Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học Journal of Biology đề tài: Genetic improvement of litter size in sheep. A comparison of selection methods | Genet Sei Evol 1995 27 43-61 Elsevier INRA 43 Original article Genetic improvement of litter size in sheep. A comparison of selection methods M Pérez-Enciso1 JL Foulley1 L Bodin2 JM Eisen2 JP Poivey2 1 Institut national de la recherche agronomique station de génétique quantitative et appliquée Jouy-en-Josas 78352 cedex 2 Institut national de la recherche agronomique station d amelioration génétique des animaux BP 27 31326 Castanet-Tolosan cedex France Received 22 February 1994 accepted 1 August 1994 Summary - The objectives of this work were to examine the usefulness of measuring ovulation rate OR in order to improve genetic progress of litter size LS in sheep and to study different selection criteria combining OR and prenatal survival ES performance. Responses to selection for 5 generations within a population of 20 male and 600 female parents were compared using Monte-Carlo simulation techniques with 50 replicates per selection method. Two breeds with low Merino and medium Lacaune prolificacy were considered. Records were generated according to a bivariate threshold model for OR and ES. Heritabilities of OR and ES in the underlying scale were assumed constant over breeds and equal to and respectively with a genetic correlation of between these traits. Four methods of genetic evaluation were compared univariate best linear unbiased prediction BLUP using LS records only b-LS univariate BLUP on OR records bOR bivariate BLUP using OR and LS records b-ORLS and a maximum a posteriori predictor of a generalised linear model whereby OR was analysed as a continuous trait and ES as a binary threshold trait t-ORES . Response in LS was very similar with b-LS b-ORLS and t-ORES whereas it was significantly lower with b-OR. Response in OR was maximum with b-OR and minimum with b-LS. In contrast response in ES was maximum with b-LS. This study raised the question as to why selection based on indices combining information from both OR and ES did not perform better
