Description

Research in temperate grasslands has addressed livestock supplementation (SUPL) mainly during winter, but more studies are needed on the impact of SUPL during summer where heat stress (HS) conditions may occur. The objective of this study was to evaluate the effects of summer SUPL on average daily gain (ADG), respiratory rate (RR), and body temperature (BT) of steers grazing native grasslands (60% TDN, 7.3% CP) in Uruguay (33°14'S, 54°15'W). Eighteen 15-month-old Angus steers (285±11 kg) were randomly assigned to 6 groups (2 treatments x 3 replicates) with free access to shade and water on a continuous stocking system (1.5 steer/ha) for 84 days. Treatments were SUPL and un-supplemented (un-SUPL) cattle. Supplement (77% TDN, 16.8% CP) was delivered 3 days/week at 2.3% BW. Animal breaths per minute (bpm) were registered in 18 days at 09:00 am, 12:00 pm, and 03:00 pm by visual observation and BT was hourly recorded using a subcutaneously implanted logger. The temperature-humidity index (THI) was calculated hourly using air temperature and relative humidity recorded by automatic sensors. According to THI, cattle was in the 'normal' category (THI < 74, absence of weather-based HS) during 72% of the time, the rest being exposed to ‘moderate’ (19%) and ‘severe’ (9%) HS. Supplemented steers had greater (P < 0.05) ADG than CONT cattle (mean ± s.e.m.: 0.729±0.053 and 0.393±0.169, respectively). Respiration rate was no affected by SUPL (P > 0.05), averaging 45±1 (09:00 am), 56±2 (12:00 pm), and 62±3 (03:00 pm) bpm across treatments. Supplementation did not increase daily BT (P > 0.05), averaging (±s.e.m.) 38.2±0.1°C across treatments. The greatest BT difference (P > 0.05) between groups was observed at 09:00-10:00 am, coincidently with the time of supplementation (SUPL: 39.3±0.1°C; un-SUPL: 38.3±0.1°C). Summer supplementation in native grasslands resulted in better animal performance without affecting animal-based heat stress indices compared to un-supplemented steers.

DOI

https://doi.org/10.13023/c8wj-6y90

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Effects of Concentrate Supplementation During Summer on Animal Performance and Heat Stress of Angus Steers Grazing Native Grasslands in Uruguay

Research in temperate grasslands has addressed livestock supplementation (SUPL) mainly during winter, but more studies are needed on the impact of SUPL during summer where heat stress (HS) conditions may occur. The objective of this study was to evaluate the effects of summer SUPL on average daily gain (ADG), respiratory rate (RR), and body temperature (BT) of steers grazing native grasslands (60% TDN, 7.3% CP) in Uruguay (33°14'S, 54°15'W). Eighteen 15-month-old Angus steers (285±11 kg) were randomly assigned to 6 groups (2 treatments x 3 replicates) with free access to shade and water on a continuous stocking system (1.5 steer/ha) for 84 days. Treatments were SUPL and un-supplemented (un-SUPL) cattle. Supplement (77% TDN, 16.8% CP) was delivered 3 days/week at 2.3% BW. Animal breaths per minute (bpm) were registered in 18 days at 09:00 am, 12:00 pm, and 03:00 pm by visual observation and BT was hourly recorded using a subcutaneously implanted logger. The temperature-humidity index (THI) was calculated hourly using air temperature and relative humidity recorded by automatic sensors. According to THI, cattle was in the 'normal' category (THI < 74, absence of weather-based HS) during 72% of the time, the rest being exposed to ‘moderate’ (19%) and ‘severe’ (9%) HS. Supplemented steers had greater (P < 0.05) ADG than CONT cattle (mean ± s.e.m.: 0.729±0.053 and 0.393±0.169, respectively). Respiration rate was no affected by SUPL (P > 0.05), averaging 45±1 (09:00 am), 56±2 (12:00 pm), and 62±3 (03:00 pm) bpm across treatments. Supplementation did not increase daily BT (P > 0.05), averaging (±s.e.m.) 38.2±0.1°C across treatments. The greatest BT difference (P > 0.05) between groups was observed at 09:00-10:00 am, coincidently with the time of supplementation (SUPL: 39.3±0.1°C; un-SUPL: 38.3±0.1°C). Summer supplementation in native grasslands resulted in better animal performance without affecting animal-based heat stress indices compared to un-supplemented steers.