| This study was used beef calves of southern China as experiments animal to investigate the effect of optimum weaning age and nutritional level of milk replacer on growth performance, rumen fermentation and serum biochemical indices for beef calves. It will provide technical guide for formulating of milk replacer recipes specialized and will establish the energy and protein parameter of milk replacer for southern China. The present study included 4 trails which described as follows.Experiment 1 aimed to study the effects of weaning age on growth performance of Red Angus hybrid calves fed with milk replacer, Sixty Angus × Simmental calves were allotted to five treatments according to body weight and age, which were 28 A, 42 B, 56 C, 70 D and control. Calves were weaned at 28, 42,56 and 70 days of age and fed with the same type of milk replacer till 90 days of age in 28 A,42B, 56 C and 70 D treatments, respectively. By contrary, Calves grew up with cows till 150 days of age in the control. Pellet starter and hay were offered ad libitum from 29 to 150 days of age. Body weight and growth parameters were measured every two weeks, in addition, the incidence of diarrhea was documented daily. The results showed that significant differences were observed in the ADG and body measurements prior to 70 days of age(P<0.05).The ADG of calves weaned at 28 days of age was lower than that of the control. However early-weaned calves presented advantage in BW gain, wither height, body length, heart girth and abdominal girth from 71 to 150 days of age. Over the entire experiment, there were no significant differences in the BW gain, body measurements and diarrhea incidence(P>0.05). Weaning age decreased BW gain and body measurements in the first 70 days of age, whereas an obvious growth advantage was detected after 70 days of age in early-weaned calves. There were no positive effects on growth performance of Chongqing Angus × Simmental calves weaned at 42 days of age with milk replacer in this trail.Experiment 2 was designed to examine the effects of weaning age on nutrient digestibility and serum sampling of calves fed with milk replacer, The experiment design was the same as experiment 1. Body weight and serum sampling were measured and documented every two weeks, two stages of digestive and metabolic experiments were conducted before a week weaning milk replacer and finishing phase.(1)The results demonstrated that there were no significant differences(P>0.05) in body weight during the whole experimental period;(2)There were no significant difference for nutrient digestibility before weaning(80~90 D)(P>0.05), OM digestibility of calves in 28 A and 42 B treatments were significantly higher than 56 C and 70 Dtreatments in post weaning performance(P<0.05);(3)there were no significant differences in serum metabolite concentrations and immune globulin(P>0.05) compared with the control in the finishing phase, in addition, there were no significant differences in HPT, IL-2, IGF-1 concentrations either(P>0.05). The optimum weaning age of Angus ×Simmental calves is 42 day of age in this trail.Experiment 3 was performed to investigate the effects of energy and protein of milk replacer on growth performance and rumen fermentation of beef calves, It will provide technical guide for formulating of milk replacer recipes specialized for southern China. Forty neonatal German yellow×Xianan calves were selected and assigned randomly to receive 1 of 4 treatments(n=10 per treatment), a milk replacer contained 16 MJ/k DE and 25% CP(HEHP), 16 MJ/kg DE and 22% CP(HELP), 14 MJ/kg DE and 25 % CP(HPLE) and 14 MJ/kg DE and 22% CP(HELP). Calves were weaned off milk at 21 days of age and milk replacer was fed to calves till 90 days of age. The results demonstrated that there were no significant differences(P>0.05) in weight gain over the entire experiment, although the value of HEHP tended to be higher and LELP tended to be lower. Heart girth of calves in HEHP were significantly higher(P<0.05) than that of LELP treatments at 77 d and 90 d; there were no significant differences in ruminal p H, the concentration of acetatic acid, propionic acid, butyric acid, valeric acid and the ratio of acetate to propionate(P>0.05), in addition, the concentration of NH3-N in HPLE treatments was significantly higher than that of LELP and HELP group(P<0.05), the concentration of isobutyric acid in HELP and HPLE treatments were significantly higher than LELP(P<0.05),the concentration of isovaleric acid of LELP treatments were significantly lower than that of other groups(P<0.05). To sum up, the high-energy(DE:16 MJ/kg) milk replacer seems to be more benefical for the growth performance and rumen fermentation in calves. And high-protein(CP:25 %) ration can provide enough protein to calves. Low-energy and Low-protein level(CP 22 %,DE 14 MJ/kg) of milk replacer can not meet the demand of calves.Experiment 4 Effect of energy and protein of milk replacer on nutrient apparent digestibility and serum biochemical parameters of beef calves,It will establish the energy and protein parameter of milk replacer, providing technical guide for formulating of milk replacer recipes specialized for southern China. The experiment design was the same as experiment 3. Digestive experiments were conducted at 77~85 age phase meanwhile blood was sampled to determine biochemical parameters. The results demonstrated that the apparent digestibility of both crude fat and Ca increased in high protein treatments(P<0.05). Whereas, in the low protein treatments, the apparent digestibility of crude protein improved as the energy level increased(P<0.05). The apparent digestibility of nutrients in low protein and low energy treatment was lower than that of other treatments(P<0.05). In addition, the concentration of serum BUN in high protein treatment was significantly greater than that of low protein treatment when they were in low energy level(P<0.05). On the contrary, the concentration of AST was significantly greater as protein increased when they were in high energy level(P<0.05). No significant differences was observed in the concentration of other serum parameters(P>0.05). To sum up, the high-energy(DE:16 MJ/kg) milk replacer seems to be more beneficial for digestion of the crude protein in calves. And high-protein(CP:25 %) ration contributed to the digestion of crude fat and Ca. Low-energy and Low-protein level(CP 22 %,DE 14 MJ/kg) of milk replacer were not proper for nutrient utilization of calves.In conclusion, The optimum weaning age of calves is 42 day of age in this trail, 25 % protein level might be beneficial to the calves. |
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