losses of crude protein during ensiling of herbages, in contrast to carbohydrates, do not affect the reduction of its content; their form is changed into greater solubility non-protein compounds and also highly degraded forms, which lower the efficiency of the microbial protein synthesis in the rumen. these processes are accompanied by a change of amino acid composition of herbage protein and decrease in intestinal digestibility of protein from feeds as a result of the formation of indigestible complexes with carbohydrates (adin). reduction of protein degradation in silages is achieved by accelerated acidity through addition of acids or dominance of homofermentative bacteria. the positive effects of fermentation inhibitors or sorbents use, as well as the wilting of raw material on the level and rate of protein degradation were demonstrated by many researchers. a greater contribution of protein nitrogen and reduction of deamination in silages can also be obtained by using bacteria inoculants. increasing the proportion of protein nitrogen is accompanied by the improved efficiency of microbial protein synthesis. Key words: silage, legumes, proteolysis, crude protein, nitrogen fractionsCurrent interest in the excessive nitrogen emission to the environment, in the form of ammonia to the atmosphere and nitrates into groundwater, in animal production primarily concerns ruminants, and results from low utilization of nitrogen (Huhtanen, 2010). The quantity of the nitrogen pool leaving the animal body depends on the efficiency of nitrogen conversion which in milk production is 18-30%, and in meat production 10-20%, which is far below the potential of cattle, which exceeds 40% (Dewhurst et al., 1996; Frank et al., 2002). These losses result from the low efficiency of microbial protein synthesis in the rumen, caused on the one hand by rapid and excessive degradation of plant protein,
When evaluating the effects of yeast culture (Saccharomyces cerevisiae $ ) supplied with or without a vitamin premix and mineral bioplexes on some intermediates and end-products involved in the synthesis of milk constituents in 30 earlylactation Black and White Lowland cows, no significant differences were found in the glucose level, mineral contents and enzyme activities of the blood serum. The effect of yeast culture on the availability of minerals for milk synthesis depended upon the dynamics of degradation of mineral bioplexes in the rumen and the cows mineral status. The insignificant increase found in blood total protein content and the simultaneous small differences in blood urea nitrogen (BUN) and milk urea nitrogen (MUN) values in cows supplied with the yeast culture were probably associated with a high ammonia incorporation into microbial protein in the rumen, which increased protein supply for milk protein synthesis and decreased the nitrogen loss.
An experiment was performed on 37 Holstein-Friesian cows during the first 120 days of lactation. The cows were fed balanced diets composed of haylage and maize silage (together 52% dry mater) and a concentrate containing 19% crude protein (group 1), a concentrate containing 17.5% crude protein and 1 kg of fat-protein supplement Megapro Plus ® (group 2) or a concentrate containing 19% crude protein and 1 kg of fat-protein supplement Megapro Plus ® (group 3). The mean daily milk yield recorded in groups 2 and 3 amounted to 32.6 kg/dand was by 10.3% higher than in the control group (P ≤ 0.01). FCM yield increased by 15.5% and 12.1% in groups 2 and 3, respectively, in comparison with group 1. Diet supplementation with Megapro Plus ® had no significant effect on the levels of fat, lactose, protein, nitrogen fractions and urea, or some physicochemical properties of milk (density, pH, heat stability). A decrease was noted in solids-non-fat (group 2) and somatic cell count (P ≤ 0.05). Megapro Plus ® supplementation of a diet with a reduced (to 3%) "00" rapeseed meal content in concentrate (group 2) resulted in a significant increase in the concentrations of unsaturated fatty acids (especially C18:1 and C18:2) and hypocholesterolaemic acids (DFA) in milk, recorded on the 120th day of lactation. Megapro Plus ® supplementation of a concentrate with a high (10%) "00" rapeseed meal content aimed at increasing the concentrations of both energy and protein (group 3), had no significant effect on improvement in the fatty acid profile, i.e. changes towards increasing unsaturation of milk fat.
To investigate the milk production limiting potential of a diet based on grass silage (40%), hay (15%), dried sugar beet pulp (13%) and grain compound mixture (32%), 28 multiparous cows in early lactation were randomly assigned to two treatment groups: a control group and a group receiving supplementary rumen protected methionine (RPMet) treatment (12 g intestinally available methionine/cow/day, given 1-120 days postpartum; Smartamine; RPAN's technology). The diet was formulated to meet the requirements for protein and net energy. RPMet supplementation had no significant effect on DMI (kg/cow/day), milk dry mass, milk lactose and milk urea contents. Responses for mean daily milk yield, mean milk fat and milk protein yields were significantly higher (P < 0.05) in cows supplied with RPMet than in controls. Mean daily milk yield, milk protein and milk fat yields increased by 2.4 kg, 108 g and 124 g, respectively. The mean daily milk protein and casein contents were increased by 1.8 g and 0.9 g and milk fat content by 1.2 g in 1 kg of milk, respectively. The results suggest that in cows fed grass silage and a grain compound mixture milk production is limited by methionine insufficiency, but milk production performance can be increased significantly by the addition of RPMet to the diet.
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