Meta-análise sobre o uso de grãos de destilaria em dietas para vacas leiteiras

Abstract

The increase in ethanol production from corn distillation provided an increase in the supply of its co-products for use in animal feed. Thus, there was a significant increase in studies on its use in diets for dairy cows in recent years, which justifies the performance of meta-analyses to better investigate the impacts and establish recommendations for use. Thus, a meta-analysis was carried out with the objective of evaluating the productive parameters and the use of nutrients in dairy cows submitted to diets with distilled grains. Data from 35 peer-reviewed articles were summarized to examine the effects of dietary distilled grains on the performance of dairy cows. Effects were compared by gross mean differences (RMD) between treatment means diet with distilled grain and control diet, weighted by inverse variance using random effect models. In the control diet, the treatments (33.8 ± 6.7 kg of milk/d, variation from 13.5 to 44.9 kg/d; dry matter (DM) intake (DMC; 23.1 ± 3.5 kg of DM/d, range from 11.9 to 29.7 kg/d); milk fat content 3.68 ± 0.47%; milk protein content 3.20 ± 0.25%). Soybean meal (80% of observations) and canola meal (16%) were used mainly as protein source. We also evaluated the effects of including distilled grains in the diet (grades: <100, 100-200, 200-300 and >300 g/kg dry matter (DM)) and DCG processing: distillery dry grains (DDG) and DDG with solubles (DDGS) (30.5 ± 3.1% crude protein (CP) DM basis, and 10.4 ± 3.2% ether extract (EE), DM basis); wet distillery grains (WDG; 33.4 ± 3.6% CP; 11.9 ± 2.3% EE); high protein distillery grains (HPDG; 46.1% CP; 4.63% EE); low-fat distillery grains (LFDG; 32.9 ± 1.5% CP; 4.7 ± 1.2% EE) and condensed distillery grains (CDG; 18.8% CP and 9.8% EE) ) about the RMD. The level of heterogeneity was analyzed using I² statistics (low ≤ 25%; moderate = 26 to 50% and high > 50%). In general, the use of distilled grains in the diet did not affect DMI (P = 0.20) and milk protein content (P = 0.31), but increased milk production (RMD = 1.05 ± 0 .40 kg d-1; P <0.01; n = 69; I2 = 23.3%) and reduced milk fat content (RMD = - 0.11 ± 0.05% in milk; P = 0. 01; n = 69; I2 = 22.8%). However, dietary inclusion of distilled grains and processing of distilled grains affected the responses. Dietary inclusion of distilled grains between 100-200 g/kg DM (RMD = 0.99 ± 0.63 kg of milk d-1; P <0.01; n = 32) and 200-300 (RMD = 1.49 ± 0.71 kg of milk d-1; P < 0.01; n = 15) increased milk production, but no effect was observed with inclusion <100 g/kg DM (P = 0.35; n = 12 ) or > 300 g/kg MS (P = 0.27; n = 10). Furthermore, inclusions below 300 g/kg DM did not affect the protein content in milk (P>0.05), but markedly reduced with levels of distilled grains above 300 g/kg DM. The use of LFDG (P = 0.25; n = 9) and CDG (P = 0.39; n = 4) did not affect milk production, but milk production tended to increase with DDG / DDGS (RMD = 0.51 ± 0.52 kg of milk d-1 ); P = 0.06; n = 45), and increased with WDG (RMD = 2.24 ± 1.21 kg of milk d-1; P < 0.01; n = 6) and HPDG (RMD = 2.55 ± 0.53 kg of milk d-1; P < 0.01; n = 5). The main effects of including distilled grains in ruminal fermentation (P<0.05) were increased production of propionate over acetate, reductions in pH and production of ruminal ammonia. The use of distilled corn grains in the diet can improve the productive performance of dairy cows, but its response depends on dietary inclusion and industrial processing. Feeding diets with DDG/DDGS, LFDG or CDG does not affect yield performance, but HPDG and WDG co-products improve yield performance. Optimum levels of dietary inclusion of distilled grains are between 100 to 300 g/kg DM. Inclusion levels above 300 g/kg DM, although not affecting milk consumption and production, cause a marked reduction in milk protein content and may increase the risk of ruminal acidosis. We recommend studies to better elucidate the mechanism by which the use of HPDG and WDG present a better response in productive performance compared to DDG/DDGS. Our findings may help to better use distilled grains in the diet of lactating cows. This study will be adopted to compose the sub-model “Co-products” of The Nutrition System for Dairy Cattle (NS Dairy Cattle), under development at the Dairy Cattle Reseaerch Lab at UFMT/Sinop.