The development and evaluation of the Small Ruminant Nutrition System

Abstract

A mechanistic model that predicts nutrient requirements and biological values of feeds for sheep and goats (Small Ruminant Nutrition System, SRNS) was developed based on the Cornell Net Carbohydrate and Protein System for sheep. The SRNS uses animal and environmental factors to predict metabolisable energy (ME) and protein requirements. This model has been subjected to an extensive evaluation. In particular, evaluation of the SRNS for sheep using published papers indicated good accuracy and precision in the prediction of organic matter and CP digestibility, while NDF digestibility was underpredicted. In addition, the SRNS accurately predicted daily ME intake (mean bias (MB) = 0.04 Mcal/d; root mean square error of prediction (RMSEP) = 0.24 Mcal/d; r2 = 0.99) of lactating goats and goat wethers. The SRNS also accurately predicted the ADG of lambs (n = 42; MB = 1 g/d; RMSEP = 37 g/d; r2= 0.84) and kids (n = 31; MB = −6.4 g/d; RMSEP = 32.5 g/d; r2= 0.85) and the gains and losses of shrunk body weight of adult sheep (MB = −5.8 g/d; RMSEP = 30 g/d; r2= 0.73) and the energy balance (n = 21; RMSEP = 0.20 Mcal/d; r2 = 0.87) of lactating goats and wethers. In conclusion, based on our accumulated evaluation of the SRNS with literature data, the SRNS accurately predicts nutrient supply and requirements of sheep and goats. Recent unpublished evaluations, however, suggested that the SRNS may underpredict ADG when compensatory growth occurs.