S. M. Holt

Feeding strategies for grain-fed cattle in a hot environment

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.

Heat load management for feedlot cattle

Altering the microclimate by providing protection from the environment is one of the most useful tools helping animals cope with climatic conditions. For most feedlot cattle, facilities and management programs do not need to eliminate environmental stress completely, but rather minimize the severity of the environmental challenge and aid the animal in adapting to it. In addition to facility changes, dietary manipulation may also be beneficial for feedlot cattle challenged by environmental conditions. Studies conducted at the University of Nebraska demonstrate that programmed feeding systems significantly lower body temperatures during periods of heat stress. Programmed feeding systems involve management of feed intake pattern so as to eliminate or minimize simultaneous occurrence of peak metabolic and climatic heat loads. Tympanic temperatures were measured via thermistors placed in the ear canal and attached to data loggers. Cattle managed on programmed feeding systems for three to six weeks, maintained equal or lower tympanic temperature when compared with cattle fed ad libitum. The reduced tympanic temperature is likely due to a reduction in metabolic rate and a concurrent reduction in metabolic heat load. Greater long-term reductions in tympanic temperature likely occur if the cattle are on the programs for 1 to 2 weeks prior to the heat wave. Utilizing programmed feeding systems from late-June to early-August would appear to be sufficient to cover most heat waves.

Strategies to reduce high heat load on feedlot cattle

High heat loading has a negative effect on performance of feedlot cattle, and at times can cause death. Cooling strategies such as sprinklers, fans or a combination of these are often used to reduce heat load effects on cattle. There is some evidence that lack of consistency in the duration and/or timing of the application of cooling strategies, and even the use of strategies when cattle are not at high risk may be detrimental to cattle by limiting their ability to adapt to hot conditions. The aim of this study was to look at the effects of inconsistent cooling strategies on rectal temperature (RT), respiration rate (RR) and pulse rate (PR) of grain fed heifers (n=6). Two strategies were imposed on cattle, which were exposed to hot conditions (THI ³ 80). The strategies used were: (i) Cattle were cooled by wetting for 2 h on day 1, then cooled for 4 h on days 2 and 3, then cooled for 2 h on day 4. (ii) Cattle were cooled by wetting for 2 h on day 1, not cooled on days 2 and 3, then cooled for 2 h on day 4. The results indicate that cooling of cattle for 4 h per day will result in a significant (P< 0.05) reduction in RT (2 % lower), RR (22 % lower) and PR (4 % lower) compared to non-cooled animals. However, cessation of cooling may result in significant heat stress, with RR increasing by 70 bpm for previously cooled cattle.