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This study investigated nutritional management strategies to reduce the impact of heat stress on feedlot steers. Twelve Angus steers (582 ± 8.92 kg LW) were housed in climate control rooms ( CCR ) for 21-days. Steers were randomly allocated to three treatments: 1) Control, fed a finisher diet (Control); 2) finisher diet to a heat load diet with 5% additional roughage, from d4 until d16 (HL Ration); 3) finisher diet supplemented with calcareous marine algae (CMA; 70 g/steer/day Acid Buf, Celtic Sea Minerals), between d4 until d16. The 21-days consisted of three phases i) d0 to d6, Phase I, Temperature Humidity Index, THI 65 to 78; ii) d7 to d11 Phase II, THI 83 to 87); and iii) d12 to d20, Phase III, THI 65 to 78, for all steers. Cattle exhibited increased respiration rate (RR), panting score (PS) and rumen temperature (T RUM ) during Phase II ( P < 0.0001). During Phase II, dry matter intake (DMI) was approximately 5kg lower when compared with Phase I. The diurnal rhythm in rumen pH and range in rumen pH differed during Phase II for both Control ( P < 0.0001) and CMA ( P < 0.0001), when compared with Phase I. Mean rumen pH was lower during Phase III compared with Phase I ( P ≤0.002). During Phase II, Lipopolysaccharide binding protein (LBP) and Serum amyloid A (SAA) differed across the treatments, with CMA cattle exhibiting the lowest concentrations ( P ≤ 0.04). Both Aspartate aminotransferase (AST) (P ≤ 0.009) and Glutamate dehydrogenase (GLDH) (P ≤ 0.004) were at a maximum during Phase III, with Control having greater AST (P ≤ 0.01) and GLDH (P ≤ 0.04). These results suggest that CMA supports DMI and markers of gut integrity, whilst potentially mediating liver damage, during heat wave events. • The heat wave protocol evoked classical heat stress responses in these animals. • Cattle under nutritional management better maintained dry matter intake. • Calcareous marine algae supplementation mediated acute phase protein response • Calcareous marine algae appeared to mediate liver damage markers post-heat wave
Sammes et al. (Wed,) studied this question.