El( 0 )/ ME ).p
usually required to walk a distance twice a day for The kl estimated from this approach is thus in-milking. The energy costs for walking are suggested fluenced by the accuracy of ME . Using this meth-m
to be 2.0 or 28 kJ / kg liveweight per km for od, and MEm of AFRC (1990), k values have oftenl
horizontal and vertical movement, respectively for been estimated to be low (0.50–0.58) with data of cattle (ARC, 1980). Brody (1945) suggested a dairy cows given diets based on either grass silage proportionately 0.08 increase in maintenance energy (Unsworth et al., 1994; Gordon et al., 1995; Yan et requirement for each km of walking. al., 1996; Ferris et al., 1999b), or maize silage or NRC (1988) recommend a proportionately 0.10 whole crop wheat (Beever et al., 1998; Sutton et al., increase in maintenance allowance for cows grazing 1998a,b, 1999). However, the above k values couldl
on good pasture and up to 0.20 on sparse pasture. be increased (0.59–0.65, mean of 0.62) by using a
0.75
SCA (1990) suggest that increases in maintenance MEm of 0.62 MJ / kg , as obtained from Eqs. (1) requirement for grazing cows are in a range of and (2). The latter mean k (0.62) is similar to thatl
0.10–0.20 in intensive grazing conditions, to approx- (0.64) predicted from AFRC (1990) (kl50.35?ME / imately 0.50 for animals grazing extensive, hilly GE10.42) using ME / GE obtained in these studies. pastures where they walk considerable distances to A further method has been adopted by some preferred grazing areas and to water. However, these workers (mainly in Germany), in which k is derivedl
allowances are not included in the current UK ME as a proportion of NE of total ME intake, where NE system (AFRC, 1993) and there is a requirement to is the sum of milk energy, retained energy multiplied address this deficiency in the future. by a constant and assumed NE . However, them
efficiency calculated using this method is a mixture of efficiencies of ME utilisation for lactation (k ) andl
3. Efficiency of ME utilisation maintenance (k ).m
3.1. Methods of estimating the efficiency of ME 3.2. Effects of dietary nutrients on the efficiency of
utilisation for lactation ME utilisation for lactation
The efficiency of ME utilisation for lactation (k )l The composition of a diet can shift the microbial can be determined using a range of regression population in the rumen and consequently influence techniques on large sets of calorimetric data. In the the production of VFAs. In general a high fibre diet literature two regression equations have often been produces VFAs with a high proportion of acetic acid, used; i.e., the linear regression relating milk energy while a concentrate diet normally generates more output (adjusted to zero energy balance) to ME propionic acid. It has been well documented that intake, and the multiple regression relating ME VFAs produced in the rumen can influence milk intake to metabolic liveweight, milk energy output composition, i.e. molar proportions of acetic and and energy balance. Using these two methods the butyric acids are positively related to milk fat present review would suggest an average k of 0.66,l concentration. The rumen VFAs can also alter energy as presented in Eqs. (1) and (2), derived from partition between milk and body tissue. A number of calorimetric data of dairy cows drawn from 42 feeding studies (e.g., Flatt et al., 1969a; Sutton et al., studies from across the world. This value is within 1993) and infusion trials (e.g., Ørskov et al., 1969; the range of k values (0.60–0.67), as presented inl Huhtanen et al., 1993) have demonstrated that in-Table 2, which were derived from regression tech- creasing propionic acid proportion can result in more niques reported in a number of studies with dairy energy partitioned into body tissue and less into
occur when the absorption of propionic acid exceeds the capacity of the liver to handle it (Ørskov and MacLeod, 1990). Some propionic acid can thus enter the peripheral circulation and stimulate the pancreas to secret insulin, so leading to utilisation of energy for tissue synthesis and depression of the cow’s milk yield and milk fat production (Ørskov and MacLeod, 1990).
The effects of VFAs produced in the rumen on energy utilisation have been studied extensively in sheep and steers. The results are not conclusive, with some workers reporting a lower efficiency of utilisa-tion of energy derived from acetic acid for body tissue synthesis, while others noting equal efficien-cies between acetic and propionic acids (Tyrrell et al., 1979; Ørskov and Ryle, 1990). The research on
Fig. 2. Relationship between forage proportion and k calculatedl
the influence of VFAs production on k with lactat-l with the ME of AFRC (1990) using calorimetric data of dairy
m
ing dairy cows is limited, but there is no evidence cows published since 1976. indicating a relationship between k and the molarl
proportion of acetic or propionic acid produced in the rumen. For example, the infusion of different
proportions of acetic and propionic acids into the Increasing fibre concentration in diets can increase rumen of lactating dairy cows has shown no effect the MEm of cattle as discussed previously. It there-on kl (Ørskov et al., 1969) or heat production fore suggests that the lower animal performance with (Ørskov and MacLeod, 1982). The infusion of acetic high forage diets may be a reflection of a higher acid either showed little effect on heat production of ME , leaving less energy available for production,m
dry dairy cows offered forage-only diets, although rather than that the high forage diet results in a lower the efficiency of utilisation of additional energy from k . This would be suggested by the findings of Yan etl
infusion of acetic acid varied with composition of al. (1997a) who showed that increasing dietary basal diets (Tyrrell et al., 1979). proportion of grass silage increased MEm but had no
The k obtained using the linear regression tech-l significant effect on k in lactating dairy cows.l
nique on large sets of calorimetric data also indicates
little differences with forage proportions in diets. In 3.3. Effect of cow genetic merit on the efficiency a single experiment Flatt et al. (1969b) observed of ME utilisation for lactation
similar k values when alfalfa proportions in dietsl
were increased from proportionately 0.2 to 0.6. Yan Dairy herds in the British Isles have been undergo-et al. (1997a) pooled data from 221 cows across ing a period of rapid increase in cow genetic merit experiments and reported that k values were notl since the mid 1980s, with Coffey (1992) reporting influenced significantly by the proportion of grass current rates of genetic gain of proportionately 0.013 silage in the diet. The data (experiment mean) used per year in milk fat plus protein yield for the indexed to develop Eqs. (1) and (2) have been used by the population in UK and Ireland. This increase is present authors to examine the relationship between approximately 4.5 kg / year of fat plus protein yield, a forage proportion in diets and k calculated usingl value which is about 62 kg / year of milk yield when
0.75
either MEm of AFRC (1990) or 0.62 MJ / kg assuming milk of standard composition (Agnew et derived from Eqs. (1) and (2). The result indicates al., 1998). It has been reported extensively that gross no relationship between forage proportion and kl energetic efficiency (milk energy output as a propor-values when using either the former MEm(Fig. 2) or tion of ME intake) is higher with high than low
lactation (e.g., Grainger et al., 1985b; Gordon et al., with which ME is utilised for lactation between 1995; Ferris et al., 1999b). The magnitude of this Holstein and Jersey cows.
increase in the efficiency was higher in multiple The discrepancy in effect of cow genetic merit on lactation than first lactation cows (Veerkamp et al., gross energetic efficiency and k may partially bel
1994). However, when tissue energy retention and derived from the difference in MEp between high MEmare taken into account, the partial efficiency for and low genetic merit cows. The main factor may lactation (k ) appears to be similar between high andl however be because high genetic merit cows have low genetic merit cows. The difference in milk the ability to shift the partition of ME absorbed, i.e. energy output between high and low genetic merit more into milk and less into body tissue. A number cows could almost entirely be explained by differ- of long term feeding studies have demonstrated this ences between genotypes in energy intake and tissue effect (Grainger et al., 1985a; Gordon et al., 1995). energy retention (Grainger et al., 1985b). When using An example of this is illustrated in Fig. 3, as reported the equations of AFRC (1990) to estimate ME ,m by Veerkamp et al. (1994) and Veerkamp and Em-neither Gordon et al. (1995) nor Ferris et al. (1999b) mans (1995), which showed that high genetic cows detected any significant difference in kl between had a higher gross energetic efficiency and a lower high, medium and low genetic merit cows. Veerkamp energy retention than low genetic cows during the and Emmans (1995) in a literature review also first 26 weeks of lactation. Lamb et al. (1977) indicated little difference in the partial efficiency assessed the first lactation of 289 daughters of 17
Holstein sires when the animals were fed according tively by Armstrong and Blaxter (1965), Aguilera et to milk yield and also concluded that the daughters al. (1990) and Rapetti et al. (1998). When using of high genetic merit bulls used less nutrient intake regression techniques on calorimetric data of lactat-for body gain and more lactat-for milk production. The ing dairy cows, Flatt et al. (1969b) and Van Es et al. difference in partition of ME between high and low (1970) found that ME was utilised no less efficiently genetic merit cows is associated with insulin con- for concomitant tissue retention than for milk secre-centration in blood. During early lactation insulin tion. The above findings indicate that during lacta-concentration was significantly higher in the plasma tion the efficiency of ME utilisation for concomitant of low genetic merit cows, that were in energy tissue retention would appear to be similar to that for surplus and gaining body weight, than in high lactation, although Moe et al. (1970) reported that genetic merit cows that were in energy deficit and ME was more efficiently utilised for concomitant losing liveweight (Hart, 1983). The difference in tissue retention than for lactation in dairy cows. insulin concentration disappeared when the animals
stopped lactating (Hart, 1983).
3.4.3. Efficiency of utilisation of mobilised tissue
energy for lactation
3.4. Energetic efficiency for liveweight gain or
The efficiency of utilisation of mobilised tissue
from mobilised tissue energy for lactation
energy for lactation was recommended by ARC (1980) to be 0.84. This value was obtained by Moe 3.4.1. ME use for production during lactation vs.
and Flatt (1969) from regression analysis of
during dry period
calorimetric data (n5126) of lactating dairy cows in It has been suggested that the utilisation of ME for
negative energy balance. There has however been milk production (adjusted to zero energy balance)
little new information available in the literature on (k ) in lactating cows is more efficient than that forl
this aspect since then. During the period from 1992 tissue retention (k ) in dry cows (ARC, 1980). In ag
to 1998, a large number of lactating dairy cows were recent study at this Institute a forced drying off
subject to gaseous exchange measurements in procedure was adopted to study how the efficiency of
calorimetric chambers at this Institute, of which 127 ME changed with physiological state of the animal
cows were in negative energy balance. These 127 (Yan et al., 1997b). A reduction in milk energy of 1
data were used to develop similar multiple regression MJ / day with lactating cows was found to be
associ-equations to those adopted by Moe and Flatt (1969). ated with an increase in tissue energy retention of
The equations are presented as below 0.82 MJ / day with dry cows. When relating to MEp
(ME intake2ME ), the efficiency (k ) for lactatingm l
cows can be proportionately 0.09 higher than that MEI51.474( 0.0552 )El11.067( 0.0891 )Eg
(k ) for dry cows. A similar reduction (0.11) withg 2
10.745 R 50.85 (3)
dry dairy cows was also reported by Moe et al. ( 0.0309 )
(1970) using multiple regression techniques on calorimetric data of dairy cattle (n5543).
El50.578( 0.0216 )MEI20.749( 0.0467 )Eg
3.4.2. ME use for lactation vs. for concomitant 2
20.359( 0.0330 ) R 50.90 (4)
tissue retention
Yan et al. (1997b) observed an increase in tissue
energy retention of 0.96 MJ / day associated with a where MEI, E and E are, respectively ME intake,l g 0.75
4. Energy value per unit of liveweight change (Bath et al., 1964; Reid and Robb, 1971; Tamminga et al., 1997). Protein mobilisation is stopped at about Energy value per unit of liveweight change for 4 weeks after calving, while fat mobilisation is not lactating dairy cows is fixed in NRC system and each stopped at 8 weeks (Tamminga et al., 1997). This of European systems, but varies with a range be- may be due to a considerable hypertrophy of both tween 19 and 30 MJ / kg of liveweight change. A gut and liver during early lactation in response to number of recent studies have reported different increased feed intake (Reynolds and Beever, 1995). energy values within the above range (Chilliard et The composition of mobilised tissue (fat and protein) al., 1991; Gibb et al., 1992; Tamminga et al., 1997). can thus differ during the first 4 weeks of lactation, The reason for this discrepancy may be attributed to i.e. the ratio of fat-to-protein would increase. If the the effects of body condition and lactation stage. water content in the mobilised tissue is assumed to Body condition factors have been recognised to remain unchanged, the energy value per unit of influence the energy value of liveweight change. liveweight loss would be higher as lactation pro-These factors include gain or loss of body fat or gresses. On the other hand, energy balance is not protein, replacement of body fat with water and always related to liveweight change of dairy cows. changes in gut fill. The lack of precision in these Beever et al. (1998) reported that high genetic merit factors can result in errors in ration formulation and cows were still in negative energy balance at 20 the prediction of animal performance, especially in weeks of lactation, but liveweight of the animals was early and late lactation when liveweight change of maintained after 5 weeks. This can be partially dairy cattle can be large. It may not be realistic in explained by the findings of Tamminga et al. (1997) practice to distinguish the effects of gut fill on gain as changes in the water content in mobilised or loss of liveweight and how much water is liveweight. The total water loss was proportional to contained in the weight of change. However, a the mobilised liveweight during the first 4 weeks of number of studies have related the energy value of lactation. Afterwards the animals retained water in liveweight change to body condition. In a serial their bodies and liveweight loss was very small, but slaughter study with Holstein–Friesian cows, Gibb energy loss was still high (Tamminga et al., 1997). and Ivings (1993) reported that the body fat and Energy value per unit of mobilised liveweight thus energy contents of animals were positively related to increased substantially from 1 to 8 weeks of lactation their liveweight and condition score and body protein (Tamminga et al., 1997).
content was positively related to their liveweight. The fixed energy value for liveweight change in Fat-free mass of Holstein cows remains similar NRC system and European systems is therefore during the dry period, early and late lactation stages, incorrect and can result in errors in practice, espe-while water content of fat-free mass is greater during cially for high genetic merit cows which have a high the dry period and early lactation than late lactation liveweight loss during early lactation. There is a stages (Andrew et al., 1994). These relationships are need to develop more appropriate measures of reflected in the Cornell net carbohydrate and protein energy status in dairy cows. If liveweight change system (Fox et al., 1992). In this system the energy continues to be used as an index of tissue energy concentration per condition score is linearly and change, it must be related to both body condition and positively related to body condition score and stage of lactation.
liveweight of dairy cattle. In Australia a linear regression equation for dairy cattle has been
de-veloped to relate the energy value of liveweight 5. Validation of the UK ME system and other
change to body condition score (SCA, 1990). energy systems
Another factor affecting energy value per
1). The energy systems examined include the UK 1
2
]
ME system (AFRC, 1990 and 1993), the Australian MSPE5
O
(A2P) (5)n
ME system (SCA, 1990), the American NE system
] ] 2 2 2 2 2
(NRC, 1988) and the Dutch NE system (Van Es, MSPE5(A2P) 1S (12b) 1S (12R ) (6)
P A
1978). AFRC (1993) is a working version of AFRC
(1990) which adds a proportionately 0.05 to total where n is the number of pairs of values of A and P
] ]
ME requirement predicted from AFRC (1990). The compared (n542); A and P are, respectively, the
2 2
Dutch NE system was chosen to represent a range of means of A and P; SP and SA are, respectively, the the NE systems based on the principles proposed by variances of A and P; b and R are, respectively, the Van Es (1975), e.g. used in France (INRA, 1989), slope and correlation coefficient of the linear regres-the Neregres-therlands (Van Es, 1978), Switzerland (Bickel sion of A on P. The three components are thus due to
] ]
and Landis, 1978) and Germany (Deutschen Land- mean bias (A2P), line bias (the deviation of the
wirtschafts Gesellschaft, 1982). The American NE slope) and random variation of the slope. In order to system (NRC, 1988) does not provide any method to compare the accuracy of prediction between ME and calculate intake of NE for lactation (NEL) from its NE systems, the MSPE is expressed as the mean
]]
Œ ¯
ME intake, so the observed NEL intake in the prediction error (MPE5 MSPE /A ).
present validation for the NRC system is based on The results of the present validation are presented the equation of Moe (1981) (NEL50.697 ME2 in Table 3 and Fig. 4a and b. The MPE was much 0.877, MJ / kg DM). The predicted NEL requirement higher with AFRC (1990) than the other three in Van Es (1978) and NRC (1988) is a sum of systems (Van Es, 1978; NRC, 1988; SCA, 1990), predicted NEm and observed E and E . The pre-l g indicating that AFRC (1990) is the least accurate at dicted ME requirement is a sum of predicted NEm predicting total energy requirements of lactating and observed E and E divided by relevant energeticl g dairy cows. The predicted error of AFRC (1990) was efficiencies. In both the ME and NE systems E wasg largely derived from an under-prediction of total] ] treated as, if E was positive then it was added; if Eg g energy requirement (mean bias, A2P), which
re-was negative then it re-was subtracted after multiplica- sulted in a large proportion of mean bias over total tion by either 0.80 (Van Es, 1978), 0.82 (NRC, MSPE. However, when a proportionately 0.05 was 1988), or 0.84 (AFRC, 1990; SCA, 1990). added to total ME requirement predicted in AFRC The model, used to compare those energy systems (1990), as suggested by AFRC (1993) (currently for actual energy (ME or NE) intake (A) and adopted in UK), total energy requirements were predicted energy requirement (P), is the mean-square predicted with a similar accuracy to NRC (1988) and prediction error (MSPE) as described by Rook et al. SCA (1990). Van Es (1978) had a marginally higher (1990). The MSPE is defined as Eq. (5) and can be MPE than NRC (1988), SCA (1990) and AFRC regarded as the sum of three components (Eq. (6)) (1993). The higher prediction error for Van Es
Table 3
Prediction precision of different energy feeding systems in calorimetric data of dairy cows published since 1976 (n542)
Systems Energy intake (MJ / day) MSPE MPE Proportion of MSPE
Actual Pred. Bias Bias Line Random
ME system
AFRC (1990) 181 171 9.9 219 0.082 0.45 0.01 0.54
AFRC (1993) 181 179 1.4 129 0.062 0.01 0.07 0.92
SCA (1990) 181 182 21.6 116 0.060 0.02 0.13 0.85
NE system
Van Es (1978) 110 106 3.6 56 0.068 0.23 0.03 0.74
likely to be the ME . This can be demonstrated inm
the validation of SCA (1990) which uses the same kl
as AFRC (1990) but a higher MEm by adjusting it with total ME intake. There is no basis to compare the validation between ME and NE systems, since in the 2 NE systems km is assumed to be same as k tol
calculate NEL. However, this assumption is not biologically correct, because research evidence has indicated that km was higher than k . The differencel
between kmand k is calculated to be 0.12 or 0.08 inl
Van Es (1975) or ARC (1980) when ME / GE ratios are from 0.55 to 0.70. The assumption that km is equal to k in both Van Es (1978) and NRC (1988)l
could thus cover the under-prediction of NE used inm
these two systems, because the metabolic rates, as discussed previously, are similar between Van Es (1978), NRC (1988) and AFRC (1990). This bias would be larger for late-lactating and dry cows because the ratios of ME / MEI is higher at thesem
two stages. Nevertheless, the more accurate predic-tion of NRC (1988) than Van Es (1978) mainly reflects that the former adds an activity allowance of 0.10.
6. Conclusions
The present review has highlighted a number of concerns in the energy metabolism of dairy cows. Recent studies have shown a higher MEm for the Fig. 4. Relationship between actual energy intake and predicted cattle of today (probably reflecting an improvement energy requirement (AFRC, 1990, 1993; SCA, 1990) using
in cow genetic merit), the influence of dietary fibre experiment mean data (n542) published since 1976 (broken line
concentration and grazing activity on ME and a
y5x). m
relationship between MEm and body protein mass (heat production is a function of protein mass). The ] ]
(1978) was attributed to a higher mean bias (A2P) k is relatively stable over a number of dietary (fibrel
and consequently a higher proportion of mean bias concentration) and animal (cow genetic merit)
fac-over total MSPE. tors. The energy value per unit of liveweight change
The addition of a proportionately 0.05, as adopted varies with body condition and stage of lactation. by AFRC (1993), to total ME requirement predicted These effects are important for dairy cattle feeding by AFRC (1990) is however questionable. The mean and should therefore be incorporated in the future
k predicted from AFRC (1990) was 0.63, which isl revision of an energy feeding system. close to the mean k values presented in Table 2 andl
obtained in Eqs. (1) and (2) using the same set of
data as the present validation. The ME requirements Acknowledgements
for lactation and liveweight change predicted from
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![Fig. 3. Effects of cow genetic merit of high (—) and low (- - -) on condition score, tissue energy retention and milk energy output as aproportion of Me intake [mean of high and low concentrate levels (from Veerkamp et al., 1994; Veerkamp and Emmans, 1995)].](https://thumb-ap.123doks.com/thumbv2/123dok/1050034.932814/9.612.123.426.319.628/effects-condition-retention-aproportion-concentrate-veerkamp-veerkamp-emmans.webp)
