Correlative variability of growth of heifers and exterior of firstborns with milk productivity of cows

Abstract

Goal. To study the relationship between the growth of heifers and the exterior of firstborns with their subsequent milk productivity on 945 animals of Holstein, Ukrainian black and red dairy breeds. Methods. The exterior was evaluated visually and instrumentally by taking measurements. Indices of the body structure of animals were calculated based on the ratio of the corresponding values. Milk productivity was determined for 305 days of I lactation by milk yield, mass fraction, and output of milk fat and protein. The live weight of heifers was estimated by its value in newborn heifers and age dyna­mics. Results. The highest intensity of growth of heifers was observed during puberty — at the age of 6–12 months. Average daily increments were characterized by the greatest variability among all the studied signs (the coefficient of variability ranged from 16.1 to 44.1%). Closer and more reliable was the correlation between the milking of firstborns and the yield of milk fat and protein with the average daily weight gain of heifers aged 6–12 months. The relative variability of the live weight of heifers in different age periods, followed by the milk productivity of the firstborns (milk yield, yield of milk fat, and protein) increased significantly (P<0.001) from 6 to 18 months of age. Positive indicators of correlation coefficients and their high reliability are evidence that the signs of milk productivity of firstborn cows of the herd depend to the greatest extent on the height in sacrum (r=48.4...50.5) and crest (r=44.0...45.8), chest girth (r=46.5...47.3), oblique trunk length (r=40.7...41.9), and wrist girth (r=47.4...50.0). Conclusions. The level of relative variability of measurements and visual evaluation of firstborns by type of exterior with indicators of milk productivity makes it possible to carry out mediated selection by type of body structure. The established degrees of heritability of the considered traits confirm the possibility of effective selection of dairy cows at the age of first lactation for selective improvement of exterior and indirect increase in milk productivity of the herd.