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The first lactation records of 340 Karan Fries cows sired by 38 bulls maintained at National Dairy Research Institute, Karnal from 1990 to 2004 (15 years) were utilized to study the effect of various genetic and non-genetic factors on cumulative part lactation and 305-day milk production. The effect of seasons was highly significant for mid-part of the lactation whereas the early (30-day milk yield) and later parts of the lactation were not influenced significantly by seasonal variation. The effect of periods on first lactation cumulative part lactation milk yields and 305-day milk yield was highly significant (P<0.01). The regression of part lactation cumulative milk yields up to 240-days on age at first calving was highly significant (P<0.01) and for 270-day partial milk yield and 305-day standard lactation milk yield was significant (P<0.05). The heritability estimates of successive cumulative yields registered an increasing trend with an increase in lactation stage. The h2 estimate was lowest (0.14 ± 0.13) for 30-day milk yield and highest (0.45 ± 0.18) for 305-day milk yield. The phenotypic and genetic correlations among cumulative partial milk yields and with 305-day milk yield were quite high, positive and highly significant (P<0.01) suggesting that the merit of the cows for milk production could be assessed effectively in early or mid stages of lactation. Relatively high phenotypic and genetic correlations among the adjacent cumulative partial yields were observed compared to the distant part yields.
Keywords: Cumulative part lactation milk yield, Karan Fries, Genetic correlations
* Part of the M.V.Sc. Thesis of the first author
Dairy Cattle Breeding Division, National Dairy Research Institute, Karnal-132001
2007-065 Date received:February 2007; Accepted:June 2007.
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