Influence of the type of fat in milk replacers on hydrolysis and digestion by the pre‐ruminant calf

Abstract Pre‐ruminant Friesian calves were fed milk replacers containing three different fat sources to observe their effect on abomasal outflow, triglyceride hydrolysis and nutritive value. The calves were fitted with re‐entrant cannulae in the duodenum and ileum. The milk replacers were prepared by homogenising 30% butterfat, tallow or soya‐bean oil with skim milk prior to spray‐drying. These milk replacers (500 g), and also skim milk, were fed once daily dissolved in 3500 ml of water. Total collections of abomasal and ileal outflow were made for 24 h periods. There were no appreciable differences in abomasal emptying of fresh matter, dry matter, total fat, or in the pH of the digesta when calves received milk replacers containing butterfat or tallow, but some inhibition of gastric emptying occurred when skim milk was fed. The extent of hydrolysis of the fats which occurred in the abomasum, as evidenced from free fatty acid concentrations in the abomasal fat, decreased in the order: butterfat > soya‐bean > tallow. There was an inverse relationship between the chain length of the fatty acids and their rate of hydrolysis. Extensive biohydrogenation in the large intestine appeared to occur only when the highly unsaturated soya‐bean oil was fed. The mean apparent digestibilities of the total dietary fats were: butterfat, 95.0%; tallow, 85.3% and soya‐bean oil, 93.9%. Between 4–16 g more fat than was ingested flowed from the abomasum during the period 0–24 h after calves received skim milk, which represented 1–4% of the total abomasal outflow. Metabolic faecal fat excretion was 5.93 ± 2.02 g 100 g −1 faecal dry matter.