Effects of Genetic and Environmental Factors on Mastitis and Performance Traits in Various Breeds of Dairy Cattle Maintained at Khyber Pakhtunkhwa, Pakistan.

Milk quantity and quality traits in cattle are affected by udder health, breed, genetic (such as heritability, repeatability, and heterosis), and environmental factors. The present study was designed to evaluate the effect of udder health, genetic factors and environmental factors on milk performance traits in cattle breeds. The study was conducted on four dairy farms in Khyber Pakhtunkhwa, Pakistan. A total of 291 milk samples and 547 records were collected from lactating cattle ranging between parities one to six. For milk performance traits and udder health, each milk sample was analysed for milk composition (fat %, protein %, and lactose %) and SSC (by direct microscopic SCC method). The data were analysed using a generalized linear model of SAS studio for the effect of the SCC, breed, and herd on milk performance while wombat and CFC for the analysis of genetic and non-genetic factors. The results showed that animals with higher SCC have significantly lower (P<0.01) milk fat %. Breed-wise analysis showed significantly higher (P<0.01) protein % in Achai, lactose % in Jersey and its crossbred (Jersey x Achai), and LMY was recorded significantly higher in Friesian and its crossbred Jersey x Friesian (JF). The analysis of the environmental effect on milk composition and LMY showed that animals kept in the different herds have significantly different (P<0.01) milk compositions and LMY. The estimates of additive genetic variance (V_a), variance of the permanent environment (V_pe), and estimates of phenotypic variation (V_p) were recorded highest for SCC. The analysis of the effect of genetic factors (i.e. heritability, repeatability, and heterosis) revealed that estimation of heritability was highest (0.59) for age at first calving (AFC) while lowest (0.00) for calving interval (CI), and estimation of repeatability was highest (0.99) for AFC while lowest (0.00) for CI. The results of heterosis analysis showed that crossbred (Achai x Jersey) had positive heterosis for milk composition traits and SCC while negative heterosis for LMY compared to their purebreds. The study concluded that crossbred, better herd management and nutrition, and selection based on genetic factors (such as heritability, repeatability, and heterosis) can bring improvement in milk performance traits and udder health. [ABSTRACT FROM AUTHOR]