title: Hormonal growth-promotant effects on grain-fed cattle maintained under different environments.
abstract: Six steers (3/4 Charolaisx1/4 Brahman) (mean body weight 314+/-27 kg) and six spayed heifers (3/5 Shorthornx2/5 Red Angus) (mean body weight 478+/-30 kg) were used to determine the effects of climatic conditions and hormone growth promotants (HGP) on respiration rate (RR; breaths/min), pulse rate (beats/min), rectal temperature (RT; degrees C), and heat production (HP; kJ). Cattle were exposed to the following climatic conditions prior to implantation with a HGP and then again 12 days after implantation: 2 days of thermoneutral conditions (TNL) [21.9+/-0.9 degrees C ambient temperature (T(A)) and 61.7+/-22.1% relative humidity (RH)] then 2 days of hot conditions [HOT; 29.2+/-4 degrees C (T(A)) and 78.3+/-13.2% (RH)], then TNL for 3 days and then 2 days of cold conditions [COLD; 17.6+/-0.9 degrees C (T(A)) and 63.4+/-1.8% (RH); cattle were wet during this treatment]. The HGP implants used were: estrogenic implant (E), trenbolone acetate implant (TBA), or both (ET). Both prior to and following administration of HGP, RRs were lower (P<0.05) on cold days and greater (P<0.05) on hot days compared to TNL. On hot days, RTs, were 0.62 degrees C higher after compared to before implanting. Across all conditions, RTs were >0.5 degrees C greater (P<0.05) for E cattle than for TBA or ET cattle. On cold days, RTs of steers were >0.8 degrees C higher than for the heifers, while under TNL and HOT, RTs of steers were 0.2-0.35 degrees C higher than those of heifers. Prior to implantation, HP per hour and per unit of metabolic body weight was higher (P<0.05) for cattle exposed to hot conditions, when compared to HP on cold days. After implantation, HP was greater (P<0.05) on hot days than on cold days. Under TNL, ET cattle had the lowest HP and greatest feed intake. On hot days, E cattle had the lowest HP, and the highest RT; therefore, if the potential exists for cattle death from heat episodes, the use of either TBA or ET may be preferred. Under cold conditions HP was similar among implant groups.
authors.affiliation: School of Animal Studies, University of Queensland, Gatton, Queensland 4343, Australia. j.gaughan@uq.edu.au
authors.forename: J B
authors.initials: JB
authors.lastname: Gaughan
authors.forename: W M
authors.initials: WM
authors.lastname: Kreikemeier
authors.forename: T L
authors.initials: TL
authors.lastname: Mader
mesh_terms: D045930:Anabolic Agents / Q000494:pharmacology; D000818:Animals; D001831:Body Temperature / Q000187:drug effects*; D002417:Cattle / Q000502:physiology*; D003080:Cold Temperature; D004343:Drug Implants; D004435:Eating / Q000187:drug effects; D002523:Edible Grain; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D006358:Hot Temperature; D008297:Male; D012119:Respiration / Q000187:drug effects; D014204:Trenbolone Acetate / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D045930:Anabolic Agents; D004343:Drug Implants; D004958:Estradiol; D014204:Trenbolone Acetate