Nutrition, digestion and absorption: small intestine of lactating ruminants

The anatomy and digestive and absorptive function of the small intestine of lactating ruminants, particularly the dairy cow, include a specialized anatomy and microflora to digest a variety of fibrous feedstuffs, in both pre-gastric and post-gastric fermentation structures. The rumen microbes ferment most carbohydrate to volatile fatty acids, which are primarily absorbed through the rumen wall, whilst starch not fermented in the rumen can potentially be digested to glucose absorbed by the small intestineDietary protein is primarily digested and converted to microbial protein in the rumen and then digested in the abomasum and small intestine for amino acid absorption. Dietary fats are primarily saturated due to the high hydrogen generation. Methods for quantifying digestion within the small intestine and appearance of absorbed nutrients in the veins draining it are challenging but have been used to determine digestive and metabolic functions. The intense metabolic rate of the enterocytes lining the intestinal lumen also affect the digestive physiology and metabolic functions of the animal