THE GROWTH RETARDATION EFFECT IN EARLY HEIFERS ONTOGENESIS ON DAIRY COWS PRODUCTIVITY

The objective of the study is to determine, whether the growth retardations of replacement cows are admissible, and in which periods of culture they most significantly affect the further productivity of the cows. The subject of the analysis was the number of animals who at the age of 15 months had the live weight no less than 300 kg (which complied with the breed standard or was inferior to the requirements for 10 % maximum). The animals were divided into 5 groups. The first group included the animals with growth retardation before the age of 3 months. The second one – at the age of 3-6 months; the third one – 6-9 months and the fourth one – 9-12 months. The fifth one was the control group, without growth retardation. The growth retardation referred to the live weight reduction at the end of the period in comparison with its beginning or the average daily weight gain less than 500 g. The authors measured the live weight, first lactation productivity and the lifetime productivity of the animals. It has been established that the growth retardation of the heifers before the age of 3 months negatively affected the growth rate in the following three-month period. They can completely compensate the growth retardation only at the age of 18 months. The other group animals compensated the live weight retardation in comparison with the control group by the age of 15 months. The firstlings which had the growth retardation at the age of 0-3 and 3-6 months, has the highest milk productivity. The same trend was observed in milk fat and protein output and the age of the first calving. However, in the growth retardation group the livability of firstlings, the number of lactations and the productive live was worse. The lifelong milk yield in the growth retardation group was 15-37 % lower than in the control group. Growth retardation at the age of 6-9 months negatively affected the higher lactation productivity. The highest daily milk yield in this group of cows was lower in the control group by 14 % (p < 0.05). Therefore, growth retardation had no negative effect on the milk yield of the firstlings, but resulted in lower survival of the animals, shortened the productive life and lifetime yield. The later the growths retardation occurs, the sooner the heifers can compensate it and the lower is its effect on the lifetime productivity of the cows. In view of the reduction of lifetime productivity, it is purposeful to draft out the animals with the growth retardation