| To investigate the requirement of dietary metabolism protein (MP) in dairy castles were in heat stress, an experiment was conducted to determine the effects of MP on Holstein cow performance and blood index. Twenty Holstein cows (n=20; 30±20 d in milk and 480±40 kg body weight) with a close range in milk yield (15.5±1.1kg) were randomly divided into 5 treatments in a single factorial design with 4 replicates each treatment. Dietary MP Levels (DM basis) included A group (A; 7.70%), B group (B; 8.23%), C group (C; 8.72%), D group (D; 9.23%) and E group (E; 9.71%). Cows were fed a diet intermediate to the treatments during a preliminary 14-d period. Treatment periods were 35 d with measurements taken throughout the period for temperature-humidity index (THI) and sample collection in begin 3d and final 3d for production variables, respectively. The results were as follows:1) in the treatment periods, the THI was more than 72 (average was 81.34), indicated the cows were in heat stress.2) The feed intake fed C dietary (13.28kg/d) was higher (P<0.05) of cows compared with other groups. And the feed intake was lower (P< 0.05) in B group than in D group or E group; In comparison with treatment B, A dietary decreased the abundance, but no prominently difference was found (P> 0.05) in between D group and E group; 3) Compared with other groups, C dietary significantly increases the milk yield (15.00kg/d) and the amount was the lowest in A group, B, D and E group had no significant effect on milk yield of cows.4) The milk protein percentage were the highest (P< 0.05) in in C group than in other group. However, no significant difference was found (P> 0.05) between A group and B group, the same trendy was discovered between D group and E group.5) The C dietary increased (P<0.05) the milk fat percentage as compared with the rest groups, especially with A group, but no significant difference was found in cows fed with among B, D and E groups (P> 0.05).6) To milk sugar rate, the highest concentration was found in C group, meanwhile the lowest content was discovered in A group, which they significantly different with others (P> 0.05), but no signicant difference was found (P> 0.05) in above indices among B, D and E groups.7) Total protein and urea nitrogen levels in serum of cows were higher (P<0.05) in E group than in other groups; and MP levels had no significantly effect on serum cortisol and endotoxin (P>0.05).8) In this study, simple and polynomial regression tests were used to determine any possible correlation between response (y) and MP levels (x), the correlation between the food intake, or the milk yield, or the milk sugar rate, or the fat percentage, or the milk protein percentage, or cortisol, or endotoxin and MP levels:y=-1.1098x2+20.064x-77.653(R2=0.8842), y=-3.0051x2+54.531x-229.30(R2=0.8996), y=-0.1466x2+2.6405x-6.8400(R2=0.6389),y=-0.1049x2+1.8759x-5.2731(R2=0.8975),y=-0.0724x2+ 1.3018x-2.7167(R2=0.6738),Respectively.These results in this experiments showed that the MP levels significantly affect the food intake and milk yield, but cortisol or endotoxin of Holstein cows; especially early-lactation dairy cows were in heat stress, the 8.72% MP added can efficiently relieve the negative effect. In conclusion, MP levels seemed to play an important role in reducing the effect of heat stress of dairy cows through increasing food intake and milk yield and MP treatment also improve the milk composition to maximize dairy cow performance. |
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