| Summary: | Data on 4023 lactation records on purebred Sahiwal cows and 2391 lactation records of Holstein Friesian X Sahiwal (FS) and Jersey X Sahiwal (JS) crossbreds from Livestock Production Research Institute (LPRI) Bahadurnagar, District Okara and Qadirabad District Sahiwal for the period 1973-1995, in Punjab, Pakistan were analysed. Crossbreeding effects were studied for production and reproduction traits: lactation milk yield (LMY), calving interval (CI), milk yield per day of calving interval (MCI), days open and days dry. Heterosis effects were significant (P<0.01) and in a favourable direction for all production and fertility traits in all groups. Compared with the mid-parent mean, the F I would increase LMY by 31 % in FS and by 41 % in JS crosses. The MCI would be increased in these crosses, by 49 % and 51 %, respectively. For reproduction traits there was a decrease in days open: 35 and 60 %; days dry: 41 and 72 % and CI: 15 and 20 % for FS and JS crosses, respectively. Heterosis effects were larger than breed additive effects. Additive breed effects for FS crosses were larger than for JS crosses, and FS crossbreds were superior to JS crossbreds in LMY and MCI. The recombination effects were found significant (P <0.01) for most of the traits in this study.
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