Resumen de Prediction and validation of dairy cows performance in Brazilian conditions
José Antonio de Freitas, Rogério de Paula Lana, André Luiz Rodriguez Magalhães
The objectives of this research were to develop prediction equations of dry matter intake, requirements and ingestion of energy and protein and to validate the equations, as well as those of NRC (1989, 2001), to predict milking cows performance. Analyses were performed on a set of 132 data from 33 purebred Holsteins and Zebu crossbred (¿ HZ) lactating cows. Mean values for body weight, milk production, milk fat and milk protein contents and dry matter intake with the respective standard deviations were 499.1 ± 37.0 kg; 21.1 ± 3.2 kg/d, 3.89 ± 0.44%, 3.16 ± 0.32%; and 16.8 ± 2.0 kg/d, respectively. Dry matter intake (DMI) was correlated positively withbody weight and milk production and negatively with TDN and NDF percentages in the consumed diet. Milk production was correlated positively with DMI and crude protein intake, and negatively with NDF content of the diet. Prediction equations of DMI and energy (TDN) and protein requirements were developed as a function of body weight and milk production and from these a table of nutritional requirements for milking cows was derived. These equations were more efficient in predicting cow performance under Brazilian conditions than those of NRC (1989; 2001). The NARC (2001) equation proved to be inadequate because it overestimated performance due to underestimating the energy requirement (Pt).
