A preliminary investigation for the dietary inclusion of calcareous marine algae for grain-fed beef steers during a simulated heat wave

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 5 kg 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.