In dairy cattle breeding, the breeding work is carried out mainly to increase the milk productivity of cows, which often leads to a decrease in the reproductive qualities of the breeding stock. Therefore, practicing breeders are faced with the task of studying and improving the qualities of animals associated with the reproduction of the herd. At the same time, in the conditions of a decrease in the number of livestock, the issue of preserving and improving the reproductive properties of animals is also put forward in the first position. For design breeding problems, it is necessary to have information about the genesis of reproduction. The conducted studies covering the period 2011-2020 reveal the dynamics of significant reproductive indicators – the age of the first fruitful insemination, the number of inseminations per fruitful one, as well as the open days in the first lactation of the breeding stock of the Swiss breed. In the process of its improvement, the age of the first fruitful insemination of animals decreased. The multiplicity of insemination and the associated open days in the first lactation do not have a stable nature of changes. To obtain more informative data on the level of organization of the biological system under study, the entropy – information analysis was used in the study. The age of the first fruitful insemination at the initial stages was poorly controlled, with an absolute organization (O) having values from 0.168 bits (H=3.292 bits) it was found however, during the selection process, the controllability of this system increases (O=0.873 bits; H=2.586 bits). The most controlled feature throughout all stages is the multiplicity of insemination (O = 0.401...1.147 bits; H=1.921 ...1.175 bits). The least controlled is the open days (O=0.136...0.604 bits; H=3.449...2.981 bits). The obtained results of the study contribute to the conduct of purposeful breeding of Brown Swiss cattle, taking into account the reproductive ability.

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The brown Swiss breed of cattle, which is currently being bred in the Smolensk region for dairy and meat productivity, is of interest from the point of view of its production feasibility and competitiveness, and the biological properties of livestock. The research was carried out in a breeding reproducer for the breeding of brown Swiss cattle of the Smolensk region, in the conditions of the farm, the age of fruitful insemination, physiological development, linear affiliation and productive qualities were analyzed (n=384). According to the terms of fertilization, the animals were conditionally divided into three groups: - early-maturing 46 heads (12%) live weight of the first insemination 329 kg, medium-maturing 191 heads (49.7%) live weight 388 kg and late-maturing 147 heads (38.3%) live weight 429 kg. The genealogical structure of the analyzed livestock includes descendants of the related groups Meridian 90827 (46.3%), Concentrate 106157 (25.4%), Master 106902 (25.4%) and line Laird  71151 (2.9%). The highest milk yield and fat for the first (4520 kg) and highest lactation (5022 kg, 3.97 %) in late-maturing animals. The group of first-calf cows of medium precocity in terms of milk yield occupies an intermediate position (4334 kg). The difference in live weight between the third and first groups is significant (P<0.05). There were no significant differences in milk fat and protein between the groups of cows. From these studies, it follows that the larger the live weight at the first insemination, the more productive they are.