Reducing rumen starch fermentation of wheat with 3% NaOH does not reduce whole tract starch digestibility and increases energy utilization in wethers during heat stress

Previous studies have suggested that feeding slowly fermentable grains might improve heat-tolerance in ruminants, due to increased post-rumen starch digestion and a reduction the heat increment of feeding. During stress gastrointestinal function may be compromised which could impact on site extent digestion. To characterize vitro rumen DM disappearance corn, wheat, 3% NaOH-treated wheat grains, grain samples were incubated during 0, 5, 8, 24 h at 39 °C buffered fluid. Then faecal pH whole tract apparent starch, DM, organic matter (OM) digestibility determined wethers fed, with either corn (CD), (WD) or NaOH- treated (TWD) based diets two experiments. In experiment 1, 22 fed CD WD (n = 11 per diet) three different stages climate controlled rooms: stage 1 (TNFR), 7 days thermoneutral conditions 18–21 40–50% relative humidity) 1.3 times maintenance feed intake; 2 (HSFR), (28–38 30–50% intake as TNFR; 3 (HSFU), HSFR 1.5 intake. 2, 31 10), 10) TWD 11) same temperature humidity regimes however TNFR received 1.7 while HSFU After incubation, untreated had fastest rate followed by (P < 0.001). Wethers lower 0.001) higher OM than those WD, was associated content diets. NaOH treatment did not affect being like WD. At low intakes (1.3 maintenance) there no effect whereas reduced OM, digestibility. However, similar metabolizable energy intake, higher. It is concluded reduce (in condition) without reducing (tested vivo) heat-stressed wethers. The study demonstrated can strategy increase retention under stress.