Genetic Parameters and Environmental Factors Associated with Type Traits Scored on an Ordered Scale During First Lactation

Abstract

Sixty subjective and linearized type data were recorded on 7375 first lactation Holstein cows. Data were analyzed by paternal half-sister analysis for genetic parameters. One hundred and six sires were represented. Two kinds of heritability estimates were obtained; the 1st was a method 3-derived estimate for the raw scale and the 2nd was a nonlinear method 3-derived estimate for an underlying scale. Whenever estimates of heritability on the raw scale were positive, larger estimates were generally obtained on the underlying scale. Some udder traits (e.g., depth, rear length, rear balance, teat placement, rear teat length, rear width) had underlying heritabilities between 10 to 30%. Suspensory strength and teat shape had no genetic variation. Of feet and leg traits only set (0.14) and cleanness of hocks (0.09) had heritabilities above 6%. Some functional traits (milking speed, edema) had heritabilities near 11%. Disposition, mastitis score and milk letdown had no genetic variation. Most body traits (e.g., pin and hip width, length and levelness of rump, rib spring) had heritabilities between 15 and 30%. Method 3 phenotypic and genetic correlations were computed for the raw scale. Most phenotypic correlations were near zero. Traits associated with size or skeletal dimension had positive phenotypic and genetic correlations. Fore udder length, rear udder width and rear udder height had positive genetic correlations (range 0.21 to 0.43). Udder depth had moderate genetic correlations with most udder traits, teat traits and body traits. The statistical models included describer, stage of lactation and calendar month of description effects. In general, describer effects were the largest and most significant kind of environmental effect. Stage of lactation effects occasionally showed consistent trends. Month effects appeared to be unpredictable.