Forty Malpura ewes, randomly divided into 5 groups, were fed on guar straw as basal roughage wherein control group (CG) fed without concentrate supplement (CS) or experimental groups (EG) fed with CS (20.8% CP and 12.8 MJ ME) in incremental levels of 4 (EG1), 8 (EG), 12 (EG3) or 20 (EG4) g/kg body weight, respectively on DM basis. Average efficiency of digestible nutrient intake was more in EG1 (P<0.001) while marginal efficiency was higher in EG3 (P<0.001). Average (P<0.05) and marginal (P<0.05) efficiency of dietary N retained was higher in EG1 and EG3, respectively and, reverse was true with net energy retained (P<0.001). Average or marginal efficiency of protein retained increased at increasing rate, when marginal efficiency of net energy was more. Average efficiency of net energy was taken for optimisation based on metabolic relationship among N and energy. Total purine derivatives excreted and microbial nitrogen production (MBN) was not significantly different among groups. Efficiency of MBN in terms of digestible OM in rumen was higher in CG than in other groups but marginal efficiency was higher in EG3. By and large, marginal efficiency of digestible nutrient intake, MBN and N retained was more when CS to guar straw was 12 g/kg body weight on DM basis and above which marginal efficiency was diminished and below which ewes still had 2 to 3 times more potential to respond to each gram of additional CS.
Concentrate supplement, Marginal efficiency, Energy, Nitrogen, Purine derivatives, Sheep
