Variations in Heat Load Nutritional Management on Animal Performance, Rumen Temperature and pH Characteristics in...

This study evaluated the effects of including additional roughage and the timing of roughage addition on rumen temperature (T_RUM), rumen pH, dry matter intake as a percentage of live weight (DMILW), water consumption as a percentage of live weight (WILW) and average daily gain of grain-fed steers exposed to a simulated heat wave. A total of forty-eight Black Angus steers (539.53 ± 4.95 kg) were housed within climate control rooms for 21 days and exposed to a 5-day simulated heat wave. Steers were randomly allocated into four cohorts with 12 steers/cohort, and then allocated to one of three dietary treatments: Treatment 1 (T1) were fed a finisher diet for the 21 days; Treatment 2 (T2) transitioned from the finisher diet to a heat load diet on d 9 and fed the heat load diet until d 14; and Treatment 3 (T3) transitioned from the finisher diet to the heat load diet on d 7 and fed the heat load diet until d 14. On d 15, T2 and T3 transitioned back to the finisher diet. The study was categorised into five phases consisting of (i) Phase I, d 0-6 (Temperature Humidity Index, THI 65 to 78); (ii) Phase II, d 7-8 (THI 65 to 78); (iii) Phase III, d 9-11 (THI 83 to 90); (iv) Phase IV, d 12-13 (THI 78 to 85); and (v) Phase V, d 14-20 (THI 65 to 78). During the heat wave challenge in Phase III, all Treatments exhibited lower DMILW (p < 0.0001), greater T_RUM and rumen pH (p < 0.0001), lower ranges in T_RUM and rumen pH (p ≤ 0.0005) and altered diurnal T_RUM and rumen pH rhythms. Average daily gain was not influenced by Treatments (p ≥ 0.98). Overall, these results suggest that nutritional management remains an important consideration to reduce the impact of hot climatic conditions on the rumen environment during heat wave and post-heat wave conditions.