Influence of the urea concentration in plasma on pregnancy and dairy components for tropical conditions

Resumen

Information was considered referring to the urea concentration in serum from 160 commercial Holstein dairy cows with average weight of 452 kg, milk yields between 9 and 13.5 L/cow/d, and feeding based on pastures and supplementation, with levels between 3 and 4.5 kg/a/d. The milk yields managed to surpass 4000 L/lactation, and two groups were formed for the analysis, according to the urea concentrations in plasma: a) animals with urea values higher than 20 mg %, and b) animals with values lower than 20 mg %. Finally, 66 cows with levels higher than 20 mg % and 94 with lower levels were grouped. For the selection, it was started from the criterion that the indicator urea in plasma was determined in the same dairy unit. Also, the percentage of pregnancy at first service and the results of both groups in respect to the milk composition (fat, protein, non-fatty solids, total solids, and protein-fat ratio) were assessed. The values of productive efficiency at first service, as well as those of the milk components, indicated that concentrations in plasma higher than 20 mg % of urea in blood may provoke upsets in the animal response and affect basic indicators. It is suggested that, for the Cuban conditions, the urea determination in blood should be a habitual search in dairy herds due to the referential value provided by this indicator.
Key words: dairy herds, urea in blood, milk components.