There are several kilometres of Highway 59 in southern Manitoba which provide a snapshot of winter-feeding programs. Despite several feet of snow in the winter, I often see many cow herds being overwintered along this stretch of road, since in each one of the adjoining yards are rows of hay bales that I can see are either put in bale feeders or rolled out. Although I cannot see the forage, I can only assume that it is fair-to-good quality, since the cows walking near the fenceline are in good body condition. I can also assume that if many of these cows are in late gestation at this time, they probably will calve out without many problems.
Calving success becomes a matter of supplying enough dietary energy and protein to late-gestation cows in order to maintain or achieve a BCS of 2.5-2.75 (thin = 1, and 5 = obese) by calving time, while replacement heifers should calve out a little better BCS of 3.0. With a growing fetus (and placenta), their energy requirements are up about 25 per cent and protein needs increased by 10-15 per cent compared to the start of gestation. The nutrient requirements of these first-calf heifers are slightly higher because their bodies are still growing. They should be fed to gain 0.25-0.50 kg daily in addition to fetal weight gain. Thin mature cows should be fed in a similar manner to gain body weight and condition.
As a beef nutritionist, the nutritional parameters of my overwinter diets for late-gestation cow herds are based upon the respective NRC (2001) beef cow requirements, namely: 55-58 per cent TDN, nine to 11 per cent protein, 0.25 per cent calcium and 0.20 per cent phosphorus and complemented with salt, essential trace mineral and vitamins.
Diet needs to meet energy requirements
Dry matter intake estimates are about 35 to 40 lbs. for mature cows, and 30 to 35 lbs. for replacement heifers. I also realize that by January the weather is going to be much colder compared to the start of winter, significantly elevating dietary energy requirements just to keep them, warm (re: maintain their body temperature).
For example, several years ago university environmental studies on beef cattle came up with a good cold weather rule of thumb: 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 that if an early morning temperature is -25 C, there is an increase of about 50 per cent in the cows’ basic dietary energy needs.
Simply feeding late-gestation beef cows more of what they are already eating will not likely achieve these new energy requirements during the coldest weather, despite metabolic triggers in the cow that stimulates her feed intake at the very most by 30 per cent. So, it is wise to take a practical approach to overwintering them. For instance, here are some of my suggested diets that should increase the winter plane of nutrition of 1,200 lbs. mature cows and 1,100 lbs. replacement heifers for their next few months before calving:
A friend who raises 400 Black Angus cows switches over to a higher-energy feeding program as outlined in Diet C, switching from a predominantly straw-based diet at the start of the winter. He ensiles a comfortable supply of barley silage every year. However, he did mention this year’s mediocre barley crop almost forced him to switch to the A or B late-gestation diets.
My friend’s philosophy is very much like my own, when it comes to feeding overwintering beef cows. That is, the sole purpose of the late-gestation cow diets is to increase their plane of nutrition in a timely fashion in order to help them cope with frigid weather and to maintain optimum body condition. The payoff of this plan is that a healthy herd of cows will be ready for a successful calving season.