Efeitos da suplementação de cromo no desempenho produtivo e metabolismo de vacas leiteiras

Abstract

Chromium is an essential micronutrient for the metabolism of carbohydrates, proteins and lipids in animal tissue. It has been suggested that chromium supplementation in dairy cows may have a positive impact on productive performance, but the responses are inconsistent. A meta-analysis on the effects of chromium supplementation may better elucidate the responses and allow proposing random mechanisms. Therefore, the objective was to investigate whether chromium supplementation affects the metabolism and productive performance of dairy cows. A data set was produced using 30 peer-reviewed articles using chromium for dairy cows. The effects were compared by difference in gross mean between diets with chromium supplementation and control diets (without chromium supplementation). Chromium sources were divided into six groups. The chromium inclusion dose was divided into four classes. The lactation stage grouped into three classes of lactating days. Chromium supplementation performed in the pre and postpartum period or only in the postpartum period was also evaluated, as well as in different levels of concentrate in the diet. In general, chromium supplementation increased the intake dry matter (DMI) by 3.3% (P<0.05), serum glucose (P<0.01) by 2.8%, serum glucagon in 11% (P<0.05) and serum cortisol in 7.5% (P<0.05) in the prepartum period. In the postpartum period, chromium supplementation increased DMI by 6.4% (P<0.01), milk production by 6.4% (P<0.01), protein yield in milk in 3% (P<0.05), the fat yield by 4% (P<0.01), and the total milk solids yield in 4% (P<0.05). In the postpartum period, chromium supplementation increased serum glucose concentration by 4% (P<0.01), insulin sensitivity in 4% (P<0.05), serum glucagon by 6% (P<0.01), serum albumin in 3% (P<0.05), serum chromium by 31% (P<0.01), and reduced the concentration of serum nonesterified fatty acids (NEFA) by 6% (P<0.01) and the insulin:glucose ratio in 10% (P<0.05). Therefore, chromium supplementation improves the action of insulin, reduces the concentration of NEFA in the blood, promoting an increase in DMI and, consequently, in milk production and its components. However, chromium sources influenced the responses. The chromium sources with the best responses were Cr-Methionine and Cr-Propionate. The addition of chromium in diets with a concentration of 451–550 g/kg DM is better to maximize milk production. The dose that presented the best productive response for dairy cows was 6.0 to 7.5 mg Cr/cow/day, equivalent to an average content of 0.32 mg Cr/kg of DM in the diet. Chromium supplementation in the period of 28 days before calving and continued in the postpartum period has a higher milk production and may reduce the risk of disturbances in lipid metabolism in dairy cows.