A proven way to increase the pregnancy rate of young beef females is to increase the number of females that are cycling at the start of the breeding season. Following are several strategies that may improve short-term reproductive performance of young cows (two- to three-year-olds) by increasing the percentage of cycling females:
1. Adjust date of weaning: Early weaning of calves from young females may have more of an effect on reproductive performance than all other strategies combined, due to the substantial effect on body condition. However, according to a USDA-National Animal Health Monitoring Service (NAHMS) survey, most beef producers decide their weaning time based on calf performance and not on cow condition. Improvements to body condition and reproductive performance can be achieved if calves are weaned early from first-calf heifers. Removal of calves immediately reduces the nutritional requirements of young females by eliminating the energy demand for lactation. In addition, since suckling has an inherent negative effect on cyclicity after calving, females tend to begin cycling sooner if calves are weaned early. Body weight and condition can also be added back to young cows during a time when forages are more readily available in the late summer. However, there are several increased costs associated with early weaning: 1) facilities able to handle early-weaned calves, 2) labor that can manage younger calves, and 3) a feeding program that enables calves to maintain optimum performance and health from the time of early weaning until they are sold.
2. Monitor body condition score (BCS): According to another NAHMS survey, 42% of cows lost weight from just after calving (seven days after) until weaning. This loss of body weight occurred primarily during the time of year when forages were most available and typically at their highest quality, which also occurred during the breeding season. Producers should monitor changes in both body weight and body condition score (BCS) in young females from calving throughout the breeding season to avoid weight loss during this time of elevated nutritional need. To avoid weight loss, supplemental energy and/or protein should be provided to females. Use of the BCS tool has been shown to improve reproductive performance; however, less than 25% of all beef producers use this tool to manage the nutritional status of their cows.
3. Formulate a ration: Most young beef females should be supplemented with energy and/or protein from prior to calving through the breeding season in order for them to become pregnant early during the next breeding season. Producers using the BCS tool are able to quickly recognize that nutritional needs are not being met and can modify their nutritional program. About half of all operations across the United States with over 300 cows formulate a ration, yet less than 25% of all operations formulate a ration. Historically, ration formulation was slow and tedious; however, current computer-based ration formulation programs are easy and very low cost (several are free). A properly formulated ration ensures that the nutritional needs of a cow are met in order to optimize performance. A ration also helps to reduce feed costs by reducing the amount of overfeeding (especially protein). Ideally, a forage analysis should be completed prior to ration development to ensure that the calculated ration is accurate.
4. Consider additional supplements: Young beef females typically need supplemental energy in order to maintain appropriate body weight and condition prior to breeding. Fat can serve as a source of energy; however, there has been some indication that specific fatty acids contained within fat sources may also be important for reproduction. Consistent benefits of fat supplementation on beef cow reproduction have not been reported; however, fat supplementation prior to calving has resulted in a larger number of pregnant females in two experiments and no differences in another. Fishmeal (which contains elevated concentrations of omega-3 fatty acids) may improve the pregnancy rate of first-calf heifers, although results have not been repeated. Based on the information that is available, fat supplementation should probably be considered only if a low-cost fat source is available and if a substantial upside potential in reproductive performance of young females is possible. In addition to fat, several trace minerals are important for reproduction in several mammalian species. However, applied research on the effects of trace minerals on young beef cows is limited. To avoid the risk of depressed reproductive performance due to inadequate trace mineral intake, producers should analyze feedstuffs for trace mineral content and develop a trace mineral supplementation program to ensure that the needs of young females are met.
5. Use bull exposure: The number of young beef females cycling at the start of the breeding season can be improved via exposure to vasectomized bulls. Researchers have shown that exposing females to bulls beginning 30 to 45 days after calving can stimulate (or hasten) cyclicity in some females. The use of commercially available hormones—such as melengestrol acetate (MGA) or controlled internal drug release (CIDR) devices—to increase the percent of young females cycling prior to breeding has also been evaluated; however, results have been inconsistent. Furthermore, the cost-benefit ratio of using these products to stimulate cycling has not been addressed. Regardless of which of the above strategies is used, the cost-benefit of each strategy mentioned should be evaluated prior to incorporating it into an operation. Based on USDA survey data, it appears that many producers could modify their cow management strategies and probably improve their reproductive performance.
The reason that young beef females (first and second calvers) have trouble re-breeding is because they are simultaneously growing, lactating, and repairing their uterus after calving. Therefore, many young beef females need special nutritional treatment to increase their likelihood of re-breeding within the next breeding season. Optimizing young cow reproductive performance on cow/calf operations is always important for ranch profitability. Researchers have shown that producers can improve reproduction by modifying their management of young females during the post-calving period. Since lower pregnancy rates are more likely to occur in younger females (first and second calvers), investing in management practices and feedstuffs that may improve pregnancy rates can be beneficial.
