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Department of Animal Science and Food Technology, Texas Tech University, Lubbock 79409-2141
3 Correspondence:
E-mail:
mgalyean{at}ttacs.ttu.edu.
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Key Words: Behavior • Feedlots • Heat Stress • Performance • Physiology • Shade
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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The experiment was conducted at the Texas Tech University Burnett Center in New Deal, TX, using soil-surfaced pens with a stocking rate (13.2 m2/animal) typical for commercial feedlots in the area. The study was conducted from June 13 until October 20, 2000. Animals were housed and used in accordance with the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999), and the Texas Tech University Animal Care and Use Committee approved the project.
Twelve soil-surfaced pens each with a pen area of 186 m2 were used. Fences were metal pipe and T-posts connected with steel cables. The concrete feed bunk in each pen was 4.9 m long and located on the north end of the pen, allowing for approximately 35 cm of bunk space/animal. A water trough, with float-activated water supply, was located on the south end of each pen. Treatments were 1) no shade and 2) shade, with six pens assigned to each treatment. The roof of the shade was galvanized aluminum/zinc-coated steel sheets (Galvalume; Bethlehem Steel, Jackson, MI) resting on 20.3-x 6.35-cm purlin construction. The roof was mounted on 7.30-cm diameter steel pipes. The height of the shade was 4 m on the north and 3.66 m on the south, which provided a slope for precipitation runoff. The orientation of the shade was east-to-west, with a length of 36.6 m and a width of 4.9 m, providing 2.12 m2 shade/heifer. Shaded pens were contiguous, as were the unshaded pens.
Approximately 2 wk before the study began, heifers to be used in the experiment were implanted with Synovex H (200 mg of testosterone propionate and 20 mg of estradiol benzoate; Fort Dodge, Websa, FL), and received injections of Vision 7 (seven-way clostridial; Bayer Animal Health, Kansas City, MO), IBR plus Lepto (Pfizer Animal Health, Exton, PA), and Ivomec Plus (Merial, Iselin, NJ). Heifers were initially fed a 65% concentrate diet.
One hundred sixty-eight heifers were used in the experiment, of which 132 were Angus-crossbred (black-hair coat) and 36 were Charolais-crossbred (white-hair coat) heifers. Heifers were blocked by BW, and assigned randomly to the six pens per treatment, with three Charolais-crossbred and 11 Angus-crossbred heifers per pen. At the time the experiment started, the heifers were receiving an 80% concentrate diet, and they were switched to the final 90% concentrate diet (Table 1
) on d 13 of the study. On d 56 of the study, heifers were implanted with Revalor H (140 mg of trenbolone acetate and 14 mg of estradiol; Intervet Animal Health, Millsboro, DE).
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Weather data (Table 2), including precipitation, wind speed and direction, relative humidity, solar radiation, and temperature were recorded at the site by a weather monitoring station (Campbell Scientific 21X Micro Logger, North Logan, UT). Ground moisture in each pen was measured on three dates during the study (July 10, August 10, and September 10, 2000) by collecting pen surface material samples (approximately 500 g/sample; sampled at a 10-cm depth from the top surface layer), which were dried (100°C) in a forced-air oven for 24 h to determine the DM content. Ground surface temperature also was measured using an infrared thermometer (Cole Parmer, Vernon Hills, IL) on the same three dates as ground moisture. Both ground moisture and ground temperature measurements were collected from under the shaded area (center of the pen) and in the corresponding location in the unshaded pens at approximately 1300.
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All BW measurements were obtained using a single animal scale (C&S Single Animal Chute, Garden City, KS), set on four load cells (Rice Lake Weighing Systems, Rice Lake, WI) that was calibrated with 454 kg of weight before every weigh day. Cattle were weighed on d 0, 28, 56, 84, 112, and 121 of the study. Cattle were provided ad libitum access to feed. Feed bunks were evaluated daily at approximately 0800; feed remaining in the bunk was estimated, and the daily allotment of feed was determined. The feed was fed once daily at approximately 1000, and water was available at all times. The feed delivered to each pen was measured to the nearest 0.45 kg, and DM content of the feed (grab samples collected once per week from the bunk at the time of feeding) was determined to calculate DMI. Chemical components (ash, CP, ADF, Ca, and P) of the 90% concentrate diet were determined using AOAC (1990) procedures. On d 121, heifers were weighed and then transported to a commercial abattoir.
Carcass Traits
Personnel from West Texas A&M University Beef Carcass Research Center obtained carcass measurements from 165 heifers. The three missing animals (all from unshaded pens) were removed from the study for illnesses and(or) injuries unrelated to the treatment. Personnel gathering carcass data were blind to the treatments. Carcasses were chilled at -3°C for approximately 36 h after slaughter, at which time carcass characteristics and USDA quality and yield grades were obtained. Carcass measurements included percentage of kidney, pelvic, and heart fat; fat thickness; marbling score; longissimus muscle area; and hot carcass weight. Incidence of dark-cutting beef also was determined according to USDA standards.
Physiology
Respiratory rates were measured on four heifers per pen once weekly from July 2 (wk 3) until September 24, 2000 (wk 14) at approximately 1500 by counting the animal’s flank movements for 1 min. Three Angus-crossbred heifers and one Charolais-crossbred heifer per pen were chosen randomly for measurement of respiration rate.
One Angus crossbred heifer per pen was randomly selected and bled to assay for immune measurements. For these 12 heifers, a blood sample (10 mL) was obtained by jugular venipuncture before feeding (between 0800 and 0900). Heparin was used as an anticoagulant. Whole blood was analyzed for total and differential white blood cell counts and neutrophil chemotaxis and chemokinesis as described by Salak-Johnson et al. (1997).
Behavior
Standing, lying, feeding, drinking, walking, agonistic, and bulling behaviors of all heifers were measured on August 21, 2000, over a 24-h period using a 10-min interval scan technique (Mitlöhner et al., 2001b). Standing was considered to be an inactive upright posture (no locomotion). Lying was defined as body contact with the ground. Feeding and drinking were defined as the head over or in the feed bunk or water trough, respectively. Walking was considered to be any change of body location within the pen. Agonistic behavior was defined as heifers fighting, and bulling was defined as heifers mounting their peers. Behaviors were measured by two trained persons by means of live observations, and the data were directly entered into a computer spreadsheet at 10-min scan intervals (Mitlöhner et al., 2001b). Data were expressed as a percentage of time of total observations and transformed (square root-arcsine) before statistical analyses.
Experimental Design and Statistical Analyses
The experiment was analyzed as a randomized complete block design. The GLM procedure in SAS (SAS Inst. Inc., Cary, NC) was used for analyses of performance, carcass, and immune measurement data, with pen was the experimental unit. The model included effects for weight block and treatment, and the residual (weight block x treatment) was used as the error term to test treatment effects. For some carcass traits (dark cutters and quality grade), the CATMOD procedure in SAS was used with categorical animal data averaged per treatment. Respiration rates, ground moisture, ground temperature, and behavior data were analyzed as a split plot with treatment and weight block in the main plot and time in the subplot. Main-plot effects were tested by block x treatment, and subplot effects were tested by the residual error. When a significant (P < 0.05) time x treatment interaction was detected, data were analyzed by time as a randomized complete block design.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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The Texas Tech University Burnett Center feedlot is situated in an area with a dry steppe climate with hot summers and mild winters. Climatic conditions during the study period were generally typical for the area, but average daily maximum temperatures for July, August, and September were somewhat higher than long-term daily maximums (Table 2
). The relative humidity throughout the months of July to September was fairly low (Table 2), as were precipitation and wind velocity.
Across the three sampling dates, percentage of ground moisture (measured in the middle of the pen) was higher in the shaded than in the unshaded pens (20% vs 14%; P < 0.05; Figure 1). Ground surface temperatures were approximately twice as high (P < 0.01) in the unshaded than in the shaded pens (directly under the shade). Ground temperature under the shade ranged from 19 to 28°C compared with 43 to 56°C in a similar location in the unshaded pens (Figure 2).
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Performance results are presented in Table 3. Initial BW (d 0) averaged 355.3 kg. The average final BW on d 121 was 11.3 kg/heifer greater (P < 0.05) for shaded than for unshaded heifers. Daily DMI for the 121-d feeding period was 2.9% greater (P < 0.01) for shaded than for unshaded heifers, and the ADG was 6.1% greater (P = 0.055) for shaded than for unshaded heifers. The gain:feed ratio did not differ between treatments (P = 0.26), and the dietary NEm and NEg concentrations calculated from performance data (Table 3) did not differ (P > 0.57) between the two treatments. Net energy values were calculated from performance data by a quadratic solution of NRC (1996) net energy equations using the BW (4% shrinkage) and DMI data in Table 3. Calculated NEg values were on average approximately 95% of the NRC (1996) tabular values (Table 1) for the 90% concentrate diet.
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The hot carcass weights of shaded heifers were 7.3 kg greater than those of unshaded heifers (P = 0.095; Table 4). Fat thickness, marbling score, LMA, and KPH did not differ (P > 0.10) between treatments; however, USDA yield grade was higher (P < 0.01) in carcasses of shaded than of unshaded heifers. The distribution of quality grades in shaded and unshaded heifer carcasses differed (P < 0.05), with 44% vs 64% for Select and 56% vs 36% for Choice. These differences in quality grade could be accounted for in large part by the difference (P < 0.05) in the percentage of dark-cutting carcasses between treatments, with 8.3% dark-cutting carcasses in the shaded heifer carcasses and 19.8% in the unshaded heifer carcasses.
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The average respiration rate (Figure 3) was consistently higher (P < 0.05) for unshaded than for shaded heifers. At the end of September, respiration rates in both treatments dropped from their higher summer values, but remained different (P < 0.05) between treatments.
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) than unshaded heifers. Neutrophil chemotaxis and chemokinesis did not differ between treatments, nor did other blood measurements.
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Observations indicated that shaded heifers were under the shade extensively from 0900 until 1730. Cattle followed the shade line and avoided standing in the direct sunlight (Figure 4). All the behaviors measured were affected by a treatment x time of day interaction (P < 0.05); hence, results are shown by time in Figure 5. No differences were noted in any of the behaviors form 0100 to 0700 or from 2200 to 2400. Shaded heifers spent more time (P < 0.05; SEM = 2.9%) standing than unshaded heifers at 1000; however, unshaded heifers had greater (P < 0.05) standing behavior at 1200 (SEM = 5.7%) and 1500 (SEM = 3.6%). Lying behavior was greater (P < 0.05) for shaded than for unshaded heifers at 0800, 1200, and 1500 (SEM = 3.1, 7.0, and 4.5%, respectively) and less (P < 0.05) for shaded than unshaded heifers at 1000 (SEM = 2.8%). Walking behavior did not differ between treatments, except at 1100, when walking was greater (P < 0.05; SEM = 0.7%) in unshaded heifers than in shaded heifers. Feeding behavior was greater (P < 0.05) for shaded heifers at 0900 and 1300 (SEM = 2.6 and 1.1%, respectively), but less (P < 0.05) for shaded than unshaded heifers at 1100 (SEM = 1.0%). More (P < 0.05) drinking behavior was measured in unshaded than shaded heifers at 1300 (SEM = 0.7%), but the opposite was true (P < 0.05) at 2000 (SEM = 0.8%). Bulling behavior did not differ between treatments, except at 2100, when more (P < 0.05; SEM = 2.2%) bulling behavior was observed in unshaded than in shaded heifers. Agonistic behavior was less (P < 0.05) for shaded than for unshaded heifers at 1900 and 2000 (SEM = 0.7 and 1.9%, respectively).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Effects of heat stress on performance are mainly a result of a decrease in DMI, which seems to occur when ambient temperatures exceed 25°C (Morrison, 1983; Hahn et al., 1992; Hahn, 1995). Such performance losses were confirmed in the unshaded heifers of the present experiment during the summer heat, whereas heifers provided with shade maintained higher performance levels.
Summer heat also seems to affect carcass quality. Kreikemeier et al. (1998) found that the highest numbers of dark cutters occurred in carcasses of cattle that were harvested in the months from July through October. They also reported an effect of month of the year on USDA quality grades, with lowest grades during the summer months. In the present study, shaded cattle had higher quality grades, which has not been reported in previous heat stress studies. The difference in quality grade largely reflected the fact that shaded heifers had less than half as many dark-cutting carcasses than unshaded heifers because marbling score did not differ between carcasses of shaded and unshaded heifers. Previous studies (Tennessen and Price, 1980; Kenny and Tarrant, 1988; Voisinet et al., 1997) have shown a relationship between the incidence of dark cutters and cattle behavior, especially agonistic and bulling behavior. The physical stress that occurs during fights or mounting is known to increase glycogenolysis in skeletal muscles, and the deficiency of glycogen at slaughter can result in dark-cutting beef (Kreikemeier et al. 1998). In the present study, shaded heifers performed less agonistic behavior during the evening (1900 and 2000), which might have been related to the decreased incidence in dark-cutting carcasses for the shaded treatment. Alternatively, the heat stress experienced by unshaded heifers might have been sufficient to increase the incidence of dark-cutting carcasses. Immune measures can be sensitive indicators of stress in animals. Blood neutrophil numbers (or percent) increase during stress (Roth and Kaeberle, 1985), and with increased stress, neutrophil chemotaxis is decreased (Salak-Johnson et al., 1997). Because shaded heifers had a lower percentage of neutrophils and a lower neutrophil:lymphocyte ratio, shade decreased the stress-induced neutrophilia found in unshaded heifers. The stress response was not severe because neutrophil migration (random or directed) as measured by chemotaxis and chemokinesis was not affected by treatments. Thus, based on the immune measures collected, unshaded cattle would have experienced mild, chronic stress that was relieved by the provision of shade.
Behavioral measurements were limited to one day in August, which was not during the hottest period of the study; however, the present data should reflect behavioral patterns that had developed over time in the two treatment groups. Shaded heifers stayed under the shade during nearly all the daylight hours, most likely because of lower radiant heat and lower ground temperatures. The prolonged time that the heifers spent under the shade led to increased soil moisture as a result of urination and defecation in this area. As noted previously, shade decreased agonistic and bulling behaviors at selected times. These behaviors are known to affect dust generation in commercial feedlots (Mitlöhner et al., 1999). Thus, the potential for the combined effects of shade on increasing ground moisture and decreasing dust-generating behaviors to provide a potential dust control method for the feedlot industry needs further study.
Although economic analyses were not conducted, effects of shade on performance were sufficiently large that it was likely cost-effective. Nonetheless, other factors that were not evaluated in our experiment, such as increased costs for pen cleaning or potential negative effects of shade during other seasons, need to be evaluated under commercial conditions.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Footnotes |
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2 Present address: Animal Science Dept., University of California, Davis, One Shields Ave., Davis, CA 95616 (E-mail: fmmitloehner{at}ucdavis.edu).
Received for publication December 3, 2001. Accepted for publication April 5, 2002.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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  N. M. Marcillac-Embertson, P. H. Robinson, J. G. Fadel, and F. M. Mitloehner Effects of shade and sprinklers on performance, behavior, physiology, and the environment of heifers J Dairy Sci, February 1, 2009; 92(2): 506 - 517. [Abstract] [Full Text] [PDF]
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 J. L. Morrow, F. M. Mitloehner, A. K. Johnson, M. L. Galyean, J. W. Dailey, T. S. Edrington, R. C. Anderson, K. J. Genovese, T. L. Poole, S. E. Duke, et al. Effect of water sprinkling on incidence of zoonotic pathogens in feedlot cattle J Anim Sci, August 1, 2005; 83(8): 1959 - 1966. [Abstract] [Full Text] [PDF]
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