Responses of Growing Lambs to Abomasal Infusion of Corn Oil, Starch, Casein, and Amino Acid Mixtures

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Abstract
The effect of abomasal infusion of corn oil, starch, casein, and amino acid mixtures on long-term feed intake of growing lambs was studied in four experiments. The infusates were diluted to 750 ml with water and supplied continuously for more than 15 days. In experiment 1, lambs were fed a semipurified diet with urea as the sole source of nitrogen. Abomasal casein infusion increased dry matter intake, nitrogen retention, and liveweight gain over the water-infused lambs. When a highly digestible natural diet (3.30 kcal/g, 2.58% N) was fed, voluntary feed intake was not affected by infusion of 14 g of corn oil or 30 g of casein daily. However, when 28 g of corn oil was infused, feed intake decreased. Feed intake increased with daily infusion of 30 g or 60 g of starch or with 60 g of casein. Casein increased the concentration of essential amino acids in the plasma and, at the high level of infusion, increased nitrogen retention. Starch, at the high level of infusion, increased the concentration of glucose and the concentration of readily gluconeogenic amino acids in the plasma. Infusion of 60 g of monosodium glutamate and glycine (60:40 w/w) or 70 g of an amino acid mixture patterned after casein but devoid of methionine, threonine, and lysine, depressed feed intake and nitrogen retention. Seventy grams of a casein-like amino acid mixture increased feed intake. Feed intake of growing lambs can be affected by changes in the amount and pattern of nutrients reaching the lower portion of the digestive tract. The effect of nutritional factors on feed intake over a long period of time differs from the short-term effect.