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The makings of a perfect storm

Nutrition with John McKinnon

The winter of 2016-17 is shaping up to be a challenge for cow-calf operators across Canada. While much of October and November were relatively stress free in terms of winter’s wrath, as we moved into the new year, extreme cold and snow has gripped much of the country. Coupled with hay shortages in Eastern Canada and a lot of poor-quality hay harvested in Western Canada, we have the makings of a perfect storm that has serious implications for the cow herd, particularly with respect to calving and subsequent reproductive performance. Since the calving season is approaching for most of you, it is an ideal time to remind oneself of the impact that cold weather has on the nutritional needs of the pregnant beef cow, particularly as she enters the last trimester of pregnancy.

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Consider a group of 635-kg (1,400-pound ) cows, five to six months in calf fed 12.5 kg of an average quality grass hay that tested 55 per cent total digestible nutrients (TDN) and nine per cent crude protein (CP; DM basis). If these cows (condition score 2.5 to 3.0) are adapted to a relatively normal winter (i.e. -15 C to -20 C with minimal wind), their energy and protein requirements would be approximately six kg of TDN (or 12.3 Mcal of net energy for maintenance) and 730 grams of crude protein, requirements which would be met by their current intake. However, exposing these cattle to -25 C and a wind speed of 15 kilometres per hour will increase daily TDN requirements to 7.4 kg (an increase of 22 per cent). Prolonged exposure to this type of weather without accounting for this increase in energy requirements would result in significant weight loss (up to 50 pounds over 36 days according to Alberta Agriculture’s Cowbytes program). While most producers feel they know their cows and would be able to recognize if they are losing weight at this rate, it is surprising how a full winter hair coat can mask this type of weight loss and lead to unexpected nasty surprises (i.e. thin cows at calving). To combat this from happening, these cows would need to be supplemented with 1.5 to two kgs of barley grain or its equivalent.

As these animals move into the last trimester of pregnancy, their energy and protein requirements increase to 6.8 to 7.5 kg of TDN and 830 to 930 grams of crude protein, depending on whether they are in the eighth or ninth month of pregnancy (assuming no cold stress). Energy requirements are 17 per cent higher than in the sixth month of pregnancy. In this case, in addition to the 12.5 kgs of grass hay, these cows require 1.0 to 1.75 kg of barley, depending on stage of pregnancy to meet their needs. As in the example above, a two- or three-week stretch of cold weather would increase the energy requirements of these cows in the eighth month of pregnancy by 18 per cent and require 2.5 to three kg of supplemental barley in order to meet requirements for maintenance and pregnancy and to prevent significant weight loss.

When you look at the conditions I have described, there are several issues at play that should concern you as a cow-calf producer. First, from an animal welfare perspective, we do not want to see cows losing excessive weight over a short period due to our failure to provide sufficient energy to combat cold stress. Not only is it difficult to visually identify cows with a heavy winter hair coat that are losing weight, but you can also get fooled by assuming that the forage you are feeding is better quality than it actually is! This situation can easily arise due to the variable nature of last year’s hay crop. The only way to accurately identify the nutritional quality of your hay is to have it feed tested. There are several laboratories in Canada that will run a near infrared analysis on your forage for a reasonable price and have results back within a couple of days! If you have not done so, it would be worth the effort to have your forage tested so you can more precisely decide on what to feed your cows as they move through the remainder of pregnancy.

Equally critical is the impact of late gestation weight loss on the subsequent reproductive performance of the cow herd. Cows losing excess weight in the third trimester of pregnancy will exhibit delayed estrus following calving, particularly if postpartum nutrition is not adequate. This delay in breeding status can have several consequences including an increase in the length of the breeding season or, if the length of the breeding season is fixed, an increase in the number of open cows. As well, more cows will be bred late in the breeding season, a factor which negatively impacts next years’ weaning weights.

As I indicated at the start of this article, as we move towards this year’s calving season, a number of factors, some within and some outside of our control are converging that can have an impact on the reproductive success of your herd. Ensuring a balanced nutrition program that accounts for the changing needs of pregnancy, as well as for the effects of the environment, is your best bet to ride out this storm.

About the author

Contributor

John McKinnon is a Professor Emeritus at the University of Saskatchewan and a consulting nutritionist who can be reached at [email protected].

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