Know when to wean in order to keep body condition score of your herd maintained.
Rick Rasby, Beef Specialist, Cow/Calf Management and Reproduction
University of Nebraska
Introduction
Many times I have discussed and you have read the importance of managing body condition of your cow herd. Body condition at calving, for spring-calving cows, has a major impact on reproductive performance during the next breeding season. Cows and 1st-calf-female in good body condition at calving, BCS 5 for cows and BCS 6 for 1st-calvers, will resume estrous cycles and breed early in the breeding season. How cows are managed late in the grazing season will have a major impact on their body condition as they enter the winter.
Time of Weaning and the Effect on Cow Body Condition
A production activity that has a major “drag” on how nutrients are partitioned in the beef cow is lactation. Cows have a nutrient need for lactation, and until the diet meets and then exceeds that requirement, nutrients will not be partitioned off to other activities, such as replenishing body energy reserves. The balance between nutrient (feed) resources available to the cow and level of milk production is critical. Too much milk matched with medium to low quality feed resources results in a cow herd that you are constantly trying to play catch-up with in regard to body condition. I think when feed resources and milk producing ability for mature cows is matched in an ideal production system: at weaning time cows would be a little thin, but once the calves are weaned, and that nutrient demand for lactation is removed, in about 45 days post-weaning, cows begin to gain back body condition. In addition, in this production system, cows would be in BCS 5 going into the winter without any supplementation. However, if weaning occurs late in the grazing season for spring-calving cows, and the grass resources are decreasing rapidly such that quality is low, then gaining back body condition will be a challenge without some supplementation.
To me the challenge is spring-calving, first-calf-cows and managing body condition of this group without a lot of supplementation. These females are the ones that are likely to be thin in the fall at weaning. Body condition is critical for this group of females and it impacts their stayability in the cow herd. Because they have not reached maturity, you are working with a smaller rumen compared to mature cows. This is the major reason why quality of the diet is so important. As we all know, warm-season pasture quality decreases as the season changes from summer and into the fall time of the year. From a young-cow management perspective, this is a critical time of the year to manage condition.
At our Gudmundsen Sandhills Laboratory, located in the heart of the sandhills of Nebraska, an experiment was conducted to look at the effect of weaning date of March-born calves on cow body condition score change. The primary grass resource at this location is warm-season native pasture where the nutrient quality peaks in late May and early June and begins to decline rapidly in August. They began weaning the March-born calves in mid-August and weaned every two weeks until the end of November. The relationship between weaning date and body condition score change appears to be highly correlated (r2 = .95) and appears to be linear or a straight line from August 18 to November 24. In addition, the slope of the line is negative. This means that for every two weeks that weaning is delayed passed the August 18, there is 0.1 of a unit decrease in BCS. In addition to the effect of weaning date on cow body condition, the data in this same experiment suggests that calf weight increased up until October 13 at the same time that cow BCS decreased. After October 13, calf gain was minimal as cow BCS continued to decrease. Knowing this information, can allow you to manage BCS of young, lactating females and more closely predict the impact of delaying weaning. In some management systems, it may be time of the grazing season to get condition back on them using the grass resource instead of waiting later in the grazing season when supplementation is likely to be needed.
Partial Weaning and Re-introduction of Calf and Dam
One management technique that in theory, to put condition back on young females and reduce the stress on the calf is to wean the calf for a period of time to “dry up” the dam then reintroduce the calf to its dam. This technique, if successful, would reduce the stress on the calf, because it is back with its non-lactating dam, and allow the cow to gain back body condition as she is no longer lactating. We have weaned calves for 4 days, 8 days, and 12 days then turned the calves and dams back together. Calves weaned at 4 days, 8 days, and 12 days all “mothered-up” and began suckling their dams. We measured milk production, and all cows that had their calves weaned at 4 days, 8 days, and 12 days produced milk after the calves were returned. Milk composition didn't change much depending on whether cows had their calves weaned for 4 or 8 days, but when calves were weaned for 12 days, milk composition was slightly different, indicating that the cows that had their calves weaned for 12 days were beginning to dry up. It appears to me that to use this management technique, calves would need to be weaned from their dam for at least 30 days for the dam "dry up" before dam and calf can be co-mingled.
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