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Proper diets take a bite out of wind chill

When temperatures dip, it’s time to torque up the ration

Beef cow diets developed at the beginning of winter when temperatures were mild are not adequate to meet their energy requirements when new year’s winds blow. That’s because pregnant beef cows need extra calories in order to keep warm, rather than burning up fat reserves needed for the upcoming calving season. Therefore, if it is suspected that your cows need an energy boost to their feeding program, now is the time to do it.

As the photo shows (see above), I know of one 200-cow-calf producer that provides better feed so his cows are in good body condition for calving during the first week of February. He often jokes that his cows are too skinny, but he knows the true value of supplying enough dietary energy to his mature cows, so they maintain a BCS of 2.5-2.75 (thin = 1, and 5 = obese) by calving time, while his replacement heifers calve out at a little better BCS of 3.0. Despite cold weather, he also takes into account with a growing fetus (and placenta), the cow herd’s energy requirements are also up about 25 per cent and protein needs increased by 10-15 per cent compared to the start of the winter.

We both believe that nothing can strip body condition (cow’s energy fat reserves) off a gestating cow like frigid wind chill values setting over the prairies without dietary energy compensation. Cattle, like human-beings, experience wind chill temperatures, which encompass both ambient air temperature, humidity and wind speed. That combination of cold, when passing over the animal, draws heat energy away at a specific rate — the lower the wind chill, the higher the rate of heat loss.

For example, air temperature (40 per cent humidity) of -12 C with a windspeed of 40 kph yields a wind chill of -34 C. It draws more heat away from an unprotected standing cow in an open field than compared to -25 C under still skies. In this simple case, related factors mitigate wind chill such as sunlight exposure, whether it is snowing or freezing rain, fog (humidity), or wind direction as well as cow condition (re: BCS — fat insulation, health and hair coat).

When I make changes to my “wind chill” feeding programs, I use a research-proven rule of thumb as follows: for every 1 C drop in temperature below 0 C, the beef cows’ TDN energy maintenance requirements are increased by about two per cent. This means if our above early morning wind chill temperature is -25 C, there is an increase of about 50 per cent in the cows’ basic dietary energy needs. On a practical basis, this can be as simple as increasing the energy density of their diets by feeding higher-quality forage and/or some extra grain during the coldest time of winter.

To help determine when extra forage and grain should be fed, the following table outlines a sample feeding guide dependent upon the wind chill conditions to which most cow herds are often exposed:

When I put this table together, I assumed that the cow herd was exposed to prolonged periods of cold weather and thus achieved a state of acclimatization. That means maintenance metabolic rate increases in order to divert more dietary energy to maintain vital body temperature. This physiological change of late-gestation cows requires about 5.0-6.0 kg of TDN per head per day. I also assumed medium quality hay of 50-55 per cent TDN and heavy barley of 75 per cent TDN is fed. Last, a well-balanced 2:1 mineral (and vitamins) is provided as loose mineral at the rate of 70-100 g per head per day.

This exercise is a good testimonial that producers should save their better-quality forage (re: energy and protein) for midwinter’s coldest months and forgo feeding a lot of straw or low-quality forages, which may not meet the cows’ increased energy requirements despite heavy grain supplementation.

Case in point: I know another producer that relies on feeding barley-straw supplemented with 14 per cent cow-calf screening pellets to his cow herd, all winter long. A couple of years ago, he told me he noticed during a period of extreme cold weather, his cow herd filled up only on the straw in the forage-ring feeders until their guts were visibly distended and a few cows died as a result. In the end, I suspect that his cows engorged on his low-quality forage and due to a significant reduction in its rate of feed digestion and passage led to the fatal cow impactions.

This producer could have saved himself a lot of trouble and money if only he implemented a suitable feed program that supplied enough dietary energy, particularly during the coldest weather, so precious body condition of beef cows was maintained.

He could have also coupled such common sense by reducing direct impact of low wind chill in the first place upon his cows. For example, I have visited many of his neighbours that make use of tree stands and portable windbreak fences that reduce wind chill temperatures by five to 10 C, or make use of pole barns that cattle can go into when wind picks up. In the same way, I also advocate fresh straw be put down in loafing pens to allow cows to lie down on an insulated and comfortable bed.

Granted, there are occasions when wind chill conditions are so severe that we cannot keep cattle entirely out of the wind or feed them enough good-quality feeds to meet their energy requirements. In these conditions, we should give it our best efforts and hope extreme weather doesn’t last.

About the author

Columnist

Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by email at [email protected]

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