Genetic trends production and somatic cell count for Jersey cattle in Zimbabwe born from 1994 to 2005.

Genetic trends for Jersey dairy cattle in Zimbabwe were estimated. A total of 10,986 lactation records were obtained from Zimbabwe Livestock Identification Trust, with cows calving in the period 1996 to 2008. An ASReml program fitting an animal model was used for the analyses. The animal model that was used included overall mean, herd-year-season, previous calving interval, and days dry as fixed effects while linear and quadratic regression coefficients of age at calving as covariates. Random effects were cow, permanent environmental effects, and residual error. The pedigree file included 1,228 animals born from 1994 to 2005. The traits studied were milk yield, fat yield, protein yield, fat percent, protein percent, and Log(10)SCC. Results indicated that milk yield, fat yield, and protein yield increased genetically (P < 0.0001) on average by 1.420, 0.160, and 0.164 kg per year, respectively. Fat percent, protein percent, and Log(10)SCC declined over the past 12 years (P < 0.0001) at the rate of -0.021, -0.015, and -0.0002 per year, respectively. This was due to the negative correlation between milk composition and milk yield. The results implies that the selection applied in the last decade has achieved genetic progress and that there is genetic variance for continued improvement and for setting up an effective dairy breeding program in Zimbabwean Jersey herds for milk, fat, and protein production.