Browsing by Author "Kgari, Ramadimetje Delight"
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- ItemGenetic analysis of heifer and cow fertility for South African Holsteins using artificial insemination records(Stellenbosch : Stellenbosch University, 2020-12) Kgari, Ramadimetje Delight; Dzama, Kennedy; Makgahlela, Mahlako Linah; Muller, Carel; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.ENGLISH ABSTRACT: Female fertility has gained significant attention in the dairy cattle industry and is increasingly being incorporated in to breeding objectives worldwide. In South Africa, genetic improvement of the trait is hampered by lack of sufficient data and the availability of estimated breeding values for traits indicating reproductive performance of dairy cows. Currently, only two traits, i.e. calving interval and age at first calving are used as indicators of fertility in the routine genetic evaluations of South African dairy cattle. The objective of this study was to derive alternative measures of heifer and cow fertility based on artificial insemination records, and estimate genetic parameters and breeding values, for their possible inclusion in the SA Holstein cattle breeding programs. A total of 64464 artificial insemination records from 18 South African Holstein herds were collected from an on-farm milk recording system. The dataset entailed information on birth date, service and calving dates of each animal, lactation number, pregnancy diagnosis statuses, dam and sire identification numbers from which heifer and cow fertility traits were defined. The following traits were defined:age at first service (AFS), number of services per conception for heifers (SPCh), the interval from calving date to first service date (CFS),number of days open (DO), the number of services per conception for cows (SPC) and binary traits indicating whether cows were inseminated within 80 days post-partum, whether cows were confirmed pregnant within 100 or 200 days open (FS80d, PD100d and PD200d). Statistical analyses ofgenetic parameters and breeding values were performed using THRGIBBSF90 and POSTGIBBSF90 of Blupf90 family of programs. The heritability estimates obtained in this study were low to moderate (0.02 to 0.24), indicating that there is genetic basis for the explored fertility traits that warrants genetic selection. The genetic correlations between fertility traits observed in the current study were generally favourable with the highest correlations between CFS and SPC (0.90), AFS and AFC (0.91) and AFC and SPC (0.95). There were unfavourable correlations although very low between DO and AFS (-0.03), between AFS and SPCh (-0.06). Positive genetic correlations indicate that genetic improvement in one trait is coupled with a correlated increase in another. There was generally no distinct trends for heifer traits indicating that not much work was done in improving the traits. There were observed favourable genetic trends obtained for the cow traits, CFS with a decrease of 0.01 days/year and DO with a decrease of 0.06 days/year. However, increases were observed in the phenotypic trends of CFS (0.16days/year) and DO (0.83days/year). The unfavourable and non-distinct trends indicates that there is a need for improving female fertility traits. Sufficient data recording and genetic evaluations are a pre-requisite for the incorporation of fertility traits in dairy cattle breeding programs towards the improvement of reproductive performance. The results from the current study shows that on farm artificial insemination records could be useful towards improving the fertility in South African Holstein cattle population.