Effects Of Protein Levels And Feeding Levels Of A Milk Replacer On Growth Performance And Nutrient Utilization In Early-Weaned Lambs

The protein concentration and feeding level of a milk replacer were eaxamined in early-weaned lambs to evaluate their effects on growth performance, digestibility and metabolism of nutrients and blood biochemical parameters. Meanwhile, the effect of feeding levels of the milk replacer on the microbial diversity in the rumen of early-weaned lambs was also investigated. The present research included four experiments as follows: Experiment 1: Effects of protein concentrations of a milk replacer on growth performance and nutrient digestion and metabolism in early weaned lambs.Thirty six Dorset×Thin-tailed Han sheep crossbred F1 lambs were randomly divided into 4 groups. One group of the lambs suckling their ewe's milk was used as control, the others were fed with a milk replacer containing 21, 25 or 29% of protein. The body weight and dimension were measured on d 20, 40, 60, 80 and 90 after birth. Two digestion trials were undertaken during d 50-60 and 80-90 after birth. The results showed that the milk replacers promoted the lambs to ingest a starter feed earlier, and the intake of the starter feeds was decreased (p<0.05) as the protein level of the milk replacer increased. The weight gains of the lambs receiving a milk replacer containing 21, 25 or 29% protein were 14.1, 14.6 and 13.9 kg, respectively. Compared with control group, the weight gains of the latter groups above were increased by 7.6, 11.5 or 6.1%, respectively (p>0.05). The tendency of body dimension changes was the same as body weight gains. The milk replacer containing 25% protein was the best. The crude protein level had no significant effects on the apparent digestibility of dry matter, organic matter, ether extract, calcium or phosphorus (p>0.05). The nitrogen retention was 73.5% for 29% protein group, which was significantly lower (p<0.05) than that of 21% protein (77.2%) and 25% protein (77.6%) groups during d 80-90. Experiment 2: Effects of protein concentrations of a milk replacer on the gastrointestinal morphology in early weaned lambs.The trial animals were the same as experiment 2. Four lambs of each treatment were slaughtered on d 90. The results showed that feeding the milk replacer to the early-weaned lambs significantly increased the rumen weight (p<0.05); the papilla height of the dorsal and ventral sac of the rumen of the milk replacer fed lambs was significantly higher than that of suckling lambs(p<0.05), however the protein level of the milk replacer did not significantly alter the width and height of rumen papillae (p>0.05). The milk replacer enhanced the weight and index of the spleen as they increased with the increasing CP level of the milk replacer. Experiment 3: Effects of feeding levels of a milk replacer on digestion and metabolism of nutrients, and serum biochemical indexes in lambs.Twenty seven newborn crossbred F1 lambs (Dorset×Thin-tailed Han sheep) were randomly divided into 3 groups and each fed with a milk replacer at 1.0 (L), 1.5 (M) or 2.0% (H) of BW. Digestion and metabolism trials were carried out from 50 to 60 and from 80 to 90 d of age, respectively. Blood metabolites were determined at 50 and 90 d of age. The results showed that the growth performance of the lambs was increased as the feeding levels of the milk replacer increased, significant differences in the BW and body length existed among three treatments (p<0.05). As feeding levels increased, the apparent digestibility of DM, OM, GE, N, EE, Ca and P rose. The digestibility of DM, GE, N, EE, Ca and P in the L group was significantly lower than that in the H group (p<0.05), but the N retention in the H group was only 70.9%, which was significantly lower than that in the L group (78.7%)(p<0.05). At 50 d of age, no significant differences in the serum concentration of TP, BUN, GLU, CHOL or TG were detected among the groups (p>0.05), but the activity of serum ALP in the lambs from the L or M group was significantly lower than that from the H group (p<0.05). At 90 d of age, the serum concentration of CHOL in the H group was significantly higher than that in the L group (p<0.05).Experiment 4: Effects of feeding a milk replacer on the microbial diversity in the rumen of early weaned lambs.Twelve Thin-tailed Han lambs were divided into 2 groups with six animals each and fed with a milk replacer (T) or suckling their mother's milk (C). The rumen fluid was collected before morning feeding at 20, 30, 40, 50, 70 and 90 days of age. The colonization of rumen bacteria and the changes of bacterial diversity in the rumen were investigated by DGGE and 16S rDNA sequence analysis method. The results indicated that the milk replacer changed the microbial diversity in the rumen of early weaned lambs, increased the DGGE fingerprint bands and affected the abundance of bacteria from the same family. The bacterial profile in the rumen of 20-day-old lambs was complex, including Prevotella ruminicola, Firmicutes and Bacteroidetes. The Fibrobacteres bacteria capable of degrading cellulose were found in the lamb's rumen. During the whole experiment, Bacteroidetes and Firmicutes were dominant bacteria in the lamb's rumen.In conclusion, the optimum protein level of the milk replacer for early weaned lambs was 25%. Appropriate feed levels of the milk replacer significantly enhanced the growth rate of lambs and digestibility of nutrients, and improved the efficiency of feed utilisation, and the optimum feed levels for the lambs aged 20-50, 50-70 and 70-90 days of age were 2.0, 1.5 and 1.0%, respectively. The milk replacer modified the bacterial diversity in the rumen as indicated by the increased DGGE fingerprint bands, and simultaneously affected the abundance of microbes of the same family in early-weaned lambs.