Cows in moderate body condition (BCS 5 to 6) usually require an average of about 55 to 65 days to resume fertile cycles after calving – meaning that mature cows that calve during the first 35 days of the calving season in moderate body condition should be cycling during the first 21 days of the next breeding season starts. In contrast, cows that calve with a BCS of less than 5 require more days to resume fertile cycles, and have very little chance of having fertile cycles by the start of the next breeding season – possibly not until late in the next breeding season.
Good body condition at calving is even more important for the reproductive performance of young cows that are nursing their first calves compared to mature cows because first-lactation cows often require 80 to 100 days to resume fertile cycles after calving. First-calf cows must have a BCS of 5 or greater (preferably 6) to have acceptable pregnancy rates for their second breeding season. In order to reach or maintain a BCS of 6 for first-lactation cows, they should be separated from the mature cowherd and fed to gain the needed weight.
During the winter months, most cattle in the U.S. are consuming dormant or baled forage. In most situations, the forage is poor to moderate in quality. When cattle graze marginal to low quality forages, supplemental protein or energy is often required to enhance either forage intake or animal performance. Poor quality forages (grazed or hay) have two negative effects on cow diets – the first effect is lower intake. While a 1250 pound cow will consume about 31 pounds (as fed) of moderate to good quality forage, she will only consume about 24 pounds of poor quality forage. The second negative effect is that the amount of energy per pound of intake is reduced compared to higher quality forage.
Because of year-to-year variation in forage quality and weather stress, cow body weight and condition can have important year-to-year variation even when fed what appears to be the same diet. Slightly lower forage quality and increased weather stress can result in cows losing more weight than expected. If cows lose condition over the winter so that that they enter the spring-calving season with a poor body condition, calf health and cow reproductive efficiency will be negatively affected.
In general, mature cows in good body condition that are not nursing a calf and that only need to maintain weight can over-winter on forage alone if forage quality is at least moderate and weather stress is low. If cows in good body condition are forced to consume lower-quality forage or if winter weather is harsh, supplemental high quality forage or concentrate will be required to maintain body weight. If cows are thin and need to gain body weight prior to calving, moderate quality forage will not supply the needed nutrients, and supplemental concentrate or high quality forage must be fed. If only poor quality forage is available, even greater levels of supplement must be fed to add body condition to thin cows prior to calving.
Young cows carrying their first pregnancy require energy and protein for their own growth as well as fetal growth, which makes their nutrient requirements higher than those of adult cows. Most dormant or baled forages do not provide all the calories needed for first-pregnancy cows over the winter, especially if the cattle face any weather stress. Ranchers should plan on providing young cows with supplemental high-quality forage or concentrate for at least part of the winter. The amount of supplement required depends on the quality of the base forage (grazed or baled).
In order to determine the amount of supplement required for the available forage, you need to be able to estimate how much energy reserve the cows’ are storing as body fat. Body condition scores (BCS) are used to describe the relative fatness or body fat reserves of a beef cow. The most commonly used system uses a range of 1 to 9, with a score of 1 representing a very thin cow and 9 representing an extremely fat animal.
Body condition scores are an accurate measure of body fat and are convenient in that cattle do not need to be weighed, merely observed and palpated at a time when other procedures are performed. Depending on mature cow size, there is approximately 80 to over 100 lbs. difference in body weight per BCS. When evaluating body condition, it is important to handle the cattle, so that one is not mistakenly evaluating hair coat, gut fill, or stage of pregnancy. The areas to palpate when determining BCS are: ribs, back, backbone, and tailhead. The entire herd, or a subset of each age group, should be evaluated for BCS during the winter to allow adjustments in winter supplementation to occur before cows lose excessive body weight.
It is very difficult for cows to gain body weight on dormant forage once they have calved and started lactating – even if heavily fed. Therefore, cows should reach their desired breeding body condition by the time they calve. In order to have enough days for thin cows to gain weight, herds should be evaluated 3 to 4 months prior to calving. If evaluated at this time, the weight gain for a BCS 3 cow to reach breeding condition (BCS 5) will be approximately 1.5 to 2.0 pounds per day (which is very possible with good forage and supplementation). In contrast, if cows only have 2 months to gain 2 body condition scores, they will need to gain over 3 pounds daily – a much more challenging task.
