Influence of triiodothyronine injections on calf immune response to an infectious bovine rhinotracheitis virus challenge and nitrogen balance of lambs.

Abstract

Three experiments were conducted to determine the influence of triiodothyronine (T3) or propylthiouracil (PTU) on the humoral immune response of calves challenged with infectious bovine rhinotracheitis virus (IBRV) and on nitrogen depletion and repletion of lambs deprived of feed and water for 3 d. In Exp. 1, 18 steer calves (BW 284 +/- 6 kg) challenged with IBRV were limit-fed (1.5% BW) a 60% concentrate diet and injected (s.c.) daily with alkaline saline, .4 mg of T3, or .8 mg of T3. Injections of T3 did not affect serum antibody titers to IBRV, blood leukocyte counts, or plasma free fatty acid, ceruloplasmin, and cholesterol concentrations but increased (P < .05) plasma glucose concentrations and decreased (P < .05) plasma urea N concentrations. In Exp. 2, 36 IBRV-challenged steers (BW 266 +/- 8 kg) were given ad libitum access to a 60% concentrate diet and injected (s.c.) daily with alkaline saline, .2 mg of T3, or .4 mg of T3. In contrast to Exp. 1, injections of T3 did not affect plasma glucose or urea N concentrations and reduced (P < .05) serum antibody titers to IBRV. In Exp. 3, eight wether lambs were limit-fed (600 g/d) a 36% concentrate pelleted diet and assigned to one of four treatments in a replicated 4 x 4 Latin square designed nutrient balance experiment involving periods of nutrient depletion and repletion. Treatments were as follows: 1) alkaline saline injection (s.c.), 2) 4 mg of PTU/kg BW in water, 3) .15 mg of T3 s.c. daily for 15 d, and 4) .15 mg of T3 s.c. daily for 7 d after the 3-d feed and water deprivation period. Thyroid status affected (P < .05) predeprivation N balance but did not affect N losses during the feed and water deprivation period. Retention of N during realimentation was affected (P < .05) by T3 treatment. Results of these experiments indicate that there is a complex interrelationship among stress, nutrient status, and thyroidal status and that the effects of T3 injections on immune and metabolic responses may be dependent on the nutritional status of the animal.(ABSTRACT TRUNCATED AT 250 WORDS)