Animal Care

COLD FEET

Mark Newton-Clarke MAVetMB PhD MRCVS, Newton Clarke Veterinary Surgeons

Back in April, the hot sun but cold wind tempted Tracey and me away for a couple of nights by the sea. When I suggested this as a treat for a birthday, bags were packed for exotic Southern European sun until I admitted we were going to Weymouth. Well, it all turned out well as the weather was fantastic and with relatively few people around, the Dorset coast rivals anywhere in the world. Snuggled down in bed on the first morning away, I was informed that a sea swim was the first thing on the day’s agenda. Without wet suits. Or dry suits. Just swimsuits. Checked the water temperature…10ºC. Hmm. But off we went, towels in hand to Preston beach where a brisk easterly was coming in off the sea. Oh I know cold water swimming is the thing but you really have to harden yourself off gradually. ‘Bit like seedlings…’ I thought as the water rose to my neck and created a hyperventilation response. Quite involuntarily, I gasped for breath just like Gabi Roslin in the ice with Wim Hof and, had my head been under the water, I would certainly have aspirated a lung full. Careful to stay in my depth, there was no problem. Certainly not for Tracey who was breast-stroking for England through the surf and shouting at me to “GET IN!”. Luckily I couldn’t answer, the effort of breathing taking away any power of speech. Eventually, I regained control over my respiration and felt proud of my 5 minutes spent in the water. Not going to discuss Tracey’s 13 minutes but I must stress she regularly practises cold water immersion and so did I up until last October. (The Outdoor Swimming Society gives good advice on the important safety aspects of cold water immersion).

This episode got me thinking about two really interesting physiological topics that affect our pets (and us); control of respiration and body temperature. We take both for granted, along with other automatic bodily functions, until something goes wrong. Breathing hard and rapidly is obviously a normal

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response to muscular exertion, caused not by a reduction in oxygen levels in the blood but by an increase in carbon dioxide as a by-product of energy production. Terrestrial mammals are exquisitely sensitive to increases in CO2 that causes acid to increase (lowering pH) leading to respiratory stimulation via a brain centre. In the lungs, the acid is converted back into CO2 and expired, allowing recovery. The system works well providing lungs and circulation are all hunky-dory but dogs and especially cats can accumulate fluid around or inside the lungs due to heart failure, infection or trauma and this can severely compromise function. CO2 levels increase, O2 decreases and unless lung function improves, the situation can become rapidly life-threatening. Immediate treatment is oxygen therapy and urgent attempts to reduce the fluid, either with a diuretic or by a chest drain, depending on its location. Longterm, there are effective treatments that can work in some cases for months or even years, depending on the underlying cause.

So what happened to me in the cold water? Very little muscular effort was involved so why the hyperventilation? Well, an initial gasp followed by uncontrolled rapid breathing is part of the cold water shock response. We think it’s due to skin temperature sensors sending a barrage of signals to the respiratory centre, by-passing the normal acid-sensitive control system. This response is not to be underestimated as it almost certainly causes many human and animal deaths by drowning. As I said, if my head had been under the water, I would have inhaled enough sea to be in serious trouble. Happily, we see very few drowning cases among dogs and cats although very old animals that fall into garden ponds or swimming pools is not unknown. My dear departed Border Terrier, Trilby, did exactly that about a year ago. Luckily, I had placed an inclined stone slab in the pond that gave him just enough purchase to keep his head above water until I came to the rescue. He wasn’t allowed out unsupervised again!

Coldwater immersion has obvious effects on thermoregulation and control of body temperature is another critical element for all warm-blooded animals. For dogs, hypothermia is much less common than hyperthermia unless there is a specific medical problem. Why? I guess they are covered in fur that water often fails to penetrate and working dogs are habituated to throwing themselves into cold water. For the healthy adult dog, low temperatures are not usually a problem although toy breeds with sparse fur coats and little fat certainly can get cold as can newborn puppies and kittens. If denied a regular supply of mum’s milk, the neonate’s body temperature falls quickly, making them weak and unwilling to feed. Here’s a vicious circle that will take the lives of young animals in a few hours, hence our advice to weigh newborn puppies and kittens daily and keep them very warm.

Hyperthermia is always a summertime issue and although I have never seen a heat-struck cat, I have seen plenty of dogs with heatstroke. Why is this? Well, cats are very rarely locked in cars and are not exercised in the midday sun. Clearly blessed with far more intelligence, on hot days cats seek a cool corner and go to sleep. They do have their evolutionary background of hot climates but all the same, they modify their behaviour to suit the conditions. Very wise and a lesson for us all.

DAY IN THE LIFE OF A VET

SILAGE TIME ON THE FARM John Walsh, Friars Moor Vets

At the time of writing this article, we were just starting to cut and bring in our grass to make silage on the dairy farm at home. I thought it would be interesting to tell you all about the process of making silage. Silage is the main reason you will see tractors and trailers on the roads at this time of year and is a very busy time of year for farmers.

In the UK we make different types of silages. Silage is the name given to a forage that has been preserved by ‘pickling’ using a natural fermentative process. Silage can be made from grass, maize or other conserved forages such as whole crop wheat or barley.

Another way of preserving grass is to make hay. This is preserved by drying in the sun and regularly turning. Due to our climate, it is much easier and quicker to make silage, which doesn’t rely on lots of sunny days to dry out the grass.

Farmers aim to cut the grass at the optimum time of its growth, so it contains the highest amount of energy and protein to feed to the cows. Higher energy and protein levels in this younger grass means farmers do not have buy-in as much feed to support the cow’s nutrient requirements to produce milk. If the grass gets too mature, it will lose much of its nutrient quality, resulting in bigger yields but of a much lower quality.

The grass is best cut in the afternoon, so it contains as much sugars as possible which have been made by photosynthesis during the day. The grass is left to wilt in the field for about 12 to 24 hours, to reduce the moisture content to around 60-75%. This moisture level will allow for optimum fermentation. If the grass is left out longer, it may get too dry, or it may get rained on – and both these will reduce proper fermentation. Also, the longer the grass is left uncut, the higher the loss of nutrients.

The cut grass is gathered in using a forage harvester. These machines can be either selfpropelled or pulled along and powered by tractors. The machine gathers in the grass and then chops into smaller pieces of about 1-2 inches and then spouts it out via a chute into the waiting trailers. The grass is then taken back to the farm and emptied in piles where it is pushed into a silage pit in thin layers which are compacted using heavy tractors to force out all the oxygen. If the silage is stored as bales, the baling machines will compact the grass as they work to force out the oxygen.

The next step is to seal the compacted grass with plastic to keep oxygen out. Mounds of silage are covered with huge polythene (plastic) sheets and weighted down; bales are covered with a plastic wrapping.

Removing and keeping out oxygen is a key part of making silage. This is because fermentation has to occur under anaerobic (oxygen-free) conditions, or the correct type of microorganisms won’t grow.

While oxygen remains, plant enzymes and other bacteria and microorganisms react with the plant sugars and proteins to make energy, reducing the amounts of these nutrients in the grass.

Once all the oxygen is used up, lactic acid bacteria start to multiply. These are bacteria that are needed to make the silage, and they turn the plant sugars into lactic acid. This causes the pH to drop (the mixture because more acidic). Once the pH is around 4-5, the sugars stop breaking down and the grass is preserved until the silage is opened and exposed to oxygen.

If the pH isn’t low enough, a different kind of bacteria will start fermenting the silage, producing by-products (like ammonia) making the grass less edible to the cows.

Once made and if the silage remains sealed, it will keep for several years. It can then be fed to the cows when needed to help farmers keep producing delicious milk during the winter months.