Effects of Growth-Promoting Agents and Season on Blood Metabolites and Body Temperature In Heifers

Authors

Terry L. Mader, University of Nebraska-LincolnFollow
W. M. Kreikemeier, Alltech Biotechnology, Heartland Regional Office, Columbus, NE

Document Type

Article

Date of this Version

2006

Comments

Published in J. Anim. Sci. 2006. 84:1030–1037. Copyright (c) 2006 American Society of Animal Science. Used by permission.

Abstract

To assess the efficacy of growth-promoting agents among seasons, triiodothyronine (T₃), thyroxine (T₄), plasma urea nitrogen (PUN), IGF-I, and tympanic temperature (TT) were measured in summer and winter studies. Heifers (n = 9/pen) were allotted to 12 pens in both December and June. Pens were assigned to 1 of 6 growth promotant treatments: control (no growth promotant), estrogenic implant (E), trenbolone acetate implant (TBA), E + TBA (ET), melengestrol acetate (MGA), and ET + MGA (ETM). Blood samples were collected from 4 heifers per pen per study on d 0, 28, 56, and 84 via jugular puncture. Near the midpoint of both studies, TT were obtained from the heifers. There was a season by sample day interaction for all blood metabolites (P < 0.05). During the winter, IGF-I levels peaked on d 28, whereas T₃, T₄, and PUN peaked on d 56. In the summer, IGF-I levels increased from d 0 to 28 and remained elevated throughout the study. Season by growth promotant interactions (P < 0.05) indicated that in the winter ET increased T₃, whereas TBA alone decreased both T₃ and T₄, compared with control, or ET, and ETM treatment groups. Across seasons, treatments ET and ETM increased (P < 0.05) IGFI and decreased (P < 0.05) PUN. However, E, TBA, and MGA alone had no effect on IGF-I or PUN concentrations. The maximum TT was greater (P < 0.01) in the summer than in the winter, whereas the minimum TT was lower (P < 0.01) in the summer. Mean TT did not differ among growth-promoting treatments. However, in the summer and over both seasons, the maximum TT was lower (P < 0.05) in E-, MGA-, and ETM-treated heifers. Although limited growth promotant by season interactions existed, changes in blood metabolite levels resulting from the use of growth promotants do not appear to influence seasonal changes in body temperature as measured by TT.