MULTIFACTORIAL RELATIONSHIPS BETWEEN INTRINSIC-FACTORS, SEASON AND HERD EFFECT, AND BIOCHEMICAL MARKERS OF THE ENERGY AND PROTEIN-METABOLISM IN DAIRY-COWS

In this study, we investigated in a multivariate approach the multifac torial relationships between intrinsic factors, season, time of sampli ng during the year, and herd effect on one side, and selected biochemi cal markers of the energy and protein metabolism on the other side. A total of 370 cows (158 in summer and 212 in winter) were investigated within 0-160 days post partum. The following metabolites were chosen: glucose, nonesterified fatty acids, b-hydroxybutyrate, cholesterol and urea. Multiple linear regression models with only intrinsic factors h ad generally low coefficients of determination (r(2)). Season had a si gnificant effect on all metabolites excepted glucose, but introduction of this factor in the models did not increase r(2) markedly. Herd eff ect was highly significant for all blood parameters. Despite the reduc tion of the number of cases, models within season showed higher r(2) t han the overall models. This leads to the conclusion that, according t o the season, some factors have different effects which neutralize the mselves during the whole year. Many interactions herd x factors were s ignificant for each metabolite. This means that the effect of the fact ors is different among herds. These interactions were especially stron g for glucose, b-hydroxybutyrate and urea nitrogen, which usually show short-term responses to feeding changes. The regression models showed generally high coefficients of determination. It is concluded that th ese factors and interactions have to be introduced as covariates in mo dels designed to investigate the relationships between biochemical mar kers and clinical findings.