Influence of average daily gain of heifers on the age of first insemination

The purpose of this study is to establish the influence of average daily gain (ADG) of heifers at different periods of their development on the age of 1st insemination (A1ins) at 12, 13, 14, 15, 16, 17, 18 months and older and milk yield of first-calving cows for 305 days of lactation according to a sample (n=1289) formed from the Seleсs database of one of the breeding plants in the Leningrad region for breeding the Ayrshire breed of dairy cattle. On average for the sample, the correlation coefficient of milk yield with A1ins indicates a negative relationship between these two characteristics (-0.218), a positive correlation of milk yield with live weight of 1st insemination LW1ins (+0.101) with a negative connection with ADG (-0.110). It was revealed that in all age groups of heifers there is a decrease in ADG at the age of 2 months, and the intensity of further development of heifers depends on ADG at the age of 3, 4, 5 months, at a level of over 800 g, contributes to the achievement of A1ins from 12 to 14 months. At the same time ADG at the age of 9—12 months should be at least 800 g. However, even with ADG 800—900 g at the age of 3—5 months, but when these indicators decrease at 9—12 months below 800 g, A1ins increases to 15—16 months. Low ADG at the age of 3—5 months and at the level of 600 - 700 g at the age of 9—12 months increases A1ins to 17 months and older. Thus, for an earlier A1ins and a high level of productivity in the 1st lactation, one should pay attention to the development of heifers at the age of 3—5 months, maintaining the ADG at a high level (more than 800 g) and avoid low weight gain at 9—12 months (less than 800 g).