The Dynamics of First-Calf Heifers’ Exterior Traits Within Different Years of Evaluation, Age and the Season of Birth and Calving

Abstract

In the herd of Ukrainian Red Dairy breed of “Rossiya” breeding farm on 2302 cows, the dynamics of first-calf heifers’ exterior of different years of evaluation, age and season of birth and calving were studied. It was established, that the investigated paratypic factors of the season of birth and calving do not have significant influence (0.02…4.9%) on the formation of the exterior of first-calf heifers. More significant (0.3…11.4%) was the influence of the age of exterior evaluation. And the most significant amongst paratypic factors was the influence of the year of evaluation of the cows (5.7…57.5%), which can be explained by the simultaneous influence of as the improvement of the level of breeding and feeding of animals, so the genetic factors of “blood share” of improving breed and parentage of different breeding (genetic) value. The chronological dynamics of the measurements of first-calf heifers led to the adequate changes in the proportions of the body in the direction of increasing of leg length, stoutness and eirisomia with simultaneous curvilinear decrease of conformation indices of stretching, rump-thoratic, thoratic, boneness, massiveness and over-growth. Determined changes in the proportions of the body structure fit the forming of more expressed milk type. Correlation analysis established, that the age of evaluation has a direct significant connection with the depth and width of the chest, indirect length of body and rumps, width of rump in hooks and pelvic width, heart girth. The age of the first calving is reliably directly proportional to the depth and width of the chest and the width at the withers and inversely – to the height at the withers and rump, pelvic width and the girth of the wrist. Less significant, but sometimes reliable, was the correlation between the investigated features of the exterior of first-calf heifers and the intensity of their growth in different periods of rearing. A higher relative variability of most exterior traits was found with the average daily weight gain of heifers during the period of intensive puberty in 6–12 months, a slightly lower – in the first and third half-year of the postnatal ontogenesis. The increase in “blood share” of cows of the Holstein breed shows the combined effect of improvement (formation of the milk type) of the exterior with an increase in the relative share of non-pigmented areas of the skin.