To maintain an annual calving interval (≤ 365 days), conception must occur within 80 days of calving; however, the period of anestrus following calving is frequently greater than 60 days. Making sure cows stay on track will increase productivity in many ways in the cow herd.
Based on data from beef herds in Missouri only 60% of postpartum beef cows were cycling at the start of the breeding season, and the percent of cows cycling at the start of the breeding season has been correlated with pregnancy rates in postpartum beef cow. In addition, data from the University of Nebraska reported that heifers born during the first 20 days of the calving season compared to the second or third 20 days of the calving season had increased weaning, pre-breeding, and pre-calving weights; more heifers had reached puberty prior to the start of the breeding season; and heifers born in the first 20 day had greater pregnancy rates. Furthermore, data from South Dakota State University reported increased longevity of heifers that calve in the first 21 days of the calving season (See Improving longevity in beef heifers). Therefore, cows and/or heifers that calve late in the calving season may need some assistance if they are retained with the intent of them returning to calve with the rest of the herd and increasing their longevity in the herd. Research has identified several management practices that, when applied, may result in moving cows ahead to calve earlier in the subsequent calving season:
Suckling: Work from Texas A&M has reported that having a calf suckling a cows will extend the postpartum interval. Therefore, management strategies that reduce suckling frequency have been employed to reduce postpartum interval length and facilitate rebreeding. Methods of reducing suckling frequency commonly include early weaning, once-daily sucking, and temporary calf removal. Normally as suckling frequency decreases the benefit to postpartum reproduction increases. However, these strategies need to be implemented prior to the breeding season and special care should be taken ensure proper health of the calves.
- Early Weaning: Early weaning is normally only used in conditions such as drought, over grazing, or inadequate feed quality. Research over the past few decades have reported that calves weaned between 45 and 80 days of age resulted in increased conception rates. However, increased costs associated with early weaning and the increased labor and management associated with early weaned calves must be carefully considered.
- Once-Daily Suckling: Calves are only allowed to suckle once a day beginning at 30 to 40 days of age. Cows are introduced to their calves once a day for approximately 30 minutes each day. This management strategy requires daily sorting of cows and calves; however, once a cow has initiated estrous cycles and has been inseminated her calf can be returned to her. Normally this strategy should not last more than 40 days, and calves need to be provided proper shelter and nutrition during this time. Calf weights may decrease during the period of once-daily suckling, but previous research in Texas has reported no reduction in weaning weights.
- Short-term calf removal: This is the least aggressive method of reducing suckling frequency and requires less labor than the two previous methods. Short-term calf removal normally only lasts for 48 hours, and calves should be at least 40 to 45 days of age at the time of calf removal. You should be sure to provide the calves sufficient water, high quality hay, and a creep feed that is approximately 14% crude protein.
Progestin Treatment: A short exposure to progesterone is believed to be necessary for reprogramming the reproductive axis to resume normal estrous cycling. Therefore, treatment with a progestin prior to the breeding season will simulate a short cycle and initiate normal estrous cycles. The only progestin legal to be used in postpartum beef cows is the CIDR (Controlled Internal Drug Release). Previous research from the USDA Research Center in Miles City, Montana reported that treatment with a CIDR for 6 days was able to induce estrous cycling in 90% of short postpartum animals that were in good body condition (BCS >5) and 100% of the animals that ovulated following CIDR removal had a normal length estrous cycle.
Nutrition both before and after calving is also a critical factor in regulating the postpartum intervals. Research from the USDA Research Center in Miles City, Montana reported the biological priorities for nutrient utilization (nutrient partitioning) by cattle: 1) basal metabolism, 2) motor activity, 3) growth, 4) basic energy reserves, 5) maintenance of pregnancy, 6) lactation, 7) additional energy reserves, 8) estrous cycles and initiation of pregnancy, and 9) excess reserves. The preceding priorities for nutrient partitioning demonstrate that reproduction (resumption of estrous cycling and pregnancy) is a low priority, and cows need to be in adequate body condition at calving to begin having normal estrous cycles following calving. Consequently, underfeeding energy and/or protein has been reported to reduce pregnancy rates, first service conception rates, and to increase the postpartum interval.
Additional factors that also need to be considered in trying to reduce the anestrous postpartum interval include the age of the cow (younger cows have longer postpartum intervals), and dystocia at calving time (increased calving difficulty will increase the postpartum interval). While management applications such as synchronization programs and bull exposure can shorten the postpartum interval, cows should be at least 30 days postpartum before trying to inseminate an animal. This will allow cows to complete recover from changes that occur during gestation (uterine involution) and fertility to return to close to normal.
Source: Jim Krantz