When the heat rises, we all suffer

Comment: The prospect of another summer of record-breaking temperatures raises issues not just for humans but for the millions of domestic animals in our care. The issues are global but have particular relevance here since we see ourselves, albeit mistakenly, as “feeding the world”.

Are we, shortsightedly, maintaining a pastoral system of raising animals that is already substantially out of date? We haven’t yet found a way of reducing the amount of methane that grazing animals produce. Even if, or when, we find a way to do so, or to reduce the numbers of animals, our summer temperatures will continue their trajectory into the unendurable.

Animal agriculture forms the basis of our diet and contributes to providing the affluence that enables our New Zealand way of life. Thus we steel ourselves against changes that question traditional farming practices and appear to threaten our economic security.

But what will it take for us to question our belief that 40 million sheep and just under five million dairy cows are able to survive temperature extremes of heat, as well as cold?

We don’t see them lying dead in the paddocks – at least not yet. But this is not to say they’re not stressed.

Heat is more difficult than cold for animals to adjust to because their ability to thermoregulate depends on how much they eat. Digesting food takes energy and this energy keeps them warm. In winter a well-fed cow or horse will always be warm, especially if the feed is hay which requires more energy to digest than fresh grass.

In summer, animals attempt to reduce their body temperature by eating less – not because they’re not hungry but because it’s the only way they have of keeping their body temperature as low as possible.

The discomfort cattle feel in heat begins earlier than ours – at about 20C – and it increases exponentially, as it does for humans, according to the humidity levels. Most at risk of heat stress are the black and white Holstein-Friesians which make up 35 percent of our dairy herds. The pale jerseys which used to populate the paddocks but are now only 10 percent of herds, remain comfortable at 24C.

Cows don’t sweat effectively, as horses do. They rely on respiration to cool themselves, so heat makes them drool and pant almost like a dog. According to Ministry for Primary Industries’ report on heat stress in farm animals, farmers can check the condition of their cows by observing their breathing rate. Normally this is 10 breaths per 10 seconds – faster is a sign of stress.

It’s hard not to believe that as temperatures rise, animals don’t feel stressed merely standing in the green treeless deserts that line our country roads, particularly in those areas susceptible to heat waves. In Canterbury for example, where dairy farms have replaced grain-growing, the northwest wind is notorious for bringing heat. Central Otago has an infamous continental climate of high summer temperatures.

But providing shade is problematic. Trees take 20 years to grow and individually or in clumps, need protection from ring-barking by animals, which will also eat growing shoots. The shelter belts we see along fence lines give limited shade.

Economics, however, may force the issue. A Temperature Humidity Index THI has been developed to understand the levels of heat tolerated by different breeds of dairy cow and the effects on production of their reduced feed intake. An increase in the index from 68 to 78 has been correlated with a drop of 10g per day in a cow’s production of milk solids. This may not sound like much but in large herds and over the summer, would likely be felt in farmers’ pockets.

Building roofed structures for shade in paddocks may be worth the expense.

In the meantime, dairy farmers are encouraged to make minor changes to their management practices. Cows can be kept in summer paddocks closer to milking sheds to shorten their walk. Water troughs are placed in farm races, yards cooled by spraying water over the animals and on the concrete floors.

The resilience of sheep to temperature extremes is often overrated, although it’s true they can maintain a near constant body temperature of 38.3C-39.9C. They, too, pant but they also sweat and their fleeces, if long, impede this process. I have seen heavily fleeced merino sheep lying in the pencil-thin shade of fenceposts and clustering in the shadow afforded by water troughs. Flocks will also stand in small groups to increase air flow rather than lie down, their heads lowered in the shade provided by the other sheep.

Mostly, though, our famous merinos are shorn before the summer heat.

MPI’s website cites research showing that heat stress is a major factor in lowering the fertility of livestock that are mated in summer. Studies also show that lactating animals produce metabolic heat (as do women) which makes them more susceptible to heat stress.

The most fascinating section of MPI’s website contains a report on wider aspects of animal welfare which, it notes, has historically focused on the physical function of animals.

“It is now, however, generally agreed that welfare assessments also need to take into consideration positive affective states, such as pleasure or being content, and the ability to perform behaviours that are important to the animals.

“This was reflected in an amendment in 2015 of the NZ Animal Welfare Act to include a statement that all animals are considered sentient, which means they can have positive and negative experiences and emotions.

“While it is still uncertain what this means to the animal industries in New Zealand, the research area of animals’ affective state is gaining increasing attention worldwide.”

Will this more profound sensitivity to animals’ needs make raising them increasingly energy-dependent and therefore costly? Facilities housing pigs intensively need air conditioning for the animals’ comfort and survival. Could this also affect industrialised dairying? Large enterprises are already moving herds away from pastures and into barns.

Recent reports of stress experienced by truck drivers transporting animals illustrate yet another problem of raising animals in a hotter world.

Drivers are legally required to take a break after five and a half hours’ continuous work. They’re also responsible for delivering the animals in good condition but keeping them cool depends on the flow of air as the truck moves. Once stationary, an ambient temperature of a mere 22C can climb towards 40C in the middle of the stock crate – with sometimes lethal consequences.

While drivers’ times at the wheel are limited and closely tracked electronically, animals are deemed fit to remain on their feet in a crate for up to 24 hours, according to MPI regulations. The maximum is 12 hours for days-old “unweaned” calves.

I once spent a night in Picton and heard the bellowing from two loaded cattle trucks also stuck, having missed the last crossing. How long, I wondered, would their total travel time have been? How often might this happen?