GENETIC PARAMETERS OF UDDER TRAITS AND THEIR RELATIONSHIP WITH MILK YIELD IN SAHIWAL COWS OF PAKISTAN - M.A. Khan; M.S. Khan (Journal of Animal and Plant Sciences, 2016)
The present study was executed with the objectives to find out the heritability estimates for udder biometrics and genetic and phenotypic correlations between udder biometrics and milk yield in Sahiwal cows. There were 790 observations of udder measurements on 310 cows, progeny of 53 sires. The udder measurements were recorded at three stages of lactation. The model included fixed effects of herd, parity and stage of lactation. The linear and quadratic effect of age of cow at measurement was included as co-variable. The herd, stage of lactation and parity was a significant source of variation for udder length, width, depth, circumference, 305 day milk yield and test day yield (P<0.001). Age of the cow affected udder length, width, depth, circumference (P<0.001). The age of the cow was also a significant source of variation for 305-day milk yield and test day yield (P<.05). The univariate animal model heritability estimates for udder length, width, depth and circumference were 0.68±0.03, 0.66±0.03, 0.54±0.04 and 0.60±0.04, respectively. Highly positive genetic correlations were found among all udder measurements and ranged from 0.71±0.05 between udder length and udder depth to 0.84±0.02 between udder length and udder width. The genetic correlation of 305-day milk yield with udder length, udder width, udder depth and udder circumference were 0.38±0.02, 0.41±0.02, 0.35±0.02 and 0.36±0.02 respectively. The udder length had the highest phenotypic correlation with test day yield 0.45±0.02 at first stage of lactation followed by udder width (0.39±0.03), udder circumference (0.31±0.03) and udder depth (0.29±0.03). The magnitude of the phenotypic correlations for udder length and udder depth decreased in second and third stage of lactation and correlations for udder circumference were even negative in later stages of lactation with test day yield. The udder length, udder width, udder depth and udder circumference had genetic correlation of 0.40±0.02, 0.43±0.04, 0.36±0.03 and 0.37±0.03 with test day yield at first stage of lactation. The high heritability estimates for udder measurement traits indicate that selection will be effective on the basis of phenotype of the traits. The high genetic and phenotypic correlations of some udder measurements with milk yield traits indicate that same genes are responsible for the expression of the traits. While selecting for udder measurements a correlated response in milk yield is expected.
Keywords: journal article; Heritability; genetic; phenotypic correlations; udder measurements; Sahiwal cows; Pakistan