The main objective of this study is to examine genetic changes in growth rate and carcass composition traits in group housed, ad libitum fed pigs, from lines of Large White divergently selected over four years for high and low post-weaning daily gain on a fixed but restricted ration. Genetic parameters for production and carcass traits were also estimated by using average information-restricted maximum likelihood applied to a multivariate individual animal model. All analyses were carried out on 1,728 records of group housed ad libitum fed pigs, and include a full pedigree of 5,324 animals. Estimates of heritability (standard errors in parentheses) were 0.11 (0.04) for lifetime daily liveweight gain (LDG), 0.13 (0.04) for daily carcass weight gain (CDG) and 0.28 (0.06) for carcass backfat (CFT). Genetic correlations between LDG and CDG were highly positive and between LDG and CFT negative, suggesting that selection for lifetime daily gain under commercial conditions of group housing with ad libitum feeding would result in favourable improvement in carcass traits. CFT showed negative genetic correlations with CDG. Correlated genetic responses evaluated as estimated breeding values (EBVs) were obtained from a multivariate animal model-best linear unbiased prediction analysis. After four years of divergent selection for 6 week post-weaning growth rate on restricted feeding, pigs performance tested on ad libitum feeding in groups exhibited changes in EBVs of 6.77 and -9.93 (g/d) for LDG, 4.25 and -7.08 (g/d) for CDG, and -1.42 and 1.55 (mm) for CFT, in the high and low lines, respectively. It is concluded that selection for growth rate on restricted feeding would significantly improve genetic performance and carcass composition of their descendants when group housed and ad libitum fed as is a common commercial practice.
Hall, A. D., W. G. Hill, P. R. Bampton and A. J. Webb. 1999. Genetic and phenotypic parameter estimates for feeding pattern and performance test traits in pigs. Anim. Sci. 68:43-48.
Kim, J. I., Y. G. Sohn, J. H. Jung and Y. I. Park. 2004. Genetic parameter estimates for backfat thickness at three different sites and growth rate in swine. Asian-Aust. J. Anim. Sci. 17:305-308.
McPhee, C. P., G. A. Rathmell, L. J. Daniels and N. D. Cameron. 1988. Selection in pigs for increased lean growth rate on a time-based feeding scale. Anim. Prod. 47:149-156.
Sellier, P. 1998. Genetics of meat and carcass traits. In The genetics of the pig (Ed. M. F. Rothschild and A. Ruvinsky). CAB International, Wallingford; UK, pp. 463-510.
Clutter, A. C. and E. W. Brascamp. 1998. Genetics of performance traits. In: The genetics of the Pig (Ed. M. F. Rothschild and A. Ruvinsky). CAB International, Wallingford; UK, pp. 427-462.
Kennedy, B. W. 1990. Use of mixed model methodology in analysis of designed experiments. pp. 77-97 in Advances in statistical methods for genetic improvement of Livestock. Springer Verlag, Berlin, Germany.
GenStat. 2002. Release 6.1 for windows. Sixth edition. VSN International Ltd., Oxford, UK.
McPhee, C. P. and M. MacBeth. 2000. A profit model for estimating economic values of traits in the national pig improvement program, PDRC DAG58/1339 final report.
Werf, J. H. J. van D. and I. J. M. D. Boer. 1990. Estimation of additive genetic variance when base populations are selected. J. Anim. Sci. 68:3124-3132.
Labroue, F., R. Gueblez and P. Sellier. 1997. Genetic parameters of feeding behavior and performance traits in group-housed large white and French landrace growing pigs. Genet. Sel. Evol. 29:451-468.
Skorupski, M. T., D. J. Garrick and H. T. Blair. 1996. Estimates of genetic parameters for production and reproduction traits in three breeds of pigs. N. Z. J. Agri. Res. 39:387-395.
Gilmour, A. R., B. R. Cullis, S. J. Welham and R. Thompson. 1999. Asreml reference manual. NSW Agriculture Biometric Bulletin No.3. Orange Agricultural Institute, Forest Road, Orange 2800 NSW Australia.
Roehe, R. and B. W. Kennedy. 1993. The influence of maternal effects on accuracy of evaluation of litter size in swine. J. Anim. Sci. 71:2353-2364.
Falconer, D. S. 1954. Validity of the theory of genetic correlation. J. Hered. 45:42-44.
Johansson, K., B. W. Kennedy and M. Quinton. 1993. Prediction of breeding values and dominance effects from mixed models with approximations of the dominance relationship matrix. Livest. Prod. Sci. 33:213-223.
Wolter, B. F. 2001. Effect of group size on pig performance in a wean-to-finish production system. J. Anim. Sci. 79:1067-1073.
Groeneveld, E. 1990. Pest user's manual. Institute of Animal Husbandry and Animal Behaviour. Federal Agricultural Research Centre, Germany.
Nguyen, N. H. and C. P. McPhee. 2005. Genetic parameters and responses in performance and body composition traits in pigs selected for high and low growth rate on a fixed ration over a set time. Genet. Sel. Evol. 37:199-213.
Nguyen, N. H. 2002. Direct and correlated responses to selection for growth rate in Large White pigs on restricted feeding. Ph.D. Thesis, University of Queensland, Australia.
Black, J. L., L. R. Giles, P. C. Wynn, A. G. Knowles, C. A. Kerr, M. R. Jones, A. D. Strom, N. L. Gallagher and G. J. Eamens. 2001. Factors limiting the performance of growing pigs in commercial environments. In: Manipulating Pig Production VIII (Ed. P. D. Cranwell). Australasian Pig Science Association, Werribee, Australia, pp. 9-36.
Von Felde, A., R. Roehe, H. Looft and E. Kalm. 1996. Genetic association between feed intake and feed intake behaviour at different stages of growth of group-housed boars. Livest. Prod. Sci. 47:11-22.
Hofer, A., C. Hagger and N. Kunzi. 1992. Genetic evaluation of on-farm tested pigs using an animal model. I. Estimation of variance components with restricted maximum likelihood. Livest. Prod. Sci. 30:69-82.