Empirical assessment of the CNCPS model to predict performance
of dairy cows fed pasture with silage supplements
A.V. CHAVES, I.M BROOKES, J.L. BURKE, G.C. WAGHORN AND
S.L.WOODWARD
AgResearch Grasslands, Private Bag 11008, Palmerston North
E-Mail:
NZSAP 2003 Abstract No. 23
Proceedings of the New Zealand Society of Animal Production
63: 91-95
The goal of this work was to determine the accuracy and utility
of the Cornell Net Carbohydrate and Protein System (CNCPS) model to
predict milk production from diets based on pasture and forage
supplements. Data were obtained from studies in which pasture was
complemented with contrasting silages including maize, pasture, sulla,
lotus and forage mixtures, comprising 30-40% of dry matter intake (DMI).
Twelve diets were used in this evaluation. DMI, live weight (LW), days
in milk, and diet composition were determined during the trials and used
as inputs in the model. Across all diets, a significant (P<0.01)
relationship existed between predicted and actual values for DMI
(r2=0.63), milk yield (r2=0.64) and LW change
(r2=0.57) but there were still large unexplained sources of
variation and the slopes of the regression lines were significantly
(P<0.01) different than 1. No significant mean bias was observed for
any of the variables, but the slope of residual differences against
predicted values was significantly different from zero (P<0.01 for
milk yield and LW change; P<0.06 for DMI). The results indicate a
satisfactory prediction of milk production when cows are neither gaining
nor losing weight, but that a systematic bias exists probably because of
the CNCPS model’s failure to account for nutrient partitioning.
Keywords: NZSAPAB;
CNCPS; dairy cows; diet formulation; modelling; nutrients
requirement
Last Updated 8/07/2004
