Reducing the Fermentability of Wheat with a Starch Binding Agent Has the Potential to Ameliorate Heat Stress in Sheep

Abstract Two experiments were conducted to determine whether a starch binding agent could (1) reduce the rate of fermentation of wheat grain and (2) improve heat tolerance in sheep. Firstly, fermentation kinetics and buffered rumen fluid pH variation were measured during in vitro incubation of wheat with 0, 1, 2, and 4% Bioprotect® (Feedworks Pty Ltd, Australia). Bioprotect® reduced gas production at 12 h in a dose-dependent manner (-6.4, -11 and -20% respectively; P < 0.001) and increased pH (P < 0.001), indicating slower ruminal fermentation. In a randomized control experiment, Merino lambs (n = 24) were fed either 50% wheat (WD, fast fermenting), corn (CD, slow fermenting), or wheat treated with 2% Bioprotect® (BD), with the balance of the diets being forage. Lambs were housed in climate-controlled rooms and exposed to 3 experimental periods: period 1 (P1: 7 days of thermoneutral conditions [18–21°C and 40–50% relative humidity (RH)] and fed 1.7×maintenance); period 2 [P2: 7 days of HS (28–40°C and 30–50% RH) and fed 1.7×maintenance]; and period 3 (P3: 7 days of HS as in P2, and 2×maintenance) with ad libitum water. Increases in respiration rate (RR), heart rate (HR), rectal temperature (RT) and left and right flank skin temperature (P < 0.001) occurred during HS, particularly during P3 (P < 0.001). Lambs fed CD and BD had lower RR (150, 137 and 140 breaths/min for WD, CD and BD, P < 0.001), HR (91.3, 85.3 and 85.9 beats/min, P < 0.001 and RT (39.7, 39.7 and 39.7°C P < 0.05). While there was no effect of diet, lambs reduced feed intake (-4%, P < 0.05) during P2 but consumed more (+16%) during P3. These data confirm that feeding corn or Bioprotect® treated wheat can be used as an ameliorative strategy to reduce the thermal load in lambs during summer.