Body temperature is often used as an indicator of animal health status. In a series of handling experiments, tympanic temperatures (TT) were obtained in unrestrained feedlot cattle. In a January experiment (BW = 531 ± 54 kg), TT were increased (P<0.05) 0.65°C and 0.58°C by moving cattle 600 m in morning and afternoon, respectively. Moving cattle (BW = 456 ± 67 kg) 150 and 600 m in August elevated TT by 0.30°C and 0.67°C, respectively. Moving cattle (BW = 415 ± 62 kg) 900 m in June elevated (P<0.05) TT by 0.78°C. Recovery TT was determined to be the time peak TT declined to levels equal to or below control (non-moved cattle) TT. Recovery times averaged 3.5 h in the winter, but ranged from <1 h to approximately 2 h in the spring and (

Angus x crossbred heifers (270 per trial) were used in an experiment conducted over one 105-d summer and one 104-d winter feeding period. Treatments were identical for each trial and included: 1) control, 2) estrogenic implant (E), 3) trenbolone acetate implant (TBA), 4) E + TBA (ET), 5) melengestrol acetate (MGA) in the feed, and 6) ET + MGA (ETM). Each treatment was replicated in five pens, with nine heifers per pen in each season. Initial weights (mean = 384 kg, SE = 57) were the same for each season. There were no treatment x season interactions for final BW, ADG, G:F, water intake, or carcass characteristics. Heifers receiving a growth-promoting agent were 11.6 kg (SE = 4.08) heavier and gained 0.108 kg/d (SE = 0.04) more (P < 0.05) than control heifers. Heifers receiving ET gained 0.09 kg/d (SE = 0.032) more (P = 0.05) than heifers not receiving ET. Heifers receiving ET (with and without MGA) had greater G:F (P < 0.05) than control, E, and TBA heifers. Carcass weights of ET-treated heifers were greater (P < 0.05) than carcass weights for unimplanted heifers, those fed MGA only, and heifers receiving either E or TBA implants. Marbling scores were increased (P < 0.05) by feeding MGA to ET-treated heifers. Water intake was greater (P < 0.01) in the summer (31 L/d) than in the winter (18 L/ d), with no difference among implant treatments. Heifers fed in the winter had heavier carcasses, less 12th-rib fat, greater marbling scores, larger LM area, and a greater incidence of liver abscesses than heifers finished in the summer (P < 0.01). A treatment x season interaction (P = 0.07) was evident for DMI during the 35-d coldest and hottest portions of the year. Heifers fed MGA and implanted with ET tended (P = 0.07) to have greater DMI in the summer but lesser DMI in the winter. In general, differences among growth-promotant programs were relatively similar over the entire summer and in winter.

ABSTRACT:To assess the efficacy of growth-promoting agents among seasons, triiodothyronine (T 3 ), thyroxine (T 4 ), 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 T 3 , T 4 , and PUN peaked on d 56. In the summer, IGF-I levels increased from d 0 to 28 and remained elevated throughout the study.

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.

Two groups of 108 Angus cross yearling heifers were utilised to determine the effects of growth-promoting agents on behaviour, when utilised under thermoneutral, hot and cold environmental conditions. Pens of heifers were observed throughout the day for feed intake pattern via bunk score, panting (hot), degree of bunching and shivering (cold). For cattle that were exposed to cold stress, feed intake was greater earlier in the day, with the majority of the feed consumed by 1500 hours and little or no feed consumed at night, while the opposite trend occurred under heat stress. Nearly 46% of the pens containing heat-stressed heifers had greater than 50% of their feed remaining in the bunk at 1900 hours. Pens of heifers exposed to thermoneutral conditions had a tendency to show elevated panting scores at 0700 hours, while heifers exposed to hot conditions did not, indicating some acclimation to heat stress had already taken place for the heifers exposed to hot conditions. Panting score did not appear to be affected by growth-promoting treatment. Under cold stress, 100% of the cattle displayed bunching behaviour throughout the day, while under hot and thermoneutral conditions, maximum bunching (25 to 30%) occurred at 1500 hours. Within an environmental condition, trenbolone acetate cattle tended to bunch more under thermoneutral and hot conditions, particularly in the morning, when compared with other treatment groups; control and oestrogen-treated cattle tended to bunch less under the same conditions, regardless of the time of day. Although data were inconclusive as to overall effects of growth promotants on mitigating cold stress, shivering scores were increased with a more aggressive growth-promoting treatment (P < 0.05). These findings suggest that if growth promotants, which are used in feedlot cattle, impact cattle exposed to adverse environmental conditions, then they tend to be more effective at mitigating heat stress than cold stress.