Research on the study of differentiated feeding of cows was carried out in the conditions of OOO “Krasnoe Sormovo” of Krasnoarmeyskiy district of Chuvash Republic. For the experiment, one control and experimental groups of cows were formed, each containing 150 heads. The control animals remained on the farm ration. The cows of the experimental group were fed with differentiated diets according to their productivity and physiological state. The first experimental group consisted of cows with a daily milk yield of 25 kg and more, the second - from 18 to 25 kg, the third - below 18 kg. The diets of dry cows were also revised: we proposed dividing the drying-off period into two stages: far-off dry period (from 8 to 3 weeks before calving) and close up dry period (from 3 weeks before calving). The principal feature of feeding in the experimental groups was that the rations were balanced directly in terms of crude protein and energy. The share of basic or bulk feed was 50% in the structure of the ration. The amount of concentrated feed was calculated taking into account the eatability of the main feed. Maintaining of balanced feeding was achieved through constant monitoring of the diet for quality parametres of milk, body condition and feces consistency. The research focused on a comparative assessment of milk productivity of cows in the control and experimental groups. Analysis of productive parametres of the cows showed a significant increase of milk yield of experimental animals for 305 days by 472 kg, an increase of daily milk yield by 1.8 kg per head. The results obtained indicate that the application of differentiated feeding of cows is advisable, as it contributes to an increase of their milk productivity. Therefore, we recommend using this strategy in feeding of dairy cows.

Sires play an important role in improvement of productive qualities of bred livestock. Most researchers and breeders estimate their impact to be at least 90%. In order to evaluate the results of using different Holstein breeding bulls, we compared the productivity of their offspring with the average values for all bulls. The following methods of variation statistics were used: observation, data grouping, and correlation analysis. It was found that the best are the descendants of the bull Estuary 2186 of the Montwick Chieftain line. Besides, Liman 2186 bull’s daughters excelled in high milk fat content - 4.46%. Daughters of Punch 2748 bull of Pabst Governor line were the best in protein content of milk (3.27%). Daughters of Liman 2186 bull had the highest fat and protein yield during 305 days of lactation. It was established that the direction and value of correlation between the main features of milk yield of cows of different lineages have a rather high degree of variation. Presence of positive genetic correlation between milk yield and protein content in milk in some lines of animals enables breeding cows by two traits simultaneously (milk yield and protein content in milk).

Relevance. In recent years, there has been a decrease in the total number of cattle of both meat and dairy production. In this regard, the study of the features of breeding of beef cattle is relevant. In the studies, the growth and development indicators of the young cattle of Hereford breed were studied, depending on their origin.Methods. The research was carried out in the conditions of a breeding reproducer of LLC "Chebomilk", Cheboksary district of the Chuvash Republic. The dynamics of growth and development were studied by monthly weighing of animals. In newborn calves at the age of 205 days, 6, 8, 9 and 12 months, and in heifers additionally at 15 and 18 months, the height in the sacrum was measured. Based on the data from the weighing results, the absolute and average daily increase was calculated.Results. It was found that the growth rate of heifers and calves on fattening is influenced by the genotype of the father. When comparing the average live weight of young animals at the age of 18 months, the best results were in bulls received from the bull Perets — 375.8 ± 17.5 kg, this is 3.8 kg more than the same indicator for bulls received from the bull Timeline and 7.8 kg more than the bull Emuleishn, and by the live weight of heifers at the age of 18 months the Timeline is leading — 352.6 ± 25.2 kg. Bulls and heifers — descendants of the bull Perets of the Mayer-Verne 88480 line are distinguished by the best growth rate. The average daily increase at 18 months of age in bulls was 931 ± 57.2 g, in heifers — 577 ± 54.1 g, which is higher than their peers by 1.2–12.2%. To improve the productive and breeding qualities of the Hereford breed, it is recommended to carry out targeted selection and selection of parental pairs.

Relevance. Prevention of ketosis in freshly calved cows is one of the urgent problems in the industry. The article presents data on the results of the use of propyleneglycol in the diets of cows during the transit period.Methods. For the study, 2 groups of cows were formed, control and experimental, with 30 heads each. The cows of the control group were fed the rations for dry and dairy cows of the highly productive group adopted on the farm. Cows of the experimental group in the dry period two weeks before calving in addition to the diet of the control group got 150 g of propyleneglycol per head per day and for two weeks after calving — 250 g.Results. It was found that the addition of propyleneglycol to the diets of cows for two weeks before calving and four — after — turned out to be expedient in the prevention of ketosis during the milking period. Analysis of milk for the presence of ketone bodies using test strips on the 10th day of lactation revealed positive results in 10% of cows in the control group, while 17% of cows were at risk. Analogical studies conducted on the 30th and 60th days of lactation showed the presence of ketone bodies in 7 and 3% of cows of the control group respectively, with questionable results in 6 and 4%. At the same time, in cowsof the experimental group, receiving propyleneglycol, this analysis did not show signs of ketosis.

The aim of the research was to evaluate the compatibility of lines and improve on this basis the traditional selection methods for creating breeding herds in dairy cattle breeding. The results of the analysis showed that the best milk yield among the other lines were the first-born heifers (n=39) of the Holstein line Vis Back Idial (6441 kg of milk). The analysis of the results of the intra-linear selection showed that the best milk yield was also distinguished by the first-born heifers of the Vis Back Idial line – 6721 kg of milk. Analyzing the cross-line of the Vis Back Idial with other lines of the Holstein breed (MCH, RS, and PG), it should be noted that they are superior to their first-calf peers by 253-530 kg of milk. The first-calf cows, derived from the cross of the Montwick Miftaine line and the Reflection Sovering and Pabst Governer lines, also have some superiority over their peers. Thus, when improving breeding herds of dairy cattle, it is necessary to use both intra-linear selection and cross-lines, taking into account their compatibility.