Grain Type Impacts Feed Intake, Milk Production and Body Temperature of Dairy Cows Exposed to an Acute Heat Event in Early Lactation

Abstract

The frequency, duration and intensity of heat events in Australia are forecast to increase. Different grain types result in different heat loads on animals, so grain selection could reduce the impact of heat exposure. Thirty-two multiparous Holstein cows at 86 days in milk were offered a basal forage diet plus one of four supplements: (1) BLY, rolled barley; (2) CAN, canola meal and rolled wheat; (3) CRN, disk-milled corn; or (4) WHT, rolled wheat. Cows were exposed to a 2-day heat wave in controlled-climate chambers. Overall, cows offered CAN had the lowest dry matter intake (DMI; 16.2 vs. 17.7 kg) but produced more energy-corrected milk (ECM; 34.9 vs. 29.6 kg) when compared with the other treatments. The results were similar during heat exposure. Cows fed CRN and CAN had the greatest body temperature (38.9 °C), and cows fed BLY had the lowest (38.4 °C). Despite this, cows fed BLY had the greatest reduction in DMI from the pre-challenge to the heat-challenge periods (-2.8 vs. -0.4 kg DM/d). There appears to be a small advantage to offering cows a concentrate with a greater protein concentration compared to one that has a greater concentration of fat or starch. The choice of grain to include in a dairy cow's ration during summers with acute heat events may simply be an economic one.

Keywords: cattle; feed type; heat stress.

Figure 1

Mean environmental conditions experienced by the cows (blue line) and mean vaginal temperature of all cows (orange line) during the base (B), pre-challenge (P), heat-challenge (H) and recovery (R) period. Shading bands show ± one standard deviation ($\widehat{\sigma }$) mapped relative to the mean ($\widehat{\mu }$). The pre-challenge and heat challenge were conducted in controlled-climate chambers. Cows were kept in ambient conditions at all other times.

Figure 2

Mean daily dry matter intake (DMI), milk yield (Milk), energy-corrected milk yield (ECM) and maximum vaginal temperature (BTmax) of cows offered barley (black line), solvent-extracted canola meal plus wheat (orange line), corn grain (blue line) or wheat grain (gold line) during the pre-challenge (P), heat-challenge (H) and recovery period (R). The gray band is ± one standard deviation ($\widehat{\sigma }$) mapped relative to the mean ($\widehat{\mu }$). The pre-challenge and heat challenge were conducted in controlled-climate chambers. Cows were kept in ambient conditions at other times.