Processamento de silagem de milho e suplementação de vacas leiteiras com enzimas fibrolíticas

Abstract

Corn silage has high potential for dry matter production per area and high concentration of energy per unit of dry matter produced, mostly derived from the starch in kernel fraction. Processing the silage into small particle size is advantageous for the ensiling process and feeding practices but may reduce the physically effective fiber content in diets with high inclusion of corn silage for dairy cows. Processing at harvest determines feed nutritional value, thereby affecting digestibility, ruminal physiology, and lactation performance by dairy cows. Three experiments were conducted to evaluate the degree of kernel processing of the corn silage. The objective of the first experiment was to evaluate the theoretical length of cut (3, 4.5, 6 and 8.5 mm) and presence of a kernel processor in a one-row harvester on degree of forage processing. The use of the harvester with a kernel processor and 8.5 mm particle size was more effective in processing the kernel fraction of the plant with minimal reduction in particle size of the stover fraction. The second experiment aimed to evaluate the response of dairy cows to diets with 31.7% of dry matter of corn silage harvested at 3 mm without kernel processor (the predominant method in Brazil) or at 8.5 mm with kernel processor. The supplementation of diets with fibrolytic enzymes was also evaluated, in 2 x 2 factorial design. Sixteen cows were individually fed in 4 x 4 Latin squares, with 21-day periods, and responses to treatment measured in the third week. Silage with longer particles improved the dairy performance and rumen function. The fibrolytic enzymes improved total tract fiber digestibility only in the short-fiber silage diets, but tended to induce ruminal acidosis. Experiment 3 evaluated the relationship between physical characteristics in the kernel fraction of corn silage and Corn Silage Processing Score (CSPS), a laboratory technique for measuring the degree of kernel processing in corn forage. The degree of kernel processing in the corn silage was better described by the geometric mean particle size after hydrodynamic separation and dry sieving of samples. Fibrolytic enzymes can improve digestibility in low physically effective fiber diets, which may reduce fiber digestibility in the rumen. The evaluation of corn silage kernel fraction by flotation technique and dry-sieving were provided a better description of degree of kernel processing than the KPS.