Scottish dairy growth: Building resilience in changing climates

Within the agricultural sector, dairy farmers are ahead of many others with most farms having undertaken a carbon footprint to identify the areas they can make improvements. This article considers another aspect of the climate change debate; the need for farming systems to be resilient and able to cope with the extreme weather events, very hot weather or periods of very heavy rainfall, which are likely to become more frequent.

If a cow becomes heat stressed, the feed intake will decline which in turn will affect milk yield about two days later (Image: web)

Heat stress

When a cow becomes heat stressed, feed intake will decline which in turn will affect milk yield about two days later. There could also be a reduction in fertility and an increase in embryonic loss and an increase in mastitis.

High producing animals are more vulnerable to heat stress since they generate more metabolic heat from the digestion of more feed. It is the combination of temperature and humidity which causes most stress and this is described as Temperature - Humidity - Index (THI). THI was originally developed by staff at University of Arizona.

When the temperature is 24°C and humidity is above 70% (THI between 72-75) cows will suffer moderate heat stress. When the temperature is 28°C and humidity is above 20% (THI 72-78) cows will also suffer moderate heat stress and if humidity reaches 80% (THI 80-82) cows suffer severe heat stress.

These may seem extreme situations and hopefully we will not get too many of them in Scotland, however researchers at SRUC analysed data from the Langhill herd between 1990 and 2011 which showed that even when the THI was above 55, milk yield and milk quality declines (Hill and Wall, 2015, Animal 9,pp 138-149).

In grazing systems heat stress can be reduced by providing shade either from trees, hedges or access to a covered area. Providing plenty of clean water is important in hot weather. If a cow eats 10kg DM of grass, this means it eats 83kg of fresh grass at 12%DM, in hot weather the grass will have a higher dry matter and at 18%DM the cow will only need to eat 55kg of fresh grass. This difference means, cows are taking in 30 litres less water from drier grass.

In hot weather, cows will not walk too far for water, so drinking troughs must be placed near shaded areas. Cows also want to drink water straight after milking so it is important to have a large enough water trough, with adequate water pressure, in the holding area if cows are kept in a group before being taken back to the field.

In housed systems the installation of fans can help with air circulation and keep the cows cooler. In very hot weather, fans combined with spraying water onto cows, can reduce the effects of heat stress.

An example given in the AHDB leaflet (https://ahdb.org.uk/knowledge-library/dairy-housing-ventilation) to reduce heat stress is spraying 1.5 litres/cow of water over a period of 60 seconds followed by four minutes of drying with a 10km/hr airflow. A convenient place for spraying the cows is in the collection area, avoid spraying water in the bedding area as damp bedding may lead to more mastitis problems.

In grazing systems heat stress can be reduced by providing shade either from trees, hedges or access to a covered area (Image: web)

Severe rainfall events

Periods of very heavy rain are a problem for all farmers. Good cow tracks are important for grazing cows as muddy tracks can lead to lameness. When cows are walking normally they put their rear foot roughly where there front foot has been, if they can’t see where their front foot is going then they could be treading on stones.

Gateways can be a similar problem if they have not been maintained. When cows are housed the challenge with heavy rain is to keep as much clean rain water out of the slurry or silage effluent systems. Keeping gutters and down-pipes in good condition is often a neglected maintenance area on farms but time spent on this can pay dividends when we have heavy rain.

Good cow tracks are important for grazing cows as muddy tracks can lead to lameness (Image: web)

Best sward for drought

Grass is a very resilient crop and will recover quickly from drought but the yield can suffer during dry periods. Deep rooting crops such as some legumes will continue to grow in dry weather. They can either be grown as a single species crop e.g. red clover or in mixed swards for grazing or conservation. There can be problems with the management of mixed swards but in the long-term, if there are drier summers, it may be worth considering.

The effects of severe weather will depend on farming system and soil type but it is likely there will be more of these events and when they occur it will be essential that the system can cope, without having to make drastic changes.