The effect of administration of soya-protein with Lys, Met, and His in two forms on casein yield and composition and AA profile in milk.

摘要

This study was conducted to determine the effect of soya protein enriched with amino acids such as lysine (Lys), methionine (Met) and histidine (His) added either as a powder or in a form of rumen-protected tablets into rumen of dairy cows on the percentage and yield of casein and changes in the proportion of casein fractions resulting in variations in amino acid profile of milk, casein and non-casein protein. The experiment was carried out in 3 lactating Holstein-Friesian cows with an average weight of 523 kg and fitted with ruminal and duodenal cannulas. The experiment was divided into 4 periods of 14 days (10 days preliminary period and 4 days experimental period). In the first period, one cow received the tablets (T group) and the other two received the non-tableted mixture (C group, control) of the same composition. In the subsequent period, the rate of animals was antipodal. Cows were fed on a diet based on maize silage, lucerne hay and supplemental mixture. Tablets or mixture consisted of purified soya protein HP 300, Lys, Met and His. The casein content and yield were higher in group T compared to group C (2.68% and 476.55 g vs. 2.46% and 408.43 g; P<0.05). The contents of beta - and kappa -casein were unaffected by the treatment, whereas the content of alpha -casein was lower in group T (54.10 vs. 55.98%; P<0.05). The yield of every casein fraction was significantly higher (P<0.05) in group T than in group C. The increase in the casein yield resulted to significantly higher (P<0.05) yields of individual amino acids in milk and casein in group T compared to control group. The concentrations of Thr in milk and Thr, Pro and Met in casein were significantly different (P<0.05) in group T compared to group C. Duodenal flows of individual amino acids through the duodenum were determined.