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

## TL;DR

Different grains in dairy cow diets affect feed intake, milk production, and body temperature during heat events.

## Contribution

The study identifies that canola meal improves milk production while barley reduces body temperature in heat-stressed cows.

## Key findings

- Cows fed canola meal produced more milk despite lower feed intake.
- Barley-fed cows had the lowest body temperatures during heat exposure.
- Protein-rich grains may offer advantages over starch- or fat-rich grains in hot weather.

## Abstract

The incidence and severity of hot weather events in Australia are expected to increase, and dairy cows are particularly susceptible to heat stress. Different grain types used in the diet of dairy cows may reduce the effect of hot weather on cow feed intake and milk production. Cows were offered one of four total mixed rations, each with the same amount of alfalfa hay, pasture silage and grain, but with a different grain in each ration. Measurements were made before, during and after a 2-day heat challenge. Overall, cows offered the diet with canola meal consumed the least feed but produced more milk compared with cows offered other diets. Also, cows offered the diet with barley had the lowest body temperatures. While there were few major differences between the diets, there appears to be a small advantage in offering cows the protein-rich canola meal over the more starch- or fat-rich grains tested. The choice of grain to include in a dairy cow’s ration during summers with acute heat events may simply be an economic one.

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.