Effect of Thyroid Status on Digestive Tract Fill and Flow Rate of Undigested Residues in Cattle

Abstract

Retention of feed residues in the digestive tract was determined in 16 thyroid intact cows and 12 cows with severe iodine-131 thyroid irradiation damage, 4 of which had been fed 8 g thyroprotein daily for 60 days. Recoveries during 6 to 10 daily doses of a nonabsorbed marker (cerium-141, cerium-144 praseodymium-144, or scandinm-46) in feces were: thyroid intact cows, 76.6; thyroid damaged cows, 54.4; and thyroid damaged cows fed thyroprotein, 78.470 of the total dose. Corresponding recoveries from the digestive tract at slaughter were marker, 21.5, 43.5, and 18.95 of the total dose and dry matter, 1.6, 2.5, and 1.7 kg per 10O kg body weight. Single oral doses of cerium-144 praseodymium-144 were used as a marker to follow movement of feed residues through digestive tracts of two intact and two thyroid damaged cows. The flow rate constant for thyroid damaged cows was less than half that for intact cows. Thyroprotein fed daily for 70 days raised plasma thyroxine to the normal range, increased feed intake, and reduced feed retention to near normal in thyroid damaged cows. Thyroprotein caused only slight changes in cows with previously normal thyroid function.