The selection of animals at the lowest number of indicators is more effective compared to selection on many grounds. The main focus during the selection of Holstein cattle was to increase milk productivity, which meant the neglect of other important features, such as fertility (fecundity) of animals.
The purpose of the work was to determine the level of milk productivity of cows of Ukrainian Black-and-White dairy breed in conditions of a particular farm, in which there would be a successful combination of reproductive capacity support for adjusting the selection of animals.
The research was carried out in the breeding plant of the Ukrainian Black-and-White dairy breed of farm "Khliborob" of Kozyatinsky district of Vinnytsia region. The material of the research was the information of 212 first-calf cows of Ukrainian Black-and-White dairy breed of this farm.
Indicators of dairy productivity were studied in 305 days of lactation according to zootechnical records.
Reproductive ability of cows evaluated index insemination, age 1 st calving (months), duration (days) of service period, the period of pregnancy, the period between calving, the dry period, a rate of reproductive capacity (CRF), the calves are emitted per 100 cows (%) and the fertility index.
The first-breed differentiation was carried out at a deviation of 0.7 σ from the mean of index (M) of the fertility index. Such a division makes it possible to divide the herd into 3 groups in a ratio of 1:2:1.
The highest level of dairy productivity have characterized by animals of the I group with low fertility (the fertility index was on average 40.8), which significantly surpassed their peers of the III group with good fertility for the livelihood for 305 days of lactation for 434 kg, milk protein production – by 15.2 kg, total milk fat and protein production – by 26.0 kg (P ≤ 0.05).
The increase in the duration of lactation and deterioration of fertility has associated with an increase in the duration of the service period, which is quite natural, since animals need more time to invade the genital organs and normalize their functioning and restore normal sexual cycle. The difference in the duration of the lactation period when comparing animals with different fertility in all cases was high-reliable at P ≤ 0.001 (td = 3.38–6.00).
The effect of cow fertility on the duration of their lactation was ηx = 0.160 (at P ≤ 0.001).
The main indicator that characterizes the economic efficiency of the industry is the profit received from the cow due to the receipt of the calfs and milk. Taking into account the duration of the service period, which exceeded the optimum terms, in the first days of the experimental groups, indicators of non-compliance of products in the form of calves per 100 cows were determined, which made 18.5%, 14.1% and 11.4% respectively.
The force of influence on the fertility of cows at the age of their first calving was ηx = 0.507 (at P ≤ 0.001).
According to the received data, the first-calf cows with a tiredness of 6274 kg of milk showed
the highest calving output in the herd is for 100 cows (89.6%) and reproductive capacity (0.91). The lowest calf output (82.5%) and reproductive capacity (0.84) was found in cows with a milk yield of 6708 kg for 305 days of lactation.
As the milk productivity increases, the duration of the service period extends from 123.1 to 158.3 days (r = 0.16 ± 0.07, at P ≤ 0.05), and the index of insemination – from 2.35 to 3,02 (r = 0.17 ± 0.08, at P ≤ 0.05). The relationship was straightforward and reliable.
It is necessary to focus on improving cow fertility, which is the basis of effective milk production. For the successful management of dairy cattle breeding in the conditions of the "Hliborob" farm, we recommend to select the herds of heifers to be retrieved from animals with satisfactory fertility, since this will be economically beneficial for the farm and physiologically optimal for animals.
A negative correlation was detected between milk productivity and reproductive capacity - with an increase in the fertility index per unit of hopes for cows, it would increase by 148.5 kg of milk.
Under existing conditions of feeding and keeping on the farm it is expedient to select for further breeding of animals with a productivity level of 6.5 thousand kg of milk for 305 days of lactation. For a more complete realization of the genetic potential of milk production of cows of Ukrainian Black-and-White milk, it is necessary to improve the conditions of their feeding, maintenance.
Effect of some factors on relationships between milk urea levels and cow fertility