With the exception of a few days, autumn in Western Canada was amazing. We enjoyed days of warm weather, which compared to other years about the same time was simply balmy. This year, many beef cows were kept out on pasture longer and remained in decent shape once they were brought home. Maintaining this precious body condition with a proper overwinter feed program is essential to a successful calving season.
It really becomes of matter of retaining the cows’ relative fat cover or energy reserves in winter, which is needed at critical times such as calving.
Field trials at various research stations around North America consistently prove that overwintered mature cows and replacement heifers that calve at a target body condition score (BCS) of 2.5 to 3.0 (scale of 1 = emaciation to 5 = obese) have a greater chance of a successful calving season compared to freshened skinny cows. Clear advantages of such optimum BCS in beef cows at calving are: an easier time at calving, nurse a more vigorous/healthier calf, show estrus/quicker to be rebred and pregnant in order to maintain a 365-day calving internal.
Although, there is no one scientific protocol to judge BCS in beef cows, one can use visual parameters and/or palpation techniques and start at the rear end of the cow. Look for and feel the magnitude of fat cover on the pin-bones, tail-head, hip bones, backbone and finally the ribs. A thin cow (BCS below 2.0) should look skinny with sharp and angular shapes, while an over-conditioned or fat cow’s bone structures are hidden. A cow with an optimum BCS of 2.5 -3.0 should have a good overall appearance without the look of being “too thin or too fleshy.” Fat still covers her hips, but they are still visible and moderate pressure on them can still identify some bone structure.
Nutrient demand changes
Retaining such optimum body condition in pregnant cows until calving is an “easier said than done” exercise, because a dramatic rise in the nutrient requirements during late gestation takes place for two main reasons: a growing unborn calf and oncoming cold winter weather.
First, during the start of winter, the cow’s fetus is small and its demand for essential nutrients remains relatively low until its dam enters her last 60 to 90 days of late gestation. From this point forward demands for total nutrients in the beef cow really start to accelerate.
Her unborn calf gains about 60 per cent of its final birth weight during this time, and this fetal growth combined with its developing placenta and accumulating ammonic fluids makes the late gestating cow gain one-half to three-quarters kilo per day. In addition, about a month prior to calving, antibody-enriched colostrum or the first milk for the newborn calf is being manufactured in the cow’s udder. Unseen to the naked eye, the cow’s reproductive system is already getting prepared to resume estrus after she calves. To meet these nutritional challenges of late gestation, an increase in the plane of nutrition is necessary. Dietary energy and protein in the diet should be increase by 25 to 30 per cent and 15 to 20 per cent, respectively.
Second, cows that calve between mid January until the end of March should also be put on a higher nutritional plane to account for an energy requirement increase by 25 to 50 per cent during periods of bitter cold weather.
Temperature rule of thumb
A cold-weather rule of thumb is for every 1 C drop in temperature below 0 C, the beef cows’ TDN energy maintenance requirements are increased by about two per cent. When the thermometer drops, metabolic triggers in the cow stimulates her feed intake, but they will only increase dry matter consumption at the very most by 30 per cent, often limited by physical constraints of the rumen and a reversal in feed digestibility. Since pre-calving cows can eat only so much feed during very cold weather, it is wise to increase the energy density of their rations by using high-energy and lower-fibre feeds.
Consequently, the existing body condition of cows (including replacement heifers), their calving date and current feeding program should dovetail with a more suitable late-gestation diet. For example: an adequate quality grass hay or mixed grass-alfalfa mixtures with an energy TDN of 55 to 60 per cent TDN and protein level of 11 to 12 per cent make excellent pre-calving ration.
If this forage TDN is energy shy, then 0.5 to 1.0 kg of grain such as barley can be supplemented. As mentioned, cold weather in January and February can further increase energy demands for cows trying to keep warm. Therefore, an additional 0.5 to 1.0 kg of grain might be provided. It is also important to purchase a commercial beef mineral with complimentary levels of calcium and phosphorus, fortified with essential trace minerals and vitamins A, D, and E.
One might want to implement some good management practices while providing these well-balanced diets to late-gestation beef cows. One suggestion warrants that thin cows and first-calf heifers be segregated from the rest of the main herd and fed as a separate group. They often do not compete well against older, more mature cows. Splitting off the younger and under-conditioned animals might also be an opportunity to feed them more nutritious pre-calving diets (higher-quality forages, or energy/protein supplements) due additional nutrient demands for growth or building back precious body condition, respectively. †