Three experiments evaluated the effects of ractopamine hydrochloride (RAC) dose and duration on growth performance and carcass characteristics of feedlot steers. In total, 1,509 crossbred steers (530 kg initial BW [SD 22]) were used in a randomized complete block design using a 3 × 3 factorial treatment structure. Treatments consisted of RAC dose (0, 100, or 200 mg/steer daily) and duration (28, 35, or 42 d) of RAC feeding prior to harvest. Initiation of RAC dose was staggered (7 d apart) based on RAC duration, which resulted in common days on feed among treatments. Data from the 3 experiments were combined for statistical analyses. There were no RAC dose × duration interactions ( ≥ 0.85) for growth performance. Live final BW was not different ( ≥ 0.24) as RAC dose increased. Dry matter intake linearly decreased ( < 0.01) as RAC dose increased. Live ADG and G:F linearly increased ( ≤ 0.01) as RAC dose increased. Carcass-adjusted ADG and G:F linearly increased ( ≤ 0.02) as RAC dose increased. Compared with steers fed 0 mg RAC/steer daily, G:F was improved by 5.0 and 13.0% when steers were fed 100 ( = 0.31) and 200 ( = 0.01) mg RAC/steer daily, respectively. Hot carcass weight tended ( = 0.10) to linearly increase as RAC dose increased, with carcasses from steers fed 100 ( = 0.38) and 200 ( = 0.10) mg RAC/steer daily being 2.2 and 4.1 kg heavier, respectively, than carcasses from steers fed 0 mg RAC/steer daily. Increasing RAC dose linearly ( < 0.01) increased LM area and linearly ( = 0.02) decreased marbling score. Live final BW was not different ( ≥ 0.60) among RAC durations. Carcass-adjusted final BW, ADG, and G:F were not different ( ≥ 0.41) as RAC duration increased. Carcass traits did not differ ( ≥ 0.18) among RAC duration. Feeding 200 mg RAC/steer daily improved ADG, feed efficiency, and HCW. Increasing the feeding duration of RAC had no effect of growth performance or carcass characteristics. These data indicate that feeding 200 mg RAC/steer daily for 28 d improves steer growth performance.

The objective of this study was to assess in situ dry matter (DM) and neutral detergent fiber (NDF) degradation kinetics for two new pre-matured brown midrib varieties (pmBMR1 and pmBMR2) that can be double-cropped by harvesting at tassel, compared with a sole crop mature BMR (mBMR) and conventional corn silage (CCS) harvested at maturity in dry and lactating dairy cows. Potentially degradable DM fraction for the BMR hybrids were greater (P<0.01) than the CCS in both dry and lactating cows and was greatest for the mBMR in dry cows, while in lactating cows potentially degradable DM was greatest for the pmBMR1. Potentially degradable NDF fraction was greater (P<0.01) for BMR hybrids compared with CCS with the exception of the pmBMR2, which had the lowest potentially degradable NDF fraction in dry cows. Estimates of ruminal degradability of NDF were greater (P<0.01) for the pmBMR varieties compared to mature silages, and were greatest (P<0.01) for the pmBMR1 in both dry and lactating cows. Taken as a whole, this experiment indicates that rumen degradability may have been influenced more by hybrid than stage of maturity, as the pmBMR1 had the greatest degradability, and the pmBMR2 was not as degradable as the mBMR.

This experiment was conducted to determine the effects of corn silage (CS) hybrids and quality of alfalfa hay (AH) in high-forage dairy diets on N utilization, ruminal fermentation, and lactational performance by early-lactating dairy cows. Eight multiparous Holstein cows were used in a duplicated 4 × 4 Latin square experiment with a 2 × 2 factorial arrangement of dietary treatments. The 8 cows (average days in milk = 23 ± 11.2) were surgically fitted with ruminal cannula, and the 2 squares were conducted simultaneously. Within square, cows were randomly assigned to a sequence of 4 diets: conventional CS (CCS) or brown midrib CS (BMR) was combined with fair-quality AH [FAH: 46.7% neutral detergent fiber (NDF) and 18.4% crude protein (CP)] or high-quality AH (HAH: 39.2% NDF and 20.7% CP) to form 4 treatments: CCS with FAH, CCS with HAH, BMR with FAH, and BMR with HAH. Diets were isonitrogenous across treatments, averaging 15.9% CP. Each period lasted a total of 21 d, with 14 d for treatment adaptation and 7d for data collection and sampling. Intake of DM and milk yield did not differ in response to CS hybrids or AH quality. Although feeding BMR-based diets decreased urinary N output by 24%, it did not affect fecal N output. Feeding HAH decreased urinary N output by 15% but increased fecal N output by 20%. Nitrogen efficiency [milk N (g/d)/intake N (g/d)] tended to increase for BMR treatments. Ruminal ammonia-N concentration was lower for cows fed BMR-based diets than for those fed CCS-based diets but was not affected by quality of AH. Feeding BMR-based diets or HAH decreased milk urea N concentration by 23 or 15%, respectively, compared with CCS-based diets or FAH. Total volatile fatty acid concentration increased with HAH but was not influenced by CS hybrids. Feeding BMR-based diets decreased urinary N-to-fecal N ratio (UN:FN), and it was further reduced by feeding HAH. Although cows fed the BMR-based diets tended to increase milk N-to-manure N ratio, the quality of AH did not affect the ratio. The lower ratio of UN:FN with a higher ratio of milk N-to-manure N ratio for the BMR-based diets indicates that feeding BMR may reduce manure ammonia-N by reducing excretion of urinary N and increasing secretion of milk N per unit of manure N excreted.

This experiment was conducted to test a hypothesis that lactating dairy cows fed 35% brown midrib (BMR) corn silage and 25% alfalfa hay (dry matter (DM) basis) would consume more DM around peak lactation compared with those fed conventional corn silage (CS), resulting in longer peak milk production. Twenty-eight multiparous Holstein cows were used starting at the onset of lactation through 180 d in milk (DIM). Treatments were formulated to maintain a forage-to-concentrate ratio of 60:40, differing only in the CS hybrids used. Two dietary treatments were assessed in a completely randomized design: total mixed ration based on conventional CS (CCS) and total mixed ration based on BMR silage. Through peak lactation (1-60 DIM), DM intake was not different between dietary treatments, whereas DM intake post-peak lactation (61-180 DIM) tended to increase by feeding the BMR diet compared with the CCS diet (25.8 vs. 24.7 kg/d). Cows fed the BMR diet tended to lose less body weight through peak lactation compared with those fed the CCS diet (-0.22 vs. -0.52 kg/d). Although milk yield was not different between dietary treatments through peak lactation, milk yield post-peak lactation increased by feeding the BMR diet compared with the CCS diet (41.0 vs. 38.8 kg/d). Yield of 3.5% fat-corrected milk was similar between dietary treatments throughout the experiment (41.4 kg/d, on average), but milk fat concentration decreased by feeding the BMR diet compared with the CCS diet post-peak lactation (3.47 vs. 3.80%). Overall milk protein concentration was similar between dietary treatments throughout the experiment (2.96%, on average), whereas milk protein yield tended to be higher for the BMR diet post-peak lactation compared with the CCS diet (1.19 vs.1.13 kg/d). Feeding BMR silage with a high dietary concentration of alfalfa hay maintained more body weight, but did not affect milk production through peak lactation; however, cows fed the BMR diet post-peak lactation consumed more feed and maintained longer peak milk yield, leading to greater overall milk production and milk protein yield.

A lactation experiment was conducted to determine the influence of quebracho condensed tannin extract (CTE) on ruminal fermentation and lactational performance of dairy cows. The cows were fed a high forage (HF) or a low forage (LF) diet with a forage-to-concentrate ratio of 59:41 or 41:59 on a dry matter (DM) basis, respectively. Eight multiparous lactating Holstein cows (62 ± 8.8 d in milk) were used. The design of the experiment was a double 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments, and each period lasted 21 d (14 d of treatment adaptation and 7 d of data collection and sampling). Four dietary treatments were tested: HF without CTE, HF with CTE (HF+CTE), LF without CTE, and LF with CTE (LF+CTE). Commercial quebracho CTE was added to the HF+CTE and the LF+CTE at a rate of 3% of dietary DM. Intake of DM averaged 26.7 kg/d across treatments, and supplementing CTE decreased intakes of DM and nutrients regardless of forage level. Digestibilities of DM and nutrients were not affected by CTE supplementation. Milk yield averaged 35.3 kg/d across treatments, and yields of milk and milk component were not influenced by CTE supplementation. Negative effects of CTE supplementation on feed intake resulted in increased feed efficiency (milk yield/DM intake). Although concentration of milk urea N (MUN) decreased by supplementing CTE in the diets, efficiency of N use for milk N was not affected by CTE supplementation. Feeding the LF diet decreased ruminal pH (mean of 6.47 and 6.33 in HF and LF, respectively). However, supplementation of CTE in the diets did not influence ruminal pH. Supplementing CTE decreased total volatile fatty acid concentration regardless of level of forage. With CTE supplementation, molar proportions of acetate, propionate, and butyrate increased in the HF diet, but not in the LF diet, resulting in interactions between forage level and CTE supplementation. Concentration of ammonia-N tended to decrease with supplementation of CTE. The most remarkable finding in this study was that cows fed CTE-supplemented diets had decreased ruminal ammonia-N and MUN concentrations, indicating that less ruminal N was lost as ammonia because of decreased degradation of crude protein by rumen microorganisms in response to CTE supplementation. Therefore, supplementation of CTE in lactation dairy diets may change the route of N excretion, having less excretion into urine but more into feces, as it had no effect on N utilization efficiency for milk production.

试验旨在确定白坚树浓缩丹宁提取物（CTE）对奶牛瘤胃发酵和泌乳性能的影响。按干物质计,奶牛喂饲草与精料比例分别为59？？41或41？？59的高饲草（HF）日粮或低饲草（LF）日粮。试验选择8头泌乳62±8.8d的经产荷斯坦奶牛,采用含2×2因子的双重4×4拉丁方设计,每个时期21d（14d适应、7d数据收集和取样）。4个日粮处理为不添加CTE的HF日粮、添加CTE的HF日粮（HF＋CTE组）、不添加CTE的LF日粮、添加CTE的LF日粮（LF＋CTE组）。商品白坚树CTE按日粮干物质3%的比例加入HF＋CTE组和LF＋CTE组。试验结果表明,处理之间的平均干物质采食量为26.7kg·d-1,不管饲草水平如何,添加CTE降低奶牛的干物质和养分采食量。干物质和养分的消化率不受添加CTE的影响。处理之间的平均产奶量为35.3kg·d-1,产奶量和乳成分不受添加CTE的影响。添加CTE对采食量的负面影响使奶牛的饲料转化率（产奶量/干物质采食量）提高。尽管日粮中添加CTE会降低乳中尿素氮（MUN）浓度,但是用于产奶的氮的利用率不受添加CTE的影响。饲喂LF组日粮的奶牛瘤胃pH下降（HF组和LF组的平均pH分别为6.47和6.33）。但是,日粮添加CTE不会影响瘤胃的pH。不管饲草水平如何,添加CTE降低挥发性脂肪酸总浓度。添加CTE、HF日粮组的乙酸盐、丙酸盐和丁酸盐摩尔比例提高,而LF日粮组的相应值则没有提高,引起饲草水平与CTE之间的相互作用。添加CTE有助于降低氨氮浓度。本研究的最显著的结果是饲喂添加CTE日粮奶牛有较低的瘤胃氨氮和乳中尿素氮浓度,表明由于因添加CTE,被瘤胃微生物降解的粗蛋白减少,使得以氨形式丧失的瘤胃氮下降。因此,在泌乳奶牛日粮添加CTE会改变氮的排泄途径,较少的氮排泄到尿中,而较多的氮排泄到粪中,因为其对奶牛用于牛奶生产的氮利用率无影响。

This experiment was conducted to determine the effects of corn silage hybrids and nonforage fiber sources (NFFS) in high forage diets formulated with high dietary proportions of alfalfa hay (AH) and corn silage (CS) on ruminal fermentation and productive performance by early lactating dairy cows. Eight multiparous Holstein cows (4 ruminally fistulated) averaging 36±6.2 d in milk were used in a duplicated 4 × 4 Latin square design experiment with a 2 × 2 factorial arrangement of treatments. Cows were fed 1 of 4 dietary treatments during each of the four 21-d replicates. Treatments were (1) conventional CS (CCS)-based diet without NFFS, (2) CCS-based diet with NFFS, (3) brown midrib CS (BMRCS)-based diet without NFFS, and (4) BMRCS-based diet with NFFS. Diets were isonitrogenous and isocaloric. Sources of NFFS consisted of ground soyhulls and pelleted beet pulp to replace a portion of AH and CS in the diets. In vitro 30-h neutral detergent fiber (NDF) degradability was greater for BMRCS than for CCS (42.3 vs. 31.2%). Neither CS hybrids nor NFFS affected intake of dry matter (DM) and nutrients. Digestibility of N, NDF, and acid detergent fiber tended to be greater for cows consuming CCS-based diets. Milk yield was not influenced by CS hybrids and NFFS. However, a tendency for an interaction between CS hybrids and NFFS occurred, with increased milk yield due to feeding NFFS with the BMRCS-based diet. Yields of milk fat and 3.5% fat-corrected milk decreased when feeding the BMRCS-based diet, and a tendency existed for an interaction between CS hybrids and NFFS because milk fat concentration further decreased by feeding NFFS with BMRCS-based diet. Although feed efficiency (milk/DM intake) was not affected by CS hybrids and NFFS, an interaction was found between CS hybrids and NFFS because feed efficiency increased when NFFS was fed only with BMRCS-based diet. Total volatile fatty acid production and individual molar proportions were not affected by diets. Dietary treatments did not influence ruminal pH profiles, except that duration (h/d) of pH <5.8 decreased when NFFS was fed in a CCS-based diet but not in a BMRCS-based diet, causing a tendency for an interaction between CS hybrids and NFFS. Overall measurements in our study reveal that high forage NDF concentration (20% DM on average) may eliminate potentially positive effects of BMRCS. In the high forage diets, NFFS exerted limited effects on productive performance when they replaced AH and CS. Although the high quality AH provided adequate NDF (38.3% DM) for optimal rumen fermentative function, the low NDF concentration of the AH and the overall forage particle size reduced physically effective fiber and milk fat concentration.

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) [HLIBG<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 (oC), 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 and respiratory dynamics of 240 yearling steers were used to assess 3 housing systems in South Dakota during summer (69 d). The housing systems were full confinement (CONF), open lot (OPN), and partial confinement (PTL). Steers were randomly allocated in equal numbers to each system (1 pen/system). Ambient temperature, black globe temperature (BG), solar radiation, wind speed, wind direction, and relative humidity were recorded at 30-min intervals from a weather station. A modified temperature-humidity index {THIMOD = (0.8 × BG) + [(relative humidity/100) × (BG − 14.4)] + 46.4} was used to assess thermal load. Panting score (0 = normal to 4 = open-mouth panting, tongue out, and excessive drooling) of each animal was recorded at 0600, 1200, and 1600h. Mean panting score (MPS) of steers in OPN (0.563) was greater than MPS of PTL (0.383;P = 0.06) and CONF (0.278;P = 0.003) steers. There were no MPS differences (P > 0.05) between CONF and PTL. During extreme events (THIMOD ≥84), the MPS of OPN (1.30) was greater (P < 0.001) than those of PTL (0.88) and CONF (0.61). An MPS >1.2 indicates an extreme heat load. Tympanic temperature was recorded from 10 animals/treatment during 3 heat waves of 8, 8, and 6 d duration. When THIMOD ≥84, the mean tympanic temperature for OPN (40.55°C) was greater (P < 0.05) than those of PTL (40.04°C) and CONF (40.02°C). Under the climatic conditions encountered, it is evident that the housing systems that offered shade (CONF and PTL) reduced the effects of extreme heat load on feedlot cattle.

Six Murray Grey×Hereford yearling steers were used to determine the effect of two cooling treatments (ENV) (day cooled (0600–1400) or night cooled (1400–2200), and two dietary treatments (DIET) – control (CON) no added fat or added fat (FAT) – on rectal temperature, respiration rate and dry matter intake (DMI). Cattle were exposed to 2 d of thermoneutral conditions followed by four hot days in a controlled climate facility. This was replicated 6 times. Steers were given a 10 d rest in outside pens between each replication. Sprinklers (2.84 L min−1; 5 min on, 20 min off) and fans (continuous; 2 m s−1) were used when ambient temperature (TA) ≥28 °C. Rectal temperature (5 min intervals) and respiration rate (hourly) were measured for 12×24 h periods on hot days (2 per replication). Individual DMI over two time periods (PER) (period 1; 0600–1500, and period 2; 1500–0600) and daily metabolisable energy (ME) intakes were also recorded. Steers fed FAT had greater (P<0.05) DMI then the CON steers during day cooling. However, there were no DIET or PER differences for DMI during night cooling. DMI of FAT and CON fed steers during night cooling was similar to the DMI of the FAT fed steers during day cooling. Overall DMI was greater during night cooling (DMI from both diets pooled). There were PER differences for DMI, with more (P<0.05) feed consumed during period 2 irrespective of ENV or DIET. ME intake was 22.9% greater (P<0.05) for the FAT fed steers during day cooling then for the CON fed steers. There were no DIET effects on ME intake during night cooling. DIET had no effect (P>0.05) on respiration rate however differences were seen for rectal temperature. Mean rectal temperature for the FAT steers was lower (P<0.05) than the mean of the CON steers, however there were no within ENV differences. Day cooled cattle had a higher (P<0.05) respiration rates (71.8 breaths/min; bpm) than the night cooled steers (65.3 bpm). There were no differences for rectal temperature. However, day cooled steers had lower (P<0.05) rectal temperature and respiration rate than the night cooled steers during the day — which corresponded with the day cooling period. Night cooling appears to be beneficial in lowering mean rectal temperature and respiration rate, and in maintaining DMI. There is no suggestion that feeding fat will replace the need for supplementary measures to alleviate heat exposure of confined cattle. However feeding fat may be worthwhile in maintenance DMI when combined with strategies involving day cooling.

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: HLIBG>25 = 8.62 + (0.38 x RH) + (1.55 x BG) - (0.5 x WS) + e((2.4-WS)), and HLIBG<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.

Angus steer calves (n=135) were used in a 55d feedlot growing study to investigate the effects of feeding schedule on tympanic temperature response when limit feeding. Steers were fed a high moisture ear corn diet (58 Mcal/cwt NEg) at 0900h (AM), 1500h (PM) or 50% at 0900h and 50% at 1500h (SPLIT) to allow for 2.50lb ADG. Climatic data were collected at 30 min intervals throughout the study via an on site automated weather station. Tympanic temperatures (TT) were collected every 30 min (5 steers/trt) for 5d (d44 to d48). Mean ambient temperature during the 5d TT collection period was -6.5F (-23.1 to 9.1F). After 55d, BW (802, 808 and 802lb), ADG (2.56, 2.67 and 2.52lb) and feed efficiency (5.73, 5.52 and 5.87) did not differ (P>.10) between AM, PM and SPLIT respectively, but followed rankings of previous research. Diurnal TT patterns were assessed by separating the day into three periods based on mean hourly wind chills (44.2, 17.8 and 7.5F) for Period 1 (0800 to 1600h), Period 2 (1630 to 2100h) and Period 3 (2130 to 0730h) respectively. Peak TT occurred during Period 2 for AM (102.4F) and Period 3 for PM (103.2F). SPLIT fed steers exhibited TT peaks of 103.9F or greater in each period. These data indicate that by adjusting feeding schedule it is possible to alter the time at which peak TT may occur, so that peak TT coincides with colder periods of the day. Elevated TT across all periods for SPLIT suggests that these steers may have increased metabolic rate to maintain normal TT during extreme cold. Additional research is needed to explain the changes in TT and how feeding times may impact energy partitioning.

Six Bos taurus (Hereford) steers (body weight 324 22 kg) were used in a 45-day study with a replicated 3 x 3 Latin-square design. Three treatments [ad libitum feeding (ADLIB); limit feeding, 85% of ad libitum (LIMIT); bunk management feeding where steers were only given access to feed from 1600 to 0800 hours the following day (BUNK)] were imposed over 3 periods, with 2 steers assigned to each treatment in each period. Cattle were managed in a temperature-controlled metabolism unit and were exposed to both thermoneutral (17.7degreesC-26.1degreesC) and hot (16.7degreesC-32.9degreesC) environmental conditions. By design, during the thermoneutral period, the ADLIB cattle displayed greater intake (P < 0.05) than the LIMIT group, with the BUNK group being intermediate. However, during the hot period, both the LIMIT and BUNK treatment groups increased feed intake 4-5%, whereas feed intake of the ADLIB treatment group declined nearly 2%. During both periods respiration rate (RR, breath/min) followed the same pattern that was observed for feed intake, with the greatest (P < 0.05) RR found in the ADLIB treatment group (81.09 and 109.55, thermoneutral and hot, respectively) and lowest (P < 0.05) RR in the LIMIT treatment group (74.47 and 102.76, thermoneutral and hot, respectively). Rectal temperature (RT) did not differ among treatments during the thermoneutral period or the first hot day, although during the thermoneutral period the ADLIB treatment group did tend to display a lower RT, possibly as a result of other physiological processes (pulse rate and RR) aiding to keep RT lower. During the hot period, differences in RT were found on Day 5, with the LIMIT cattle having lower (P < 0.10) RT (38.92degreesC) than the ADLIB (39.18degreesC) cattle, with BUNK cattle RT (39.14degreesC) being intermediate. However, when hourly data were examined, the ADLIB cattle had greater(P < 0.05) RT than the BUNK and LIMIT at 1800 hours and greater RT (P < 0.05) than the LIMIT group at 1400, 1500, and 1600 hours. Clearly, a change in diurnal RT pattern was obtained by using the LIMIT and BUNK feeding regimen. Both of these groups displayed a peak RT during the hot conditions, between 2100 and 2200 hours, whereas the ADLIB group displayed a peak RT between 1400 and 1500 hours, a time very close to when peak climatic stress occurs. Based on these results it is apparent that feedlot managers could alleviate the effects of adverse hot weather on cattle by utilising either a limit-feeding regimen or altering bunk management practices to prevent feed from being consumed several hours prior to the hottest portion of the day.

Three experiments were conducted to evaluate the effect of different management strategies on body temperature of feedlot steers finished in the summer months. In Exp. 1, 24 crossbred steers were chosen to assess the effect of altered feed intake and feeding time on tympanic temperature (TT) response. Managed feeding (MF) treatments were applied for 22 d only and provided 1) ad libitum access to feed at 0800 (ADLIB), 2) feed at 1600 with amount adjusted so that no feed was available at 0800 (BKMGT), 3) feed at 1600 at 85% of predicted ad libitum levels (LIMFD). During heat stress conditions on d 20 to 22 of MF, LIMFD and BKMGT had lower (P < 0.05) TT than ADLIB from 2100 through 2400. A carryover effect of limit-feeding was evident during a severe heat episode (d 36 to 38) with LIMFD steers having lower (P < 0.05) TT than ADLIB. In Exp. 2, TT were obtained from 24 crossbred steers assigned to three treatments, consisting of no water application (CON), water applied to feedlot mound surfaces from 1000 to 1200 (AM) or 1400 to 1600 (PM). From 2200 to 0900 and 1200 to 1400, steers assigned to morning sprinkling treatment had lower (P < 0.05) TT than steers assigned to afternoon sprinkling treatment. In Exp. 3, 24 steers were utilized in a 2 x 2 factorial arrangement of treatments with factors of feeding time [0800 (AMF) and 1400 (PMF)] and sprinkling (WET and DRY). Tympanic temperatures were monitored under hot environmental conditions on d 30 to 32 and 61 to 62. A feeding time x sprinkling interaction (P < 0.001) was evident on d 30 to 32, although AMF/DRY steers had the highest (P < 0.05) TT. On d 61 to 62, TT of PMF steers was higher (P < 0.05) than AMF between 1500 to 1800. Use of sprinklers can effectively reduce TT of feedlot cattle, whereas shifting to an afternoon vs morning feeding time was most beneficial when bunks were empty several hours prior to feeding.

The objectives of this study were to evaluate effects of breed of sire, age of dam and gender on exit velocity (EV, m/s), chute temperament score (CS; 1=calm, no movement to 5=jumping and rearing, highly agitated) and pen temperament score (PS; 1=non-aggressive, not excited by humans to 5=aggressive, runs into fences and at humans if approached) and measure relationships between EV, CS and PS at two times near weaning. Crossbred calves (n=195) were assigned a PS, then calves were weighed on a platform scale and CS was assigned. Calves were then released to a squeeze chute and restrained. After a blood sample was obtained the calf was released and time recorded to travel 1.83 m. Measurement one (T1) occurred 21 d after weaning and the second measurement (T2) 90 days later. Least square means were obtained from PROC MIXED with main effects of sire breed, gender and age of dam. Breed of sire (Angus or Brangus) was not a significant source of variation for EV, CS or PS. Gender was a significant source of variation for EV and PS at T1 and was different for EV at T2 (P < 0.06). Heifers had a greater EV at T1 and T2 (1.75 ± 0.10 and 2.48 ± 0.14 m/s, respectively) compared to steers (1.56 ± 0.10 and 2.22 ± 0.15 m/s, respectively). The correlation coefficient (r) between EV at T1 and T2 was 0.68 (P < 0.001). The r between EV and CS was 0.26 (P < 0.002) at T2. The r between EV and PS were 0.489 (P < 0.001) at T1 and 0.487 (P < 0.001) at T2. In conclusion, breed of sire was not a significant source of variation in chute exit velocity however, differences existed between steers and heifers. Although the correlation coefficients between velocity and temperament score were significantly different from zero the magnitudes were only moderate. In this case, pen score had a better correlation with velocity than chute score. The exit velocity may be preferred due to the subjective nature of the temperament score.