Increasing shade area in feedlot heifers during heat stress: physiological and performance parameters.

Heat stress is a great challenge for feedlot operations established in arid zones. The aim of this study was to evaluate if increasing shade area in the pen improved physiological and productive variables in feedlot heifers under hot climate. A total of 510 European and Zebu heifers were randomly assigned to six pens which were divided in two treatments: (1) three pens with 100 heifers each with a shade area of 2.7 m2/head (control group [C]); and (2) three pens with 70 heifers each with a shade area of 3.7 m2/head (treated group [T]). Physiological variables respiratory frequency (RF) and body surface temperature (BST) of several anatomic regions were taken from 30 heifers per treatment (i.e., 10 heifers/pen). Feed intake on pen basis was recorded weekly and heifers were individually weighted on days 1, 26, and 66 of the study to calculate performance variables. Relative humidity (RH) and ambient temperature (AT) were recorded and used to estimate the temperature-humidity index (THI). Data was analyzed with analysis of variance. The average THI during the study was 81.7 units, which was categorized as dangerous heat stress. In both shaded areas, European heifers showed higher (P < 0.05) RF than Zebu heifers. In the afternoon, the temperature of head, neck, loin, paddle, and belly was higher (P < 0.05) in C compared with T. Heifers under T showed better (P < 0.05) daily weight gain (DWG), total weight gain (TWG), feed conversion (FC), and feed efficiency (FE) than heifers in C, with no effect on dry matter intake (DMI). Results indicate that during hot summer months, Zebu showed more tolerance to heat stress than European heifers; however, heifers under a shade area of 3.7 m2/head had better productive performance than those under a shade area of 2.7 m2/head during the finishing phase of the feedlot. Increasing the shade area in the finishing phase of beef cattle on feedlot improved some physiological and productive responses during heat stress.

Evaluation of the efficacy of Grofactor, a beta-adrenergic agonist based on zilpaterol hydrochloride, using feedlot finishing bulls.

Beta-adrenergic agonists (ß-AA) have been shown to positively impact finishing performance and some carcass traits of feedlot cattle. Our objective was to evaluate the efficacy of a ß-AA on the basis of zilpaterol hydrochloride (Grofactor, Laboratorios Virbac México, Guadalajara, Mexico) on growth and DMI, carcass characteristics, and meat quality of finishing bulls. Forty-five bulls (75% 25% ) initially weighing 448.7 ± 2.58 kg were blocked by BW and randomly assigned to 1 of 3 diets, using pens of 3 animals, in a randomized complete block design: 1) daily feeding without ß-AA in the basal diet (Control), 2) daily feeding with 0.15 mg/kg BW of Grofactor added to the basal diet (ZHG), or 3) daily feeding with 0.15 mg/kg BW of Zilmax (MSD Salud Animal México, Mexico City, Mexico) added to the basal diet (ZHZ). The duration of the feeding period was 30 d with a subsequent 4-d withdrawal period. Compared with Control bulls, the group fed ZHG had a 12% better ( < 0.025) G:F ratio, and their final BW ( 0.094) and ADG ( 0.084) tended to be enhanced. Feedlot performance of ZHG and ZHZ bulls was similar, although the DMI was ∼4% lower ( 0.05) in ZHG bulls vs. the ZHZ and Control groups. The HCW ( 0.001) and dressing percentage ( 0.015) were higher by 20 kg and 3%, respectively, in ZHG bulls vs. Control bulls. The KPH fat was lower ( 0.007) in bulls fed ZHG than in nonsupplemented bulls, but other carcass characteristics were not different in the ZHG and ZHZ bulls, and noncarcass components were not affected by ZHG or ZHZ supplementation. At 48 h postmortem, ZHG bulls had lower ( 0.007) water holding capacity and trended toward ( 0.06) increased chroma and reduced pH ( 0.09) compared to Control bulls. However, compared to ZHZ bulls, ZHG bulls had higher ( 0.02) chroma and a trend ( 0.08) toward increased hue angle. At 14 d postmortem, meat quality variables did not differ between the 3 groups of bulls. Supplementation of ZH Grofactor improved feedlot performance and some carcass characteristics of finishing bulls without affecting meat quality. The effects of Grofactor on feedlot performance, carcass traits, and meat quality were similar to those of Zilmax.

Effects of fat and/or methionine hydroxy analog added to a molasses-urea-based supplement on ruminal and postruminal digestion and duodenal flow of nutrients in beef steers consuming low-quality lovegrass hay.

Five crossbred beef steers (initial BW = 338.6 ± 7.8 kg) fitted with ruminal and duodenal cannulas were used in a 5 × 5 Latin square design experiment to evaluate the effects of methionine hydroxy analog (MHA) and/or yellow grease (fat) added to a molasses-urea-based supplement on intake and characteristics of digestion. Steers were fed low-quality hay (long-stem lovegrass : 3.3% CP, 76.8% NDF; DM basis) ad libitum and supplemented with 0.91 kg/d (as fed) of 1 of 4 supplements in a 2 × 2 + 1 factorial arrangement of treatments. Supplemental treatments were 1) control (no supplement, NC); 2) molasses-urea liquid supplement (U); 3) U containing (as-fed basis) 1.65% MHA (UM); 4) U containing (as-fed basis) 12% fat (UF); and 5) U containing (as-fed basis) 1.65% MHA and 12% fat (UMF). Total and forage OM intake (kg/d and as % of BW) increased ( < 0.01) with molasses-urea, decreased ( ≤ 0.04) with MHA, and were not affected ( = 0.61) with fat supplementation. Total tract NDF digestibility increased ( = 0.01) with molasses-urea supplementation, and was less ( = 0.01) for fat than for nonfat supplementation. Total and microbial N flowing to the duodenum increased ( = 0.01) with molasses-urea supplementation. Although, total N flowing to duodenum was not affected ( = 0.27), microbial N decreased ( = 0.01), and nonammonia nonmicrobial N (NANMN) increased ( = 0.01) with fat supplementation. Extent of in situ OM and NDF digestibility at 96 h increased ( = 0.01) with molasses-urea supplementation, but were not affected ( ≥ 0.14) by either MHA or fat supplementation. Duodenal flow of total AA, essential AA, and nonessential AA increased ( ≤ 0.02) with molasses-urea supplementation. Total and nonessential serum AA concentration decreased ( < 0.01) with molasses-urea supplementation. Total ruminal VFA concentration increased ( = 0.01) with molasses-urea supplementation, and was not affected ( ≥ 0.14) by MHA or fat supplementation. Fat can be used in molasses-urea liquid supplements for cattle consuming low-quality forage to increase energy intake without negatively affecting forage intake or characteristics of digestion. However, adding MHA did not further improve the response to urea supplementation of cattle consuming low-quality forage. Conversely, the inclusion of MHA on urea supplement decreased forage intake.

Effects of seasonal ambient heat stress (spring vs. summer) on physiological and metabolic variables in hair sheep located in an arid region.

Twenty Dorper × Pelibuey primiparous ewes were used to evaluate effects of seasonal ambient heat stress (i.e., spring vs. summer) on physiological and metabolic responses under production conditions in an arid region. Ten ewes experiencing summer heat stress (i.e., temperature = 34.8 ± 4.6 °C; THI = 81.6 ± 3.2 units) and 10 under spring thermoneutral conditions (temperature = 24.2 ± 5.4 °C; THI = 68.0 ± 4.8 units) were corralled together to measure rectal temperature, respiratory frequency, and skin temperatures at 0600, 1200, 1800, and 2400 h on four occasions over 40 days. Blood metabolite and electrolyte concentrations were also measured at 0600 and 1800 hours. Data were analyzed with a completely randomized design using repeated measurements in time. Rectal and skin temperatures, as well as respiratory frequency, were higher (P < 0.01) in summer than spring at all measured days. Blood serum glucose, cholesterol, triglycerides, and chlorine concentrations were lower (P < 0.01) in summer than spring at 0800 and 1800 hours. In contrast, summer heat stress increased (P < 0.01) blood urea and potassium concentrations at 0800 and 1800 hours. Compared with spring thermoneutral conditions, summer heat stress affected the physiological and metabolic status of hair breed ewes in an arid region, which included blood metabolite and electrolyte adjustments to efficiently cope with summer heat stress.