Effect of forage quality and protein level in the diet on growth performance and nitrogen balance in lambs after weaning

Three trials have been done to investigate growth performance, nutrient digestibility, N balance and plasma levels of Insulin and some metabolites in lambs weaned at４５days after birth and fed diets consisted with concentrates and roughages of different protein level（high?protein; HCP and low?protein; LCP）, and also compared the food value of ammoniated barley straw, ammoniated rice straw or the mixed hay（predominant Italian ryegrass hay）as basal feed for growing stage in early weaned lambs. Total１４lambs（４, trial I;６, trial II;４, trial III）were adopted after drinking colostrum, and thereafter they were reared by feeding a milk replacer supplemented with casein tomeet the protein requirement of animals during their growth. They were weaned at４５days, and were raised in metabolism cages（Trial I & III）or individual pen（Trial II）through the entire experimental period. There were no clear differences of feed intake of lambs between HCP and LCP groups. As a whole, average DG during０to２０−２４weeks did not clearly reflect the difference of dietary protein level, though the values tended to high in HCP group than that in LCP group. Through the experimental period, CP digestibility tended to high in HCP group than in LCP group, and contrarily urinary N excretion tended to high in HCP group than LCP group. Consequently, there was no clear difference in retained N between both groups, and the ration of retained N to absorbed N was resulted in higher in LCP group than in HCP group. As basal feed for growing stage in weaned lambs, the utilization of mixed hay（predominant Italian ryegrass）could be superior as compared with ammoniated barley and/or rice straws.