Genetic evaluation of persistency of milk production and its association with production and reproduction traits in Karan Fries cattle.

摘要

This study was undertaken to investigate the effect of genetic and non-genetic factors on the persistency of milk production and to estimate the relationship of persistency with production and reproductive traits. 400 lactational milk records of 284 Karan Fries cows sired by 53 bulls maintained at NDRI, Karnal, India, during 1990-2001 were used for this study. The milk persistency was estimated by 7 different measures: P1 and P2 for Johansson and Hanson (1940); P3 and P4 for Ludwick and Peterson (1943); P5 for Mahadevan (1951); P6 for Rao and Sundaresan (1982); and P7 for Prasad et al. (1999). The overall least square means for persistency indices (PIs) i. e. P1, P2, P3, P4, P5, P6 and P7 were 91.25+or-1.09, 57.68+or-1.31, 0.91+or-0.01, 0.94+or-0.01, 1.53+or-0.02, 207.88+or-2.18 and 0.70+or-0.01, respectively. The season of calving, parity and pre-peak yield had highly significant effects (P<0.01) on all the 7 measures of milk persistency indices. The cows calving in the rainy season were most persistent, whereas those calving in the winter season were least persistent for all measures of persistency. The highest persistency was observed for first calver cows (P<0.05) as compared to subsequent lactations. The cows that attained the peak at 9-15 weeks after calving were most persistent. The cows with pre-peak period up to 5 weeks were least persistent for all the measures. The persistency was highest for high-producing cows and lowest for low-producing cows. The cows having a service period of less than or equal to 84 days were less persistent than the cows which conceived after 84 days of calving. The persistency was optimum for service period between 85 and 126 days. The correlation between peak yield and lactational milk yield was higher than that observed between the persistency and lactational milk yield. In general, the heritability estimates were very low and had high standard errors. Johansson and Hanson's measures of persistency (P1 and P2) were found to be most reliable with repeatabilities of 0.19 and 0.20, respectively..