Reproductive ability of cattle is an important economic trait determining increase in the amount of animals and improving their breeding value. The majority of the reproductive ability traits are influenced significantly by genetic factors, which indicate the possibility of breeding improvement. Study of the non-genetic factors effects on fertility traits indicates the need to consider their impact to correct it in assessing the cattle breeding value.

The research aimed at studying the peculiarities of the reproductive ability of cows Ukrainian black-and-white, red-and-white dairy breeds as well as Holstein breed and the effect of cows fertility indicators on their subsequent milk productivity in the raised domestic breeds.

Insemination index, i.e. the amount of inseminations per one successful one, is an important indicator of fertility. A high insemination index indicates low fertility and high infertility rate of cows. Under a high insemination index the cows fertility rate is reduced, their new calving  and service periods increase.

Insemination index in cows varies depending on their age and milk production level. It was found out that insemination index decreases from the first to the third calving in Ukrainian black-and-white dairy cows (P>0.99), then it increases slightly. The optimal value of insemination index should be considered 1.5-1.8. In the studied farms insemination index in the cattle breeds is slightly higher than the normal. Variability of insemination index is within 58,3-74,1. First insemination fertilization, bull sperm fertilizing ability and other biological, economic and organizational factors influence its variability significantly.

A trend of increasing insemination index in cows with higher milk yields in the animals of these dairy breeds at the studied farms was observed; the lowest insemination index was observed in cows with milk yield of 3000 kg – 1.9 inseminations. In cows of Holstein, Ukrainian black-and-white (P>0.99), red-and- white dairy breeds with an increase in yield from 3000 kg to 6000 kg the insemination index increases and makes 3.8; 2.6 and 2.4 respectively. However, in cows with over 6000 kg milk production there was revealed a tendency to fewer inseminations per fertilization (2.5, 2.3 and 2.0). The conducted research on the relationship between fertilization indicators and the dairy breeds cows productivity prove that they should be considered as independent ones in the selection.

An evident indicator of reproductive ability is a cow fertility index offered by Hungarian scientist Dokhi (1961). In cows of Ukrainian black-and-white and red-and -white dairy breeds in the studied farms the fertility index is within 42-44 on average, but in Holstein this index  is low – 40. Fertility index variability is in the range of – 9,9-10 4% and belongs to the indices of the average degree of variability.

Service period is a reliable criterion of cows reproductive function. Analysis of the service period duration reveals a problem with the reproductive ability of dairy cattle of these breeds in the herd. Every year the service period in cows exceeds the optimal value by 22-152 days. One of the factors affecting the reproductive ability of dairy cattle is age. In order to identify the influence of age on reproductive ability of cows we have studied it in the first, second and third cows lactations. Thus,  in a herd of Holstein dairy cattle breed indices of service and new calving  periods in the second lactation cows period reduced to
26 days, and in the third lactation cows the length of these periods is extended to 46 days. Similar results were obtained in cows of Ukrainian black-and-white and red-and-white dairy breeds.

It should be noted that the Holstein breed cows of all ages have worse reproductive ability indicators compared with those of Ukrainian black-and-white and red-and-white dairy breeds animals. Low reproductive performance in Holstein breed can be explained by complications related to the adaptation of animals to the local climatic conditions. However, similar problems in animals of Ukrainian black-and-white dairy cattle in "Terezine" Ltd., and "Agrosvit" JSC indicate a negative influence of loose box farming technology without exercising during the lactation.

Thus, the key to raising cows fertilization is constant assessment of dairy cattle performance fertility, timely identifying and addressing the main causes of low female fertility can minimize the amount of infertility and further increase in cows milk production.

Key words: dairy cattle, service period, dry period, new calving period, insemination index, age of first insemination, fertility index, Ukrainian red-and -white and black-and-white dairy breeds, Holstein breed.