Study Of Methods For Predicting Ruminal Microbial Protein Synthesis In Mutton Sheep

This study used Dorper thin-tailed Han crossbred sheep were used to firstly compare the accuracyof two microbial nitrogen (MN) markers,15N and purine base (PB), and secondly to investigate theeffect of dietary treatments on urinary excretion of purine derivatives (PD), and finally to establish therelationship between PD and MN, and to evaluate the effectiveness of using spot urine samplingtechnique.Experiment1: Effect of feed intake on urinary excretion of purine derivatives and microbialprotein synthesis in mutton sheepThis study aimed to compare the MN measured by using two microbial markers,15N and PB, and toinvestigate the effect of dietary treatment on urinary PD excretion, and to establish the relationshipbetween MN and PD. Twelve6-month-old ram lambs were randomly assigned to three levels of drymatter intake: ad libitum (AL) intake, or70%(70%AL) or50%(50%AL) of the ad libitum intake. Theresults showed that: MN measured by15N had lower variability than that measured by PB (P<0.05).Urinary excretion of allantoin was affected by feed intake (P<0.05). Significant difference was found inurinary excretion of uric acid and xanthine+hypoxanthine between AL and50%AL groups (P<0.05).PD was linearly correlated with MN estimated from either15N or PB: MN (g/d)=0.74×PD (mmol/d)+0.030, R2=0.91.Experiment2: Effect of dietary forage to concentrate ratios on urinary excretion of purinederivatives and microbial protein synthesis in mutton sheepThis study aimed to establish the model for predicting MN using urinary PD, and to predict intestinalmetabolizable N. Twelve10-month-old ram lambs were randomly assigned to12levels of dietary F:Cin an incomplete Latin-square experimental design (12lambs4periods). The results showed that:Allantoin and total PD increased (P<0.05) with decreasing F:C. Uric acid and xanthine plushypoxanthine was unaffected by F:C (P>0.05). Both PNI and NCE decreased with decreasing F:C(P<0.05) and a linear relationship existed between PNI and NCE calculated with15N: NCE=3.67×PNI+0.574, R2=0.82. Metabolizable protein (Y, g/d) was quadriatically correlated with digestibileorganic matter (DOM; X1, g/d) or organic matter apparently digested in the rumen (OMADR; X2, g/d):Y=0.0002X21–0.181X1+46.435, R2=0.81; Y=0.0002X22–0.081X2+16.961, R2=0.95. A linearcorrelation was observed between PD excretion and MN: MN (g/d)=–0.52+1.49PD (mmol/d)(R2=0.86, n=45, P<0.05).Experiment3: Study on the effectiveness of use of spot urine samples to predict daily PDexcretionThis study aimed to investigate the effect of dietary treatment on PD excretion and to evaluate theeffectiveness of using spot urine technique to predict daily PD excretion. Four10-old-month ram lambswere randomly assigned to four dietary treatments including two levels of non-fibrous carbohydrate andtwo levels of undegraded dietary protein, according to a44Latin-square experimental design. During the digestibility trial, spot urines were collected between08:00–09:30,14:00–15:30, and20:00–21:30,respectively. In spot urine samples, a linear correlation existed between the PDC index from spot urinesamples and daily PD excretion (P<0.05): PD (mmol/d)=0.22×PDC+3.45, R2=0.88, whichindicated that spot sampling technique accurately predicted daily PD output.