Effects of metabolizable energy intake on tympanic temperature and ADG of steers finished in southern Chile during wintertime

Abstract Text: A total of 24 Angus x Hereford steers (BW= 479.8 ±4.48) were used to assess the effect of ME intake (MEI) on ADG and tympanic temperature (TT) during the wintertime in southern Chile. The study was conducted at the experimental field of the UC Temuco, and included a period of 21 days for adaptation to diet and facilities. Steers were randomly allocated in 4 pens (6/pen) equipped with a Calan Feeding System. Steers were sorted by BW, assigned to block (lighter or heavier), and then allocated into one of two treatments: T1=1.85x or T2=2.72x MEI for maintenance. All steers were fed once per day with the same diet; treatments were applied by controlling DMI. Subsequently, five animals/treatment received a device to collect TT; those were retrieved 10 d later. Climatic data were obtained from a weather station located 5 km southeast from the research site. All data were analyzed under a complete randomize block experimental design (α=0.05), each steer was considered an experimental and observational unit. The steers fed with higher MEI showed higher TT than those fed with lesser MEI (P<0.0001) through all days. In addition, both groups followed the same TT pattern throughout the TT collection period. This could be explained by changes in precipitations (PP) and wind speed (WS). The highest TT was observed in those days without PP and low WS. On the other hand, the lowest TT was observed when WS and PP were higher. Thus, in adult animals it appears that WS has an important role in the thermal balance during the wintertime. Similarly, steers fed with less MEI showed lesser TT when compared with those fed high MEI (P<0.0001), through every hour of the day, even when both groups had theoretically enough energy to cover maintenance requirements. Following the same trend, observed ADG was higher (P= 0.0004) for those steers fed the high MEI compared with those fed the less MEI (0.54 vs. 0.17 ±0.06 kg/d, respectively). This represents a performance of 3.18 times better for T2, however MEI was only 1.47 times higher in this treatment. In conclusion, based on the data collected so far it can be said that MEI has a direct effect on the TT and ADG of steers finished during the winter period in an open feedlot. In addition, both variables are directly affected by climatic conditions

Keywords: Tympanic temperature, thermal comfort, climate