Phenotypic and genetic parameters for selected production and reproduction traits of Mpwapwa cattle in low-input production systems
The objective of this study was to assess the genetic improvement programme of the Mpwapwa dairy cattle breed over the past four decades, based on on-station selection and breeding. Estimates of genetic parameters and genetic trends for total lactation milk yield (LMY), 305-day lactation milk yield (305LMY), lactation length (LL), age at first calving (AFC), and calving interval (CI) were derived. The study used 1,003 lactation records from 385 cows and 78 sires collected from 1967 to 2012. Genetic parameters were estimated using an animal model procedure with ASReml software. The heritability for LMY and 305LMY were moderately high (0.33 ± 0.11–0.44 ± 0.04) and low for LL (0.13 ± 0.17.0). Repeatability for LMY and 305LMY was high (0.62 ± 0.04–0.70 ± 0.03) and moderate for LL (0.27 ± 0.06). The heritability for AFC (0.13 ± 0.11) and CI (0.10 ± 0.05) were low. The repeatability for CI was low (0.10 ± 0.05). Genetic correlation of 305LMY with LMY and CI were 0.87 ± 0.02 and -0.06 ± 0.009, respectively, while the corresponding phenotypic correlation estimates were 0.82 ± 0.01 and -0.01 ± 0.001. Variation among animal estimated breeding values (EBV) was significant, suggesting that selection to improve these traits is feasible. Thirty seven out of 78 sires had favourable EBV (0–900 kg) for milk yield, which suggests that selection for specific sires could result in increased LMY. Annual rates of sires EBV change for 305LMY, LL, CI, and AFC were -0.05, 0.15, and -0.14 days, respectively. All these traits showed that a decline in genetic progress for Mpwapwa dairy cattle in the on-station breeding programme.
Keywords: Fertility, genetic correlation, genetic trend, milk yield, variance components