Genetic and phenotypic trends for milk yield per lactation in Sahiwal cattle under arid and semi arid conditions of Pakistan

The aim of the study was to evaluate the sahiwal cattle genetically. annual genetic and phenotypic trends were drawn for lactation milk yield to evaluate previous selection strategies. data on (n=24182) multiple lactations of 7351 sahiwal cows maintained at five institutional herds of punjab,pakistan from 1969 to 2006 were used. the heritability for total milk production was estimated by using paternal half-sib analysis. overall least squares means and standard errors for total milk production for five institutional herds ranged from 1028±16 to 1401±16 kg with the mean value of 1323±701 kg. total milk production was significantly influenced by herd,year,season of calving,lactation number and days in milk (p<0.01). an heritability of 0.27±0.01 for total milk yield was estimated,and breeding values of sires and cows ranged from -266 to 702 and - 893 to 1469 kg,respectively. the least squares means during the examined periods showed greatly fluctuations. genetic and phenotypic trends for total milk production showed slightly upward increasing tendency. the phenotypic trends was maximum in 1972 (1648 kg) and minimum in 1978 (954 kg).