The influence of growth retardation of heifers to yearling age on the milk productivity of cows

The purpose of the research was to analyze the impact of growth delays in repair heifers in different periods of the first year of rearing on the compensatory growth of heifers and subsequent productivity of cows. The research was carried out in the herd of the breeding farm “Agrofirma “Svitanok” LLC of the Mariinsky district of the Donetsk region, based on information on the growth, reproductive ability and milk productivity of 1126 cows of the Ukrainian Red and Black-and-White Dairy and Holstein breeds with a dated first calving during the years 2007–2020. Animals without growth retardation were included in the control group, and animals with growth retardation at the age of 0–3, 3–6, 6–9, and 9–12 months, respectively, were included in the four experimental groups. Average daily weight gain of heifers of less than 500 g was considered growth retardation. It was established that despite catching up in growth intensity during the first year of growing, heifers in groups with growth retardation do not have the necessary live weight for insemination in the optimal period (15–16 months), and are characterized by a correspondingly older (by 3.5...15.5 %) age of first calving, lower milk yield by 3.1...21.3 %, milk fat by 3.6...21.0 % and by 3,3...23.9 % – protein in 305 days of the first lactation. Losses in milk productivity continue in subsequent lactations by 8.8...18.5 % in milk yield, 9.1...21.7 % in milk fat output, and by 9.2...22.0 % in milk protein. Growth retardation during the period of intensive puberty at the age of six to twelve months has the most negative effect on productive characteristics. Therefore, growth retardation of repair heifers during the first year of breeding should be avoided. Heifers with the greatest growth retardation are not advisable to leave for herd repair.