Managing stock in the hot weather

IT would have been difficult to imagine even a few weeks ago that we would be considering the effects of a sustained period of hot, dry weather at present. Drought conditions in Ireland are very unusual, and it is timely to look at the implications for farm animals.

Compared to other animals, cattle cannot dissipate heat load from their bodies very well. Cattle don’t sweat effectively and rely on respiration to cool themselves. Cattle, of course, are ruminants, and the fermentation process within the rumen generates additional heat.

Cattle tend to accumulate a heat load during the day due to feeding, and dissipate heat at night when it is cooler. Demand for water will increase in hot weather, as the animals lose water from increased respiration and perspiration.

Consumption of water is the quickest method for cattle to reduce their core body temperature, and for this reason, water consumption will be greater than normal metabolic requirements under hot weather conditions. Essentially, all animals need access to fresh clean water at all times and should never be left without water. The signs of heat stress are increased breathing rate, sweating, water intake, decreased feed intake, milk production and composition.

You will notice changes in behaviour where animals seek shade, crowd together, and stand next to water troughs. As heat stress increases, cattle will begin to salivate and respiration rates will increase.

In severe cases of heat stress, cattle will be breathing openmouthed, with laboured effort. Animals with lighter coat colour tend to be more tolerant of heat; though sunburn can occur, particularly in white areas and hairless areas around the nose or muzzle. Heavier cattle tend to be more susceptible to heat stress.

Photo-sensitization may occur in sporadic cases. Photo-sensitization is different to sunburn, as it occurs when skin becomes more susceptible to UV light because of the presence of photo-dynamic agents.

Photo-sensitizing agents are mostly plant-derived and are thought to include plants such as St John’s Wort, buckwheat, and bog asphodel. The condition can be exacerbated when an animal’s liver function is compromised by issues such as liver fluke. Susceptible animals are affected immediately when exposed to sunlight and appear agitated and uncomfortable. They may scratch or rub exposed areas of skin (such as ears, eyelids, and muzzle).

Lesions may appear in whitehaired, non-pigmented, or hairless areas. If exposure to light stops at this stage, the lesions will soon resolve. The condition ‘galar ramhar’, which occurs in hill sheep in some area of Kerry. is an example of photo-sensitization.

If a farmer has concerns, he or she should contact his or her local veterinary practitioner. During times of increased heat stress, cattle should be observed closely to identify if additional strategies need to be implemented. Ensure access to clean drinking water at all times. Use paddocks with access to shade, provided by trees if possible, especially during the heat of the day.

Try to reduce time spent in holding yards and keep movement of stock to a minimum. Rotate stock in the evening rather than the morning.

This will encourage grass intake in the cooler evenings. With rumen fermentation and digestion taking place overnight, the heat associated with digestion will be less of an additional heat stress during the hot daytime.