Performance and carcass characteristics of steers fed with two levels of metabolizable energy intake during summer and winter season.

Climate change is producing an increase on extreme weather events around the world such as flooding, drought and extreme ambient temperatures impacting animal production and animal welfare. At present, there is a lack of studies addressing the effects of climatic conditions associated with energy intake in finishing cattle in South American feed yards. Therefore, two experiments were conducted to assess the effects of environmental variables and level of metabolizable energy intake above maintenance requirements (MEI) on performance and carcass quality of steers. In each experiment (winter and summer), steers were fed with 1.85 or 2.72 times of their requirements of metabolizable energy of maintenance. A total of 24 crossbred steers per experiment were used and located in four pens (26.25 m2/head) equipped with a Calan Broadbent Feeding System. Animals were fed with the same diet within each season, varying the amount offered to adjust the MEI treatments. Mud depth, mud scores, tympanic temperature (TT), environmental variables, average daily gain, respiration rates and carcass characteristics plus three thermal comfort indices were collected. Data analysis considered a factorial arrangement (Season and MEI). In addition, a repeated measures analysis was performed for TT and respiration rate. Mean values of ambient temperature, solar radiation and comfort thermal indices were greater in the summer experiment as expected (P<0.005). The mean values of TT were higher in steers fed with higher MEI and also in the summer season. The average daily gain was greater during summer v. winter (1.10±0.11 v. 0.36±0.06) kg/day, also when steers were fed 2.72 v. 1.85 MEI level (0.89±0.12 v. 0.57±0.10) kg/day. In summer, respiration rate increased in 41.2% in the afternoon. In winter, muddy conditions increased with time of feeding, whereas wind speed and rainfall had significant effects on TT and average daily gain. We conclude that MEI and environmental variables have direct effects on the physiology and performance of steers, including TT and average daily gain, particularly during the winter. In addition, carcass characteristics were affected by season but not by the level of MEI. Finally, due to the high variability of data as well as the small number of animals assessed in these experiments, more studies on carcass characteristics under similar conditions are required.

Bill E. Kunkle Interdisciplinary Beef Symposium: Animal welfare concerns for cattle exposed to adverse environmental conditions.

Increasing awareness of animal welfare has become a priority in food production systems involving animals. Under normal working environments, production practices are constantly evaluated to maintain optimum levels of animal well-being. However, during periods of adverse weather, optimum conditions for animal comfort, as well as animal performance, are often compromised. In the Midwest and Great Plains states, the heat waves of 1995, 1999, 2006, 2009, 2010, and 2013 were particularly difficult on animals reared in confinement, with documented cattle losses approaching 5,000 head each year. Additionally, during the summer of 2011, nearly 15,000 head of cattle across 5 states were lost as a result of heat stress. During prolonged periods of heat stress, lower conceptions rates are observed in livestock. In addition, animals reared in confinement buildings are often compromised because of limitations in ventilation systems. Under the opposite environmental spectrum, the winters of 1992 to 1993, 1996 to 1997, 1997 to 1998, 2006 to 2007, and 2008 to 2009 caused hardship for livestock producers, particularly for those rearing animals in an outdoor environment. During the winters of 1996 to 1997 and 2008 to 2009 up to 50% of the newborn calves were lost in many areas, with over 75,000 head of cattle lost in the northern plains states. Late fall and early winter snowstorms in 1992, 1997, 2006, and 2013 resulted in the loss of over 25,000 head of cattle each year in the Great Plains region of the United States. Economic losses from reduced performance of cattle experiencing severe environmental stress likely exceed losses associated with livestock death by 5- to 10-fold. Use of alternative supplementation programs may need to be considered for livestock challenged by adverse environmental conditions. Use of additional water for consumption and cooling, shade, and/or alternative management strategies need to be considered to help livestock cope with heat stress. For animals reared outside during the winter, strategies that increase animal space and environmental buffers need to be employed to minimize effects of mud, wet conditions, and wind chill. The above-mentioned weather events suggest that there are ample opportunities for livestock producers to enhance animal welfare and minimize impact of environmental stress. Caretakers need a greater understanding of animal responses to weather challenges to help animals cope with adverse climatic conditions.

Body temperature and respiratory dynamics in un-shaded beef cattle.

In this study body temperature (BT, °C) and panting score (PS, 0-4.5; where 0 = no panting/no stress and 4.5 = catastrophic stress) data were obtained from 30 Angus steers housed outside over 120 days Steers were implanted with a BT transmitter on day -31, BT was recorded at 30-min intervals to a data logger and downloaded each day to a database. The cattle were housed in ten outdoor un-shaded pens with an earthen floor, eight of which had a pen floor area of 144 m2 (three transmitter steers plus five non-transmitter steers; 18 m2/steer) and two had an area of 168 m2 (three transmitter steers and six non-transmitter steers; 18.7 m2/steer). Only data from the transmitter steers were used in this study. The PS of the steers was obtained daily (± 15 min) at 0600 hours (AM), 1200 hours (MD) and 1600 hours (PM). At the same times climate variables (ambient temperature, black globe temperature, solar radiation, relative humidity, wind speed and rainfall) were obtained from an on-site weather station. PS observations were made from outside the pens so as not to influence cattle responses. The two closest BT values to the time when PS was obtained were downloaded retrospectively from a logger and averaged. A total of 8,352 observations were used to generate second order polynomial response curves: (AM) y = 39.08 + 0.009 x + 0.137x2 (R2 = 0.94; P < 0.001) (MD) y = 39.09 + 0.914x − 0.080x2 (R2 = 0.89; P < 0.001) and (PM) y = 39.52 + 0.790x − 0.068x2 (R2 = 0.83; P < 0.001) where y = BT (°C) and x PS. These data suggest that PS is a good indicator of body temperature. The BT at MD corresponded to slightly lower PS compared with PM, e.g., for PS 1; BT at MD = 39.1 ± 0.05 °C whereas BT at PM = 39.5 ± 0.05 °C. However during AM, BT was lower (P < 0.05) at PS 1, 2 and 2.5 compared with MD and PM. For example, when PS was 2.5 the BT at AM was 40.2 ± 0.04 °C, at MD it was 40.9 ± 0.04 °C and at PM BT was 41.1 ± 0.04 °C. When PS was 0 the BT at AM and MD were similar. The AM response curve suggests animals attempt to increase heat dissipation during the cooler AM period relative to MD and PM. Morning observation of cattle (before feeding) are crucial for effective heat load management especially on days when high heat load is expected. The MD and PM observations provide a good indication of the impact of high environmental heat load on cattle. Differences in PS between AM and PM observations suggest that more research is needed to determine the effect of night time conditions on BT, PS and overall respiratory dynamics of cattle during periods of hot weather.

The effect of myostatin genotype on body temperature during extreme temperature events.

Extreme heat and cold events can create deleterious physiological changes in cattle as they attempt to cope. The genetic background of animals can influence their response to these events. The objective of the current study was to determine the impact of myostatin genotype (MG) on body temperature during periods of heat and cold stress. Two groups of crossbred steers and heifers of unknown pedigree and breed fraction with varying percentages of Angus, Simmental, and Piedmontese were placed in a feedlot over 2 summers and 2 winters. Before arrival, animals were genotyped for the Piedmontese-derived myostatin mutation (C313Y) to determine their MG as either homozygous normal (0 copy; n = 84), heterozygous (1 copy; n = 96), or homozygous for inactive myostatin (2 copy; n = 59). Hourly tympanic and vaginal temperature measurements were collected for steers and heifers, respectively, for 5 d during times of anticipated heat and cold stress. Mean (±SD) ambient temperature for summer and winter stress events were 24.4 (±4.64) and -1.80 (±11.71), respectively. A trigonometric function (sine + cosine) with periods of 12 and 24 h was used to describe the diurnal cyclical pattern. Hourly body temperature was analyzed within a season, and fixed effects included MG, group, trigonometric functions nested within group, and interaction of MG with trigonometric functions nested within group; random effects were animal and residual (Model [I]). A combined analysis of season and group was also investigated with the inclusion of season as a main effect and the nesting of effects within both group and season (Model [C]). In both models, the residual was fitted using an autoregressive covariance structure. A 3-way interaction of MG, season, and trigonometric function periodicities of 24 h (P < 0.001) and 12 h (P < 0.02) for Model [C] indicate that a genotype × environment interaction exists for MG. For MG during summer stress events the additive estimate was 0.10°C (P < 0.01) and dominance estimate was -0.12°C (P < 0.001). During winter stress events the additive estimate was 0.10°C (P < 0.001) and dominance estimate was 0.054°C (P > 0.05). The current study illustrated that a genotype × environment interaction exists for MG and 1-copy animals were more robust to environmental extremes in comparison with 0- or 2-copy animals.

Effects of chronic heat stress on plasma concentration of secreted heat shock protein 70 in growing feedlot cattle.

Sixty Angus steers (449.2±11.0 kg) with implanted body temperature (BT) transmitters were used in a 110-d study to determine the effect of chronic stress (housing, diet, and climate) on extracellular heat shock protein 70 (eHsp70) concentration in plasma. The steers were a subset of a larger study involving 164 steers. Before the start of the study (d -31), 63 steers were implanted with a BT transmitter between the internal abdominal muscle and the peritoneum at the right side flank. Steers were housed in 20 pens (10 with shade and 10 without). Within each pen, 3 steers had a transmitter, and BT was recorded at 30-min intervals throughout the study. On d 0, 30, 60, 90, and 110, steers were weighed, BCS assessed (1 to 9 scale in which 1=emaciated and 9=obese), and 10 mL of blood from the coccygeal vein was collected for determination of inducible heat shock protein 70 (Hsp70) concentration by ELISA. Climatic variables (ambient temperature, relative humidity, solar radiation, black globe temperature, and wind speed) were obtained every 30 min from an on-site weather station. The relationship between the climatic variables and Hsp70 concentration were examined. As we failed to detect an effect of shade, all data were pooled. Mean BT over the duration of the study was 39.6±0.10°C. Mean BT was lowest (38.7±0.10°C) on d 0 and highest on d 110 (40.2°C±0.10). The Hsp70 concentration was least on d 0 (2.33±0.47 ng/mL) and greatest on d 30 (8.08±0.78 ng/mL). The Hsp70 concentration decreased from d 30 but remained above the d-0 concentrations on d 60, 90, and 110. There was a strong relationship between Hsp70 concentration and ambient temperature (r2=0.86; P<0.0001) and Hsp70 concentration and photoperiod (r2=0.94; P<0.0001) and no relationship with BT (r2=0.06; P<0.0001). When assessed with both BCS and BT, the relationship was moderate (r2=0.48; P<0.001). The relationship between Hsp70 and change in BT (BTΔ) above 38.6°C was also moderate (r2=0.54; P<0.0001). The BT at a given time does not appear to be related to Hsp70 concentration. However, Hsp70 expression may be a useful indictor for BTΔ when BT>38.6°C. The Hsp70 concentration is a reliable indicator of chronic stress but is not a reliable indicator of a single stressor when animals are exposed to multiple chronic stressors.

Effect of shade area on performance and welfare of short-fed feedlot cattle.

One hundred twenty-six Black Angus yearling heifers were used in a 119-d study to assess the effect of shade allocation (0, 2.0, 3.3, or 4.7 m(2)/animal) on the performance and welfare of feedlot cattle. Shade treatments were replicated 4 times and the no-shade treatment was replicated twice. Shade was provided by 70% solar block shade cloth, attached to a 4-m-high frame with a north-south orientation. Cattle were randomly allocated to a pen (9/pen; 19.2 m(2)/animal) within treatment. Performance was assessed using DMI, G:F, ADG, HCW, dressing percentage, and rump fat depth. Climatic data (ambient and black globe temperature, solar radiation, wind speed, relative humidity, and rainfall) were recorded. From these data, the heat load index (HLI) was calculated. When the daily maximum HLI (HLI(Max)) was <86, individual panting score (0 = no panting; 4 = open mouth, tongue extended), animal location (eating, drinking, under shade), and animal posture (standing or lying) were collected at 0600, 1200, and 1800 h. When HLI(Max) was ≥ 86, these data were collected every 2 h between 0600 and 1800 h. Feed intake was recorded weekly and water intake was recorded daily on a pen basis. When HLI(Max) was ≥ 86, mean panting score (MPS: mean of animals within treatment) was greatest (1.02; P < 0.001) for unshaded cattle compared with cattle in the shade treatments, which were similar (0.82; P = 0.81). During heat waves, the MPS of unshaded cattle was greater (2.66; P < 0.001) than that for shaded cattle. The MPS of cattle in the 2.0 m(2)/animal treatment (2.43 ± 0.13) was greater (P < 0.001) than that of cattle in the 3.3 (2.11 ± 0.13) and 4.7 m(2)/animal (2.03 ± 0.13) treatments. The MPS of cattle in the 3.3 and 4.7 m(2)/animal treatments were similar (P = 0.09). Number standing was similar (P = 0.98) between unshaded and shaded at 2.0 m(2)/animal treatments with 4.75 and 4.76 animals/pen, respectively. Fewer (P < 0.0001) were standing in the 3.3 (4.19 animals/pen) and 4.7 m(2)/animal (4.06 animals/pen) treatments. Fewer (P = 0.004) cattle were under the shade at 2.0 m(2)/animal (47.1%) compared with the number under the shade at 3.3 (53.7%) and 4.7 m(2)/animal (53.6%). Unshaded cattle had the smallest (0.085 ± 0.006) G:F ratio (P = 0.01), followed by cattle shaded at 4.7 m(2)/animal (0.104 ± 0.006; P ≤ 0.001). There was no difference (P = 0.12) between the 2.0 and 3.3 m(2)/animal treatments. There were no differences (P > 0.10) for final BW, HCW, dressing percentage, and rump fat depth. Cattle with access to shade had smaller panting scores, which suggests improved welfare, and had better feed efficiency. Shade reduced the intensity of the heat load but did not fully remove the effect of heat.

Evaluation of 2 sources of Angus cattle under South Florida subtropical conditions.

The objective of this study was to compare performance and aspects of adaptability attributes of cattle from a Florida Angus bloodline (local source from a mostly closed herd for over 50 yr) to cattle that are representative of modern Angus bloodlines (outside source) in US subtropical conditions. Embryos from both sources were transferred to Brahman-crossbred cows in South Florida, and calves (n=82) were born in 3 yr. Before weaning, summer tympanic temperatures were recorded hourly for 3 d in each year. Heifers were placed with fertile bulls until diagnosed pregnant. Traits relative to sexual maturation of bulls were recorded at 1- or 2-mo intervals until approximately 17 mo of age. Calves from outside sources had greater hip height at weaning than calves from the local source (P<0.001; 108.8 ± 0.62 and 104.7 ± 0.68 cm, respectively). Local-source calves (n=37) had greater (P=0.03) exit velocity (2.7 ± 0.3 m/s) than outside-source (n=45) calves (2.0 ± 0.29 m/s), which may be indicative of more nervous or temperamental disposition. However, no source differences were detected for other assessments of disposition (chute or pen score, P>0.8). Few source differences for minimum, maximum, or range of daily tympanic (inner ear) temperatures were detected. At 17 mo of age, outside-source heifers were heavier (P = 0.05) and had greater (P<0.001) hip height than Angus heifers from the local source. Heifers from the outside source were younger (P<0.001) at the time of their first conception (454 ± 17.5 d) than heifers from the local source (550 ± 16.9 d). Outside-source heifers also had greater (P<0.02) pregnancy and calving rates (0.7 ± 0.119 and 0.62 ± 0.125, respectively) from exposure to bulls within a year from weaning than the heifers from the local source (0.29 ± 0.089 and 0.19 ± 0.077, respectively). Bulls from the outside source were heavier (P=0.05) at 320 d of age than local-source bulls. From 14 through 17 mo of age, outside-source bulls had greater (P≤0.05) scrotal circumference and tended (P≤0.15) to be heavier than local-source bulls. There appeared to be no performance or adaptation advantages for the local-source Angus through 17 mo of age. The large source difference for age at first conception in heifers merits additional attention and comparison with cow lifetime production performance for the 2 sources.

Effects of diet type and metabolizable energy intake on tympanic temperature of steers fed during summer and winter seasons.

A summer study and a winter study were conducted using an incomplete factorial structure in a complete randomized design. Within season, the factors studied were 1) type of diet, which included 2 levels of ME, classified as either concentrate (3.04 Mcal of ME/kg) or roughage (2.63 Mcal of ME/kg) diets, and 2) daily ME intakes (MEI) of 11, 18, and 25 Mcal of ME/d for the roughage diets and 18, 25, and 32 Mcal of ME/d for the concentrate diets. In Exp. 1 (summer study), 30 steers (5 steers/treatment combination) were used to collect tympanic temperatures (TT). In Exp. 2 (winter study), 24 steers (4 steers/treatment combination) were used to collect TT. Mean TT was 0.3°C greater for summer than winter (38.9 vs. 38.6°C, respectively; P < 0.05). Steers fed diets based on concentrate tended to display greater TT than steers fed diets based on roughage. Season × diet × hour interactions were found for TT (P = 0.01). In the winter, greater TT (P < 0.05) were found from 0900 to 1400 h when an equal amount of MEI was derived from a concentrate-based vs. roughage-based diet. In cattle fed roughage-based diets during the summer, TT = 38.63 + 0.0114•MEI, whereas for cattle fed concentrate-based diets, TT = 38.69 + 0.0114•MEI. During the winter, for cattle fed a roughage-based diet, TT = 37.65 + 0.0856•MEI - 0.0018•MEI(2), whereas for cattle fed a concentrate-based diet, TT = 35.37 + 0.2635•MEI - 0.0051•MEI(2). In summary, results demonstrate that increases in the energy of the diet resulted in increases in TT. However, the response was dependent on season of the year, with a linear response in TT for summer and a quadratic response during winter.

Environmental factors affecting daily water intake on cattle finished in feedlots.

Records from 7 studies conducted during 1999 to 2005 were utilized to assess the effects of environmental factors on daily water intake (DWI) of finishing cattle. Data from unshaded feedlot pens (up to 24 pens utilized per study; 6 to 9 animals·pen(-1)) containing predominantly Angus crossbred cattle were obtained by dividing total water intake by the number of animals utilizing that waterer. Each waterer was shared by 2 pens; therefore, data were derived from a database containing 72 experimental units comprising 144 pen records. Climatic data were compiled from weather stations located at the feedlot facility. The database included daily measures of mean ambient (Ta), maximum (Tmax), and minimum (Tmin) temperature (°C), precipitation, relative humidity (%), wind speed (m•s(-1)), solar radiation (SR, W•m(-2)), and temperature-humidity index (THI), as well as DMI (kg•d(-1)) and DWI (L•d(-1)). Simple and multiple regression analyses were conducted by season and for the overall data set. Results confirmed that DWI increases during the summer (P < 0.01). When seasons were combined and analyzed by linear regression, the best predictors of DWI were THI (r(2) = 0.57), Ta (r(2) = 0.57), Tmin (r(2) = 0.56), and Tmax (r(2) = 0.54). In multiple regression analyses, smaller coefficients of determination (R(2) < 0.25) were found within summer and winter seasons. Across season, the largest R(2) (0.65) were obtained from the following prediction equations: 1) DWI = 5.92 + (1.03•DMI) + (0.04•SR) + (0.45•Tmin); and 2) DWI = -7.31 + (1.00•DMI) + (0.04•SR) + (0.30•THI). In conclusion, Ta, Tmin, and THI were found to be the primary factors that influence DWI in finishing cattle, whereas SR and DMI were found to have a smaller influence on DWI.

Effect of shade on body temperature and performance of feedlot steers.

A 120-d feedlot study using 164 Angus steers (BW = 396.7 ± 7.0 kg) was undertaken in Queensland Australia (24°84' S, 149°78' N) to determine the effect of shade on body temperature (T(B)) and performance. Cattle were allocated to 20 pens: 16 with an area of 144 m(2) (8 steers/pen) and 4 with an area of 168 m(2) (9 steers/pen). Treatments (10 pens/treatment) were unshaded (NS) vs. shaded (SH). Shade (3.3 m(2)/steer) was provided by 80% solar block shade cloth. Before the study (d -31), 63 steers were implanted (between the internal abdominal muscle and the peritoneum at the right side flank) with a T(B) transmitter. Within each pen, 3 steers had a T(B) transmitter. Individual T(B) was obtained every 30 min. The cattle were fed a feedlot diet and had ad libitum access to water. Water usage and DMI were recorded daily on a pen basis. Average daily gain and G:F were calculated on a pen basis. Climatic variables were obtained from an on-site weather station every 30 min. Individual panting scores (PS) were obtained daily at 0600, 1200, and 1600 h. From these, mean PS (MPS) were calculated for each pen. At slaughter (d 121), individual HCW, loin muscle area (LMA), rump fat depth (P8), 12th-rib fat depth, and marbling score were obtained. Mean T(B) was not affected (P > 0.05) by treatment (SH = 39.58°C; NS = 39.60°C). However, during a 21-d heat wave when cattle were exposed to a mean ambient temperature (T(AM)) > 30°C for 8 h each d (T(AM) between 0800 and 1800 h = 29.7°C, and 23.4°C between 1830 and 0730 h), the T(B) of SH steers (40.41 ± 0.10°C) was less (P < 0.01) than the T(B) of NS steers (41.14 ± 0.10°C). During this period, pen-MPS were greater (P < 0.05) for the NS cattle at all observation times. Over the first 6 d of the heat wave, MPS of NS steers at 1200 h was 2.47 (P < 0.01) vs. 1.39 for SH steers. Hip height, DMI, ADG, and G:F were greater (P < 0.05) for SH cattle. Exit BW (final BW) of SH steers (596.1 kg) was greater (P < 0.05) when compared with NS steers (578.6 kg). During the heat wave, DMI was 51% less for NS steers and 39% less for SH steers when compared with the pre-heat wave period (P < 0.01). The HCW of SH steers (315.4 ± 0.8 kg) was greater (P < 0.05) than for NS steers (321.4 ± 0.8 kg). No treatment differences (P > 0.05) were found for LMA, P8, or marbling score. Access to shade improved (P < 0.05) ADG and G:F, increased HCW, and decreased MPS; however, shade did not completely eliminate the impact of high heat load.

A comprehensive index for assessing environmental stress in animals.

Numerous models and indices exist that attempt to characterize the effect of environmental factors on the comfort of animals and humans. Heat and cold indices have been utilized to adjust ambient temperature (Ta) for the effects of relative humidity (RH) or wind speed (WS) or both for the purposes of obtaining a "feels-like" or apparent temperature. However, no model has been found that incorporates adjustments for RH, WS, and radiation (RAD) over conditions that encompass hot and cold environmental conditions. The objective of this study was to develop a comprehensive climate index (CCI) that has application under a wide range of environmental conditions and provides an adjustment to Ta for RH, WS, and RAD. Environmental data were compiled from 9 separate summer periods in which heat stress events occurred and from 6 different winter periods to develop and validate the CCI. The RH adjustment is derived from an exponential relationship between Ta and RH with temperature being adjusted up or down from an RH value of 30%. At 45 degrees C, the temperature adjustment for increasing RH from 30 to 100% equals approximately 16 degrees C, whereas at -30 degrees C temperature adjustments due to increasing RH from 30 to 100% equal approximately -3.0 degrees C, with greater RH values contributing to a reduced apparent temperature under cold conditions. The relationship between WS and temperature adjustments was also determined to be exponential with a logarithmic adjustment to define appropriate declines in apparent temperature as WS increases. With this index, slower WS results in the greatest change in apparent temperature per unit of WS regardless of whether hot or cold conditions exist. As WS increases, the change in apparent temperature per unit of WS becomes less. Based on existing windchill and heat indices, the effect of WS on apparent temperature is sufficiently similar to allow one equation to be utilized under hot and cold conditions. The RAD component was separated into direct solar radiation and ground surface radiation. Both of these were found to have a linear relationship with Ta. This index will be useful for further development of biological response functions, which are associated with energy exchange, and improving decision-making processes, which are weather-dependent. In addition, the defined thresholds can serve as management and environmental mitigation guidelines to protect and ensure animal comfort.

Assessing the heat tolerance of 17 beef cattle genotypes.

Cattle production plays a significant role in terms of world food production. Nearly 82% of the world's 1.2 billion cattle can be found in developing countries. An increasing demand for meat in developing countries has seen an increase in intensification of animal industries, and a move to cross-bred animals. Heat tolerance is considered to be one of the most important adaptive aspects for cattle, and the lack of thermally-tolerant breeds is a major constraint on cattle production in many countries. There is a need to not only identify heat tolerant breeds, but also heat tolerant animals within a non-tolerant breed. Identification of heat tolerant animals is not easy under field conditions. In this study, panting score (0 to 4.5 scale where 0 = no stress and 4.5 = extreme stress) and the heat load index (HLI) [HLI(BG<25°C) = 10.66 + 0.28 × rh + 1.30 × BG - WS; and, HLI (BG> 25°C) = 8.62 + 0.38 × rh + 1.55 × BG - 0.5 × WS + e((2.4 - WS)), where BG = black globe temperature ((o)C), rh = relative humidity (decimal form), WS = wind speed (m/s) and e is the base of the natural logarithm] were used to assess the heat tolerance of 17 genotypes (12,757 steers) within 13 Australian feedlots over three summers. The cattle were assessed under natural climatic conditions in which HLI ranged from thermonuetral (HLI < 70) to extreme (HLI > 96; black globe temperature = 40.2°C, relative humidity = 64%, wind speed = 1.58 m/s). When HLI > 96 a greater number (P < 0.001) of pure bred Bos taurus and crosses of Bos taurus cattle had a panting score ≥ 2 compared to Brahman cattle, and Brahman-cross cattle. The heat tolerance of the assessed breeds was verified using panting scores and the HLI. Heat tolerance of cattle can be assessed under field conditions by using panting score and HLI.

Tympanic temperature in confined beef cattle exposed to excessive heat load.

Angus crossbred yearling steers (n = 168) were used to evaluate effects on performance and tympanic temperature (TT) of feeding additional potassium and sodium to steers exposed to excessive heat load (maximum daily ambient temperature exceeded 32°C for three consecutive days) during seasonal summer conditions. Steers were assigned one of four treatments: (1) control; (2) potassium supplemented (diet containing 2.10% KHCO3); (3) sodium supplemented (diet containing 1.10% NaCl); or (4) potassium and sodium supplemented (diet containing 2.10% KHCO3 and 1.10% NaCl). Overall, additional KHCO3 at the 2% level or NaCl at the 1% level did not improve performance or heat stress tolerance with these diet formulations. However, the addition of KHCO3 did enhance water intake. Independent of treatment effects, TT of cattle displaying high, moderate, or low levels of stress suggest that cattle that do not adequately cool down at night are prone to achieving greater body temperatures during a subsequent hot day. Cattle that are prone to get hot but can cool at night can keep average tympanic temperatures at or near those of cattle that tend to consistently maintain lower peak and mean body temperatures. In addition, during cooler and moderately hot periods, cattle change TT in a stair-step or incremental pattern, while under hot conditions, average TT of group-fed cattle moves in conjunction with ambient conditions, indicating that thermoregulatory mechanisms are at or near maximum physiological capacity.

Effects of sodium chloride and fat supplementation on finishing steers exposed to hot and cold conditions.

Three studies were conducted to evaluate the effects of supplemental fat and salt (sodium chloride) on DMI, daily water intake (DWI), body temperature, and respiration rate (RR) in Bos taurus beef cattle. In Exp. 1 and 2, whole soybeans (SB) were used as the supplemental fat source. In Exp. 3, palm kernel meal and tallow were used. Experiment 1 (winter) and Exp. 2 (summer) were undertaken in an outside feedlot. Experiment 3 was conducted in a climate-controlled facility (mean ambient temperature = 29.9 degrees C). In Exp. 1, three diets, 1) control; 2) salt (control + 1% sodium chloride); and 3) salt-SB (control + 5% SB + 1% sodium chloride), were fed to 144 cattle (BW = 327.7 kg), using a replicated 3 x 3 Latin square design. In Exp. 2, 168 steers (BW = 334.1 kg) were used. In Exp. 2, the same dietary treatments were used as in Exp. 1, and a 5% SB dietary treatment was included in an incomplete 3 x 4 Latin square design. In Exp. 3, three diets, 1) control; 2) salt (control + 0.92% NaCl); and 3) salt-fat (control + 3.2% added fat + 0.92% NaCl) were fed to 12 steers (BW = 602 kg) in a replicated Latin square design. In Exp. 1, cattle fed the salt-SB diet had elevated (P < 0.05) tympanic temperature (TT; 38.83 degrees C) compared with cattle fed the control (38.56 degrees C) or salt (38.50 degrees C) diet. In Exp. 2, cattle fed the salt and salt-SB diets had less (P < 0.05) DMI and greater (P < 0.05) DWI than cattle in the control and SB treatments. Cattle fed the salt-SB diet had the greatest (P < 0.05) TT (38.89 degrees C). Those fed only the salt diet or only the SB diet had the least (P < 0.05) TT, at 38.72 and 38.78 degrees C, respectively. Under hot conditions (Exp. 3), DMI of steers fed the salt and salt-fat diets declined by approximately 40% compared with only 24% for the control cattle. During hot conditions, DWI was greatest (P < 0.05) for steers on the salt-fat diet. These steers also had the greatest (P < 0.05) mean rectal temperature (40.03 +/- 0.1 degrees C) and RR (112.7 +/- 1.7 breaths/min). The RR of steers on the control diet was the least (P < 0.05; 98.3 +/- 1.7 breaths/min). Although added salt plus fat decreased DMI under hot conditions, these data suggest that switching to diets containing the combination of added salt and fat can elevate body temperature, which would be a detriment in the summer but a benefit to the animal during winter. Nevertheless, adding salt plus fat to diets resulted in increased DWI under hot conditions. Diet ingredients or the combination of ingredients that can be used to regulate DMI may be useful to limit large increases in DMI during adverse weather events.

A new heat load index for feedlot cattle.

The ability to predict the effects of extreme climatic variables on livestock is important in terms of welfare and performance. An index combining temperature and humidity (THI) has been used for more than 4 decades to assess heat stress in cattle. However, the THI does not include important climatic variables such as solar load and wind speed (WS, m/s). Likewise, it does not include management factors (the effect of shade) or animal factors (genotype differences). Over 8 summers, a total of 11,669 Bos taurus steers, 2,344 B. taurus crossbred steers, 2,142 B. taurus x Bos indicus steers, and 1,595 B. indicus steers were used to develop and test a heat load index (HLI) for feedlot cattle. A new HLI incorporating black globe (BG) temperature ( degrees C), relative humidity (RH, decimal form), and WS was initially developed by using the panting score (PS) of 2,490 Angus steers. The HLI consists of 2 parts based on a BG temperature threshold of 25 degrees C: HLI(BG>25) = 8.62 + (0.38 x RH) + (1.55 x BG) - (0.5 x WS) + e((2.4-WS)), and HLI(BG<25) = 10.66 + (0.28 x RH) + (1.3 x BG) - WS, where e is the base of the natural logarithm. A threshold HLI above which cattle of different genotypes gain body heat was developed for 7 genotypes. The threshold for unshaded black B. taurus steers was 86, and for unshaded B. indicus (100%) the threshold was 96. Threshold adjustments were developed for factors such as coat color, health status, access to shade, drinking water temperature, and manure management. Upward and downward adjustments are possible; upward adjustments occur when cattle have access to shade (+3 to +7) and downward adjustments occur when cattle are showing clinical signs of disease (-5). A related measure, the accumulated heat load (AHL) model, also was developed after the development of the HLI. The AHL is a measure of the animal's heat load balance and is determined by the duration of exposure above the threshold HLI. The THI and THI-hours (hours above a THI threshold) were compared with the HLI and AHL. The relationships between tympanic temperature and the average HLI and THI for the previous 24 h were R(2) = 0.67, P < 0.001, and R(2) = 0.26, P < 0.001, respectively. The R(2) for the relationships between HLI or AHL and PS were positive (0.93 and 0.92 for HLI and AHL, respectively, P < 0.001). The R(2) for the relationship between THI and PS was 0.61 (P < 0.001), and for THI-hours was 0.37 (P < 0.001). The HLI and the AHL were successful in predicting PS responses of different cattle genotypes during periods of high heat load.

Effect of sprinkling on feedlot microclimate and cattle behavior.

Experiments were conducted to evaluate strategies designed to reduce heat stress of cattle. In the first experiment, cattle were sprinkled for 20 min every 1.5 h between 1000 hours and 1750 hours (WET) versus not sprinkled (DRY). In a second experiment, treatments consisted of: (1) control, no water application; (2) water applied to the pen surfaces between 1000 hours and 1200 hours (AM); and (3) water applied to pen surfaces between 1400 hours and 1600 hours (PM). In both experiments, sprinkling lowered (P < 0.05) mid-afternoon temperatures. In the first experiment, relative humidity (RH) of WET versus DRY pens differed (P < 0.05) and averaged 72.4 and 68.9%, respectively. The average temperature-humidity index (THI) in WET pens was 0.5 units lower (P < 0.05), than the THI in DRY pens. In the second experiment, RH in sprinkled pens was also greater (P < 0.05) than RH in control (CON) pens However, THI differed (P < 0.05) among treatments, being 81.5, 80.9, and 80.3, respectively for CON, AM, and PM. Pens with sprinklers had a larger percentage of steers in areas where sprinkling took place, even on days when sprinkling had not occurred. Based on differences in percentage of cattle panting in sprinkled and non-sprinkled treatments, sprinkling was found to have a positive effect on cattle feeding area microclimate and to reduce the susceptibility of cattle to hyperthermia. However, cattle acclimatization to being sprinkled can result in slight hyperthermia even during cooler days when sprinkling would normally not be utilized.

Environmental effects on pregnancy rate in beef cattle.

Ten years of calving records were examined from Bos taurus crossbred cows (mean of 182 cows/yr) to quantify the effects of environmental conditions during the breeding season on pregnancy rate. Estimated breeding dates were determined by subtracting 283 d from the calving date. Relationships were determined between the proportion of cows bred during the periods from the beginning of the breeding season until d 21, 42, and 60 of the breeding season and the corresponding environmental variables. Weather data were compiled from a weather station located approximately 20 km from the research site. Average daily temperature and relative humidity were used to calculate daily temperature-humidity index (THI). Daily averages for each environmental variable were averaged for each period. Minimum temperature (MNTP) and THI for the first 21 and 42 d of the breeding season were negatively associated (P < 0.001) with pregnancy rate. For the 0-to 21-d, 0- to 42-d, and 0- to 60-d breeding periods, respective r2 for average temperatures were 0.32, 0.37, and 0.11, whereas r2 for MNTP were 0.45, 0.40, and 0.10 and r2 for THI were 0.38, 0.41, and 0.11, respectively, for the same breeding periods. The negative associations of temperature and THI with pregnancy rate are most pronounced during the first 21 d of the breeding season, with a -3.79 and -2.06% change in pregnancy rate for each unit of change in MNTP and THI, respectively. A combination of environmental variables increased the R2 to 0.67. In this analysis, windspeed was found to be positively associated with pregnancy rate in all equations and increased the R2 in all breeding periods. Optimum MNTP for the 0- to 21-d, 0- to 42-d, and 0- to 60-d breeding periods was 12.6, 13.5, and 14.9 degrees C, respectively. For the 0- to 60-d breeding period, optimum THI was 68.0, whereas the THI threshold, the calculated level at which cattle will adapt, was found to be 72.9. Reductions in pregnancy rate are likely when the average MNTP and THI equal or exceed 16.7 degrees C and 72.9, respectively, and for Bos taurus beef cows that are pasture bred during a 60-d spring-summer period.

Effects of growth-promoting agents and season on blood metabolites and body temperature in heifers.

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) IGF-I 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.

Environmental factors influencing heat stress in feedlot cattle.

Data from 3 summer feedlot studies were utilized to determine the environmental factors that influence heat stress in cattle and also to determine wind speed (WSPD; m.s(-1)) and solar radiation (RAD; W.m(-2)) adjustments to the temperature-humidity index (THI). Visual assessments of heat stress, based on panting scores (0 = no panting to 4 = severe panting), were collected from 1400 to 1700. Mean daily WSPD, black globe temperature at 1500, and minimums for nighttime WSPD, nighttime black globe THI, and daily relative humidity were found to have the greatest influence on panting score from 1400 to 1700 (R2 = 0.61). From hourly values for THI, WSPD, and RAD, panting score was determined to equal -7.563 + (0.121 x THI) - (0.241 x WSPD) + (0.00082 x RAD) (R2 = 0.49). Using the ratio of WSPD to THI and RAD to THI (- 1.992 and 0.0068 for WSPD and RAD, respectively), adjustments to the THI were derived for WSPD and RAD. On the basis of these ratios and the average hourly data for 1400 to 1700, the THI, adjusted for WSPD and RAD, equals [4.51 + THI - (1.992 x WSPD) + (0.0068 x RAD)]. Four separate cattle studies, comparable in size, type of cattle, and number of observations to the 3 original studies, were utilized to evaluate the accuracy of the THI equation adjusted for WSPD and RAD, and the relationship between the adjusted THI and panting score. Mean panting score derived from individual observations of black-hided cattle in these 4 studies were 1.22, 0.94, 1.32, and 2.00 vs. the predicted panting scores of 1.15, 1.17, 1.30, and 1.96, respectively. Correlations between THI and panting score in these studies ranged from r = 0.47 to 0.87. Correlations between the adjusted THI and mean panting score ranged from r = 0.64 to 0.80. These adjustments would be most appropriate to use, within a day, to predict THI during the afternoon hours using hourly data or current conditions. In addition to afternoon conditions, nighttime conditions, including minimum WSPD, minimum black globe THI, and minimum THI, were also found to influence heat stress experienced by cattle. Although knowledge of THI alone is beneficial in determining the potential for heat stress, WSPD and RAD adjustments to the THI more accurately assess animal discomfort.

Hormonal growth-promotant effects on grain-fed cattle maintained under different environments.

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.