Suplementação com ácido málico sobre o desempenho, parâmetros ruminais e metabólitos sanguíneos de ruminantes: estudo meta-analítico

Abstract

The thesis aimed to determine, through meta-analysis, the effects of malic acid supplementation on performance, ruminal parameters, blood metabolites and diet digestibility on ruminants. Only studies that present results for a control group vs. malic acid/malate were considered. The effect of organic acid addition was evaluated using the effect size method. Meta-regression analysis was used to find covariates capable of explaining the heterogeneity observed in the results. In the first paper, the objective was to evaluate the effect of the organic acid on milk production and composition of Holstein cows. Malate supplementation did not affect the dry matter intake, milk fat and protein. However, an increase in milk production was observed in the animals in the malate-supplemented group. The meta-regression indicated that covariates related to concentrate intake interfere in the magnitude of the effect related to supplementation. In the second paper, the objective was to determine the effect of malate supplementation on performance, carcass traits, nitrogen balance and ruminal parameters of lambs. Supplementation increased the average daily gain and reduced the feed conversion rate of lambs; the effect was reduced due to high doses of malate. Malate did not affect diet digestibility, meta-regression indicated starch intake as an interfering factor. Furthermore, the use of malate increased the production of total volatile fatty acids (VFA) and was able to raise the lambs ruminal pH. In the third paper, the objective was to determine the effects of malic acid/malate supplementation on ruminal parameters, blood metabolites and diet digestibility on cattle. Supplementation with malate/malic acid increased rumen pH and also the concentration of propionate and VFA. In addition, it increased the digestibility of dry matter, neutral detergent fiber and protein, in addition to increasing glucose and decreasing the level of non-esterified fatty acids (NEFA) in blood. Diet-related covariates were important to explain the heterogeneity in the results related to rumen fermentation, but not for the variability associated with digestibility and blood parameters. In conclusion, malic acid supplementation is able to increase pH and VFAs in the rumen of ruminants. The presence of such effects is reinforced by the better performance of the animals. There was an effect of organic acid on the apparent total digestibility of the main diet fractions for cattle, but not for sheep. In addition, supplementation resulted in an increase in glucose and a decrease in blood NEFA. The high heterogeneity of the results can be explained, in part, by factors associated with the diets provided to the animals.