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Genetic and phenotypic relationships between milk production and body weight in Chios sheep and Damascus goats
Livestock Production Science 67 (2000) 81–87 www.elsevier.com / locate / livprodsci
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 Genetic differences among species in body size *Corresponding author. Tel.: 1357-2-305-101; fax: 1357-2316-770.
and milk yield are large. Relationships, therefore, between those two characters are relatively easy to establish. When dealing with genetic differences within breeds the inter-species relationships provide a useful null hypothesis (Taylor, 1973). Early reports on phenotypic correlations between
0301-6226 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 00 )00187-1
82
A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87
body size and milk production were generally small and positive (Harville and Henderson, 1966; Meyer et al., 1987; Sieber et al., 1988). More recently Persaud et al. (1991) in studies on the associations among milk yield, feed intake and efficiency in dairy cattle, reported negative phenotypic and genetic associations between milk yield and live weight. On the other hand, Moore et al. (1992) showed positive, but small, phenotypic correlations between live weight at calving and total milk production (corrected for fat content at 3.5%). Estimates of genetic correlations between body size and milk production traits range from zero (Mason et al., 1957; Grantham et al., 1974; Meyer et al., 1987) to about 0.25 (McDaniel and Legates, 1965; Harville and Henderson, 1966). Similar findings were reported by Hooven et al. (1968) and Ahlborn and Dempfle (1992). The latter reported genetic correlations of unusual magnitude (0.39) suggesting that correlated responses from selection on milk yield would result in larger cows with higher maintenance requirements. On the contrary, Moore et al. (1992) reported negative genetic correlations between the two traits, consistent with values reported by Badinga et al. (1985) and Persaud et al. (1991). It is evident that in dairy cattle there is a great inconsistency in reports regarding both phenotypic and genetic associations between body weight (at various ages) and milk production. Studies in sheep on this subject are very limited, mainly because of the main utility of most sheep breeds. A recent study (Nasholm and Danell, 1996) examined genetic relationships among maternal ability and mature weight. Since maternal ability reflects, among others, preweaning milk production available during suckling, then the positive genetic correlation between the two traits would indicate that selection for milk production in the preweaning period would result in increased body size through a correlated response. However, selection for postweaning milk production or total milk production in the absence of suckling lambs (0-day weaning) is not influenced by the suckling stimulus of the lamb or of component parts of the composite trait mothering ability. A number of investigations have suggested that genetic associations among measures of growth and milk production are mostly positive, but very low
(Turner, 1972; Mavrogenis, 1982; Mavrogenis, 1988) indicating that those traits are genetically independent. The objectives of the present investigation are to examine genetic and phenotypic relationships between measures of milk production (part and total lactation yield) and body weight in sheep and goats, and discuss the possible consequences on body weight from selection on milk yield.
2. Materials and methods
2.1. Ewes Data on 2087 lactations from 737 Chios ewes, collected between 1978 and 1989 at the Experimental Station of the Agricultural Research Institute, located at Athalassa, Nicosia, Cyprus, were utilized. The data comprised information on full pedigree, part (90-day) and total milk yield, lactation length, parity, age at lambing and body weight at mating. Year and season of lambing were also recorded. The ewes were the progeny of 101 sires (the average sire family size was 7.3 ewes) that lambed each year between September and April. Season of lambing was defined as late Autumn (September– October), early Winter (November–December), late Winter (January–February) and early Spring (March–April). All ewes were exposed to vasectomized males who joined the flock twice daily (morning and afternoon) for about 90 min for heat detection. Ewes in heat were hand-mated to avoid matings between close relatives and for pedigree identification of the offspring. They were all weighed at mating for mostly management purposes. Milk production (part and total) was computed from test-day records using the Fleischman method. Milk tests were initiated 763 days following weaning (4263 days after lambing) and continued at monthly intervals thereafter, until individual daily production (the sum of morning and afternoon milkings) dropped below 0.3 kg / ewe. The drying-off period beyond this daily production was not considered in the calculation of total milk production. Ewes with lactations shorter than 90 days were excluded from the data. Mature equivalent body weight was
A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87
computed using multiplicative adjustment factors, obtained from preliminary analyses of the complete data set. Live weight at fifth parity was considered as mature body weight.
2.2. Goats Data on 1611 lactations from 482 Damascus goats collected between 1982 and 1998 at the Experimental Station of the Agricultural Research Institute at Athalassa, Nicosia, were utilized. The data comprised the same information as for Chios ewes except that goats were the progeny of 101 sires (average sire family size was 4.8 goats / sire). Parturitions in the case of goats extended from November to April and seasons were defined as in sheep with the exception of September–October, which was absent. Goats were hand-mated using the same procedure as for ewes, but they were weaned at 4963 days after kidding. Milk tests and calculation procedures to determine part (90-day) and total lactation milk yield and mature equivalent body weight were identical to sheep. Goats with lactations shorter than 90 days were eliminated from the data set.
2.3. Statistical methods Both data sets were analyzed using least squares procedures (Harvey, 1975). The effects of year of lambing, season of lambing (as defined above), sires within years and parity (1 through 7) were accounted for by the multivariate mixed model used. Sires within years and error were considered random effects, and all other factors in the model were considered fixed. Sires were used for a single
83
breeding season and were all replaced at the end of the mating season (May to September). The sire components of variance and covariance from the multivariate analyses were used for the estimation of genetic parameters using the following expressions: h 2 5 4s s2 /(s s2 1 s e2 ) r g 5 s sij /s si s sj where: s 2s is the sire component of variance; s 2e is the environmental component of variance, s sij is the sire component of covariance between traits i and j, and s si and s sj are the standard deviations of sire components of variance for traits i and j, respectively. Standard errors for heritability estimates and genetic correlations were computed using formulae developed by Robertson (1959) and Dickerson (1959).
3. Results and discussion
3.1. Environmental effects Descriptive statistics for milk production (90-day and total) and body weight at mating for sheep and goats are given in Table 1. Both part lactation and total milk production were substantially higher than previous estimates for the two species (Mavrogenis et al., 1988, 1989). These results can be partly explained by the 10-year difference between the two studies. Standard deviations and relative standard deviations are reasonable for both yield traits and within the range reported by other investigators. Mean body weight at mating was also higher in the
Table 1 Descriptive statistics for milk production and body weight at mating of sheep and goats a Statistic
Mean (kg) S.D. (kg) CV (%) a
Ewes
Goats
MILK90
MILK
BWT
MEBWT
MILK90
MILK
BWT
MEBWT
141.6 54.7 38.6
181.0 85.9 47.5
57.0 9.1 16.0
63.0 8.3 13.2
169.5 56.3 33.2
317.7 108.2 37.2
63.1 14.1 22.3
73.8 11.8 16.0
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87
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present study compared to an earlier report (Constantinov et al., 1985). Mature equivalent body weights were higher in goats (63.0 kg for sheep and 73.8 kg for goats) and reflect differences in size between the two species. All traits were significantly influenced by the factors included in the model, except for season of parturition, which was not a significant source of variation for body weight (P.0.05) (Tables 2 and 3). Year effects have been known to be a significant source of variation and have been ascribed to several factors, such as availability of forage for grazing animals, changes in management and feeding practices or even changes in weather conditions during critical stages of growth and production (Tables 2 and 3). Season effects are usually the result of different available feed resources and variations in vegetation, but also of differences in humidity and temperature that are expressed as microbial built-up in housing facilities. In this particular study (Tables 1 and 2) another important factor was the uneven distribution of age classes in the winter and spring months. The main period of freshening for older ewes (80 to 85%) and goats (65 to 75%) is late
September to early December, whereas all yearlings and the remaining older ewes / goats deliver between late January and early April. Parity effects were highly significant (P,0.01) and quadratic in nature for all traits studied (Tables 2 and 3). Highest milk yields were obtained from third parity ewes and goats, whereas maximum body weight at mating was reached in the fifth parity. Similar findings regarding either lactation number (parity) or age at parturition effects have been reported previously for the same breeds (Mavrogenis et al., 1989).
3.2. Genetic effects Estimates of heritability for 90-day and total milk yield as well as for body weight at mating and mature equivalent body weight for sheep and goats are presented in Tables 4 and 5, respectively. Genetic and phenotypic correlations among all traits studied are also given in Tables 4 and 5 for sheep and goats, respectively. Heritability estimates for 90-day and total milk production were moderately high for both sheep
Table 2 Mean squares and tests of significance for milk production (part and total) and body weight of Chios sheep a Source Years Sires / years Seasons Parity Error
df
MILK90
MILK
BWT
MEBWT
11 525 3 6 1603
69 890.5 ** 3207.9 ** 20 207.8 ** 13 065.8 ** 2122.3
150 659.0 ** 8355.5 ** 11 963.3* 22 444.6 ** 5125.7
1365.3 ** 64.7 ** 19.8 165.2 ** 32.3
1737.0 ** 76.3 ** 18.7 19.0 39.8
a
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
Table 3 Mean squares and tests of significance for milk production (part and total) and body weight of Damascus goats a Source Years Sires / years Seasons Parity Error a
df
MILK90
MILK
BWT
MEBWT
15 646 2 6 1096
44 883.9 ** 2810.4 ** 41 921.3 ** 20 718.1 ** 2063.8
235 664.3 ** 17 491.0 ** 452 409.5 ** 49 753.1 ** 10 536.0
484.6 ** 101.3 ** 102.2 792.3 ** 59.5
890.9 ** 138.8 ** 79.9 7.9 84.2
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87 Table 4 Estimates of heritability (diagonal), genetic (above diagonal) and phenotypic (below diagonal) correlations for traits studied in Chios sheep a
MILK90 MILK BWT MEBWT
MILK90
MILK
BWT
MEBWT
0.4560.08 0.90 0.08 0.08
0.9060.02 0.5460.09 0.08 0.08
0.0860.11 0.0860.10 0.7960.09 –
0.1660.11 0.0560.11 – 0.7660.09
a MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
(0.4460.08 and 0.5460.09, respectively) and goats (0.4560.11 and 0.4960.11, respectively). Similar findings have been reported for the Chios sheep (Mavrogenis et al., 1988) and the Damascus goat (Mavrogenis et al., 1989), and other European sheep breeds (Soller et al., 1966; Casu et al., 1975) and goat breeds (Roningen, 1967). Lower estimates, however, have also been reported for both sheep and goats (Bonneli, 1969; Ojeda, 1974). Body weight at mating (both unadjusted and adjusted to mature equivalent) was highly heritable in sheep (0.7960.09 and 0.7660.09, respectively) and goats (0.7960.11 and 0.8060.11, respectively). A high estimate for mature weight in Damascus goats, but lower than the present values has been reported by Mavrogenis (1985). On the other hand, estimated heritability for Chios sheep was considerably lower (0.3060.15) in a previous study (Mavrogenis and Constantinou, 1990). In addition, estimates for the Rambouillet breed (Mathenge, 1981) and Western range ewes (Stobart et al., 1986) were also much lower than those in the present study. Such estimates are generally low in dairy cattle. Genetic and phenotypic correlations between part
85
and total lactation milk yield were high for both species (Tables 4 and 5) and in agreement with previous estimates for the same species (Mavrogenis et al., 1988, 1989). Genetic correlations between milk production (part and total) and body weight at mating were positive in sheep, but very low. Considering the associated standard errors, the traits may be regarded as virtually independent. Similar results were obtained when mature equivalent body weight at mating was considered. The corresponding genetic correlations for Damascus goats were also very low and regardless of the fact that 90-day milk and body weight were negatively correlated, production traits (90-day and total milk yield) and live body weight were independent of each other. Similar findings have been reported by Mason et al. (1957) and Lefebvre and Ricordeau (1966). On the contrary, measures of association between yield and body weight in dairy cattle were either positive (Hooven et al., 1968) or negative (Persaud et al., 1991). Moderately high and positive genetic correlations between milk production and body size in dairy cattle have been reported by a number of investigators (Ahlborn and Dempfle, 1992; Sieber et al., 1988). Unlike other investigators who obtained significant genetic associations between milk production and body size or weight (whether positive or negative), there seems to be little reason of concern about correlated responses in body size from selection on milk production traits. The traits appear to be independent of each other and improvement in milk production should not be expected to result in heavier ewes or goats. There was a trend for higher body weights at mating through years, but apparently 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 goats a
MILK90 MILK BWT MEBWT a
MILK90
MILK
BWT
MEBWT
0.4560.11 0.80 0.04 0.06
0.8260.04 0.4960.11 0.03 0.04
20.0860.12 0.1460.11 0.7960.11 –
20.0360.11 0.1160.11 – 0.8060.11
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
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A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87
and management practices and to perhaps correlated responses from selection on early measures of growth. Indeed, previous studies on the relationships among early measures of growth and mature body weight revealed that there were positive genetic associations among those traits in goats (Mavrogenis, 1988; Mavrogenis and Constantinou, 1990) Phenotypic correlations between milk production and mating live weight were very low, virtually zero. This strongly suggests that body size is not a determinant of the volume of milk production. Similar conclusions had been reached by Moore et al. (1992) for dairy cattle. On the other hand, Ahlborn and Dempfle (1992) and Sieber et al. (1988), reported positive phenotypic correlations of moderate magnitude, suggesting that larger cows produce more milk. The results were not consistent with other studies (Persaud et al., 1991) reporting negative phenotypic correlations and suggesting that smaller dairy cows produced more milk or were more efficient than larger cows. The results of the present study, which are mostly in agreement with studies in other sheep and goat breeds, clearly suggest that milk yield is independent of body size. The latter does not seem to determine milk output and no correlated responses should be expected in body size. Increased body size, when expressed, is probably the consequence of better feeding and improved management practices during periods of stress.
References Ahlborn, G., Dempfle, L., 1992. Genetic parameters for milk production and body size in New Zealand Hostein–Friesian and Jersey. Livest. Prod. Sci. 31, 205–219. Badinga, L., Collier, R.J., Wilcox, C.J., Thatcher, W.W., 1985. Interrelationships of milk yield, body weight, and reproductive performance. J. Dairy Sci. 68, 1828–1835. Bonneli, P., 1969. Quantitative aspects of lactation and milk fat components of Sardinian sheep at first parity. Heritability coefficients. Rivista Zoot. 42, 504–511. Casu, S., Carta, R., Flamant, J.C., 1975. Genetic improvement of milk production in Sardinian ewes. I. Heritabilities and correlations between characters. Ann. Gen. Sel. Anim. 7, 73–90. Constantinov, A., Bening, R., Marrogenis, A.P., 1985. Genetic and phenotypic parameters for some reproduction and milk production characters of the Damascus goat. Sonderdruck aus ¨ Tierzuchtung ¨ ¨ Zeitschrift fur und Zuchtungsbiologie 102, 301– 307.
Dickerson, G.E., 1959. Techniques and Procedures in Animal Science Research. American Society of Animal Science, Albany, NY. Grantham, J.A., White, J.A., Vinson, W.E., Kliewer, R.H., 1974. Genetic relationships between milk production and type in Holsteins. J. Dairy Sci. 57, 1483–1488. Harvey, W.R., 1975. Least squares analysis of data with unequal subclass numbers. U.S. Department of Agriculture, ARS HS [-4, Washington, DC. Harville, D.A., Henderson, C.R., 1966. Interrelationships among age, body weight and production traits during first lactations of dairy cattle. J. Dairy Sci. 49, 1254–1261. Hooven, N.W., Miller, R.H., Plowman, R.D., 1968. Genetic and environmental relationships among efficiency, yield, consumption and weight of Holstein cows. J. Dairy Sci. 51, 1409–1415. Lefebvre, J., Ricordeau, G., 1966. Genetic correlations between milk production and conformation in the Montbeliard and Normandy cattle breeds. In: 9th Int. Congr. Anim. Prod., Edinburgh, p. 16, Sci. Prog. Abstr., Eng. Ed. Mason, I., Robertson, A., Gejlstad, B., 1957. The genetic connection between body size, milk production and efficiency in dairy cattle. J. Dairy Res. 24, 135–143. Mathenge, J.M., 1981. Growth curve analysis of Rambouillet ewes. M.S. Thesis, Texas A&M University, Texas. Mavrogenis, A.P., 1982. Environmental and genetic factors influencing milk production and lamb output of Chios sheep. Livest. Prod. Sci. 8, 519–527. Mavrogenis, A.P., 1988. Genetic and Phenotypic Relationships Among Early Measures of Growth and Milk Production in Sheep and Goats. Technical Bulletin No. 103. Agricultural Research Institute, Nicosia. Mavrogenis, A., Constantinou, A., 1990. Relationships between pre-weaning and post-weaning growth and mature body size in Chios sheep. Anim. Prod. 50, 271–275. Mavrogenis, A.P., Papachristoforou, C., Lysandrides, P., Roushias, A., 1989. Environmental and genetic effects on udder characteristics and milk production in Damascus goats. Small Rum. Res. 2, 333–343. Mavrogenis, A.P., Papachristoforou, C., Lysandrides, P., Roushias, A., 1988. Environmental and genetic factors affecting udder characteristics and milk production in Chios sheep. Gen. Sel. Evol. 20, 477–488. McDaniel, D.T., Legates, J.E., 1965. Associations between body weight predicted from heart girth and production. J. Dairy Sci. 48, 947–956. Meyer, K., Brotherstone, S., Hill, W.G., 1987. Inheritance of linear type traits in dairy cattle and correlations with milk production. Anim. Prod. 44, 1–10. Moore, R.K., Kennedy, B.W., Schaeffer, L.R., Moxley, J.E., 1992. Relationships between age and body weight at calving, feed intake, production, days open, and selection indexes in Ayrshires and Holsteins. J. Dairy Sci. 75, 294–306. Nasholm, A., Danell, O., 1996. Genetic relationships of lamb weight, maternal ability, and mature ewe weight in Swedish finewool sheep. J. Anim. Sci. 74, 329–339. Ojeda, S.E., 1974. Spanish Manchega Sheep breed: repeatability and heritability of milk production. In: 1st World Congress on
A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87 Genetics Applied to Livestock Production, Madrid, pp. 1047– 1052. Persaud, P., Sinum, G., Hill, W.G., 1991. Genetic and phenotypic parameters for yield, food intake and efficiency of dairy cows fed ad libitum. Anim. Prod. 52, 435–444. Robertson, A., 1959. The sampling variance of the genetic correlation coefficient. Biometrics 15, 469–485. Roningen, K., 1967. A Study of Genetic Parameters For Milk Characteristics in Goats. Meldinger fra Norges Landbrutshagskole, Vol. 46(2), 17 pp. Sieber, M., Freeman, A.E., Kelley, D.H., 1988. Relationships between body measurements, body weight, and productivity in Holstein dairy cows. J. Dairy Sci. 71, 3437–3445.
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Soller, M., Visoki, M., Zamiri, H., Sharav, E., 1966. Heritability and repeatability of some selection criteria for milk production in Awassi (fat-tail) sheep. Israel J. Agric. Res. 16, 29–35. Stobart, R.H., Basset, J.W., Cartwright, T.C., Blackwell, R.L., 1986. An analysis of body weights and maturity patterns in Western range ewes. J. Anim. Sci. 63, 729–740. Taylor, St.C.S., 1973. Genetic differences in milk production in relation to mature body weight. Proc. Br. Soc. Anim. Prod. 2, 15–26. Turner, H.N., 1972. Genetic interaction between wool, meat and milk production in sheep. Anim. Breeding Abstr. 40, 621–643.
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 Genetic differences among species in body size *Corresponding author. Tel.: 1357-2-305-101; fax: 1357-2316-770.
and milk yield are large. Relationships, therefore, between those two characters are relatively easy to establish. When dealing with genetic differences within breeds the inter-species relationships provide a useful null hypothesis (Taylor, 1973). Early reports on phenotypic correlations between
0301-6226 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 00 )00187-1
82
A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87
body size and milk production were generally small and positive (Harville and Henderson, 1966; Meyer et al., 1987; Sieber et al., 1988). More recently Persaud et al. (1991) in studies on the associations among milk yield, feed intake and efficiency in dairy cattle, reported negative phenotypic and genetic associations between milk yield and live weight. On the other hand, Moore et al. (1992) showed positive, but small, phenotypic correlations between live weight at calving and total milk production (corrected for fat content at 3.5%). Estimates of genetic correlations between body size and milk production traits range from zero (Mason et al., 1957; Grantham et al., 1974; Meyer et al., 1987) to about 0.25 (McDaniel and Legates, 1965; Harville and Henderson, 1966). Similar findings were reported by Hooven et al. (1968) and Ahlborn and Dempfle (1992). The latter reported genetic correlations of unusual magnitude (0.39) suggesting that correlated responses from selection on milk yield would result in larger cows with higher maintenance requirements. On the contrary, Moore et al. (1992) reported negative genetic correlations between the two traits, consistent with values reported by Badinga et al. (1985) and Persaud et al. (1991). It is evident that in dairy cattle there is a great inconsistency in reports regarding both phenotypic and genetic associations between body weight (at various ages) and milk production. Studies in sheep on this subject are very limited, mainly because of the main utility of most sheep breeds. A recent study (Nasholm and Danell, 1996) examined genetic relationships among maternal ability and mature weight. Since maternal ability reflects, among others, preweaning milk production available during suckling, then the positive genetic correlation between the two traits would indicate that selection for milk production in the preweaning period would result in increased body size through a correlated response. However, selection for postweaning milk production or total milk production in the absence of suckling lambs (0-day weaning) is not influenced by the suckling stimulus of the lamb or of component parts of the composite trait mothering ability. A number of investigations have suggested that genetic associations among measures of growth and milk production are mostly positive, but very low
(Turner, 1972; Mavrogenis, 1982; Mavrogenis, 1988) indicating that those traits are genetically independent. The objectives of the present investigation are to examine genetic and phenotypic relationships between measures of milk production (part and total lactation yield) and body weight in sheep and goats, and discuss the possible consequences on body weight from selection on milk yield.
2. Materials and methods
2.1. Ewes Data on 2087 lactations from 737 Chios ewes, collected between 1978 and 1989 at the Experimental Station of the Agricultural Research Institute, located at Athalassa, Nicosia, Cyprus, were utilized. The data comprised information on full pedigree, part (90-day) and total milk yield, lactation length, parity, age at lambing and body weight at mating. Year and season of lambing were also recorded. The ewes were the progeny of 101 sires (the average sire family size was 7.3 ewes) that lambed each year between September and April. Season of lambing was defined as late Autumn (September– October), early Winter (November–December), late Winter (January–February) and early Spring (March–April). All ewes were exposed to vasectomized males who joined the flock twice daily (morning and afternoon) for about 90 min for heat detection. Ewes in heat were hand-mated to avoid matings between close relatives and for pedigree identification of the offspring. They were all weighed at mating for mostly management purposes. Milk production (part and total) was computed from test-day records using the Fleischman method. Milk tests were initiated 763 days following weaning (4263 days after lambing) and continued at monthly intervals thereafter, until individual daily production (the sum of morning and afternoon milkings) dropped below 0.3 kg / ewe. The drying-off period beyond this daily production was not considered in the calculation of total milk production. Ewes with lactations shorter than 90 days were excluded from the data. Mature equivalent body weight was
A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87
computed using multiplicative adjustment factors, obtained from preliminary analyses of the complete data set. Live weight at fifth parity was considered as mature body weight.
2.2. Goats Data on 1611 lactations from 482 Damascus goats collected between 1982 and 1998 at the Experimental Station of the Agricultural Research Institute at Athalassa, Nicosia, were utilized. The data comprised the same information as for Chios ewes except that goats were the progeny of 101 sires (average sire family size was 4.8 goats / sire). Parturitions in the case of goats extended from November to April and seasons were defined as in sheep with the exception of September–October, which was absent. Goats were hand-mated using the same procedure as for ewes, but they were weaned at 4963 days after kidding. Milk tests and calculation procedures to determine part (90-day) and total lactation milk yield and mature equivalent body weight were identical to sheep. Goats with lactations shorter than 90 days were eliminated from the data set.
2.3. Statistical methods Both data sets were analyzed using least squares procedures (Harvey, 1975). The effects of year of lambing, season of lambing (as defined above), sires within years and parity (1 through 7) were accounted for by the multivariate mixed model used. Sires within years and error were considered random effects, and all other factors in the model were considered fixed. Sires were used for a single
83
breeding season and were all replaced at the end of the mating season (May to September). The sire components of variance and covariance from the multivariate analyses were used for the estimation of genetic parameters using the following expressions: h 2 5 4s s2 /(s s2 1 s e2 ) r g 5 s sij /s si s sj where: s 2s is the sire component of variance; s 2e is the environmental component of variance, s sij is the sire component of covariance between traits i and j, and s si and s sj are the standard deviations of sire components of variance for traits i and j, respectively. Standard errors for heritability estimates and genetic correlations were computed using formulae developed by Robertson (1959) and Dickerson (1959).
3. Results and discussion
3.1. Environmental effects Descriptive statistics for milk production (90-day and total) and body weight at mating for sheep and goats are given in Table 1. Both part lactation and total milk production were substantially higher than previous estimates for the two species (Mavrogenis et al., 1988, 1989). These results can be partly explained by the 10-year difference between the two studies. Standard deviations and relative standard deviations are reasonable for both yield traits and within the range reported by other investigators. Mean body weight at mating was also higher in the
Table 1 Descriptive statistics for milk production and body weight at mating of sheep and goats a Statistic
Mean (kg) S.D. (kg) CV (%) a
Ewes
Goats
MILK90
MILK
BWT
MEBWT
MILK90
MILK
BWT
MEBWT
141.6 54.7 38.6
181.0 85.9 47.5
57.0 9.1 16.0
63.0 8.3 13.2
169.5 56.3 33.2
317.7 108.2 37.2
63.1 14.1 22.3
73.8 11.8 16.0
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
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present study compared to an earlier report (Constantinov et al., 1985). Mature equivalent body weights were higher in goats (63.0 kg for sheep and 73.8 kg for goats) and reflect differences in size between the two species. All traits were significantly influenced by the factors included in the model, except for season of parturition, which was not a significant source of variation for body weight (P.0.05) (Tables 2 and 3). Year effects have been known to be a significant source of variation and have been ascribed to several factors, such as availability of forage for grazing animals, changes in management and feeding practices or even changes in weather conditions during critical stages of growth and production (Tables 2 and 3). Season effects are usually the result of different available feed resources and variations in vegetation, but also of differences in humidity and temperature that are expressed as microbial built-up in housing facilities. In this particular study (Tables 1 and 2) another important factor was the uneven distribution of age classes in the winter and spring months. The main period of freshening for older ewes (80 to 85%) and goats (65 to 75%) is late
September to early December, whereas all yearlings and the remaining older ewes / goats deliver between late January and early April. Parity effects were highly significant (P,0.01) and quadratic in nature for all traits studied (Tables 2 and 3). Highest milk yields were obtained from third parity ewes and goats, whereas maximum body weight at mating was reached in the fifth parity. Similar findings regarding either lactation number (parity) or age at parturition effects have been reported previously for the same breeds (Mavrogenis et al., 1989).
3.2. Genetic effects Estimates of heritability for 90-day and total milk yield as well as for body weight at mating and mature equivalent body weight for sheep and goats are presented in Tables 4 and 5, respectively. Genetic and phenotypic correlations among all traits studied are also given in Tables 4 and 5 for sheep and goats, respectively. Heritability estimates for 90-day and total milk production were moderately high for both sheep
Table 2 Mean squares and tests of significance for milk production (part and total) and body weight of Chios sheep a Source Years Sires / years Seasons Parity Error
df
MILK90
MILK
BWT
MEBWT
11 525 3 6 1603
69 890.5 ** 3207.9 ** 20 207.8 ** 13 065.8 ** 2122.3
150 659.0 ** 8355.5 ** 11 963.3* 22 444.6 ** 5125.7
1365.3 ** 64.7 ** 19.8 165.2 ** 32.3
1737.0 ** 76.3 ** 18.7 19.0 39.8
a
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
Table 3 Mean squares and tests of significance for milk production (part and total) and body weight of Damascus goats a Source Years Sires / years Seasons Parity Error a
df
MILK90
MILK
BWT
MEBWT
15 646 2 6 1096
44 883.9 ** 2810.4 ** 41 921.3 ** 20 718.1 ** 2063.8
235 664.3 ** 17 491.0 ** 452 409.5 ** 49 753.1 ** 10 536.0
484.6 ** 101.3 ** 102.2 792.3 ** 59.5
890.9 ** 138.8 ** 79.9 7.9 84.2
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
A.P. Mavrogenis, C. Papachristoforou / Livestock Production Science 67 (2000) 81 – 87 Table 4 Estimates of heritability (diagonal), genetic (above diagonal) and phenotypic (below diagonal) correlations for traits studied in Chios sheep a
MILK90 MILK BWT MEBWT
MILK90
MILK
BWT
MEBWT
0.4560.08 0.90 0.08 0.08
0.9060.02 0.5460.09 0.08 0.08
0.0860.11 0.0860.10 0.7960.09 –
0.1660.11 0.0560.11 – 0.7660.09
a MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
(0.4460.08 and 0.5460.09, respectively) and goats (0.4560.11 and 0.4960.11, respectively). Similar findings have been reported for the Chios sheep (Mavrogenis et al., 1988) and the Damascus goat (Mavrogenis et al., 1989), and other European sheep breeds (Soller et al., 1966; Casu et al., 1975) and goat breeds (Roningen, 1967). Lower estimates, however, have also been reported for both sheep and goats (Bonneli, 1969; Ojeda, 1974). Body weight at mating (both unadjusted and adjusted to mature equivalent) was highly heritable in sheep (0.7960.09 and 0.7660.09, respectively) and goats (0.7960.11 and 0.8060.11, respectively). A high estimate for mature weight in Damascus goats, but lower than the present values has been reported by Mavrogenis (1985). On the other hand, estimated heritability for Chios sheep was considerably lower (0.3060.15) in a previous study (Mavrogenis and Constantinou, 1990). In addition, estimates for the Rambouillet breed (Mathenge, 1981) and Western range ewes (Stobart et al., 1986) were also much lower than those in the present study. Such estimates are generally low in dairy cattle. Genetic and phenotypic correlations between part
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and total lactation milk yield were high for both species (Tables 4 and 5) and in agreement with previous estimates for the same species (Mavrogenis et al., 1988, 1989). Genetic correlations between milk production (part and total) and body weight at mating were positive in sheep, but very low. Considering the associated standard errors, the traits may be regarded as virtually independent. Similar results were obtained when mature equivalent body weight at mating was considered. The corresponding genetic correlations for Damascus goats were also very low and regardless of the fact that 90-day milk and body weight were negatively correlated, production traits (90-day and total milk yield) and live body weight were independent of each other. Similar findings have been reported by Mason et al. (1957) and Lefebvre and Ricordeau (1966). On the contrary, measures of association between yield and body weight in dairy cattle were either positive (Hooven et al., 1968) or negative (Persaud et al., 1991). Moderately high and positive genetic correlations between milk production and body size in dairy cattle have been reported by a number of investigators (Ahlborn and Dempfle, 1992; Sieber et al., 1988). Unlike other investigators who obtained significant genetic associations between milk production and body size or weight (whether positive or negative), there seems to be little reason of concern about correlated responses in body size from selection on milk production traits. The traits appear to be independent of each other and improvement in milk production should not be expected to result in heavier ewes or goats. There was a trend for higher body weights at mating through years, but apparently 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 goats a
MILK90 MILK BWT MEBWT a
MILK90
MILK
BWT
MEBWT
0.4560.11 0.80 0.04 0.06
0.8260.04 0.4960.11 0.03 0.04
20.0860.12 0.1460.11 0.7960.11 –
20.0360.11 0.1160.11 – 0.8060.11
MILK90590-day milk yield; MILK5total milk yield; BWT5body weight at mating; MEBWT5mature equivalent body weight at mating.
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and management practices and to perhaps correlated responses from selection on early measures of growth. Indeed, previous studies on the relationships among early measures of growth and mature body weight revealed that there were positive genetic associations among those traits in goats (Mavrogenis, 1988; Mavrogenis and Constantinou, 1990) Phenotypic correlations between milk production and mating live weight were very low, virtually zero. This strongly suggests that body size is not a determinant of the volume of milk production. Similar conclusions had been reached by Moore et al. (1992) for dairy cattle. On the other hand, Ahlborn and Dempfle (1992) and Sieber et al. (1988), reported positive phenotypic correlations of moderate magnitude, suggesting that larger cows produce more milk. The results were not consistent with other studies (Persaud et al., 1991) reporting negative phenotypic correlations and suggesting that smaller dairy cows produced more milk or were more efficient than larger cows. The results of the present study, which are mostly in agreement with studies in other sheep and goat breeds, clearly suggest that milk yield is independent of body size. The latter does not seem to determine milk output and no correlated responses should be expected in body size. Increased body size, when expressed, is probably the consequence of better feeding and improved management practices during periods of stress.
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