Dairy Cows Offered Fresh Chicory Instead of Ensiled Pasture during an Acute Heat Challenge Produced More Milk and Had Lower Body Temperatures

SIMPLE SUMMARY: Dairy cows are particularly susceptible to heat stress, and the type and amount of forage offered could affect their heat load during hot weather. Our aim was to determine the impact of offering dairy cows two different forage types at two different amounts. Cows offered chicory (low fiber) produced more milk and had a lower body temperature than cows that were offered pasture silage (high fiber). Overall, cows that were offered the high amount of forage ate more feed and produced more milk than cows that were offered the low amount, but there was no difference in body temperature between these cows. However, during the heat challenge, cows that were offered the high amount of forage had a greater body temperature than cows that were offered the low amount. This single disadvantage is not sufficient to justify the restriction of feed intake as a strategy for managing hot weather events. While feeding chicory to dairy cows appears to be beneficial, our experiment was not done under commercial conditions, so further work is necessary to confirm our findings. ABSTRACT: The frequency, duration, and intensity of heat waves in Australia are increasing. To reduce the impact of heat waves on milk production, novel management strategies are required. Altering the forage type and amount offered affect the heat load on dairy cows and offer potential strategies to ameliorate the effects of hot weather. Thirty-two multiparous, lactating Holstein–Friesian cows were assigned one of four dietary treatments: chicory high amount, chicory low amount, pasture silage high amount, or pasture silage low amount. These cows were exposed to a heat wave in controlled-environment chambers. Cows that were offered fresh chicory had similar feed intake to cows that were offered pasture silage (15.3 kg DM/d). However, cows that were offered chicory produced greater energy-corrected milk (21.9 vs. 17.2 kg/d) and had a lower maximum body temperature (39.4 vs. 39.6 °C) than cows that were offered pasture silage overall. Cows that were offered the high amount of forage had greater feed intake (16.5 vs. 14.1 kg DM/d) and energy corrected milk yield (20.0 vs. 17.9 kg/d) than cows that were offered the low amount, as intended, but with no difference in maximum body temperature (39.5 °C). We conclude that feeding chicory instead of pasture silage to dairy cows shows promise as a dietary strategy to ameliorate the effect of heat exposure, and there was no advantage in restricting feed amount.