The analysis of growth parameters of heifers in connection with the age of onset of reproductive use was carried out. The research was carried out with Black Spotted Ukrainian Milk heifers. According to the age of fertile insemination animals were divided into three groups. The first group consisted of the most fast-growing animals with the age of fertile insemination of 10,9 ... 12,9 months. Animals with an age of fertilization close to the average for a herd (13.1 ... 16.2 months) were included in the second group. The third group consisted of slow-growing heifers (fruitful insemination at the age of 17.0 ... 22.0 months). Live weight and daily average gain in the groups was studied. It was revealed the heifers with an average age of fertile insemination had the smallest live weight (378 kg) at the age of 12 months. Fast and slow-growing animals exceeded them in the process of growing up to 12 months by 2.5-13.7%. After 12 months of age, heifers from the first group reduced the growth rate the most. Animals from the third group had the largest daily average weight gain after 12 months of age. Early-mature animals behind the growth rate of up to 6 months exceeded heifers, which had average age of fertilization. The slow-mature animals exceeded them behind the growth rate up to 15 months of age. Animals of different types of fast-growing appear predisposition to rapid growth in various conditions. Slow-growing animals had greater weight gains with normalized feeding and individual maintenance in the milk period. That is probably due to the anabolism of body tissues. Earlymature heifers grew faster when they were keeping in groups and with not limited to feed.
heifers, age of fertile insemination, early-mature animals, average daily increments, live weight, dairy cattle