The biological significance of sexual dimorphism is that leaders of herd receive preference for mating with a female in natural populations.

This leaders-bulls who have surpassed their opponents in tournament battles. Due to the natural selection of bulls with marked sexual dimorphism led to the spread and maintenance in populations of cattle are important for species such features as high reproduction performance, endurance, resistance to disease, survival of young animals and others.

Pursuing of economic goals, people in their activities directs the development of exterior features in future breeder on the presence of a dense delicate constitution, good chest development, proportional development of the posterior third of the body, a lightweight skeleton, quiet temper, etc. Therefore, the selectors do not pay attention to signs of sexual dimorphism of sires breeders.

However, it is not difficult to see that in the selection process of the bulls, throughout generations, there is a convergence of the type of males and females body structure, the result of which there is a phenomenon of "somatic feminization" sires, leveling features of sexual selection. Among today's specialized high-performance species versus species of combined type performance there received widespread such undesirable features as a breach of fertility, irregular cyclical phases of sexual inclination, ovarian cysts, nymphomania, etc. Most of these disorders have hereditary basis.

Development of signs of sex is determined by genotype and environmental factors as any other characteristics of the organism.

The process of differentiation of the sex is difficult and predefined by the large number of alleles of different loci of cumulative action, the synchronous work of ductless glands, the endocrine system, by the presence of those or other hormones.

Thus, clearly expressed sexual dimorphism in animals is an important criterion in the estimation of constitution and influences on appearance of the animal and her habitus.

Unfortunately the generally accepted index of estimation of degree of development of sexual dimorphism is not worked out yet, and the selection of breeding bulls on this characteristic is practically not come true.

Considering the above information, we have studied the energy of growth descendants of bulls with well-defined characteristics of dimorphism and researched the fertilizing capacity of sperm in bulls with varying degrees of expression characteristic of sexual dimorphism. There were used materials of tribal accounting of breeding plants "Shamrayevskyy" and "Polyvanivka" which had 1300–1400 kg live weight at the age of 3–4 years. The manifestation of sexual was dimorphism evaluated in the herd visually.

The findings proved that. 1. The intensity of growth of the posterity of bredeer with high dimorphism significantly higher (2–30 %) of the indices in the offspring of bulls slightly pronounced dimorphism.

2. The fertilizing capacity of sperm bulls with distinct manifestation of sexual dimorphism significantly higher (6.5–14.2 %) compared to their peers who have poorly pronounced dimorphism.

3. Maternal influence is 4.46–18.6 % by the magnitude of the increase in body weight of offspring with varying degrees of dimorphism.

An assessment refine sires and cows at linear exterior evaluation system of animals.

Key words: sexual dimorphism, development signs, increased fertility, the degree of manifestation, bull-sires, cows.