It is known that the rationing of protein supply of cows by the amount of raw or digestible protein does not take into account the synthesis of the microbial protein in the rumen and the contribution of unsplit protein in the rumen to the provision of the organism with amino acids that are necessary for the synthesis of animal protein. Low productive cows provide their needs for amino acids due to microbial protein, and highly productive cows – due to microbial protein and protein forage, that was not a subject of degradation in the rumen, and disintegrates in the small intestine. It occurs due to the "exchange protein" that consists of amino acids that are absorbed in the small intestine from the fodder and microbial protein and are available for metabolism in the tissues of the body. That is why, it is necessary to normalize rations for highly productive cows for raw protein and its easy soluble and insoluble infractions.

Important problems for today are protein supply of highly productive cows and provision of rations with insoluble in the rumen forms of the protein. Insoluble protein fraction must contain all essential amino acids that are available for digestion in the small intestine. Imbalance of insoluble protein fractions by amino acid composition results in significant exchange of amino acids and nitrogen excretion from the body, which also leads to energy losses. Rations of highly productive cows should be balanced for crude protein fractions in the first 100 days of lactation, by choosing forage rich in insoluble protein fraction (cereal and legume hay, bran, extruded and granulated concentrated forage) or concentrated forage with high protein solubility fed three times per day, contributing to prolonged break down of protein and efficient digestion and fiber.

The objective of our research was to set the effect of soya bypass on rumen metabolism of highly productive cows in the first 100 days of lactation as a source of insoluble fraction of protein on the background of rations with gradually changing of soybean into bypass soy.

Investigation on studying the effectiveness of bypass soy using in feeding highly productive cows was conducted in the LTD "Vitchyzna" Konotop Region Sumy District. By the principle of analogues there were chosen four groups of cows of Ukrainian Black-and -White breed after the first lactation, they were in the first half of dry period. In the preparing period - the second phase of dry period (30 days) – tested cows were fed the same ration that consisted 2.0 kg of soybean. In the investigating period and during the first 100 days of lactation cows from the control group were fed a preparing ration consisted of soybean. Feeding rations of tested groups differed from the 1st control group, for the 2nd tested group 1kg of soybean was substituted into 1 kg of bypass soy, the 3rd – 1.7 kg of soybean – into 1.7 kg of bypass soy, the 4 th – 2.0 kg of soybean – into 2.0 kg of bypass soy.

The intensity of microbiological processes in the rumen and its direction significantly affect digestion, assimilation and efficiency of individual nutrients of forage and rations in general. It was therefore examined indicators of rumen fluid in the experimental cows taken by the probe two hours after feeding animals.

It was set that the pH of the rumen liquid in the experimental cows shifted to the alkaline side in compare to control – increased. In the cows from the 1st control group it was 7.15, analogues from the research – 7.18–7.36 (P<0.05–0,001). In the rumen fluid of cows from the research groups total nitrogen content reduced compared with control counterparts to 0.9–5.7 mmol/L or 0.8–5.7 % (P<0.05), indicating its better absorption in the blood.

Regarding protein nitrogen, it is similar to the total nitrogen in the rumen fluid of research cows (3rd and 4th groups), it was significantly (P<0.01) decreased. At the same time, cows from the experimental group differed from animals of the control groups by significantly lower content of ammonia nitrogen in rumen fluid, which can be considered as a positive phenomenon.

One of data of carbohydrate and fat metabolism in the rumen of cows are fatty acids. In the rumen fluid of cows from the research groups alkaline fat coefficient was clearly large compared with control at 0.12–0.42 mmol/100 ml, but statistically, the difference was unlikely. Regarding ciliates, depending on the level of crude protein their amount in rumen fluid of cows from the research groups exceeded the control at 7–83 thousand/ml (P<0.05–0.001).

Consequently, the use of bypass soy in feeding highly productive cows during the first 100 days of lactation with crude protein on the level of 16.0–16.5 % from dry matter, its insoluble fraction on the level of 27.3 % crude protein in the 1st control group – 31.1 % in the 2nd experimental group, 35.2 % – in the 3rd experimental group and 40.0 % – in 4 experimental group positively affects their rumen metabolism. The most effective was feeding 2 kg of soybean bypass per head per day, providing a higher level of protein, including protein insoluble fraction.

Key words: ration, bypass soy, highly productive cows, crude protein, insoluble protein fraction, rumen metabolism, pH of rumen liquid, general, protein, residual ammonia and nitrogen.