Effects Of Dietary Energy And Protein Level On Growth Performance And Gastrointestinal Development Of Lambs

The aim of this research was to assess the effects of protein and energy level on growth performance, gastrointestinal development and liver metabolism in 0~2 and 3~4 months lambs. The growth performance were determined by feeding experiment, slaughter performance, gastrointestinal histomorphology were observed in slaughtering experiment, and high-throughput sequencing technologies was used to study the rumen microflora. The present research was described as follows.Experiment 1: Effects of dietary energy and protein level on growth performance and gastrointestinal development in 0 ~ 2 month lambs.This experiment was aimed to study the effects of dietary energy and protein level on growth performance, gastrointestinal development and liver metabolism in 0 ~ 2 month lambs. With two factors and two levels of experimental design, sixty-four 17-d Hu lambs were selected according to the weight(6.5± 0.2 kg), birthday and birth weight(2.5±0.2kg) and were randomly divided into four groups including high-energy and high-protein group, high-energy and low-protein group, low-energy and high-protein group and low-energy and low-protein group. The intakes of milk replacer and starter were recorded, and all the lambs were weighed and collected blood for determination of serum index at 20, 40 and 60 days of age, then 4 of them from each group were slaughtered at 40 and 60 days of age for weighing organs, collecting gastrointestinal tissue samples for observing gastrointestinal histomorphology, collecting ruminal fluid for observation of rumen microbial diversity and rumen fermentation parameters, collecting liver sample for determine liver key enzyme activity. The results showed as follows: 1. Reducing protein level significantly reduced the lamb weight and average daily gain in 0 ~ 2 months(P<0.05), reducing energy level reduced lamb weight at 60 days of age(P<0.05). 2. Reducing energy level significantly reduced the rumen weight at 40 and 60 days of age, the length of the rumen nipple( P<0.05) and the concentration of volatile fatty acids(P<0.05), but no the rumen microbial diversity(P>0.05); Reducing protein levels significantly lowered rumen weight at 40 days of age(P<0.05) and the concentration of volatile fatty acids(P<0.05), but not the rumen weight at 60 days of age, rumen nipple histomorphology and rumen microbial diversity(P>0.05). 3. Reducing energy level significantly reduced the small weight and large intestine weight(P < 0.05), protein levels had no significant effect on small intestine weight(P> 0.05). Energy levels had no significant effects on intestinal tissue histomorphology(P>0.05), but protein level significantly reduced the duodenum and jejunum V: C ratio at 40 and 60 days of age(P<0.05). 4. Energy level reduced the weight of liver at 40 and 60 days of age(P<0.05), low-protein diets can reduce the weight of rumen at 60 days of age(P<0.05); energy and protein levels had no significant effects on activity of Enol phosphate carboxylase propionate, Hexokinase and the concentration of Insulin-like growth factor-1 in liver(P >0.05).Summary: Energy levels had a significant effect on gastrointestinal tract weight and protein level had effect on the intestinal tissue morphology and growth performance in 0~2 month lamb.Experiment 2: Effects of dietary energy and protein level on growth performance and gastrointestinal development in 3 ~ 4 month lambs.This experiment was aimed to study the effect of energy and protein level on growth performance, gastrointestinal development and liver metabolism in 3~4 month lambs. Eighty early-weaned Hu lambs were selected according to the weight(6.5± 0.2 kg), birthday and birth weight(2.5±0.2kg) and fed milkreplacer and starter until 60 days of ages. Then 64 Hu lambs were selected according to weight of 60 days of age(14.95±0.56kg), randomly divided into four groups including high-energy and high-protein group, high-energy and low-protein group, low-energy and high-protein group and low-energy and low-protein group. The intakes of diets from 61 days of age were recorded every day, and all the lambs were weighed and collected blood for determination of serum index at 60, 90 and 120 days of age, then 4 of them from each group were slaughtered at 120 days of age for weighing organs, collecting gastrointestinal tissue samples for observing gastrointestinal histomorphology, collecting ruminal fluid for the observation of rumen microbial diversity and rumen fermentation parameters, collecting liver sample for deter mining liver key enzyme activity. The results showed as follows: 1.The energy level and protein level significantly affected lamb weight(P<0.05) and average daily gain at 61-90 days of age(P<0.05); reducing energy level reduced the slaughter performance(P<0.05), and reducing protein level can reduced eye muscle area(P < 0.05). 2. Reducing energy level significantly reduced the rumen weight at 120 days of age and its percentage to complex stomach(P<0.05), concentration of total volatile fatty acids(P< 0.05), and the proportion of propionic acid(P<0.05), increased the rumen pH(P<0.05), but not the height of rumen nipple(P>0.05); Deduction of protein level significantly improved the concentration of propionic acid(P<0.05). Reducing energy level significantly increased the rumen microbial diversity(P <0.05), reduced the abundance of Proteobacteria at phylum level(P<0.05), and reduce the abundance of Succinivibrionaceae-uncultured at genus(P<0.05); reducing protein level can reduce the rumen microbial diversity(P<0.05), lower the abundance of Bacteoidetes(P<0.05). 3. Reduction of energy level significantly decreased the weight of the small intestine weight, the weight of liver(P<0.05), but not the live weight before slaughter(P>0.05). Energy and protein levels had no significant effects on activity of Enol phosphate carboxylase propionate, Hexokinase and the concentration of Insulin-like growth factor-1 in liver(P>0.05).Summary: Energy levels had a significant effect on slaughter performance, gastrointestinal tract weight and rumen microflora and protein level had an effect on the intestinal tissue morphology in 3~4 month lamb.In conclusion, under the presented experiment condition, the protein level have significant effect on growth performance in 0~2 month, and energy level have significant effect on slaughter performance in 3~4month. Energy level mainly affect the development of rumen, liver and intestine, and protein levels have significant effect on gastrointestinal histomorphology. Energy and protein levels showed no significant difference on the rumen microflora of 0 ~ 2 month, but significantly affect the rumen microbial diversity at 3~4 months.