Genetic and environmental factors influencing persistency of milk production in karan fries cattle*

A total of 618 lactational milk yield records of first four parities at weekly interval from 1990 to 2001 (12 years) were collected for 284 Karan Fries cows sired by 53 bulls maintained at Dairy Cattle Breeding Division, NDRI, Karnal. The persistency indices were estimated by five different measures viz. Johansson and Hanson method (P₁ and P₂), Mahadevan method (P₃), Ratio method (P₄) and Prasad method (P-₅). The overall least square means for P₁, P₂, P₃, P₄ and P₅ were 87.34±1.27, 52.80±1.16, 1.46±0.02, 204.03±1.56 and 0.68±0.00 respectively. The first calvers had the highest persistency of lactation across all the methods followed by second calvers. The rainy calvers were most persistent whereas the winter calvers were least persistent. The correlation between peak yield and lactation milk yield (0.610) was positive and highly significant. There was significant and negative correlation of peak yield with all the persistency indices across all the four parities. In general, the heritability estimates were very low (0.01 to 0.17) with high standard errors. Johansson and Hanson's measures of persistency (P₁ and P₂) were found to be more reliable with values of their repeatability being 0.190 and 0.200 respectively. The lactational milk yield was predicted with around 62% accuracy using the peak yield as a predictor.