Effects of genetic and environmental factors on lactation components in Holstein-Friesian cattle

Data on 100 Holstein-Friesian cows for a period of 14 years (1988- 2002) were collected from Government Dairy Farm Quetta and analyzed. The lactation components such as lactation length, peak yield, milk yield, and age at calving averaged 319 plus minus 56 days, 474 plus minus 42 liters, 3661 plus minus 785 liters, 1963 plus minus 636 days respectively. The heritability estimates obtained as 0.49, 0.29, 0.32 and 0.53 for lactation length, peak yield, milk yield and age at calving respectively. Seasonal effects revealed that there is no influence of season of calving on lactation components. Summer, Autumn, Winter and Spring had lactation length 323 plus minus 50, 317 plus minus 49, 313 plus minus 56 and 321 plus minus 55 days, monthly peak yield 477 plus minus 77, 472 plus minus 70, 466 plus minus 53 and 482 plus minus 73 liters, and milk yield 3685 plus minus 766, 3593 plus minus 817, 3645 plus minus 677, 3724 plus minus 864 liters, respectively. Parity-wise (1st, 2nd, 3rd 4th and 5th) average lactation length was, 312 plus minus 51, 319 plus minus 59, 337 plus minus 55, 311 plus minus 50 and 318 plus minus 54 days, monthly peak yield 470 plus minus 81, 464 plus minus 69, 481 plus minus 79, 475 plus minus 68 and 480 plus minus 57 liters, and milk yield, 3657 plus minus 786, 3740 plus minus 813, 3938 plus minus 750, 3486 plus minus 645, 3484 plus minus 670 liters respectively. Positive correlations were observed between lactation length and peak yield (0.056), lactation length and milk yield (0.693), peak yield and milk yield (0.382), and peak yield and age at calving (0.110), while negative correlation was recorded between milk yield and age at calving (-0.171) and lactation length and age at calving (-0.104). The regression co-efficient between lactation length and peak yield (0.043), lactation length and milk yield (0.050), peak yield and milk yield (0.036), and peak yield and age at calving (0.946) was positive, while negative correlation was recorded between milk yield and age at calving (-0.139) and lactation length and age at calving (-0.009).