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Data on 98 lactations of Fi Holstein—Friesian x Sahiwal cows kept at the University of Agriculture, Faisalabad were analysed for the magnitude of seasonall,ariation in various lactation para-meters. Peak daily milk yield averaged 16.39 + 0.41 kg, attained at 31.2 + 2.9 days after calving. Initial 60 day milk yield and 305•day milk yield averaged 805.8 ± 24 0 and 3056.3 ± 106.5 kg, respectively. The cows calving in winter had the highest peak yield (I.7.85 kg), initial yield (889.6 kg) and 305-day milk yield (3398.6 kg). The spring salvers attained the peak earlier (22.0 days) but milk yield was 28 per cent less than the winter salvers. The peak and initial yields were the lowest in summer salvers. Further analyses indicated that variation in these traits due to calving season was non-significant. Persistency averaged 93,21 0.79 per cent and it was significantly affected by the season of calving The cows calving in spring season were the least persis-tent,
INTRODUCTION
A massive programme of upgrading local non descript cattle with the Bos taurus semen is underway in Pakistan since 1975. Majority of cattle popula-tion in areas where artificial insemination facilities exist contain some degree of exotic inheritance, The crossbred animals have been widely commended for high milk production and early maturity. A wide variation exists in the eco-nomic traits of these crossbreds which could be attributed to numerous genetic and environmental factors. The season of calving deserves attention because the crosbred cows are greatly inconvenienced by climatic stresa during summer months. Milk production and allied traits viz. peak yield, initial yield, persis.
*Faculty of Animal Husbandry, University of Agriculture, Faisalabad, 74
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Zaheer Ahmad, M. D. Ahmad. (1985) Influence of calving season on milk yield and persistency in Holstein Friesian X Sahiwal cows, , Volume 22, Issue 2.
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