Effects of Feeding Functional Oils or Monensin on Rumen Morphometrics of Nellore Cattle.

This study, conducted at the São Paulo State University feedlot, Dracena campus, Brazil, was designed to test the effects of adding functional oils (Essential) or monensin on rumen morphometrics and rumenitis incidence of Nellore cattle fed high-concentrate diets. Eighty-eight 22-mo-old Nellore yearling bulls (377.9 ± 32.0 kg) were assigned to 24 pens (4 animals/pen) and used in a completely randomized block design with a 2×2 factorial arrangement of treatments, replicated 6 times. Factors were inclusion (DM basis) or not of functional oils or monensin, at a dose of 500 ppm or 27 ppm, respectively. Animals were adapted for 16-d to the high-concentrate diets fed. The finishing diet contained 68.5% cracked corn grain, 14.0% sugarcane bagasse, 14.1% cottonseed meal, 2.1% supplement, 0.8% urea, and 0.5% limestone (DM basis). Cattle were fed ad libitum three times daily for 105-d, and DMI was recorded daily. At harvest, rumenitis incidence was determined on the entire washed rumen, using a scale of 0 (no lesions noted) to 10 (severe ulcerative rumenitis). Likewise, a 1-cm² fragment of each rumen was collect from the cranial sac. The number of papillae per cm² of rumen wall (NOP) was determined, as well as the mean papillae area (MPA). The rumen wall absorptive surface area (ASA) in cm² was calculated as follows: 1+(NOP*MPA)-(NOP*0.002). No significant (P > 0.10) functional oils or monensin main effects were observed for rumenitis (with functional oils = 1.41, without functional oils = 1.77; with monensin = 1.73, without monensin = 1.45). Also, no significant (P > 0.10) functional oils main effect was observed for MPA in cm² (with functional oils = 0.54, without functional oils = 0.55) and ASA in cm² (with functional oils = 33.60, without functional oils = 34.70). However, the addition of monensin led to larger (P < 0.10) MPA in cm² (with monensin = 0.60, without monensin = 0.48) and ASA in cm² (with monensin = 37.23, without monensin = 31.06). A significant (P = 0.03) interaction between functional oils and monensin was observed for NOP in cm² (control = 61.48^ab, monensin = 67.61^a, functional oils = 69.17^a, monensin + functional oils = 58.18^b), where the feeding of both additives reduced NOP when compared to the feeding of only monensin or functional oils. Thus, based on these results, the feeding of monensin promoted greater development of rumen epithelium, which could indicate greater short-chain fatty acids absorption.