Research On Responses Of Ruminal Fermen-Tation Parameters And Nutrient Digestibility To Dietary Feeding Level,and The Nitrogen Maintenance Requirement Of Tibetan Sheep

The object of this study is to evaluate the effects of dietary restriction of oat hay on ruminal fermentation parameters of Tibetan sheep, and to estimate maintenance requirement of nitrogen. Five20-month-old castrated male Tibetan sheep with similar body weight [(45±2)kg] were selected in a feeding trail and a fasting metabolism trail. Five Tibetan sheep were randomly divided into four groups(two sheep in one of the groups as replicate) in the feeding trails using a4X4Latin square design. Four dietary restriction levels were set, which were90%,70%,50%and30%of voluntary intake, respectively. Feces, urine were collected to measure the indicators of the digestion and metabolism of nutrients. Saliva, plasma and rumen fluid(after0,2,4,6and8hours of feeding) were collected to measure the concentration of urea nitrogen and ammonia nitrogen, and rumen fermentation metabolic parameters. During feces and urine samples were collected to measure daily output of fecal and urinary nitrogen in the fasting metabolism trail.The results showed as follows:1. Dietary restriction level had no significant effects on rumen pH, the contents of acetate, propionate, isobutyrate, valerate and isovalerae, and acetate/propionate (P>0.05), but had significant effects on butyrate content and total volatile fatty acid concentration (P<0.05ot P<0.01).2. Dietary restriction level had significant effects on the amount of urea nitrogen in Saliva and plasma, and the concentration of ammonia nitrogen in rumen fluid(P<0.05), but had no significant effects on the concentration of urea nitrogen in rumen fluid(P>0.05).3. Dietary restriction level had no significant effects on the digestibility of dry matter (DM), organic matter (OM),crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber(ADF)(P>0.05).4. A significant linear correlation between intake digestible nitrogen and nitrogen retention can get the equation as follow:[N retention](g/kg BW0.75)=-0.0994+0.8124×[intake digestible N](g/kgBW0.75),(n=20, R2=0.9607).When N retention is0, can be concluded that nitrogen maintenance requirement is0.12g/(kg BW0.75·d). 5. With the increase of fasting time, fecal nitrogen showed a tendency of being firstly decreased and then balanced, and urinary nitrogen and total nitrogen output both showed a tendency that first decreased and then increased and finally balanced. In conclusion, during fasting period the nitrogen maintenance requirement is0.15g/(kg BW0.75·d).