A genetic evaluation system was developed for 5 fertility traits of dairy cattle: interval from first to successful insemination and nonreturn rate to 56 d of heifers, and interval from calving to first insemination, nonreturn rate to 56 d, and interval first to successful insemination of cows. Using the 2 interval traits of cows as components, breeding values for days open were derived. A multiple-trait animal model was applied to evaluate these fertility traits. Fertility traits of later lactations of cows were treated as repeated measurements. Genetic parameters were estimated by REML. Mixed model equations of the genetic evaluation model were solved with preconditioned conjugate gradients or the Gauss-Seidel algorithm and iteration on data techniques. Reliabilities of estimated breeding values were approximated with a multi-trait effective daughter contribution method. Daughter yield deviations and associated effective daughter contributions were calculated with a multiple trait approach. The genetic evaluation software was applied to the insemination data of dairy cattle breeds in Germany, Austria, and Luxembourg, and it was validated with various statistical methods. Genetic trends were validated. Small heritability estimates were obtained for all the fertility traits, ranging from 1% for nonreturn rate of heifers to 4% for interval calving to first insemination. Genetic and environmental correlations were low to moderate among the traits. Notably, unfavorable genetic trends were obtained in all the fertility traits. Moderate to high correlations were found between daughter yield-deviations and estimated breeding values (EBV) for Holstein bulls. Because of much lower heritabilities of the fertility traits, the correlations of daughter yield deviations with EBV were significantly lower than those from production traits and lower than the correlations from type traits and longevity. Fertility EBV were correlated unfavorably with EBV of milk production traits but favorably with udder health and longevity. Integrating fertility traits into a total merit selection index can halt or reverse the decline of fertility and improve the longevity of dairy cattle.

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SummaryThis paper reviews the successful N'Dama cattle genetic improvement programme implemented in a low input production system at the International Trypanotolerance Centre (ITC) in 1994, in The Gambia. The first part of the paper presents the genetic improvement programme. The second part deals with the analysis of the genetic improvement programme. The success of the genetic improvement programme expressed through genetic progress and the benefits for the farmers is encouraging. Recommendations to strengthen the implementation process in the field are made. RésuméCet article se donne pour objectif de passer en revue le programme d'amélioration génétique du bétail trypanotolérant N'Dama. La première partie de l'article fait découvrir le programme d'amélioration. La seconde partie traite particulièrement de l'analyse du programme, cette analyse se base sur le progrès génétique obtenu et les bénéfices que peuvent en tirer les éleveurs. Pour conclure, certaines recommandations pour le renforcement du programme d'amélioration génétique sont proposées.