This was originally published in the DairyNZ Technical Series and showcases how important shade is to the health of a herd. High air temperatures (above 21°C) and exposure to solar radiation can affect cattle physiology and behaviour.

Cows limit heat load by seeking shade, lower heat production by reducing activity levels and feed intake, and dissipate heat by sweating and panting. In warm weather, lactating cows also spend more time around water sources and less time lying, a response which may expose more surface area for convective heat loss, or reduce heat conducted from a warm surface to the body.

When these strategies are ineffective, accumulated heat load can increase the core body temperature leading to decreased milk yield. In New Zealand, a reduction in milk production starts to occur at a Temperature Humidity Index (THI) of 68 (equivalent to 21°C and 75% humidity).

AgResearch and DairyNZ have developed a heat load index (HU) model to predict the likelihood of thermal stress based on weather predictions for grazing dairy cows. While THI models are widely used overseas to predict and manage heat stress, they do not account for solar radiation and wind flow, which alter heat load in grazing dairy cows.

Cows’ responses to excess heat load were assessed using measures of biological function and affective state to determine thresholds for moderate and severe heat loading. The model has enabled regional mapping of the seasonal risk of heat stress, showing that the Waikato, Bay of Plenty and Northland are at greatest risk of heat stress in summer.

The predictive model is being developed into a web-based tool for farmers to use to predict heat stress in risk areas and provide tactical management advice. 

Production and welfare benefits of providing shade to dairy cows are likely to occur before the animals develop signs of heat stress.

Summary

• High air temperature (above 21°C) and solar radiation levels can affect cows’ physiology, production and behaviour.
• Shade protects cows from solar radiation and is a valuable resource in summer. Providing shade will improve production by 0.5 L/cow/day in late lactation, as well as welfare.
• The shaded area should be sufficient for all cows to use simultaneously (at least 3-4 m2 shade/cow) to reduce aggression and improve the cooling benefits (reduced body temperature and respiration rate).

Dairy cows regard shade as a highly valuable resource in warm weather, for which they are willing to compete to gain access. Research shows that shade use increases with ambient air temperature and solar radiation1419 and provision of shade (3.6 m2/cow) in late lactation improved daily milk production by 0.5 L/cow.

One important feature of shade is the level of protection from solar radiation. Cows are able to distinguish between different levels of solar radiation and, when given a choice, prefer at least 50% blockage.

Another important feature is the total area of shade provided, yet few studies have compared the effects of different shade areas per cow. The focus has generally been on production parameters such as milk production of shaded versus unshaded groups of cattle.

These studies have recommended 3.5-5.6 m2 of shade/cow. However, changes in production may be a ‘downstream’ indicator of heat stress, in comparison to immediate physiological responses, such as respiration rate. For example, Mader ef a/22 demonstrated that beef cattle with access to 3.5 m2 shade/animal had higher feed intake and lower respiration rates than animals with less shade, but found no difference in weight gain.

The shade area provided is vital to reduce competition and optimise cooling benefits. Under high HLI conditions, cows provided with some shade (2.4 m2 shade/cow, cows could not use the shade resource simultaneously, so had to compete) had a smaller increase in respiration and body temperature than cows without shade. However, when cows were offered 9.6 m2 of shade/cow (all cows could use the shade simultaneously), the cooling benefits were greater and shade use doubled.

Cows’ use of natural shade on commercial farms in the Waikato was investigated. All cows could physically fit under the (tree) shade when they had access to 2 m2 shade/ cow, but there were many aggressive interactions and competition for the shade. Animals had high respiration rates and panting scores, indicating that the shade area was not sufficient for animals to cool down efficiently.

When cows had access to bigger areas of shade, more cows could use the resource simultaneously and the cooling benefits were greater.

In summary, cattle will use shade to prevent an increase in internal body temperature, but this heat mitigation strategy is only effective if sufficient shade is available. Preliminary findings indicate that cows should have access to at least 3 m2 shade/cow for effective cooling, but more research is needed to confirm this. 

While it is clear that shade is beneficial and valuable to cows at pasture, cooling with water when at the dairy is more efficient in reducing respiration rate and body temperature. The body temperature of dairy cattle often peaks during the afternoon milking, when it is affected, in part, by the distance and speed of the walk to dairy.

Sprinklers (and shade) at afternoon milking are effective ways to reduce heat load. Sprinklers alone, and sprinklers combined with shade, reduced respiration rate by 60 and 67%, respectively, compared with no cooling. Standing under shade and sprinklers while waiting to be milked both reduced body temperature, compared with no cooling.

Cooling with sprinklers can lower the body temperature for at least four hours after milking. However, on cooler days e.g. when THI <69 (equivalent to 21°C and 75% humidity), sprinklers may cool too much.

There is evidence that New Zealand cows find sprinklers aversive and prefer shade over sprinklers23. Research showed that 62% of cows preferred shade despite sprinklers being more efficient in reducing heat load and insect avoidance behaviours.

High voluntary use of sprinklers by cows has been reported in warmer climates, such as in California, thus indicating that water may be heavily used and beneficial in specific situations. Reasons for the difference between countries may be that the cooler weather conditions reduce voluntary use of water sprinklers, or due to the high levels of solar radiation in New Zealand.

SmartShelters have a range of suitable shelters for your dairy cow and herd health including loafing barns, compost barns and calf shelters.