Abstract:

The purpose of this experiment was to study the effects of relative feeding level on rate of bodyweight gain， carcass dressing out performance， meat quality and organ development in Altay sheep. Thirty 3.0 to 3.5 month old Altay female lambs with a similar body weight of （19.16±10.54） kg and uniform tail size were randomly divided into 3 groups with 10 lambs per group. After 60 daysof adlibitumfeeding， three differential feeding levels were imposed for a further 30 days. The differential feeding levels were calculated based on feeding standards published by the National Research Council， USA， in 2007， defining maintenance energy （Em） requirements and lambs in each group were fed diets supplying 1.5× （1.5Em）， 1.0× （1.0Em） or 0.5× （0.5Em） the calculated Em （0.75， 0.50 and 0.25 MJ metabolizable energy per kg^0.75 body weight， respectively）. It was found that： 1） The weights of the whole stomach， rumen， and small intestine and a rumen size index decreased with decrease in feeding level， and the weights of the whole stomach， rumen and small intestine fed at 1.5Em were significantly higher （P<0.05） than in groups fed 1.0Em and 0.5Em， while the length of small intestine and a small intestine size index in groups fed 1.5Em and 1.0Em were significantly increased （P<0.05） compared with the group fed 0.5Em. And there was no significant difference between the 1.5Em and the 1.0Em groups （P>0.05）. 2） The pH of rumen fluid was highest in the 1.0Em group and rumen pH for the group fed 1.5Em was significantly lower （P<0.05） than both the 1.0Em and 0.5Em groups. NH₃-N content decreased gradually with decrease feeding level， but the differences between the three groups was not statistically significant （P>0.05）. Total volatile fatty acids （TVFA）， acetic acid， propionic acid， butyric acid， valeric acid， isobutyric acid and isovaleric acid concentrations in rumen fluid of lambs fed 1.0Em were the lowest， and rumen TVFA， acetic acid and propionic acid levels of lambs fed 1.0Em were significantly lower （P<0.05） than in lambs fed 1.5Em and 0.5Em. The length of the small intestine and the small intestine size index of lambs fed 1.5Em and 1.0Em were increased significantly （P<0.05） compared to lambs fed 0.5Em. Rumen butyric acid and valproic acid concentrations and acetic∶propionic acid in groups fed 1.0Em and 0.5Em groups were significantly lower （P<0.05） than in the group fed 1.5Em. 3） The activities of digestive enzymes in rumen fluid decreased with the decrease of feeding level； the activities of lipase and protease in the group fed 1.5Em were significantly higher （P<0.05） than in the groups fed 1.0Em and 0.5Em， and there was no significant difference （P>0.05） between the groups fed 1.0Em and 0.5Em. Alpha-amylase activity differed significantly （P<0.05） among three groups. 4） The relative abundance of fungi and protozoa in rumen fluid of lambs fed 1.5Em was significantly higher （P<0.05） than in lambs fed 1.0Em and 0.5Em， and the differences between 1.0Em and 0.5Em groups were not significant （P>0.05）. Counts of Fibrobacter succinogenes and Ruminococcus albus were the lowest in lambs fed 1.0Em， and were significantly lower （P<0.05） than counts in the 1.5Em and 0.5Em groups. Ruminococcus flavefaciens counts did not differ significantly among the three groups （P>0.05）. These results show that feeding level has a significant effect on the gastrointestinal development， rumen fermentation parameters， activities of digestive enzymes and rumen microbiota in Altay sheep.

Key words: feeding level, Altay sheep, gastrointestinal development, fermentation parameters, digestive enzyme, microbial flora