How can I get late calving cows to breed earlier so they calve earlier in the calving season next year?

A:  There are a number of things that producers can do that will encourage cows to return to estrus more quickly after calving and be more likely to conceive and calve earlier in the next calving season.

1. Body condition score at calving and plane of nutrition.
   Cows that are nursing a calf have the highest nutrient requirements of the year approximately 45 days after calving. These high nutrient demands are also when we want the cow to begin cycling again. Mature cows that are in a body condition score of 5 or higher at the time of calving and are maintaining or gaining weight will be more likely to return to estrus sooner than cows that are in a body condition score of 4 or less. Cows that are losing weight between calving and breeding are less likely to return to estrus and conceive.
    

2. Temporary removal of calves.
   Removing calves from cows for 48 hours or weaning calves has been shown to trigger cows that are in a body condition score 4 or 5 but are in anestrus to start cycling. 

   Dr. Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist, wrote,

   Short-term calf removal is the term that describes the temporary physical separation of the calf from its mother. This removes the nursing stimulus from the cow for about 2 days. Removing the suckling stimulus can encourage a few cows to start having estrus cycles a few days sooner than otherwise would occur. Removal of calves for 48 hours has shown to improve rebreeding rates of moderately conditioned (Body Condition Score 4 to 5) cows by 4-8%. This improvement, although seemingly small in magnitude, is substantial compared to the out-of-pocket investment. Short-term calf removal can be used at the first of the breeding season or in the middle or both depending on the labor situation. Do not expect short term calf removal to replace normal good nutritional management. Short term calf removal is not a powerful enough stimulus to "jump start" very thin cows. Those that are in a body condition score of 4 or less may need to have the calves weaned completely to allow the cow to recycle early in the upcoming breeding season.

   "The care of the calf during that 48 hours is actually quite simple. Most producers will make certain that calves access to some "sweet" feed and plenty of fresh drinking water. The calves will eat very little during this time.

   "Those cows that calve in the body condition score 6 or fatter can be expected to return to estrus early in the breeding season and should have high rebreeding rates. Although not harmful, the practices of early weaning, short-term calf removal, or feeding extra feed will NOT show significant advantages for these cows. In this situation, producers will want to continue their normal lactating cow supplementation programs until green grass provides the nutrients that these cows need.

   There is a myth that time of suckling during the 24 hour day influences return to estrus. There are no data that would support day-only nursing or night-only nursing has any effect on post-calving return to estrous cycles.

   Completely weaning calves is a more drastic practice but can be very effective. For more information on early weaning calves see the article Early Weaning Calves Sometimes Makes Sense (PDF 1.18MB).
    

3. Use of a progesterone controlled internal drug releasing device (CIDR) for 7 days.
   Research has shown that once a cow is 20 days after calving, the use of a progesterone CIDR can initiate cycling earlier than may occur naturally. By initiating estrus earlier, cows are more likely to conceive earlier in the breeding season. This initial estrus induced through the use of a CIDR is fertile and cows can be bred either by artificial insemination or through the use of natural service. Many producers associate the use of a CIDR device with estrus synchrony for the purpose of artificial insemination. However, a CIDR device may also be used effectively with natural service. Cow-calf producers who utilize natural service may benefit from identifying non-cycling cows that are at least 20 days post calving and utilizing a 7-day CIDR protocol to initiate estrus that coincides with the start of the breeding season. For more information on the use of estrus synchronization utilizing a CIDR with natural service, please see the UNL Extension Circular EC283 Synchronizing Estrus in Beef Cattle. 
    
4. Bull exposure to cows after calving.
   This practice has, in some circumstances been shown to decrease the time interval that it takes for a cow to return to estrus when compared to herd mates that were not exposed to a bull. The use of a bull that has had an epididymectomy can be used to induce estrus, but keep cows from conceiving until the start of the breeding season.
    
5. Nutritional "flushing" of cows with high levels of energy from calving through breeding.
   Nutritional "flushing" may have limited benefit in reducing the time that it takes for cows to return to estrus. However, adequate nutrition to maintain or improve body condition right prior to and through the breeding season has been shown to be beneficial for conception rates.

A cow must conceive by approximately 85 days after calving to maintain a yearly calving interval.

Calves born in the first 30 days of the calving season have many advantages over their contemporaries who are born later. Early-born calves weigh more at weaning and replacement heifers born early in the calving season are more likely to conceive early in the breeding season as a yearling.

Research has shown in a fixed-breeding season, two-year-old heifers that calve early in the calving season are more productive throughout their lives than herd mates calving later.

In a fixed-breeding season, cows that calve late in the calving season are less likely to become pregnant in the subsequent breeding season than early-calving cows. Cows calving early will have more opportunity to have multiple estrus cycles during the breeding season and therefore be more likely to conceive. The economic loss associated with later-born calves and the higher tendency of late-calving cows to not conceive in a fixed-breeding season highlights the potential benefits of inducing estrus earlier than may naturally occur for later-calving cows.