Most producers start unpredictable western Canadian winters by reckoning feed supplies against cow numbers, judging whether the hay pile will get the herd through until pastures are ready next spring. In the high-tech environment of today, it’s easy to overlook the simple things like the long-term implication of monitoring body condition of brood cows through winter.
Inadequate nutrition during gestation creates lingering reproductive losses for the entire herd. More specifically, there is a loss of reproductive momentum measured as increased calving intervals, open cows and failure of replacement heifers to be successfully integrated into the herd. Thin cows at parturition affect calf-weaning weights in the fall and long-term calf health. Post-calving reproductive performance is seriously affected when cows are thin at calving. The importance of fetal programming and the role it plays in long-term development of replacement heifers born from dams nutritionally compromised during gestation is just starting to be understood.
A critical element of managing brood cow nutrition through winter comes down to managing energy reserves of individual cows and groups of cows based on maturity and body condition. A practical way to estimate energy reserves is by hands-on evaluation of skeletal fat deposits through body condition scoring. Body condition scores (BCS) are based on a scale of 1 to 5, with a 1 being extremely thin and 5 obese. BCSs at key times through a production cycle reveal if cows are losing or gaining body condition. For optimal performance mature cows should be maintained at a BCS of 2.5 to 3.0 and first-calf heifers at 3 to 3.5 at calving and through their first breeding season.
Producers should talk to their veterinarian or beef extension specialist for more information on body condition scoring. The Beef Cattle Research Council (BCRC) website offers videos, fact sheets and other tools that describe how to do it.
Assessing BCS in the winter is critical because it corresponds to the third trimester of pregnancy for most spring calving herds. The majority of fetal growth occurs during the last trimester. The template for many organ systems is established during this period, including things like the structure of skeletal muscle and future ovarian function. Nutrient requirements of the cow sharply increase, especially through the last 45 days prior to calving. If body condition scores indicate cows are thinner than desired, the plane of nutrition can be altered, but adding weight through the last trimester requires close attention to the adjustment of energy and protein. To improve BCS by one point in 90 days — about 200 pounds for a 1,400-pound cow — requires 20 per cent more energy; to increase one point in 60 days requires 30 per cent more. It’s not a bad idea to seek help in balancing rations if these kinds of adjustments are called for prior to calving.
After calving, the nutrient demands associated with lactation make it more difficult and expensive to add condition. Eighty-two days after calving represents the most crucial period in the beef cow’s year. Not only must she nurse a calf, she must be ready to rebreed within 80 to 85 days to calve at the same time next year.
A common misconception regarding pre-calving nutrition is that feeding cows too well results in increased calving difficulty. This is seldom the case. Some over- conditioned cows may deposit fat in the birth canal, which can lead to calving difficulty. The bigger problem lies with underfeeding cows prior to calving. Thin cows produce lower-quality colostrum and overall calf survival is reduced. Research shows that the plane of nutrition prior to calving influences calf vigour. Calves from cows on a maintenance or high plane of nutrition stand and nurse more quickly.
With everything else staying equal, a two per cent improvement in reproductive efficiency lowers cost of production by $16.50/head (2012 figures).
The replacement heifer
The objective with repalacements is to develop an adequate number of heifers that reach puberty and cycle regularly at the start of their first breeding season. Because of her increased nutritional needs, a first-calf heifer should remain on the heifer development ration until she breeds back and weans her first calf.
A replacement heifer represents the future profitability and genetic improvement of the herd. Assuming a restricted breeding season and a somewhat static weaning date each year, the age of calf at weaning has a large impact on pounds of calf weaned. This is particularly important if calves are sold at weaning. Therefore, it is important that heifers conceive early in the first breeding season. Researchers at Montana State University concluded heifers that conceive the earliest contribute the most to the efficiency of the herd.
A replacement heifer is costly to develop. She must be managed and fed separately from the rest of the herd. However, since she will not produce any economic return until she is approximately 2-1/2 years of age (when she weans her first calf), she is also an easy target for mismanagement. The expense involved in her development only adds to the importance of the future calves weaned from this properly managed first-calf heifer. It is more economical to spread her development costs over several calves, rather than one if she happens to show up open after her first calf.
The weight and body condition of pregnant cows is dependent on a given plane of nutrition. A cow’s nutrient intake directly impacts nutrition of the developing fetus. Nutrient intake for the beef cow varies considerably from year to year depending on the growing and harvesting conditions of forages. There are also dietary changes that typically occur during critical times of gestation as cows transition from grazing to stored feeds. There are fluctuations in energy needs as temperatures decline from fall into winter.
The end result is that pregnant cows often undergo significant changes in body weight and fat level during the course of gestation, and these changes often vary from year to year.
Research has shown that major changes in the level of energy and protein in the diet of cows in late gestation affects birth weight, vigour, and health status of the newborn calf. More recent research shows that cow nutrition through early gestation may have an impact on traits exhibited much later in a calf’s life. As well, dietary intake during late gestation may exert an influence on calf performance much later down the road.
Optimal nutrition through the calendar year governs the success of heifer development. The ideal feeding program is one that recognizes the ability of the beef cow to safely and economically gain and lose body condition. Benefits from doing this well get carried forward into a heifer’s years as a brood cow. Performance gains show up as reproductive events like postpartum interval, services per conception, and calving interval. Milk production, weaning weight, and calf survival get added to the mix.
In this way, monitoring energy reserves during late pregnancy should be seen as an investment in the future. That’s why it is critical to make body condition scoring a part of your routine management.