Effects Of Protein Level And Source On Nutrient Utilization And Gastrointestinal Characteristics In Early-weaning Calves

In these series of research, preruminant calves were used as animal models to study the effects of protein level and source, lysine level in milk replacers on performance, digestive physiology, serum biochemical parameters, and gastrointestinal characteristics. The present research consists of five experiments which were listed as follow:Experiment 1: Influence of weaning age on performance of early-weaning calves using milk replacer.In this experiment, 25 neonatal healthy Holstein calves were allotted to five treatments, four of them were feeding milk replacer from the age of 6 day, 16 day, 26 day and 36 day to 70 day respectively, and labed as 6E, 16E, 26E and 36E treatment, another one was feeding fresh milk through whole experiment period about 70 days as control (C treatment). The results showed that BW and ADG of 6E treatment were higher than C treatment(p<0.05), but there had no significant differences among other four treatments (p>0.05). Body Length and Heart Girth of 6E, 16E treatments were greater than that of C treatment(p<0.05).Experiment 2: Grow performance, nutrients digestibility and gastrointestinal characteristics of dairy calves fed milk replacers containing different protein sources.In this experiment, 15 neonatal calves were allotted to three treatments, fed three milk replacers whose protein were come from milk and vegetable with different ratios 80:20, 50:50 and 20:80, respectively, labeled as S20, S50 and S80. A metabolism trial of 10d duration was conducted on all the experimental calves from 46th day to 55th day. Three calves of each treatment were slaughtered on the ending of experiment. The results showed that there were no significant differences on the grow performance and nutrients digestibility among three treatments (p>0.05). Vegetable protein might be good at development of rumen-reticulum of calves. The proportion of liver and pancreas to BW of calves were affected by protein sources (p<0.05). Dietary protein sources could affect small intestines morphological criteria, however, there were no significant effect on the rate of villous height to crypt depth (p>0.05).Experiment 3: Effect of different protein levels in milk replacers on nutrients digestibility in preruminant calvesNine healthy neonatal calves were selected, randomly divided into three treatments and fed three milk replacers with different protein levels (18, 22, 26%) respectively, labeled as LP, MP and HP. Five period-digestion-metabolism trials were taken between 12-20days, 22-30 days, 32-40 days, 42-50 days, and 52-60days after birth. The results showed that the apparent digestibility of DM declined gradually with age, whereas, the apparent digestibility of CP and EE rose slightly. The apparent digestibility of DM and EE increased following the increasing of dietary CP level, however, the average apparent digestibility of CP in MP treatment was higher than other treatments. BUN concentration increased following the increasing of dietary CP level (p<0.05), but the highest GLU and TP concentrations were found in MP treatment at the end of the trials.Experiment 4: Grow performance, nutrients digestibility and gastrointestinal characteristics of dairy calves fed milk replacers containing different amounts of protein.In this experiment, 15 neonatal calves were randomly allotted to three treatments which still labeled as LP, MP and HP, dietaries were improved by those of experiment 3. Rumen liquid was extracted before first feeding at morning at 4-w, 5-w, 6-w and 7-w age of calves. Three calves of each treatment were slaughtered on the ending of experiment. The results showed that BW gain of three treatments achieved 25.1, 34.8 and 26.4kg respectively. Protein levels had no significant effect on AA apparent digestibility (p>0.05). 22% protein level might be good at development of rumen papilla of calves, and was advantage of VFA production(p<0.05). Dietary protein levels could affect small intestines morphological criteria (p<0.05), and the rate of villous height to crypt depth was decreased as dietary crude protein levels increased.Experiment 5: Grow performance, nutrients digestibility and gastrointestinal characteristics of dairy calves fed milk replacers containing different amounts of lysine.In this experiment, 15 healthy neonatal calves were randomly allotted to three experimental treatments and fed with different milk replacer that containing 1.35% (LY), 1.8% (CY) or 2.25% (HY) of lysine. A metabolism trial of 7d duration was conducted on all the experimental calves from 48th day to 55th day. Three calves of each treatment were slaughtered on the ending of experiment. The results showed that BW gains of three treatments were 21.6, 25.0 and 24.3kg, and ADG achieved 515, 595 and 579g/d, respectively. BUN concentration was lowest, but TP concentration was highest in CY treatment among three. The rumen papillae in CY treatment were having a better development degree than in other treatments. However, dietary lysine levels could not affect small intestines morphological criteria (p>0.05).It could be concluded that: 1 There were no significant effects on the performance of early-weaning calves by using milk replacer. 2 The performance and nutrients digestibility were not affected by protein sources in milk replacers, and vegetable protein content increasing in milk replacer might be favor of early development of rumen-reticulum of calves. 3 Calves age and dietary protein levels affected nutrients digestibility and serum parameters. 22% protein level might be beneficial to the development of rumen functional in calves; however, higher protein level could impair intestines morphological criteria. 4 Calves fed 1.80% lysine in milk replacer gained better growth performance. There was no significant effect of dietary lysine levels on small intestines morphological criteria.