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Are your beef cows ready to rebreed?

March 12, 2021
Cows in field

For any cow-calf operation, a primary goal is to enhance the ratio of pounds of calf weaned per cow bred annually. A critical component of reaching this goal is keeping the herd as close to a 365-day calving cycle as possible. To this end, shortening the postpartum anestrus interval and increasing first-service conception rates to reduce the need for cattle rebreeding are key topics of discussion and research within the industry. Both nutrition and body condition affect anestrus and conception, dictating the cows’ ability to rebreed successfully.

Identifying and correcting problem cows between calving and breeding is not an easy proposition. As such, the best option is to set a cow up for success before calving by ensuring that her BCS is between 5.5 and 6 and that her nutritional needs are met.

Return to estrus

The length of the postpartum anestrus is fundamental to determining the calving interval. Given a typical 283-day cow gestation period, cows must have a postpartum interval of 82 days to produce one calf every 12 months. Cows cycle from anywhere between 30 to 100 days after calving, with nutrition and cow age contributing to the anestrus length. In beef cows, the uterus returns to its non-pregnant size by around 30 days post-calving. Before cows are ready to cycle normally, an additional 10 days is required to complete the uterine involution.

Beef cows that calve early in the season and cycle early have better chances of fully completing their uterine involution and returning to their normal cyclicity before the start of the breeding season. Cows that are cycling before starting the breeding season are most likely to conceive on first breeding — and within the first 21 days of the breeding season.

Research has also shown that the nutritional requirements for beef cattle in late gestation affect the cow’s health and return to normal cyclicity. The importance of body condition scores and nutrition in relation to conception and pregnancy rates has been thoroughly studied, with results indicating that:

  • Cows need access to sufficient protein and energy to calve with a BCS between 5.5 and 6. Not only is being in the proper condition important for allowing the cow to produce high-quality colostrum, but this BCS must then be maintained throughout the breeding season.
  • Underconditioned cows are slower to cycle, skewing the 365-day calving cycle, and cows that lose condition between calving and breeding are significantly less likely to conceive.
  • Immediately following calving, the cow is using the nutrition she is provided with to recover from the stresses of the gestation period and calving, as well as to produce milk for her new calf. Only after those needs are met will the cow redirect her energy and nutrients toward preparing for the next breeding season.

A significant body of external work supports the use of fat supplementation to enhance reproduction, generally in relation to managing cattle BSC and/or avoiding a negative energy balance in transition animals. In these cases, oleic acid (C18:1) may be the preferred fat source, as it boosts energy being partitioned toward the cow’s body reserves. 

Alternatively, stearic acid (C18:0) is preferentially used as an energy source, and dietary supplementation may reduce the cow’s reliance on mobilizing her body reserves. All fat feeding should be carefully considered — especially the type of fat and the timing of the feeding, as there are instances in which supplemental fat has reduced reproductive efficiency by increasing anestrous, reducing intake and, in turn, the energy balance, or inhibiting prostaglandin synthesis.  

Conception success and embryo mortality

A lot of attention is given to conception rates in beef cattle. However, research from Ft. Keogh in Montana indicates that 90–100% of cows will conceive at first breeding and that it is actually early embryo mortality that gives rise to many open cows. 

  • Approximately 25% of cows suffer embryonic loss before the 28th day of their gestation period, with a further 8% of pregnancies lost before day 42. 
  • Unlike late-term pregnancy losses, early embryo mortality is often not noticed on the farm. These losses are often miscategorized as cows that didn’t catch on the first round of breeding.
  • Embryo mortality is estimated to cost U.S. cattle producers $1.4 billion annually as a result of open cows, lost productive days and rebreeding costs. 
  • Embryo survival is affected by a variety of factors, including maternal and fetal nutrition, genetics, maternal stress, parity and health. As a result, research examining this issue is limited, and often, no clear answer for reducing embryonic loss is determined.  

How nutrition affects reproductive success

Balancing energy and protein in cow diets is important, as lower conception rates are often observed in cows with very high dietary protein intakes. Excess protein can increase the urea concentration in uterine secretions, which results in elevated prostaglandin levels. As prostaglandin is a signal for the body to return to cyclicity, this mechanism may be partly responsible for early embryonic losses in some herds.

As with body condition maintenance, research indicates that fat supplementation may additionally have a direct impact on reproduction.

  • Dietary fat has been reported to increase follicle formation in super-ovulated cows, possibly by increasing the serum insulin levels as a mediating step. 
  • Luteinizing hormone (LH) secretion, which triggers ovulation and CL development, is controlled in part by an animal’s energy status; thus, fat supplementation that enhances the energy balance will also aid in LH regulation.
  • Dietary fat supplementation has also been reported to increase serum progesterone. A poor-quality CL or insufficient progesterone can both be responsible for pregnancy losses before implantation, particularly in cows that are bred on their first cycle after calving. This once again highlights the importance of early calving to provide cows sufficient time to complete their anestrus and return to normal cyclicity before the start of the breeding season.

Beyond energy and protein, trace minerals — such as copper, zinc, manganese and selenium — play key roles in health, metabolism and the general nutritional requirements of beef cattle. Sub-clinical deficiencies in trace minerals can lead to reduced cyclicity and diminished reproductive health. Minerals impact colostrum quality and calf immunity, but their value for the cow should also not be forgotten. 

Optimizing trace minerals can aid in maintaining optimal uterine health by reducing the risk of:

  • Metritis.
  • Retained placentas.
  • Other adverse events that lengthen the time needed for uterine involution and a return to normal cyclicity.

Nutrigenomics research has also shown that minerals affect several metabolic pathways related to the preparation of the endometrium for implantation.

Other factors affecting success

The period before the start of the calving season is a good time to go over your herd health plan. Connect with your veterinarian and other experts to ensure that your management and vaccination programs are in line with the best practices for your region.

This is also a good time to make sure that your recordkeeping is up to date. Diagnosing breeding and reproductive issues is often an exercise in looking back. Working from accurate records can make the difference in identifying the underlying causes and developing a plan to prevent them next year.

The bottom line

Beyond the importance of individual nutrients, timing the supplemental feeding of cows correctly is important. The last 50 to 60 days of the cow’s gestation period are well-known to be critical for colostrum quality, as well as calf health and growth — but preparation for calving and rebreeding go hand in hand. As it takes time for nutrients to be absorbed, metabolized and take effect in the animal, a feeding program to support reproductive soundness and breeding-related stresses should begin before calving and continue through the confirmation of pregnancy.

A few key indicators to monitor are the percentages of mature cows calving during the first 21 days of the calving season and of late-season-calving cows. If either of these metrics run above average, it is time to take a close look at your calving and breeding season program.

Simply put, cows need to be set up for successful rebreeding before calving. Waiting to think about the breeding season until after the calf hits the ground is too late to affect major change in your cow herd’s performance.


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