Factors affecting productive life and fertility in Nguni cows

[摘要] English: The objective of the study was to assess factors that affect productive herd life and fertility in the Nguni cows using different models. The data set was obtained through the SA Stud book Logix information system. Cattle in the data were registered Nguni cows with their pedigree information from three herds reared extensively in three different environments in South Africa. The raw data included animal identity numbers born between 1968 and 2015, with sire, and sire of sire, dam of sire, dams, sire of dam and dam of dam. One herd had 12 788 animal identity records, the second one had 6 929 and the third one had 8 421 identity records. Amongst other important things included in the original data are the birth dates of each animal, culling date, death date, inspection date, registration date, breeder number, owner number and ownership date. Necessary edits were done to prepare data for analysis.The age at first calving and inter-calving period were used as traits to assess productive herd life length. Age at first calving was calculated as the difference between birth date and first calving date in days. The inter-calving period was calculated as the difference between two successive birth dates. First analysis was done for productive herd life on the combined data of all three herds using animal models through ASREML program.For the combined data all effects fitted in the model were significant (P<0.05). The mean obtained for age at first calving (AFC) and inter-calving period (ICP) was 893.5 and 408.4 days, respectively. The minimum and maximum age at first calving (AFC) was 512 and 1 099 days, respectively. The minimum and maximum ICP was 313 and 800 days, respectively. The mean, minimum and maximum number of parities (NP) was 7.2 and 15, respectively. Productive herd life (HL) mean and standard deviation was 2 542 and 1 272 days, respectively, with a minimum and maximum of 655 and 6 088 days, respectively. The variance components were 770.7, 2 7196 and 1 103, respectively for additive genetic effects, phenotypic effects and residual and the heritability (h2) and standard error was 0.028 and 0.04, respectively.The analysis was also carried out on separate herds using ASREML. The mean for AFC in all three separate herds was 848.1, 893.4 and 918.5 for Komga (KM), Perdeberg (PG) and the Vaalharts (VH) herd, respectively. The minimum AFC was 512, 602 and 534 for KM, PG and VH, respectively and the maximum AFC was 1 099 for all three herds. The mean for inter-calving period (ICP) was in the KM, PG and VH herd was 404.5, 403.5 and 404.2, respectively. The minimum AFC was 329, 315 and 313 in the KM, PG and VH herd. The maximum AFC in the KM, PG and VH herd was 701, 655 and 800, respectively. Variance components for the direct additive effects, phenotypic and residual effects were 19 801, 1 508.2 and 1 743.2, respectively in the KM herd. In the PG herd the variance components were 0.1950, 36 339 and 2 731.4, respectively for the direct additive effects, phenotypic and residual effects. The variance components in the VH herd for direct additive, phenotypic and residual effects were 19 048, 582.98 and 1 220.4, respectively. The heritability estimate was 0.08, 0.00 and 0.03, respectively in the KM, PG and VH herd.Age at first calving (AFC) and inter-calving period (ICP1 and ICP2), were used as traits to assess cow fertility using linear multiple trait animal models of ASREML and repeatability model. The inter-calving period was used as the repeated trait in the model. The mean for AFC was 896.8. Minimum and maximum age was 512 and 1 230days, respectively. For the first inter-calving period (ICP1) the mean was 423 days, while the minimum and maximum was 270 and 823 days, respectively. The second inter-calving period (ICP2) obtained a mean of 400.3 days, with minimum and maximum of 275 and 810 days, respectively. Variance components for AFC were 6 476.6, 18 238 and 11 762, respectively, respectively for direct additive effects, phenotypic effects and residual and the heritability was 0.36. ICP1 yielded 1 139.8, 10 691 and 9 551.5, respectively for direct additive effects, phenotypic effects and residual with a heritability estimate of 0.11. For ICP2 1 890.1, 8 520 and 6 630.1, respectively were variance components for direct additive effects, phenotypic effects, residual; with a heritability estimate of 0.22. The correlation estimate between AFC and ICP1 was 0.58, and it was 0.59 between AFC and ICP2. ICP1 and ICP2 had a correlation estimate of 0.12 between them. For the repeatability model, the variance component values for ICP used as the repeated trait were 381, 8 155.8 and 7 774.8, respectively for direct additive effects, phenotypic and residual effects. The heritability and repeatability estimate was 0.05 and 0.22, respectively.The Nguni cow productive herd life was analyzed using the Survival kit V3.12 (Ducrocq & Solkner, 1998) featured models. The Cox model which is the semi-parametric model featured in the Survival kit was used to analyze the Nguni cow data. The Nguni cow herd herd data set analyzed using the Cox model had 1 245 cow records starting from year 1996 to 2015 with parities from one up to the 9th parity. Animal records for cows in the productive herd between the 1st of January 1984 and 31 December 1995 were truncated because of lack of information on the culling or death date. The cow herd was stratified into 3 groups of ages at first calving (18, 24 and 36 months).This likelihood risk ratio results indicated that year, AFC and parity were significant (P<0.05). The model yielded a heritability estimate of 0.02 and a standard error of 0.003. Risk ratios for culling differed for different ages at first calving (18, 24 and 36 months AFC), over the years (from 1996 to 2015) and at different parities (from the 1st to the 9th parity). For 24 months AFC the culling risk ratio was the least compared to 18 and 36 months age at first calving. Heifers that had their first calf at 18 months age were at a 0.061 risk of being culled, whereas the ones that had their first calf at 24 months were at a 0.042 probability of being culled. For heifers that calved for the first time at 36 months age the culling risk ratio was 1.000. In the year 2015 about 250 cows were culled which was more than any other year included in the study. More animals were culled in their 9th (120 cows) and the least number was culled in their first parity (4). Only 4 cows were culled in the group of cows that had their first calf at 18 months, 27 were culled in the group of cows that had their first calf 24 months and 95 were culled in the group that had their first calf at 36 months of age.

[发布机构] University of the Free State