O impacto nutricional sobre o rúmen, tecido laminar e coxim digital de bovinos de corte confinados

Abstract

The understanding of the associations between ruminal acidosis and claudication are well studied topics particularly in dairy cattle. However, few randomized controlled interventions involving beef cattle under commercial production conditions (confinement) have been conducted so far. Therefore it is possible that variations in dietary starch ratios in beef cattle can promote rumen damage, with systemic deleterious effects to the constituent tissues of the digit, such as the digital cushion and corium / laminar tissues. The objective of this study was to identify macroscopic and histological effects caused by highly energetic diets, rumen and corium / laminar structures and digital cushion of the hull of cattle raised in a feedlot system. Forty heifers were divided into four groups and fed diets containing different levels of concentrated feed. The slaughter occurred after 60 days of feedlot in a certified refrigerator. The digits of the thoracic and pelvic limbs of these animals were measured using a mechanical pachymeter and with the aid of ImageJ® software. Samples of rumen, laminar tissue and digital cushion were collected, which, after processing by conventional histological technique, were evaluated by tissue morphoquantification and microstructural analysis, using optical microscope and Motic Images Plus 2.0 software. The impact of different diets on the ruminal environment was recorded (p<0.05). Inconsistent feces, reduced rumination and general momentary depression in the first 12 hours after infusion of sucrose were recorded in heifers' appearance. Lameness were not observed clinically (p> 0.05). Groups 3 and 4 showed lower motility (p<0.05) and ruminal pH (p<0.01) than the control group. It was possible to observe 22.5% (n = 9) of the macroscopic lesions in the ruminants in the animals submitted to diets 3 and 4. The histopathological analysis characterized mild degeneration of aglandular keratinized squamous epithelial cells, associated with discrete lymphocytic infiltrates in the lamina propria and some papillary vessels with the presence of inflammatory cells in the interior. Histopathological differences in digital tissues (p<0.05) were evident, characterizing a milder form of aggression to corium and laminar tissue. The ruminal acidity promoted by diets 3 and 4 did not influence the lipid content and fat composition of the digital cushion (p> 0.05). The clinical signs presented by the heifers during the experiment were discrete, to the point that they did not lose performance (p> 0.05). Therefore, high grain diets promoted a moderate alteration in the ruminal environment and corium / laminar tissue, without damaging the heifers' digital cushion.