Effects of different feeding frequencies on rumen tissue histology and cell proliferation of feedlot cattle
This study, conducted at the São Paulo State University feedlot, Dracena Campus, Brazil, was designed to determine the effects of different feeding frequencies on rumen tissue histology and cell proliferation of rumen papillae of feedlot cattle. The experiment was designed as a completely randomized block, replicated 12 times, in which 48 18-mo-old yearling Nellore bulls (358.2±19.4 kg) were fed in individual pens for 94-d according to the following treatments: 1) feeding one time daily (1x; 0800), 2) feeding two times daily (2x; 0800 and 1400), 3) feeding three times daily (3x; 0800, 1100 and 1400), and 4) feeding four times daily (4x; 0800, 1100, 1400 and 1700). The adaptation program consisted of ad libitum feeding of two adaptation diets over period of 14-d with concentrate level increasing from 60% to 86% of diet DM. The finishing diet contained: 67.0% cracked corn grain, 14.0% sugarcane bagasse, 9.0% soybean hulls, 5.5% soybean meal, 4.0% supplement containing 30% of urea, and 0.5% limestone (DM basis). At harvest, a 1-cm2 fragment of each rumen was collected from ventral sac for histological assessment. Histological sections were stained with hematoxylin and eosin, embedded in paraffin wax, and sectioned. Morphometric measurements, such as papillae surface area, papillae height, papillae width, keratinized layer thickness, and mitotic index, were determined in four papillae per animal using computer-aided light microscope image analysis. In addition, cell proliferation was determined by immunohistochemistry technique using the monoclonal mouse anti-proliferating cell nuclear antigen. Orthogonal contrasts were used to assess linear, quadratic, and cubic relationship between feeding frequency and the dependent variable. Feeding frequency did not affect (P > 0.10) papillae width, keratinized layer thickness, and cell proliferation. However, as feeding frequency increased, papillae surface area in cm2 (1x = 1.11; 2x = 1.11; 3x = 1.29; 4x = 1.22), papillae height in mm (1x = 2.85; 2x = 2.79; 3x = 3.29; 4x = 3.14), and mitotic index, as % of basal cells (1x = 9:12; 2x = 10.60; 3x = 12.85; 4x = 12.63) linearly increased (P < 0.05). Papillae surface area and papillae height were also affected (P = 0.01) cubically as feeding frequency increased. Thus, increasing feeding frequencies affected rumen tissue histology variables. In a practical way, feeding yearling Nellore bulls three times daily seems to be the most feasible option.
Keywords: mitosis, Nellore, papillae