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Genetic and phenotypic relationships between milk production
and body weight in Chios sheep and Damascus goats
*
A.P. Mavrogenis , C. Papachristoforou
Agricultural Research Institute, P.O. Box 22016, 1516 Nicosia, Cyprus
Received 17 August 1999; received in revised form 21 December 1999; accepted 16 February 2000
Abstract
Data on 2087 lactations from 737 Chios ewes collected between 1978 and 1989, and 1611 lactations from 486 Damascus goats collected from 1982 to 1998 at the experimental station of the Agricultural Research Institute were utilized. The ewes were the progeny of 101 sires (mean sire family size 7.3) and the goats of 101 sires (mean sire family size 4.8). A mixed linear model that accounted for the year and season of lambing / kidding and parity of ewes or goats (fixed effects) and sires within years (random effects) was used. Phenotypic and genetic variance and covariance estimates were obtained from paternal halp sib correlations. The study was conducted to investigate genetic and phenotypic relationships between milk production (90-day and total milk) and live weight at mating. Year effects were significant (P,0.01) for all traits studied, while season of parturition significantly affected (P,0.01) only milk production (part and total). Parity had a significant quadratic effect (P,0.01) on all traits examined; the highest response in milk production was reached in the third parity and the highest body weight at mating in the fifth parity. Heritability estimates for 90-day (0.4460.08 and 0.4560.11) and total milk yield (0.5460.09 and 0.4960.11) for sheep and goats, respectively, were high, indicating that genetic progress from direct selection on either trait would be effective. Heritability of body weight at mating, unadjusted or adjusted to mature equivalent, was high in both species (sheep: 0.7960.09 and 0.7660.09, respectively; goats: 0.7960.11 and 0.8060.11, respectively). Genetic and phenotypic correlations between part and total lactation yield were both high and positive, justifying selection on early measures of milk production. The genetic associations between production traits and body weight at mating were very low in both species. It was positive in sheep and negative in goats, but no or extremely small correlated responses could be expected in body weight from selection on milk production. Increased body size, when expressed, should be the consequence of better feeding and improved management practices during periods of stress.
2000 Elsevier Science B.V. All rights reserved.
Keywords: Milk yield; Mating weight; Sheep; Goat; Relationships; Genetics
1. Introduction and milk yield are large. Relationships, therefore,
between those two characters are relatively easy to Genetic differences among species in body size establish. When dealing with genetic differences within breeds the inter-species relationships provide a useful null hypothesis (Taylor, 1973).
*Corresponding author. Tel.: 1357-2-305-101; fax: 1
357-2-316-770. Early reports on phenotypic correlations between
body size and milk production were generally small (Turner, 1972; Mavrogenis, 1982; Mavrogenis, and positive (Harville and Henderson, 1966; Meyer 1988) indicating that those traits are genetically et al., 1987; Sieber et al., 1988). More recently independent.
Persaud et al. (1991) in studies on the associations The objectives of the present investigation are to among milk yield, feed intake and efficiency in dairy examine genetic and phenotypic relationships be-cattle, reported negative phenotypic and genetic tween measures of milk production (part and total associations between milk yield and live weight. On lactation yield) and body weight in sheep and goats, the other hand, Moore et al. (1992) showed positive, and discuss the possible consequences on body but small, phenotypic correlations between live weight from selection on milk yield.
weight at calving and total milk production (cor-rected for fat content at 3.5%).
Estimates of genetic correlations between body 2. Materials and methods
size and milk production traits range from zero
(Mason et al., 1957; Grantham et al., 1974; Meyer et 2.1. Ewes al., 1987) to about 0.25 (McDaniel and Legates,
1965; Harville and Henderson, 1966). Similar find- Data on 2087 lactations from 737 Chios ewes, ings were reported by Hooven et al. (1968) and collected between 1978 and 1989 at the Experimen-Ahlborn and Dempfle (1992). The latter reported tal Station of the Agricultural Research Institute, genetic correlations of unusual magnitude (0.39) located at Athalassa, Nicosia, Cyprus, were utilized. suggesting that correlated responses from selection The data comprised information on full pedigree, on milk yield would result in larger cows with higher part (90-day) and total milk yield, lactation length, maintenance requirements. On the contrary, Moore et parity, age at lambing and body weight at mating. al. (1992) reported negative genetic correlations Year and season of lambing were also recorded. between the two traits, consistent with values re- The ewes were the progeny of 101 sires (the ported by Badinga et al. (1985) and Persaud et al. average sire family size was 7.3 ewes) that lambed (1991). each year between September and April. Season of It is evident that in dairy cattle there is a great lambing was defined as late Autumn (September– inconsistency in reports regarding both phenotypic October), early Winter (November–December), late and genetic associations between body weight (at Winter (January–February) and early Spring various ages) and milk production. Studies in sheep (March–April).
on this subject are very limited, mainly because of All ewes were exposed to vasectomized males the main utility of most sheep breeds. A recent study who joined the flock twice daily (morning and (Nasholm and Danell, 1996) examined genetic rela- afternoon) for about 90 min for heat detection. Ewes tionships among maternal ability and mature weight. in heat were hand-mated to avoid matings between Since maternal ability reflects, among others, pre- close relatives and for pedigree identification of the weaning milk production available during suckling, offspring. They were all weighed at mating for then the positive genetic correlation between the two mostly management purposes.
computed using multiplicative adjustment factors, breeding season and were all replaced at the end of obtained from preliminary analyses of the complete the mating season (May to September).
data set. Live weight at fifth parity was considered as The sire components of variance and covariance mature body weight. from the multivariate analyses were used for the estimation of genetic parameters using the following expressions:
2.2. Goats
2 2 2 2 h 54s /(ss s1s )e Data on 1611 lactations from 482 Damascus goats
collected between 1982 and 1998 at the
Experimen-rg5ssij/s ssi sj tal Station of the Agricultural Research Institute at
2 2
Athalassa, Nicosia, were utilized. The data com- where: s is the sire component of variance; s is the
s e
prised the same information as for Chios ewes except environmental component of variance, s is the sire sij
that goats were the progeny of 101 sires (average sire component of covariance between traits i and j, and family size was 4.8 goats / sire). s and s are the standard deviations of sire
com-si sj
Parturitions in the case of goats extended from ponents of variance for traits i and j, respectively. November to April and seasons were defined as in Standard errors for heritability estimates and ge-sheep with the exception of September–October, netic correlations were computed using formulae which was absent. Goats were hand-mated using the developed by Robertson (1959) and Dickerson same procedure as for ewes, but they were weaned at (1959).
4963 days after kidding.
Milk tests and calculation procedures to determine part (90-day) and total lactation milk yield and
3. Results and discussion
mature equivalent body weight were identical to sheep. Goats with lactations shorter than 90 days
3.1. Environmental effects were eliminated from the data set.
Descriptive statistics for milk production (90-day 2.3. Statistical methods and total) and body weight at mating for sheep and goats are given in Table 1. Both part lactation and Both data sets were analyzed using least squares total milk production were substantially higher than procedures (Harvey, 1975). The effects of year of previous estimates for the two species (Mavrogenis lambing, season of lambing (as defined above), sires et al., 1988, 1989). These results can be partly within years and parity (1 through 7) were accounted explained by the 10-year difference between the two for by the multivariate mixed model used. studies. Standard deviations and relative standard Sires within years and error were considered deviations are reasonable for both yield traits and random effects, and all other factors in the model within the range reported by other investigators. were considered fixed. Sires were used for a single Mean body weight at mating was also higher in the
Table 1
a
Descriptive statistics for milk production and body weight at mating of sheep and goats
Statistic Ewes Goats
MILK90 MILK BWT MEBWT MILK90 MILK BWT MEBWT
Mean (kg) 141.6 181.0 57.0 63.0 169.5 317.7 63.1 73.8
S.D. (kg) 54.7 85.9 9.1 8.3 56.3 108.2 14.1 11.8
CV (%) 38.6 47.5 16.0 13.2 33.2 37.2 22.3 16.0
a
present study compared to an earlier report (Con- September to early December, whereas all yearlings stantinov et al., 1985). and the remaining older ewes / goats deliver between
Mature equivalent body weights were higher in late January and early April.
goats (63.0 kg for sheep and 73.8 kg for goats) and Parity effects were highly significant (P,0.01) reflect differences in size between the two species. and quadratic in nature for all traits studied (Tables 2 All traits were significantly influenced by the and 3). Highest milk yields were obtained from third factors included in the model, except for season of parity ewes and goats, whereas maximum body parturition, which was not a significant source of weight at mating was reached in the fifth parity. variation for body weight (P.0.05) (Tables 2 and Similar findings regarding either lactation number 3). Year effects have been known to be a significant (parity) or age at parturition effects have been source of variation and have been ascribed to several reported previously for the same breeds (Mavrogenis factors, such as availability of forage for grazing et al., 1989).
animals, changes in management and feeding
prac-tices or even changes in weather conditions during 3.2. Genetic effects critical stages of growth and production (Tables 2
and 3). Season effects are usually the result of Estimates of heritability for 90-day and total milk different available feed resources and variations in yield as well as for body weight at mating and vegetation, but also of differences in humidity and mature equivalent body weight for sheep and goats temperature that are expressed as microbial built-up are presented in Tables 4 and 5, respectively. in housing facilities. In this particular study (Tables Genetic and phenotypic correlations among all 1 and 2) another important factor was the uneven traits studied are also given in Tables 4 and 5 for distribution of age classes in the winter and spring sheep and goats, respectively.
months. The main period of freshening for older Heritability estimates for 90-day and total milk ewes (80 to 85%) and goats (65 to 75%) is late production were moderately high for both sheep
Table 2
a
Mean squares and tests of significance for milk production (part and total) and body weight of Chios sheep
Source df MILK90 MILK BWT MEBWT
** ** ** **
Years 11 69 890.5 150 659.0 1365.3 1737.0
** ** ** **
Sires / years 525 3207.9 8355.5 64.7 76.3
**
Seasons 3 20 207.8 11 963.3* 19.8 18.7
** ** **
Parity 6 13 065.8 22 444.6 165.2 19.0
Error 1603 2122.3 5125.7 32.3 39.8
a
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
Table 3
a
Mean squares and tests of significance for milk production (part and total) and body weight of Damascus goats
Source df MILK90 MILK BWT MEBWT
** ** ** **
Years 15 44 883.9 235 664.3 484.6 890.9
** ** ** **
Sires / years 646 2810.4 17 491.0 101.3 138.8
** **
Seasons 2 41 921.3 452 409.5 102.2 79.9
** ** **
Parity 6 20 718.1 49 753.1 792.3 7.9
Error 1096 2063.8 10 536.0 59.5 84.2
a
Table 4 and total lactation milk yield were high for both Estimates of heritability (diagonal), genetic (above diagonal) and species (Tables 4 and 5) and in agreement with phenotypic (below diagonal) correlations for traits studied in
a previous estimates for the same species (Mavrogenis
Chios sheep
et al., 1988, 1989). Genetic correlations between
MILK90 MILK BWT MEBWT
milk production (part and total) and body weight at MILK90 0.4560.08 0.9060.02 0.0860.11 0.1660.11 mating were positive in sheep, but very low. MILK 0.90 0.5460.09 0.0860.10 0.0560.11 Considering the associated standard errors, the
BWT 0.08 0.08 0.7960.09 –
traits may be regarded as virtually independent.
MEBWT 0.08 0.08 – 0.7660.09
Similar results were obtained when mature
equiva-a
MILK90590-day milk yield; MILK5total milk yield;
lent body weight at mating was considered. BWT5body weight at mating; MEBWT5mature equivalent body
The corresponding genetic correlations for Damas-weight at mating.
cus goats were also very low and regardless of the (0.4460.08 and 0.5460.09, respectively) and goats fact that 90-day milk and body weight were nega-(0.4560.11 and 0.4960.11, respectively). Similar tively correlated, production traits (90-day and total findings have been reported for the Chios sheep milk yield) and live body weight were independent (Mavrogenis et al., 1988) and the Damascus goat of each other. Similar findings have been reported by (Mavrogenis et al., 1989), and other European sheep Mason et al. (1957) and Lefebvre and Ricordeau breeds (Soller et al., 1966; Casu et al., 1975) and (1966). On the contrary, measures of association goat breeds (Roningen, 1967). Lower estimates, between yield and body weight in dairy cattle were however, have also been reported for both sheep and either positive (Hooven et al., 1968) or negative goats (Bonneli, 1969; Ojeda, 1974). (Persaud et al., 1991). Moderately high and positive Body weight at mating (both unadjusted and genetic correlations between milk production and adjusted to mature equivalent) was highly heritable body size in dairy cattle have been reported by a in sheep (0.7960.09 and 0.7660.09, respectively) number of investigators (Ahlborn and Dempfle, and goats (0.7960.11 and 0.8060.11, respectively). 1992; Sieber et al., 1988).
A high estimate for mature weight in Damascus Unlike other investigators who obtained significant goats, but lower than the present values has been genetic associations between milk production and reported by Mavrogenis (1985). On the other hand, body size or weight (whether positive or negative), estimated heritability for Chios sheep was considera- there seems to be little reason of concern about bly lower (0.3060.15) in a previous study (Mav- correlated responses in body size from selection on rogenis and Constantinou, 1990). In addition, esti- milk production traits. The traits appear to be mates for the Rambouillet breed (Mathenge, 1981) independent of each other and improvement in milk and Western range ewes (Stobart et al., 1986) were production should not be expected to result in also much lower than those in the present study. heavier ewes or goats. There was a trend for higher Such estimates are generally low in dairy cattle. body weights at mating through years, but apparently Genetic and phenotypic correlations between part that tendency should be ascribed to better feeding
Table 5
Estimates of heritability (diagonal), genetic (above diagonal) and phenotypic correlations (below diagonal) for traits studied in Damascus
a
Dickerson, G.E., 1959. Techniques and Procedures in Animal and management practices and to perhaps correlated
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age, body weight and production traits during first lactations of This strongly suggests that body size is not a dairy cattle. J. Dairy Sci. 49, 1254–1261.
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Mathenge, J.M., 1981. Growth curve analysis of Rambouillet gesting that smaller dairy cows produced more milk
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