Morfologia e histomorfometria de rúmen, ceco e fígado de bovinos de corte, alimentados com aditivos zootécnicos em terminação intensiva em pastagem tropical

Abstract

We evaluated the morphological and histomorphometric characteristics of the rumen, cecum and liver of beef cattle fed a combination of livestock additives in intensive pasture finishing (IFP). We used 225 Nellore cattle (average body weight (BW) = 454 ± 27 kg), randomly distributed in 15 paddocks (15 cattle per paddock and 3 paddocks per experimental diet). For sample collection, we selected 45 animals (n = 45), with 3 cattle with average BW from each paddock, totaling 9 animals per experimental diet. The diets with the respective additives evaluated were randomly distributed to the paddocks and consisted of: lasalocid sodium (L; control); lasalocid and Actigen (LACT); lasalocid and ADV Fortuna LM (LADV); lasalocid and Probios Precise (LPP); lasalocid and LithoNutri (LLN). After slaughter, we collected fragments of rumen, cecum and liver, which were identified and fixed in 10% formalin for histological analysis. The morphological and histomorphometric variables were analyzed using the generalized mixed linear procedure, testing different distributions for continuous data. Comparisons between means were performed using ANOVA, with breakdowns made by the Tukey test, considering a significance level of 0.05. The histopathological variables were statistically evaluated by the nonparametric Kruskal-Wallis test, also with a significance level set at 0.05. In chapter 1, we discuss the results of the morphometric, histomorphometric and histopathological evaluation of the rumen and cecum of the animals. There was no difference (P>0.10) in the morphometry of the papillae, which presented average length and width of 4.41 mm and 1.68 mm, respectively. Ruminal histomorphometry showed no effect among the diets tested (P>0.10), except for the tendency to reduce the stratum corneum of the middle portion of the ruminal papillae of animals that received LADV compared to L (P=0.060), LACT (P=0.096) and LPP (P=0.081). The changes were considered mild, and no effect was established on the histopathological variables of the rumen and cecum of the animals between the diets (P>0.10). In cecal histomorphometry, the LLN association increased the depth of the cecal crypts by 14.9% in relation to L (P=0.035), with average depths of 409.4 µm and 356.3 µm, respectively. In addition, LLN showed a tendency in the depth of crypts 12.8% greater compared to LACT (P=0.073), with an average depth of 362.7 µm. Similarly, animals supplemented with LPP tended to have greater cecal crypt depth (13.4%) compared to those that received L (P=0.057), with mean crypt depth of 404.2 µm and 356.3 µm, respectively. In chapter 2, we evaluated the macroscopic, microscopic morphology and histomorphometry of the animals' livers. Macroscopically, we observed no changes in the livers evaluated and all were considered healthy and suitable for consumption. The liver histopathological variables did not show differences according to the non-parametric test (P>0.05), with changes limited to mild. The histomorphometric variables of hepatocytes in the centrilobular and portal triad regions were not influenced (P>0.05) by the diets, except for those of the animals that received LPP, which presented a greater proportion (P=0.033) of nucleus in relation to cytoplasm compared to those that received LADV. Therefore, the inclusion of the ionophore lasalocid in the diet of beef cattle on IFP, alone or associated with other zootechnical additives, proved to be an effective strategy in promoting animal health and welfare. In addition to preventing liver disorders, such as abscesses, lasalocid also contributed to the health of the gastrointestinal tract, especially when associated with LithoNutri and Probios Precise.