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Components of variance for growth traits among Zebu and South devon beef cattle in southeastern Nigeria
Livestock Production Science, 14 (1986) 231--238 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
231
COMPONENTS OF VARIANCE FOR GROWTH TRAITS AMONG Z E B U A N D S O U T H D E V O N B E E F C A T T L E IN S O U T H E A S T E R N NIGERIA
M.U. ILOEJE
Federal University of Technology, Owerri (Nigeria) (Accepted 30 October 1985)
ABSTRACT Iloeje, M.U., 1986. Components of variance for growth traits among Zebu and South Devon beef cattle in southeastern Nigeria. Livest. Prod. Sci., 14: 231--238. A total of 31 488 Zebu and 23 708 South Devon records were used to estimate components of variance for birth weight, weaning weight, pre-weaning average daily gain (ADG), yearling weight, slaughter weight, ADG from weaning to yearling, and ADG from yearling to slaughter. Components of variance were estimated by Henderson's Method 2 with a mixed effects model, which included fixed effects of sex and random effects of herd, year-season, sire, and sire × year-season. Herd, year-season, sire and error components accounted for 22--37, 10--17, 3--5 and 43--58%, respectively, of the total variation for the growth traits evaluated. Estimates obtained for the sire X year-season components suggest a small but real year--sire interaction effect on the traits studied. Paternal half-sib estimates of heritability of various growth traits ranged from 0.28 to 0.37, whereas the genetic and phenotypic correlations between the traits were positive and high. There were no significant breed differences in the correlations obtained for the various traits studied.
INTRODUCTION I t has b e e n generally established t h a t c o m p o n e n t s o f variance have wide applications in genetic a n d animal breeding research (Van Vleck et al., 1 9 6 1 ; K e n n e d y and H e n d e r s o n , 1 9 7 5 ; V a n Vleck and Searle, 1 9 7 9 ; Iloeje et al., 1981). T h e y are useful in measuring the relative i m p o r t a n c e o f sources o f r a n d o m variation w h i c h a f f e c t traits o f e c o n o m i c i m p o r t a n c e , as well as being an a d j u n c t t o t h e p r e d i c t i o n o f breeding values o f sires o r d a m s and real p r o d u c i n g ability o f animals. P h e n o t y p i c and additive genetic variances, as well as heritabilities and repeatabilities derived f r o m variance c o m p o n e n t s , are n e e d e d for t h e design o f effective breeding p r o g r a m m e s . This r e p o r t presents estimates o f herd, year-season, sire, sire X yearseason, and error c o m p o n e n t s o f variance for g r o w t h traits o b t a i n e d f r o m large samples o f Z e b u and S o u t h D e v o n b e e f cattle p o p u l a t i o n s in south-
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© 1986 Elsevier Science Publishers B.V.
232
eastern Nigeria. The Zebu cattle are represented by the Gudali breed, which is a short-horned, medium sized, deep-bodied, docile and sturdy animal with a cervico-thoracic hump (Williamson and Payne, 1978). MATERIALS AND METHODS
The data used in this study were field records accumulated from 1961 to 1984 from the Government Cattle ranch in the tropical grasslands of the Obudu plateau (6°50"N, 9°10 '' E, 1582 m above sea level) in southeastern Nigeria. The raw data were edited such that the utilized records gave complete information on sex, dates and weights at birth, weaning, yearling and slaughter, and proper identifications for herd, sire, dam and breed. Two seasons of freshening were defined: the dry season, D e c e m b e r April, and the wet season, May--November. Bearing in mind that calf growth is linear within the 160- to 250
.
TABLE I Subclass numbers for random effects in estimation of variance components for growth traits Breeds
Total No. of Records No. of herds No. of year-seasons No. of sires No. of sire X year-seasons
Zebu
South Devon
31 488 386 134 1735 2241
23 708 218 108 1184 1811
233
c o m m o n to calves of the m th sex; and e~]kl m is a random error associated with the record, with expectation 0 and variance o 5e. Covariances between pairs of non-identical random variables are assumed to be zero. Numbers o f records, herds, year-seasons, sires, and sire × year-season subclasses are given in Table t. Paternal half-sib estimates of heritability were calculated by /~5 (4 as)l(o ^5 ^5 + =
The relationship Vat (A+B) =
Var (A) + Vat (B) + 2 Coy (A,B)
allows the covariance between any two traits,A and B, to be estimated with the same procedure that estimates variances. Covariances between birth weight and weaning weight, weaning weight and yearling weight, yearling weight and slaughter weight, and pre-weaning average daily gain (ADG) and postweaning A D G were used to estimate genetic and phenotypic correlations. RESULTS AND DISCUSSION
Least squares means for growth traits in Zebu and South Devon cattle are given in Table II. South Devon calves were consistently heavier and showed higher ADG t h a n Zebu calves. This observation may be relevant in the choice of beef cattle breeds for fattening operations in southeastern Nigeria. Components of variance expressed as percentages o f the total variation are given in Table III. Herd effects accounted for 22--32 and TABLE II
Least squares means for growth traitsin Zebu and South Devon cattle Traits
Breeds Zebu
South Devon
Pre-weaning traits Birth wt. (Kg) Weaning wt. (Kg)* ADG (Kg/day)*
28.3 143.9 0.63
39.4 183.5 0.77
Post-weaning traits Yearling wt. (Kg)* Slaughter wt. (Kg)* A D G (weaning to yearling)* A D G (yearling to slaughter)*
224.5 301.6 0.44 0.20
293.8 405.4 0.61 0.31
Age at slaughter = 738 +- 14 days. *Means differ with P <0.05.
234 TABLE III Estimated components of variance for growth traits in Zebu and South Devon cattle Traits
Breeds
% of total Herd
Yearseason
Sire
Yearsire
Error
Birth wt.
Zebu South Devon
31 26
11 12
4 4
1 2
53 56
Weaning wt.
Zebu South Devon
26 31
10 12
5 3
2 2
57 52
Pre-weaning AGD
Zebu South Devon Zebu South Devon
22 32 32 37
11 12 14 15
5 4 5 4
3 2 2 1
59 50 47 43
Slaughter wt.
Zebu South Devon
25 25
11 13
5 4
1 0
58 58
ADG (weaning to yearling)
Zebu South Devon
32 25
15 17
4 5
2 0
47 53
ADG (yearling to slaughter)
Zebu South Devon
30 22
17 18
4 5
2 0
49 55
Yearling wt.
2 2 - - 3 7 % o f t h e v a r i a t i o n in g r o w t h traits o f Z e b u a n d S o u t h D e v o n cattle, respectively. T h e s e h e r d c o m p o n e n t s o f variation, w h i c h m a y c o m p r i s e b o t h genetic and e n v i r o n m e n t a l c o n t r i b u t i o n s , i n d i c a t e large d i f f e r e n c e s in g r o w t h p e r f o r m a n c e d u e t o feeding and overall h e r d m a n a g e m e n t . In b o t h Z e b u a n d S o u t h D e v o n cattle, t h e y e a r - s e a s o n e f f e c t s a c c o u n t e d f o r 1 0 - - 1 2 % o f t h e v a r i a t i o n in p r e - w e a n i n g g r o w t h traits, and 1 1 - - 1 7 % o f t h e v a r i a t i o n in p o s t - w e a n i n g traits. G e n e r a l l y , t h e e f f e c t s o f y e a r - s e a s o n o n all t h e traits s t u d i e d w e r e higher f o r S o u t h D e v o n t h a n Z e b u cattle. Bearing in m i n d t h a t t h e y e a r - s e a s o n c o m p o n e n t consists m a i n l y o f env i r o n m e n t a l and s o m e genetic c o n t r i b u t i o n s , d u e t o t h e t r e n d in g e n e t i c m e r i t , t h e higher p e r c e n t a g e s o f y e a r - s e a s o n e f f e c t s s h o w n b y S o u t h D e v o n c a t t l e m a y be e x p l a i n e d b y t h e f a c t t h a t all b r e e d s are n o t likely t o r e a c t similarly t o d r o u g h t , w e a t h e r , t e m p e r a t u r e , or f e e d s u p p l y c o n d i t i o n s . B o t h t h e sire a n d t h e sire × y e a r - s e a s o n i n t e r a c t i o n c o m p o n e n t s w e r e o f lesser m a g n i t u d e , and a c c o u n t e d f o r a b o u t 5 and 2% o f t h e t o t a l variat i o n , respectively. E s t i m a t e s o b t a i n e d f o r t h e sire × y e a r - s e a s o n c o m p o n e n t suggest a small b u t real y e a r - s e a s o n - - s i r e i n t e r a c t i o n . In o t h e r w o r d s , t h e d i f f e r e n c e s b e t w e e n sires varied u n d e r d i f f e r e n t w e a t h e r , t e m p e r a t u r e , o r feed s u p p l y c o n d i t i o n s . A b o u t 4 3 - - 5 8 % o f t h e t o t a l v a r i a t i o n r e m a i n e d u n e x p l a i n e d and was a t t r i b u t e d t o e r r o r variance. Since t h e r e c o r d s used in this s t u d y are field d a t a , t h e y lack m u c h o f t h e p r e c i s i o n a n d a c c u r a c y o f m e a s u r e m e n t s in c o n t r o l l e d e x p e r i m e n t a l
235 conditions. Consequently, the interpretation o f estimates of variance comp o n e n t s obtained from these field data must be treated with caution. Despite these concerns, general conclusions can be drawn regarding these variance co mp o n en ts . Differences be t w een herds constitute the most i m p o r t a n t source of identifiable r a n d o m variation affecting growth traits in t he Zebu and South Devon cattle studied. This observation is consistent with earlier reports on Her ef o r d and Aberdeen Angus calves by K e n n e d y and Henderson (1975). Estimates o f herd variance obtained for pre-weaning growth traits in this study are similar to estimates r e por t ed by Cunningham and Henderson (1965) and Wilson et al. (1972). However, t he variances obtained in this study for post-weaning growth traits were large. This observation probabl y reflects the wider herd differences in post-weaning nutritional practices, in contrast to the similar manner in which cows nourish their calves, irrespective o f herd management. The magnitude o f the year-season variance suggests that it cannot be ignored, but must be considered jointly with the effects of t he individual herds involved. Although Cunningham and Henderson (1965) and Dinkel and Busch (1973) confirmed t hat sire X year variances were o f little practical concern, the results from this study suggest a small but consistent sire X year-season interaction effect on growth traits. This may be attributable to non-random mating practices, where young sires are assigned mates on a different basis than older sires. Estimates o f heritability for the growth traits considered in this st udy are presented in Table IV. T he heritabilities for birth weight, weaning weight and yearling weight are consistent with the range o f values r e p o r t e d b y P e t t y and Cartwright (1966), McDowell (1972) and Warwick (1969), but are slightly smaller t h a n t he 0.32 and 0.48 values r e p o r t e d by K ennedy and Henderson (1975). Considering the fact that calves may be culled at weaning on the basis o f pre-weaning growth perform ance, it is possible th at some of the post-weaning data in this study may represent a selected TABLE IV Estimates of heritability for growth traits in Zebu and South Devon cattle Traits
Birth wt. Weaning wt. Pre-weaning ADG Yearling wt. Slaughter wt. ADG (weaning to yearling) ADG (yearling to slaughter)
Breeds Zebu
South Devon
0.28 0.31 0.30 0.37 0.31 0.30 0.29
0.26 0.21 0.29 0.33 0.26 0.34 0.33
± 0.01 -+ 0.01 ± 0.01 ± 0.01 ± 0.02 ± 0.01 ± 0.02
± 0.01 ± 0.01 ± 0.01 ± 0.01 ± 0.02 ± 0.01 ± 0.02
236 TABLE V Genetic and phenotypic correlations between growth traits in Zebu and South Devon cattle Traits
Breeds
Correlations Genetic
Phenotypic
Birth wt. and weaning wt.
Zebu South Devon
0.81 +- 0.01 0.83 ± 0.02
0.92 ± 0.01 0.94 ± 0.01
Weaning wt. and yearling wt.
Zebu South Devon
0.74 ± 0.02 0.74 ± 0.02
0.85 ± 0.01 0.83 ± 0.01
Yearling wt. and slaughter wt.
Zebu South Devon
0.48 ± 0.03 0.51 ± 0.02
0.61 -+ 0.02 0.68 ~ 0.02
Pre-weaning ADG and Post-weaning ADG
Zebu South Devon
0.32 ± 0.02 0.38 ± 0.01
0.51 ± 0.01 0.48 ± 0.01
subset of the pre-weaning data. Such a selection will bias heritability estimates for post-weaning growth traits downwards, given a positive genetic correlation between pre- and post-weaning growth. Genetic and phenotypic correlations are given in Table V. Birth weight and weaning weight showed high genetic and phenotypic correlations of 0.82 and 0.93, respectively, while the correlations between pre-weaning and post-weaning ADG were as low as 0.32 and 0.48. There were no significant breed differences in the correlations obtained for the various traits studied. ACKNOWLEDGEMENT
The special assistance of Messrs A. Odii and K.C. Imanyi, and the staff and Management of the Obudu Cattle Ranch in the provision of the data is gratefully acknowledged.
REFERENCES Cunningham, E.P. and Henderson, C.R., 1965. Estimation of genetic and phenotypic parameters of weaning traits in beef cattle. J. Anim. Sci., 24 : 182--187. Dinkel, C.A. and Busch, D.A., 1973. Genetic parameters among production, carcass composition and carcass quality traits of beef cattle. J. Anim. Sci., 36: 832--846. Henderson, C.R., 1953. Estimation of variance and covariance components. Biometrics, 9 : 226--252. Iloeje, M.U., Van Vleck, L.D. and Wiggans, G.R., 1981. Components of variance for milk and fat yields in dairy goats. J. Dairy Sci., 64: 2290--2293. Kennedy, B.W. and Henderson, C.R., 1975. Components of variance of growth traits among Hereford and Aberdeen Angus calves. Can. J. Anita. Sci., 55 : 493--502.
237 McDowell, R.E., 1972. Improvement of Livestock Production in Warm Climates. Freeman and Company, San Francisco, CA, 711 pp. Petty, R.R. and Cartwright, T.C., 1966. A summary of genetic and environmental statistics for growth and conformation traits of young beef cattle. Tex. Agric. Exp. Sta. Dep. Tech. Rep. No. 5, 21 pp. Van Vleck, L.D. and Searle, S.R., 1979. Variance components and animal breeding. Proc. Conf. in Honour of C.R. Henderson, 16--17 July 1979, Cornell Univ., Ithaca, NY, 227 pp. Van Vleck, L.D., Wadell, L.H. and Henderson, C.R., 1961. Components of variance associated with milk and fat records of artificially sired Holstein daughters. J. Anita. Sci., 20: 812--816. Warwick, E.J., 1969. Effective performance recording in beef cattle. Proc. 2nd. World Conf. Anita. Prod. Bruce Publ. Co., Paul, MN, pp. 201--208. Williamson, G. and Payne, W.J.A., 1978. An Introduction to Animal Husbandry in the Tropics. 3rd edn. Longmans, London, pp. 231--232. Wilson, L.L., Rishel, W.H. and Harvey, W.R., 1972. Influence of herd, sire, and herd × sire interaction on live and carcass characters of beef cattle. J. Anita. Sci., 35: 502--506.
RESUME Iloeje, M.U., 1986. Composantes de la variance des caract~res de croissance chez les bovins Z~bus et South Devon dans le sud ouest de la Nigeria. Livest. Prod. Sci., 14: 231--238 (en anglais). A partir des enregistrements sur 31 488 Z6bus et 23 708 South Devon, on a estim~ les composantes de la variance des poids fi la naissance, au sewage, ~ un an et ~ l'abattage et des croi"ts journaliers aux diff4rentes p6riodes. On a utilis~ la m4thode 2 de Henderson avec un module ~ effets mixtes incluant les effets fixes du sexe et les effets au hasard du troupeau, de l'ann~e-saison, du p~re et du p~re x ann~e-saison. Le troupeau, l'ann~esaison, le p~re et l'erreur rendent compte respectivement de 22 ~ 37%, 10 ~ 17%, 3 fi 5% et 43 ~ 58% de la variation totale des caract~res de croissance consid4r~s. Les estim~es obtenues pour la composante p~re X ann4e-saison sugg~rent une interaction faible mais r~elle entre annie et p~re pour les caract4res ~tudi~s. Les estim~es de l'h~ritabilit~ ~ partir des demi-fr~res et soeurs paternels varient de 0.28 ~ 0.37 pour les diff4rents caract~res tandis que les correlations g~n4tiques et ph~notypiques entre les caract~res sont positives et 61ev~es. I1 n'y a pas eu de differences significatives entre les races dans les corr41ations obtenues pour les diff4rents caract4res ~tudi6s. KUR ZF AS S UN G Iloeje, M.U., 1986. Varianzkomponenten fiir Wachstumsmerkmale zwischen Zebu und South Devon Fleischrindern in Siidost-Nigeria. Livest. Prod. Sci., 1 4 : 2 3 1 - - 2 3 8 (auf englisch). Mit Hilfe der Daten von 31 488 Zebus und 23 708 South Devons wurden die Varianzkomponenten fiir Geburtsgewicht, Absetzgewicht, durchschnittliche ti/gliche Zunahme vor dem Absetzen, J~hrlingsgewicht, Schlachtgewicht, durchschnittliche ti/gliche Zunahme vom Absetzen bis zum J~hrlingsalter und durchschnittliche t~'gliche Zunahme vom J~hrlingsalter bis zum Schlachten bestimmt. Die Varianzkomponenten wurden mit Hilfe der Henderson-Methode Nr. 2 mit einem "mixed effect"-Modell gesch~tzt, dass das
238 Geschlecht als fixen Effekt und den Herdeneinfluss, den Jahressaisoneinfluss, den Bulleneinfluss und den Bulle X Jahressaisoneinfluss als zuf~llige Effekte beinhaltete. Herdeneinfluss, Jahressaisoneinfluss, Bulleneinfluss und die Fehlerkomponenten machten 22-37%, 10--17%, 3--5% bzw. 43--58% der Gesamtvarianz der gesch~tzten Wachstumsmerkmale aus. Die Sch~/tzwerte der Bulle x Jahressaison-Komponenten lassen einen kleinen, aber reellen Jahres × Bullen-Interaktionseffekt bei den untersuchten Merkmalen erkennen. V~terliche Halbgeschwistersch~/tzwerte ffir die Heritabilitgt der verschiedenen Wachstumsmerkmale liegen zwischen 0.28--0.37, wobei die genetischen und ph~/notypischen Korrelationen zwischen den Merkmalen positiv und hoch sind. Es traten keinen signifikanten Differenzen zwischen den Rassen fiir die Korrelationen der untersuchten Merkmale auf.
231
COMPONENTS OF VARIANCE FOR GROWTH TRAITS AMONG Z E B U A N D S O U T H D E V O N B E E F C A T T L E IN S O U T H E A S T E R N NIGERIA
M.U. ILOEJE
Federal University of Technology, Owerri (Nigeria) (Accepted 30 October 1985)
ABSTRACT Iloeje, M.U., 1986. Components of variance for growth traits among Zebu and South Devon beef cattle in southeastern Nigeria. Livest. Prod. Sci., 14: 231--238. A total of 31 488 Zebu and 23 708 South Devon records were used to estimate components of variance for birth weight, weaning weight, pre-weaning average daily gain (ADG), yearling weight, slaughter weight, ADG from weaning to yearling, and ADG from yearling to slaughter. Components of variance were estimated by Henderson's Method 2 with a mixed effects model, which included fixed effects of sex and random effects of herd, year-season, sire, and sire × year-season. Herd, year-season, sire and error components accounted for 22--37, 10--17, 3--5 and 43--58%, respectively, of the total variation for the growth traits evaluated. Estimates obtained for the sire X year-season components suggest a small but real year--sire interaction effect on the traits studied. Paternal half-sib estimates of heritability of various growth traits ranged from 0.28 to 0.37, whereas the genetic and phenotypic correlations between the traits were positive and high. There were no significant breed differences in the correlations obtained for the various traits studied.
INTRODUCTION I t has b e e n generally established t h a t c o m p o n e n t s o f variance have wide applications in genetic a n d animal breeding research (Van Vleck et al., 1 9 6 1 ; K e n n e d y and H e n d e r s o n , 1 9 7 5 ; V a n Vleck and Searle, 1 9 7 9 ; Iloeje et al., 1981). T h e y are useful in measuring the relative i m p o r t a n c e o f sources o f r a n d o m variation w h i c h a f f e c t traits o f e c o n o m i c i m p o r t a n c e , as well as being an a d j u n c t t o t h e p r e d i c t i o n o f breeding values o f sires o r d a m s and real p r o d u c i n g ability o f animals. P h e n o t y p i c and additive genetic variances, as well as heritabilities and repeatabilities derived f r o m variance c o m p o n e n t s , are n e e d e d for t h e design o f effective breeding p r o g r a m m e s . This r e p o r t presents estimates o f herd, year-season, sire, sire X yearseason, and error c o m p o n e n t s o f variance for g r o w t h traits o b t a i n e d f r o m large samples o f Z e b u and S o u t h D e v o n b e e f cattle p o p u l a t i o n s in south-
0301-6226/86/$03.50
© 1986 Elsevier Science Publishers B.V.
232
eastern Nigeria. The Zebu cattle are represented by the Gudali breed, which is a short-horned, medium sized, deep-bodied, docile and sturdy animal with a cervico-thoracic hump (Williamson and Payne, 1978). MATERIALS AND METHODS
The data used in this study were field records accumulated from 1961 to 1984 from the Government Cattle ranch in the tropical grasslands of the Obudu plateau (6°50"N, 9°10 '' E, 1582 m above sea level) in southeastern Nigeria. The raw data were edited such that the utilized records gave complete information on sex, dates and weights at birth, weaning, yearling and slaughter, and proper identifications for herd, sire, dam and breed. Two seasons of freshening were defined: the dry season, D e c e m b e r April, and the wet season, May--November. Bearing in mind that calf growth is linear within the 160- to 250
.
TABLE I Subclass numbers for random effects in estimation of variance components for growth traits Breeds
Total No. of Records No. of herds No. of year-seasons No. of sires No. of sire X year-seasons
Zebu
South Devon
31 488 386 134 1735 2241
23 708 218 108 1184 1811
233
c o m m o n to calves of the m th sex; and e~]kl m is a random error associated with the record, with expectation 0 and variance o 5e. Covariances between pairs of non-identical random variables are assumed to be zero. Numbers o f records, herds, year-seasons, sires, and sire × year-season subclasses are given in Table t. Paternal half-sib estimates of heritability were calculated by /~5 (4 as)l(o ^5 ^5 + =
The relationship Vat (A+B) =
Var (A) + Vat (B) + 2 Coy (A,B)
allows the covariance between any two traits,A and B, to be estimated with the same procedure that estimates variances. Covariances between birth weight and weaning weight, weaning weight and yearling weight, yearling weight and slaughter weight, and pre-weaning average daily gain (ADG) and postweaning A D G were used to estimate genetic and phenotypic correlations. RESULTS AND DISCUSSION
Least squares means for growth traits in Zebu and South Devon cattle are given in Table II. South Devon calves were consistently heavier and showed higher ADG t h a n Zebu calves. This observation may be relevant in the choice of beef cattle breeds for fattening operations in southeastern Nigeria. Components of variance expressed as percentages o f the total variation are given in Table III. Herd effects accounted for 22--32 and TABLE II
Least squares means for growth traitsin Zebu and South Devon cattle Traits
Breeds Zebu
South Devon
Pre-weaning traits Birth wt. (Kg) Weaning wt. (Kg)* ADG (Kg/day)*
28.3 143.9 0.63
39.4 183.5 0.77
Post-weaning traits Yearling wt. (Kg)* Slaughter wt. (Kg)* A D G (weaning to yearling)* A D G (yearling to slaughter)*
224.5 301.6 0.44 0.20
293.8 405.4 0.61 0.31
Age at slaughter = 738 +- 14 days. *Means differ with P <0.05.
234 TABLE III Estimated components of variance for growth traits in Zebu and South Devon cattle Traits
Breeds
% of total Herd
Yearseason
Sire
Yearsire
Error
Birth wt.
Zebu South Devon
31 26
11 12
4 4
1 2
53 56
Weaning wt.
Zebu South Devon
26 31
10 12
5 3
2 2
57 52
Pre-weaning AGD
Zebu South Devon Zebu South Devon
22 32 32 37
11 12 14 15
5 4 5 4
3 2 2 1
59 50 47 43
Slaughter wt.
Zebu South Devon
25 25
11 13
5 4
1 0
58 58
ADG (weaning to yearling)
Zebu South Devon
32 25
15 17
4 5
2 0
47 53
ADG (yearling to slaughter)
Zebu South Devon
30 22
17 18
4 5
2 0
49 55
Yearling wt.
2 2 - - 3 7 % o f t h e v a r i a t i o n in g r o w t h traits o f Z e b u a n d S o u t h D e v o n cattle, respectively. T h e s e h e r d c o m p o n e n t s o f variation, w h i c h m a y c o m p r i s e b o t h genetic and e n v i r o n m e n t a l c o n t r i b u t i o n s , i n d i c a t e large d i f f e r e n c e s in g r o w t h p e r f o r m a n c e d u e t o feeding and overall h e r d m a n a g e m e n t . In b o t h Z e b u a n d S o u t h D e v o n cattle, t h e y e a r - s e a s o n e f f e c t s a c c o u n t e d f o r 1 0 - - 1 2 % o f t h e v a r i a t i o n in p r e - w e a n i n g g r o w t h traits, and 1 1 - - 1 7 % o f t h e v a r i a t i o n in p o s t - w e a n i n g traits. G e n e r a l l y , t h e e f f e c t s o f y e a r - s e a s o n o n all t h e traits s t u d i e d w e r e higher f o r S o u t h D e v o n t h a n Z e b u cattle. Bearing in m i n d t h a t t h e y e a r - s e a s o n c o m p o n e n t consists m a i n l y o f env i r o n m e n t a l and s o m e genetic c o n t r i b u t i o n s , d u e t o t h e t r e n d in g e n e t i c m e r i t , t h e higher p e r c e n t a g e s o f y e a r - s e a s o n e f f e c t s s h o w n b y S o u t h D e v o n c a t t l e m a y be e x p l a i n e d b y t h e f a c t t h a t all b r e e d s are n o t likely t o r e a c t similarly t o d r o u g h t , w e a t h e r , t e m p e r a t u r e , or f e e d s u p p l y c o n d i t i o n s . B o t h t h e sire a n d t h e sire × y e a r - s e a s o n i n t e r a c t i o n c o m p o n e n t s w e r e o f lesser m a g n i t u d e , and a c c o u n t e d f o r a b o u t 5 and 2% o f t h e t o t a l variat i o n , respectively. E s t i m a t e s o b t a i n e d f o r t h e sire × y e a r - s e a s o n c o m p o n e n t suggest a small b u t real y e a r - s e a s o n - - s i r e i n t e r a c t i o n . In o t h e r w o r d s , t h e d i f f e r e n c e s b e t w e e n sires varied u n d e r d i f f e r e n t w e a t h e r , t e m p e r a t u r e , o r feed s u p p l y c o n d i t i o n s . A b o u t 4 3 - - 5 8 % o f t h e t o t a l v a r i a t i o n r e m a i n e d u n e x p l a i n e d and was a t t r i b u t e d t o e r r o r variance. Since t h e r e c o r d s used in this s t u d y are field d a t a , t h e y lack m u c h o f t h e p r e c i s i o n a n d a c c u r a c y o f m e a s u r e m e n t s in c o n t r o l l e d e x p e r i m e n t a l
235 conditions. Consequently, the interpretation o f estimates of variance comp o n e n t s obtained from these field data must be treated with caution. Despite these concerns, general conclusions can be drawn regarding these variance co mp o n en ts . Differences be t w een herds constitute the most i m p o r t a n t source of identifiable r a n d o m variation affecting growth traits in t he Zebu and South Devon cattle studied. This observation is consistent with earlier reports on Her ef o r d and Aberdeen Angus calves by K e n n e d y and Henderson (1975). Estimates o f herd variance obtained for pre-weaning growth traits in this study are similar to estimates r e por t ed by Cunningham and Henderson (1965) and Wilson et al. (1972). However, t he variances obtained in this study for post-weaning growth traits were large. This observation probabl y reflects the wider herd differences in post-weaning nutritional practices, in contrast to the similar manner in which cows nourish their calves, irrespective o f herd management. The magnitude o f the year-season variance suggests that it cannot be ignored, but must be considered jointly with the effects of t he individual herds involved. Although Cunningham and Henderson (1965) and Dinkel and Busch (1973) confirmed t hat sire X year variances were o f little practical concern, the results from this study suggest a small but consistent sire X year-season interaction effect on growth traits. This may be attributable to non-random mating practices, where young sires are assigned mates on a different basis than older sires. Estimates o f heritability for the growth traits considered in this st udy are presented in Table IV. T he heritabilities for birth weight, weaning weight and yearling weight are consistent with the range o f values r e p o r t e d b y P e t t y and Cartwright (1966), McDowell (1972) and Warwick (1969), but are slightly smaller t h a n t he 0.32 and 0.48 values r e p o r t e d by K ennedy and Henderson (1975). Considering the fact that calves may be culled at weaning on the basis o f pre-weaning growth perform ance, it is possible th at some of the post-weaning data in this study may represent a selected TABLE IV Estimates of heritability for growth traits in Zebu and South Devon cattle Traits
Birth wt. Weaning wt. Pre-weaning ADG Yearling wt. Slaughter wt. ADG (weaning to yearling) ADG (yearling to slaughter)
Breeds Zebu
South Devon
0.28 0.31 0.30 0.37 0.31 0.30 0.29
0.26 0.21 0.29 0.33 0.26 0.34 0.33
± 0.01 -+ 0.01 ± 0.01 ± 0.01 ± 0.02 ± 0.01 ± 0.02
± 0.01 ± 0.01 ± 0.01 ± 0.01 ± 0.02 ± 0.01 ± 0.02
236 TABLE V Genetic and phenotypic correlations between growth traits in Zebu and South Devon cattle Traits
Breeds
Correlations Genetic
Phenotypic
Birth wt. and weaning wt.
Zebu South Devon
0.81 +- 0.01 0.83 ± 0.02
0.92 ± 0.01 0.94 ± 0.01
Weaning wt. and yearling wt.
Zebu South Devon
0.74 ± 0.02 0.74 ± 0.02
0.85 ± 0.01 0.83 ± 0.01
Yearling wt. and slaughter wt.
Zebu South Devon
0.48 ± 0.03 0.51 ± 0.02
0.61 -+ 0.02 0.68 ~ 0.02
Pre-weaning ADG and Post-weaning ADG
Zebu South Devon
0.32 ± 0.02 0.38 ± 0.01
0.51 ± 0.01 0.48 ± 0.01
subset of the pre-weaning data. Such a selection will bias heritability estimates for post-weaning growth traits downwards, given a positive genetic correlation between pre- and post-weaning growth. Genetic and phenotypic correlations are given in Table V. Birth weight and weaning weight showed high genetic and phenotypic correlations of 0.82 and 0.93, respectively, while the correlations between pre-weaning and post-weaning ADG were as low as 0.32 and 0.48. There were no significant breed differences in the correlations obtained for the various traits studied. ACKNOWLEDGEMENT
The special assistance of Messrs A. Odii and K.C. Imanyi, and the staff and Management of the Obudu Cattle Ranch in the provision of the data is gratefully acknowledged.
REFERENCES Cunningham, E.P. and Henderson, C.R., 1965. Estimation of genetic and phenotypic parameters of weaning traits in beef cattle. J. Anim. Sci., 24 : 182--187. Dinkel, C.A. and Busch, D.A., 1973. Genetic parameters among production, carcass composition and carcass quality traits of beef cattle. J. Anim. Sci., 36: 832--846. Henderson, C.R., 1953. Estimation of variance and covariance components. Biometrics, 9 : 226--252. Iloeje, M.U., Van Vleck, L.D. and Wiggans, G.R., 1981. Components of variance for milk and fat yields in dairy goats. J. Dairy Sci., 64: 2290--2293. Kennedy, B.W. and Henderson, C.R., 1975. Components of variance of growth traits among Hereford and Aberdeen Angus calves. Can. J. Anita. Sci., 55 : 493--502.
237 McDowell, R.E., 1972. Improvement of Livestock Production in Warm Climates. Freeman and Company, San Francisco, CA, 711 pp. Petty, R.R. and Cartwright, T.C., 1966. A summary of genetic and environmental statistics for growth and conformation traits of young beef cattle. Tex. Agric. Exp. Sta. Dep. Tech. Rep. No. 5, 21 pp. Van Vleck, L.D. and Searle, S.R., 1979. Variance components and animal breeding. Proc. Conf. in Honour of C.R. Henderson, 16--17 July 1979, Cornell Univ., Ithaca, NY, 227 pp. Van Vleck, L.D., Wadell, L.H. and Henderson, C.R., 1961. Components of variance associated with milk and fat records of artificially sired Holstein daughters. J. Anita. Sci., 20: 812--816. Warwick, E.J., 1969. Effective performance recording in beef cattle. Proc. 2nd. World Conf. Anita. Prod. Bruce Publ. Co., Paul, MN, pp. 201--208. Williamson, G. and Payne, W.J.A., 1978. An Introduction to Animal Husbandry in the Tropics. 3rd edn. Longmans, London, pp. 231--232. Wilson, L.L., Rishel, W.H. and Harvey, W.R., 1972. Influence of herd, sire, and herd × sire interaction on live and carcass characters of beef cattle. J. Anita. Sci., 35: 502--506.
RESUME Iloeje, M.U., 1986. Composantes de la variance des caract~res de croissance chez les bovins Z~bus et South Devon dans le sud ouest de la Nigeria. Livest. Prod. Sci., 14: 231--238 (en anglais). A partir des enregistrements sur 31 488 Z6bus et 23 708 South Devon, on a estim~ les composantes de la variance des poids fi la naissance, au sewage, ~ un an et ~ l'abattage et des croi"ts journaliers aux diff4rentes p6riodes. On a utilis~ la m4thode 2 de Henderson avec un module ~ effets mixtes incluant les effets fixes du sexe et les effets au hasard du troupeau, de l'ann~e-saison, du p~re et du p~re x ann~e-saison. Le troupeau, l'ann~esaison, le p~re et l'erreur rendent compte respectivement de 22 ~ 37%, 10 ~ 17%, 3 fi 5% et 43 ~ 58% de la variation totale des caract~res de croissance consid4r~s. Les estim~es obtenues pour la composante p~re X ann4e-saison sugg~rent une interaction faible mais r~elle entre annie et p~re pour les caract4res ~tudi~s. Les estim~es de l'h~ritabilit~ ~ partir des demi-fr~res et soeurs paternels varient de 0.28 ~ 0.37 pour les diff4rents caract~res tandis que les correlations g~n4tiques et ph~notypiques entre les caract~res sont positives et 61ev~es. I1 n'y a pas eu de differences significatives entre les races dans les corr41ations obtenues pour les diff4rents caract4res ~tudi6s. KUR ZF AS S UN G Iloeje, M.U., 1986. Varianzkomponenten fiir Wachstumsmerkmale zwischen Zebu und South Devon Fleischrindern in Siidost-Nigeria. Livest. Prod. Sci., 1 4 : 2 3 1 - - 2 3 8 (auf englisch). Mit Hilfe der Daten von 31 488 Zebus und 23 708 South Devons wurden die Varianzkomponenten fiir Geburtsgewicht, Absetzgewicht, durchschnittliche ti/gliche Zunahme vor dem Absetzen, J~hrlingsgewicht, Schlachtgewicht, durchschnittliche ti/gliche Zunahme vom Absetzen bis zum J~hrlingsalter und durchschnittliche t~'gliche Zunahme vom J~hrlingsalter bis zum Schlachten bestimmt. Die Varianzkomponenten wurden mit Hilfe der Henderson-Methode Nr. 2 mit einem "mixed effect"-Modell gesch~tzt, dass das
238 Geschlecht als fixen Effekt und den Herdeneinfluss, den Jahressaisoneinfluss, den Bulleneinfluss und den Bulle X Jahressaisoneinfluss als zuf~llige Effekte beinhaltete. Herdeneinfluss, Jahressaisoneinfluss, Bulleneinfluss und die Fehlerkomponenten machten 22-37%, 10--17%, 3--5% bzw. 43--58% der Gesamtvarianz der gesch~tzten Wachstumsmerkmale aus. Die Sch~/tzwerte der Bulle x Jahressaison-Komponenten lassen einen kleinen, aber reellen Jahres × Bullen-Interaktionseffekt bei den untersuchten Merkmalen erkennen. V~terliche Halbgeschwistersch~/tzwerte ffir die Heritabilitgt der verschiedenen Wachstumsmerkmale liegen zwischen 0.28--0.37, wobei die genetischen und ph~/notypischen Korrelationen zwischen den Merkmalen positiv und hoch sind. Es traten keinen signifikanten Differenzen zwischen den Rassen fiir die Korrelationen der untersuchten Merkmale auf.