Всероссийский научно-исследовательский институт физиологии, биохимии и питания животных – филиал Федерального государственного бюджетного научного учреждения «Федеральный научный центр животноводства – ВИЖ имени академика Л.К. Эрнста»
ABSTRACT. The trial was carried out by the method of periods using the Latin square scheme on 4 bulls of Black-and-White breed with an initial live weight of 335 kg at the age of 10 months with an average daily live weight gain of 1450 g. For four periods of experiment, duration 28 days each, the level of the metabolizable protein in the diet was consistently increased by the introduction of the feed additive with reduced protein degradability (soybean meal). The level of metabolizable energy in all periods was the same (89 MJ), and the level of crude protein consistently increased from 1291 to 1395 g. The protein degradability (%) in I, II, III and IV periods was 58.9; 69.4; 68.2 and 67.9, the level of metabolizable protein (MP) was 478, 491, 513, 526 g respectively. The effective degradability of feed protein was calculated from the data of the relative degradability in the rumen determined by in sacco method and the rate of evacuation from the rumen. The metabolizable protein was determined from the sum of the digested non-degradable protein and the microbial protein digested in the intestine. In samples of rumenal fluid taken 3 hours after morning feeding, the pH, the content of VFA and ammonia, the number of bacteria and infusoria, amylolytic and celluloseolytic activity were determined. Protein feed additives did not have a significant effect on enzymatic and microbiological processes in the rumen and on digestion in the intestine of the components of the ration, with the exception of protein, digestibility of which increased and, accordingly, the amount of exchange protein increased. An increase in the level of metabolizable protein in rations from 7.8 to 8.5 grams per 1 MJ of metabolizable energy (ME) was accompanied by an increase in nitrogen deposition from 57.9 to 69.6 g (P<0.05) while maintaining high efficiency of its use. The value of daily live weight gain began to decrease with the ratio MP/ME equal to 8.2. It was concluded that an increase in the level of MP up to 8.2 g per 1 MJ of ME due to the addition of sources of a low degradable protein for has a positive effect on the efficiency of feed protein use in intensive growing Black-and-White bulls.
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