OMASAL MORPHOLOGY OF DAIRY COWS FED WITH HIGH OR LOW GRAIN CONTENT DIET PRIOR PARTURITION

ABSTRACT Little is known about the morphological response of the omasum in dairy cows that consume a high-energy diet pre-partum. The aim of this study was to investigate whether a transitional diet with high grain content is able to induce changes in omasum morphology. Six weeks before the expected calving, four Holstein cows were fed a standardization diet, and four weeks before delivery, the cows were fed a diet with high grain content (HGC) or low (LGC) grain content. After calving, all of the cows were fed a high energy lactation diet. The cows that were fed the HGC diet pre-partum had higher dry matter and nutrient intake than the cows that were fed the LGC diet. The mitotic index of the omasum epithelium was higher than the mitotic index in the rumen, but apparently the response to the diet stimuli was slower. In the cows that were fed the HGC diet, the omasum papillae were taller one week before parturition and two weeks post-partum. Cows that were fed the HGC diet had a thinner epithelium due to thinner non-keratinized layers of the omasum epithelium. We conclude that the omasum mucosa of dairy cows responds to the stimuli of a pre-partum HGC diet, which was indicated by the greater height of the omasum papillae and by the reduced thickness of the omasum epithelium. It seems that the mitotic index responds a little more slowly, but the response to the diet stimuli is stronger in the omasum epithelium than in the rumen. RESUMO Pouco é conhecido a respeito da resposta morfológica do omaso de vacas leiteiras que consomem dieta alta em energia no pré-parto. Este estudo visou investigar se a dieta de transição com alto teor de grãos induz mudanças na morfologia do omaso. Seis semanas antes do parto esperado, quatro vacas Holandesas foram alimentadas com uma dieta de padronização e a partir de quatro semanas antes foram alimentadas com dieta com alto (ATG) ou baixo (BTG) teor de grãos. Após o parto, todas as vacas foram alimentadas com dieta lactacional de alta energia. As vacas que foram alimentadas com ATG antes do parto tiveram maior ingestão de matéria seca e de nutrientes do que as vacas que foram alimentadas com BTG. O índice mitótico (IM) do epitélio do omaso foi mais alto do que o do rúmen, mas aparentemente a resposta ao estímulo da dieta foi mais lenta. As papilas do omaso nas vacas que foram alimentadas com ATG foram mais altas uma semana antes e duas semanas após o parto. As vacas que foram alimentadas com ATG tiveram o epitélio do omaso men