An assessment of the contributions of Afrikaner, Hereford and Simmentaler in composite breed development in beef cattle

[摘要] ENGLISH ABSTRACT:The objective of this study was to obtain more information regarding the characterisation ofAfrikaner (A), Hereford (H) and Simmentaler (S) breeds in an initial crossbreeding programme andsubsequent composite development. This involves the estimation of breed additive effects, breedmaternal, individual heterotic effects and maternal heterotic effects in the initial crossbreedingphase and the estimation of genetic parameters and prediction of breeding values in latergenerations for birth weight (BW), weaning weight (WW) and cow efficiency (CE; WW/damweight 75 x 100) in an intensive environment under high stocking rates.In the analysis of the initial crossbreeding phase, the S breed direct effects, expressed as deviationfrom the general mean, were positive (P :s; 0.01) for both BW and WW. Hereford and A breed directeffects were negative (P :s; 0.01) for both BW and WW. Afrikaner direct maternal effects werepositive (P :s; 0.01) for both BW and WW. The H direct maternal effect was negative (P :s; 0.05) (-2.8%) for WW. Simmentaler maternal effect was negative (P :s; 0.01) for BW but non-significant (P;:::0:.05) for WW. Individual heterotic effects for BW were significant (P:S; 0.01) in H x S (3.5%)and S x A (11.0%) only. Individual heterotic effects were positive (P :s; 0.01) for WW, with that ofthe H x A (9.8%) and S x A (6.7%) crosses exceeding the H x S (3.1%) cross. Maternal heteroticeffects were non-significant (P ;:::0:.05) for both BW and WW.Investigations of the contributions of the A, Hand S during composite development in latergenerations, respectively, were made to estimate direct heritabilities (h2a) and maternal heritabilities(h2 m) for BW and WW of the calf and CE of the dam. Calves were born between 1968 and 1993 (n= 52628). Calves of this composite population had varying levels of A, Hand S genes ranging fromo to 75%, 0 to 100% and 0 to 96.9%, with an average of 4.3,19.3 and 33.4%, respectively. For the A, direct heritabilities fitting unitrait models were 0.67, 0.53 and 0.19 for BW, WW and CE,respectively, with corresponding estimates of h2mbeing 0.22, 0.36 and 0.58. Genetic correlationsbetween direct and maternal effects (ram)were negative for all three traits, varying from -0.32 to -0.62. Direct breeding values for BW increased and reached a maximum value at 0.11 proportion ofA. The maternal breeding values for BW decreased linearly between 1.6 to 37.5% A proportion andincreased linearly between 37.5 to 75% A proportion. For WW, the direct breeding valuesdecreased linearly with increasing A proportion, while the maternal breeding values were notaffected by proportion of A. Cow efficiency was unaffected by an increase in proportion of A.For the H, direct heritabilities fitting unitrait models were 0.67,0.52 and 0.21 for BW, WW and CE,respectively, with corresponding estimates of h2mbeing 0.22, 0.36 and 0.60. Genetic correlationsbetween direct and maternal effects (ram)were negative for all three traits, varying from -0.32 to -0.64. Direct breeding values and maternal breeding values for BW and WW decreased withincreasing proportion of H. Direct breeding value for CE increased, while the maternal breedingvalue for CE reached minimum value at 0.62 proportion ofH.For the S, direct heritabilities fitting unitrait models were 0.66, 0.53 and 0.21 for BW, WW and CE,respectively, with corresponding estimates of h2m being 0.22, 0.36 and 0.59. Genetic correlationsbetween direct and maternal effects (ram)were negative for all three traits, varying from -0.32 to -0.63. Direct breeding values for BW and WW decreased and maternal breeding values increasedwith increasing proportion of S. Cow efficiency was unaffected by an increase in proportion of S.The study suggests that in the initial crossbreeding phase, purebred S breeding seems to be the bestbreeding practice for this environment and that during composite development, high A and Hcontributions could lead to low BW and WW (except the maternal contribution of the A for BWand WW). The advantage of the S lies more in the maternal contribution than in the directcontribution suggesting that the S is a large-framed maternal line rather than a terminal sire line.

[发布机构] Stellenbosch University