How many days this summer will your herd be at risk of heat stress?

Cows are at risk when temperatures exceed 24 degrees Celsius at relative humidity of about 75 per cent or higher.

In some parts of the country, including the Waikato, Northland and Bay of Plenty, there are typically upwards of 18-19 days during the summer months where risk of heat stress is very high.

Heat stress affects not only cows' comfort and wellbeing but can also reduce feed intake, milk production and conception rates.

There are some low-cost actions that can be implemented mid-season to help cows cope with heat stress, sustain appetites and improve summer milk production.

Here are some ways farmers can reduce the impact of heat on cows:

• Delay afternoon milking until after 4pm on high-risk days.

• Plan grazing rotations so that close paddocks and paddocks with shade can be reserved for hot days (see paddock scoring system below).

• Bury reticulation pipes (water can get as hot as 50 degrees Celsius in a black pipe in direct sunlight). Keeping water temperature down will help improve the cooling effects of drinking water for cows on hot days.

• Install sprinklers over the yard – sprinklers that deliver a medium to large droplet size are best to minimise humidity. Put sprinklers on a 15 minute on/off cycle to maximise wetting, while minimising water wastage.

• Wetting down the yard's concrete for 30-60 minutes before bringing cows in will also cool down the dairy and yard area for milking.

• If feeding out, do it following the afternoon milking or early in the morning, when temperatures are cooler and cows' appetites are not suppressed. Offer highest quality pasture breaks at night for the same reason.

• Watch your highest producers for indications of heat stress because they tend to be more affected by heat, due to greater metabolic heat production.

• Look out for crowding around the drinking trough and/or shaded areas, not lying down as much as normal, reduced feed intakes, slowed rumination and increased breathing rates (greater than 60 breaths per minute).

• Take action when you start to see these signs in your herd and also when weather forecasts predict high temperatures.

Is your farm a heat trap?

Score your paddocks for heat risk.

Individual paddocks can be scored for their usefulness in reducing the effects of heat.
The system described on the Australian Cool Cows website (www.coolcows.com.au), can be used to estimate this risk. This is detailed below.

1. Give each paddock a score from 1 to 10 based on the amount of shade provided in the middle of the day (1 = no shade; 10 = each cow has 4m2 shade available).

2. Give each paddock a score from 1 to 5 based on distance from the dairy (1 = more than 2km; 3 = 1-2km; 5 = less than 1km).

3. Combine the scores for each paddock and rank paddocks according to their risk. Paddocks with the highest scores are the ‘coolest paddocks'.

Use this information when planning summer grazing rotations; for example, reserve paddocks with high scores for hotter days or daytime grazing, and use paddocks with low scores for the ‘once a-day' herds or night grazing.