Heat stress: Cost-effective cooling for outdoor dairy cows

Heat stress is a major limiting factor in dairy production in tropical, sub-tropical and temperate climates during summer, presenting a significant risk to the sustainability of global dairy production. The common effects of heat stress in dairy cows are reduced feed intake and reduced milk yield and milk quality. The possible but less obvious effects are decreased reproductive performance and increased prevalence of animal health problems, as heat stress negatively influences animal welfare.

Evaporative cooling is the main means by which dairy cows can reduce heat load. Evaporative cooling is affected by wind speed, dry bulb temperature, relative humidity and the physical properties of the cow’s hair coat. Cooling infrastructure comes at a cost, and therefore cooling strategies must be cost-effective.

Most published work on cooling strategies for dairy cows has focused on cows housed in barns or feedlots. The current study focuses on cows housed on a feedpad or stand-off areas that are often used to get cows off wet paddocks as part of a strategy to reduce pasture and soil damage, increase pasture regrowth and as a place for the supplementary feeding of a dairy herd.

Reports show that in most dairies, heat load is usually managed during the hottest parts of the day using shade, fans, sprinklers or various combinations of these; however, an increasing trend is to have fans and other cooling strategies running 24 hours per day.

Day-only versus day-plus-night cooling

In this study, researchers from The University of Queensland used Holstein-Friesian dairy cows to determine the effects of adding nighttime cooling to daytime cooling on milk yield, rumen temperature and welfare of early lactation cows exposed to heat waves. The cows were equally assigned to one of 2 groups as follows:

• Day-only cooling group: Day cooling, which included overhead sprinklers (large droplet) and fans while in the dairy holding yard, plus ducted air blowing onto cows during milking, plus shade and fans at the feedpad and a shaded loafing area.

• Day-plus-night cooling group: Enhanced day and night cooling, which included overhead sprinklers (large droplet) and fans in the dairy holding yard, plus ducted air blowing onto cows during milking, plus thorough wetting (shower array) on exit from dairy, plus shade and overhead fans at feedpad, plus shaded loafing area and ducted fan-forced air blowing onto cows at night. In this group, the fans at the feedpad were turned off at night.

Higher milk production with day-plus-night cooling

Reduction in milk yield is common when dairy cows are subjected to high heat loads. Over the 6 days following one heat wave, milk production was greater in the day-plus-night cooling cows (3.61kg/cow/day) compared to the day-only cooling cows. This higher production was observed for the rest of the study period. Overall, the milk yield was 2.05kg/cow/day greater in the day-plus-night cows than in the day-only cooling cows.

“Enhanced cooling during the heat wave allowed the day-plus-night cows to recover faster than the day-cooling cows,” said the researchers. “Although the major aim during a heat wave is to reduce negative effects on health, well-being and performance, recovery after a heat event is important; that is, animals need to return, as close as possible, to performance before the heat wave, without any negative effects on health and well-being.”

Dry matter intakes were similar between treatments during the heat wave; however, over the 6 days following the heat wave, intake was 9.4% higher for the day-plus-night cows.

Rumen temperature and panting scores

The day-plus-night cooling cows had lower (39.51°C vs 39.66°C) rumen temperatures than day-only cooling cows on each day of an 8-day heat wave. The panting score of animals can be used to determine the severity of heat stress or animal welfare. The panting score for the day-plus-night cooling cows was lower than that of the day-only cooling cows at 0.68 and 0.75 units, respectively.

It was concluded that the lower panting score for the day-plus-night cows suggests that their recovery from the heat wave was quicker than for the day-only cows, but whether this was due to the cooling effect during the heat wave or the enhanced cooling after the heat wave was difficult to determine since the researchers did not measure the nighttime panting score.

“Collecting 24-hour respiratory data is an essential requirement for future studies. The use of panting scores without respiration rate data should be reconsidered because it does not permit fine-scale data analysis,” they said.

Cost-effectiveness

Following calculations based on 200 cows, the researchers concluded: “The combination of the shower array and the ducted air systems had a beneficial effect on milk production and cow welfare and is a cost-effective strategy for producers to consider with outdoor herds managed on a feedpad.” The cost of the ducted system used in the study was approximately AU$31,500 (€18,900) but produced AU$21,308 (€12,800) of additional milk income, meaning that 67.7% of the installation cost was recovered over the first summer.

“Over time, this kind of enhanced day-plus-night cooling system could provide powerful benefits for outdoor herds, from increased production and profits to boosted cow welfare,” they said.

This article is based on the original article by B. Gaughan, K. Sharman and M. R. McGowan. 2023. The effect of day-only versus day-plus-night cooling of dairy cows. Journal of Dairy Science, 106:5002–5017.