| This paper from the actual production by yak calves cultivation, according to the characteristics of yak milk nutrition itself and the existing resources in qinghai plateau, developed and designed 25%, 27%, 29% of three kinds of protein level breeding fodder, which yak calves weight change, blood biochemical, gastrointestinal tract growing and organizational change were determined and analysed after fed with breeding fodder on grazing conditions, to study the influence on yak calves growing of 2-month-old yak calves fed by breast milk and different-protein-levels breeding fodder. The results provide reference data for the research on physiological and biochemical indicators of breast-feeding yak calves, and provide a scientific basis for the determination of protein levels of the yak breeding fodder, at the same time, for the generation of yak calves cultivation in plateau the feasibility of application laid a theoretical foundation.Experimentâ… . Study on weight change of two-month-old yak calves fed by Breast milk and different protein levels. 48 healthy two-month-old yak calves of close to birthday and similar body weight were chosen and randomly divided into four groups named Groupâ… , Groupâ…¡, Groupâ…¢and Control group, and 12 calves of each group. The calves of Control group were fed by breast milk followed the grazing yak cows, according to the traditional way to cultivate. The calves of Groupâ… , Groupâ…¡and Groupâ…¢were separated from the cows, stopped breast-feeding and fed with breeding fodders that called BF1(25% protein), BF2(27% protein)and BF3(29% protein) for the whole trial period of four months. The results showed after 60 days the differences of calves'weight in each group began to emerge that the end weight between Control group and Groupâ… did not show significant differences, and significantly higher than Groupâ…¡and Groupâ…¢(P <0.05), the end weight of Groupâ… and Groupâ…¡were not obviously different, the two groups were significantly higher than Groupâ…¢(P <0.05), and with the age increased, the difference trend was gradually growing, but not obvious. In the end of the experiment, Groupâ… gained the highest body-weight-gained ratio of 154.88%, that of Groupâ…¢was 95.23% while Groupâ…¡and Control group gained 140.08% and 135.37% respectively that were in the middle. Statistics of periods of 30 days showed that the net weight gained of yak calves in each group was lowest in the 0-30d period, and soared to peak in the 30-60d period and then slow down. In the 0-30d period, the Control group gained 8.31kg net weight which was the most of all groups, and much higher than 4.87kg, 3.83kg, 2.5kg gained by Groupâ… , Groupâ…¡and Groupâ…¢respectively. In the 30-60d period, the net weight gained of the three groups fed by breeding fodder jumped to 11.81kg, 10.71kg and 8.33kg while the Control group weight gained slightly increased to 10.43kg. In the 60-90d and 90-120d periods the net weight gained of each group have declined. It was clearly seen that the three groups fed by breeding fodders in the 0-30d period gained less net weight than the Control group, but the net weight gained had a compensatory risen in the 30-60d period.Experimentâ…¡. The selection and feeding of test animal were the same as experimentâ… , blood Parameters were determined and analysed at 30d, 60d, 90d, 120d respectively. The results showed that during the experiment, the change of each index among four groups has a similar trend with the experimental end, serum total protein of Control group calves were significantly lower than the three groups that fed breeding fodders at the end of experiment(P <0.05), the difference with Groupâ…¡and Groupâ…¢were significant (P <0.01), and that the three groups fed by breeding fodders were not significant (P >0.05). Serum albumin data of the calves among four groups were not significant difference (P >0.05), but the data of globulin, A/G ratio of the control group showed significantly lower than that of the other three groups (P <0.01). Data of urea nitrogen and cholesterol in four groups were not significant difference (P >0.05), in which the average urea nitrogen of Groupâ… was slightly higher than other groups, while serum cholesterol levels of Control group was the highest (P >0.05).Experimentâ…¢. Three yak calves of similar body weight in each group were selected to slaughter, determined and analysed gastrointestinal tract growing and organizational change index when the experiment finished. The results showed that the ratio value of rumen weight to the whole stomachus compositus weight of Control group slightly lower than that of Groupâ…¡and Groupâ…¢, slightly higher than Groupâ… , and the values of three groups fed breeding fodder slightly raised with the nutrient levels lowing, but the differences among the four groups were not significant (P >0.05). The ratio value of rumen volume and stomach volume showed that the differences among four groups was not significant (P >0.05), Control group rumen average pH value were higher than the other three groups, and the rumen pH value of the three groups fed breeding fodder showed that Groupâ… > Groupâ…¡>Groupâ…¢of the gradient change. Rumen ammonia concentration of four groups was no significant difference (P >0.05), but obviously showed Groupâ… > Groupâ…¡> Groupâ…¢> Control group gradient. The pile length of duodenum, middle and bottom of jejunums of three groups calves decreased with rising protein level of breeding fodder. The muscle wall thickness of duodenum and jejunum with the upper decreased with lowing protein level of breeding fodder, in which the duodenal muscle wall thickness of Groupâ… was significantly higher than Groupâ…¢and the control group (P <0.05), Groupâ…¡and other groups no significant difference (P >0.05). The entire thickness of duodenum and upper jejunum decreased with lowing protein level of breeding fodder, in which the whole thickness of the upper jejunumof Groupâ… were significantly higher than that of other groups (P <0.05), and middle and bottom of jejunums showed an opposite trend (P >0.05). This study conclusion as followed that yak calves at the age of two to three months old were fed by using breeding fodder in order to early weaning not to affecting their growth performance. The economic benefits of yak calves fed breeding fodder was better than fed by breast milk followed the grazing yak cows, and feeding breeding fodder of high protein levels (29% protein) got the best growth performance, feeding breeding fodder of middle protein levels (27% protein) got the highest rate return on investment. Breeding fodder of high protein levels increased bovine serum urea nitrogen, serum total protein, globulin, urea nitrogen content to calf yak, and decreased rumen pH value, ammonia nitrogen concentration. Fed breeding fodder can promote the calf rumen papillae length and width increase, with increasing the protein levels of breeding fodder, the length of rumen papillae of yak calves decreased, nipple width increased, villi shortened, the upper half of the small intestine and intestinal muscle wall thickness and total thickness increased. Comprehensive measure of produce cost-effective and calf growing indicators, which can initially determine breeding fodder the appropriate level of protein is 27% for early weaned two-months-old yak calf.
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