As calving season starts heating up in spring-calving herds across the U.S., livestock producers should start planning for the breeding season and managing the postpartum interval, which would be the time frame from calving to the resumption of estrus.
A successful breeding season begins with management decisions made prior to the start of the breeding season. Some of these management decisions that may help to increase rebreeding efficiency would include managing and monitoring body condition score (BCS) and developing a plan to shorten the postpartum interval in first-calf heifers and late-calving cows. This period from calving until the cow conceives is the most critical period in a cow’s production cycle, and minimizing this time period is important for several reasons.
A shortened postpartum interval or large percentage of cows cycling prior to breeding will result in having increased conception rates than cows that cycle later, which is largely due to cows having more chances of getting pregnant during a defined breeding season.
Early conception results in two additional benefits, which are calving earlier the following cycle that allow for more opportunities to get pregnant and increase their longevity in the herd, and will also result in larger calves weaned at weaning time. These benefits of early conception are why managing the postpartum interval is important for economic sustainability.
Managing the postpartum interval
To optimize rebreeding success, livestock producers should develop a plan to manage the postpartum interval during early lactation, which is especially important in their first-calf heifers and late-calving cows. To maintain a yearling calving interval, recovery from calving and rebreeding should occur within 80 to 85 days postpartum. The early postpartum period has the greatest nutrient demands a cow will experience during the entire production cycle. Nutrient requirements will increase after calving until peak lactation, which generally occurs around 60 days postpartum.
Adequate nutrition in the form of energy and protein to the cow is important for uterine involution, critical for colostrum and meeting the nutrient needs to support milk production. This can be a large challenge in some environments due to limited nutrients in semi-arid and arid environments. If requirements are not being met, the postpartum interval can be increased, causing a delay in conception date and subsequent delay in calving. Prolonged anestrous periods are one of the major factors reducing percent calf crops and economic loss in beef cattle operations. Young cows and late-calving cows have one characteristic in common that will greatly impact their reproductive success: anestrus or prolonged anestrous periods.
After each calving, cows undergo a period of time when they do not come into estrus. This anestrous period can be as short as 17 days but can also last as long as 150 days depending upon a number of factors. On average, mature cows will have a postpartum interval of 45 to 70 days, while first-calf heifers are more challenged to recovery from calving and cycling again with a postpartum interval of 70 to 120 days. This prolonged anestrous period or postpartum interval is why pregnancy rates in young cows are often the lowest in the cow herd, which is tied to their inability to consume enough energy for maintenance, lactation and growth.
Body condition score
Proper nutrition and adequate BCS at calving can reduce the postpartum anestrous period and reduce the postpartum interval. Body condition scoring is an effective management tool to estimate the energy reserves of a cow. Traditional recommendations suggest cows need to be nutritionally managed at a BCS 5 or greater at calving for optimal reproductive performance. However, within any year, the normal variation among animals in a herd will result in some cows being below and some above the average BCS of the herd at any given time. This variation may reflect differences in stage and level of production (especially milk), cow size (maintenance energy requirements) and fleshing ability.
As discussed above, constraint to reproductive efficiency in beef herds is the duration between calving and resumption of estrus post-calving. Cows that calve in a thin BCS (BCS 4 and less) have been shown to have a longer postpartum interval and reduced pregnancy rates than cows calving in a BCS of 5 or greater. Although calving BCS can influence rebreeding and performance of cows, it does not mean thin cows will always result in decreased reproductive performance. There is evidence that thin cows at calving can achieve a high pregnancy rate. If thin cows are not nutritionally challenged after calving with inclement weather conditions or nutritional restrictions, reproduction may not be reduced.
A large impact on reproduction is direction and magnitude of bodyweight change post-calving and through breeding. The goal is to shorten the period of weight loss by increased nutrient supply so positive bodyweight gain can be initiated as soon as possible and the cows can start cycling. If nutrient intake is decreased postpartum in overconditioned beef cows during late gestation, cows with greater BCS at calving may exhibit a greater bodyweight loss and decreased reproductive performance.
Bodyweight nadir
Weight loss occurs after calving to supply nutrients for milk production since forage intake is insufficient. This is often the case in early spring-calving systems that don’t have quality forage or green-up until late April/early May. Bodyweight nadir is the time point when cows go from losing weight into gaining weight. Although bodyweight nadir measurements would be extremely difficult to measure for livestock producers, understanding the impact of the change of cows losing to gaining bodyweight is an important part of a successful breeding season. Research has shown that first postpartum ovulation in dairy cattle occurs 10 to 14 days after cows achieve bodyweight nadir. Similar responses in range beef cows have been found with high correlations between bodyweight nadir and timing of resumption of estrus.
Not only is achieving bodyweight nadir important for managing the postpartum interval, rate of gain during early lactation and into breeding can also impact conception date. Previous research has shown cows gaining 2 pounds per day versus 1 pound per day during the breeding season have almost a twofold increase in number of cows pregnant during the first cycle of the breeding season. At the end of the day, the goal should be to get cows gaining bodyweight as soon as possible after calving and maintain a positive gain during the breeding season.
Supplementation strategies
Post-calving is the most challenging time to increase BCS of cows because of the nutrient demands of lactation, but if cows are thin at this time, additional protein and energy are required in improving BCS. Because of the nutritional demands of lactation, it can be difficult to get cows to gain bodyweight economically post-calving. However, protein supplementation fed strategically has shown to improve fertility under certain conditions, including thin body conditioned cows. One thing to remember is: Not all protein is created equal for ruminants due to rumen fermentation. Rumen-degradable protein supplements like alfalfa hay or cottonseed meal help increase forage intake and digestibility of low-quality forages; however, once rumen microbes’ need for protein is met, rumen-undegradable protein like dried distillers grains can have a larger impact on cow performance.
Studies have shown that protein sources high in rumen-undegradable protein and low in rumen-degradable protein can increase pregnancy rates and decrease the postpartum interval in young beef cows. In addition to protein type, some feed additives have been used to effectively shorten the postpartum interval of young beef cows. Ionophores such as Bovatec or Rumensin have been shown to shorten postpartum interval on average of 18 days across several different studies with cows and first-calf heifers. A product called NutroCal, which increases glucose availability to ruminants, fed in protein cubes at low amounts (40 grams per day) during early lactation has shown to shorten postpartum interval of young range beef cows by seven days and increase overall pregnancy rates.
Reproductive strategies
Synchronization of the estrous cycle has the potential to shorten the postpartum interval and increase calf weaning weights and uniformity. Utilizing a controlled intravaginal drug release (CIDR) or a slow-release progesterone device can be used to “jump start” the cycle of late-calving cows. Research has shown that inserting the CIDR no sooner than 20 days after calving can initiate cycling earlier than it would have naturally occurring. For instance, estrous synchronization at 21 days postpartum in late-calving cows has been shown to shift subsequent calving date up by 28 days. Even if artificial insemination (A.I.) is not being utilized, estrous synchronization can help shorten the postpartum interval of thin cows or late-calving cows in the breeding season.
