| Efficient growth of young calves is very important in dairy industry. Neonatal calf is characteristic with high metabolic rate and rapid grow rate, however, due to limited energy reserves in their body at birth, their growth performance can be affected by numerous conditions including early feeding. The key to successful breeding is to guarantee the energy requirement, especially at the early postnatal developmental stage when milk replacer (MR) is supplied, and therefore, to promote rapid growth of the calves.Experiment 1. Twelve newborn Holstein calves were used and assigned randomly to receive 1 of 3 experimental treatments (labeled as Low, Middle and High) consisted of 18.51 MJ/kg,19.66 MJ/kg and 20.80 MJ/kg energy, respectively (n=4 per treatment). A pellet starter was offered ad libitum and refusal were weighed daily. Changes in body weight,growth parameters and concentration of blood metabolites were determined at 10, 20, 30, 40, 50 and 60 days of age prior to morning feeding.The starter consumption of calves fed with Low, Middle and High was 706.9,666.9,569.3 g, respectively. And the average daily gain (from day10~60) was 498,544 g/d,488 g/day, respectively.Body weight gain of Middle treated group was greater than that of the other groups. On the 60 days of age, wither height,body length(from the point of shoulder to the ischium) and cannon bone circumference were significantly higher with Middle treatment(P<0.05).There were no significant differences in the concentration of serum glucose,triglyceride and urea N among treatments, whereas a significant age effect was found on the level of triglyceride(P<0.05).Experiment 2. Experimental animals and dietary composition were same with experiment 1. Digestion/Metabolism trials were carried out between 12~20, 22~30, 32~40, 42~50, 52~60 days of age. The results indicated that increasing energy level of milk replacer improved utilization of DM,OM,EE,CP,GE and P(P<0.05).During 12 to 20 days of age, medium-energy group's OM digestibility was significantly higher than the others(P<0.05).While from 42 to 52 days of age, digestibility of EE,CP and GE of that group were significantly higher than the others(P<0.05).During 52 to 60 days of age,N digestibility: EE13>EE9>EE17,whereas,Ca retention: EE9>EE13>EE17.Experiment 3. Twelve newborn Holstein calves were used and assigned randomly to receive 1 of 3 experimental treatments,similar in protein level(25%) and energy value(19.30 MJ/kg), consisted of 10% lactose,10% lactose plus 10% compound-glucose and 10% lactose plus 10% compound-starch, respectively (n=4 per treatment).The occurrence of diarrhea was detected each day. Changes in body weight and growth parameters were determined at 10, 20, 30, 40, 50 and 60 days of age prior to morning feeding. The results indicated that diarrhea incidence of compound-starch treated calves were obviously higher than that of the other groups and declined as age advanced.The average daily gain of calved treated with lactose,compound-glucose and compound-starch was 451.2 g,501.25 g and 417.08 g, respectively and little difference was detected among them (P>0.05). Body parameters increased as age advance,while no difference was found among treatments(P>0.05). Results derived from economic analysis indicated that the usage of compound-glucose was better than that of compound-starch,with lactose presenting the medium value.Experiment 4. Experimental animals and dietary composition were same with experiment 1. During 50~60 days of age,digestive/metabolism trial was carried out. The results indicated that N apparent digestibility was significantly higher with lactose treatment than that of compound-starch treatment(P<0.05). DM,OM,EE apparnt digestibility and Ca,P retention of calves treated with 10% compound-glucose presented the highest value,whereas differences didn't reach the significant level(P>0.05).On the whole, feeding and digestive/metabolism trials were carried out to systematicly evalue effects of various energy sources and content of milk replacer on calves and determined 15.50 MJ/kg as the optimal energy level(DE) to promote rapid and health growth of calves.In addition, the possibility of non-milk carbohydrate utilization in the preruminants has been disscussed and pointed out compound-glucose could be selected to substitute part of lactose,whereas compound-starch presented acceptable performance merely at the age of more than 1 month,which suggested both practical and economic merit of recipes of its phase and will provide theoretic basis to the practice.
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