Abstract
In Sverdlovsk region Holstenized black-and-white cattle of the Ural type are used for milk production. Animals of this type feature high productivity indices, however, the breeding stock encountered decrease in the productive longevity. The first-calves showed an increase in milk yield per lactation, along with an increase in their live weight up to 624 kg. The difference in milk yield was significant in favor of cows with a live weight of 600-624 kg. in comparison with the groups of cows with a live weight below 575 kg at P≤0.05-P≤0.01. Among the cows of the third lactation the highest milk yield was obtained from the cows with the highest live weight - 625 kg and more - 10122 ± 118.59 kg. All animals feature an excess over the optimal duration of service period by 19-83 days, i.e. by 23.8-103.8%. The average duration of the lactation period for first-calves is 140 ± 4.69 days, for the full-aged cows - 149 ± 3.98 days. The coefficient of reproductive capacity is 0.85 on average. The positive relationship between milk yield per lactation period and the duration of the service period is confirmed. No general pattern for correlation of live weight and duration of service period.
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