How the first-calf heifer performs in the breeding season and beyond begins long before that. Bob Larson, DVM, PhD, Kansas State University, says a goal to shoot for is over 90% of cross-bred heifers pregnant in a 60-day breeding season. If the heifers are examined prior to breeding to remove any questionable breeders, the success should approach 93–95%. "If the breeding season is confined to 45 days, I would expect a lower percent pregnant," Larson notes.
Dan Goehl, DVM, Canton Veterinary Clinic, Canton, Mo., often artificially inseminates the heifers. "Timed AI has become very popular due to labor issues," Goehl says. When timed AI is used, he plans to get 60% conception on Day 1. "These rates will vary but 60% is very attainable and often we can get higher conception rates than this. If we can get 60% AI on Day 1 and 70% of the remaining 40% at (or around) Day 21 then we would strive to attain 85–90% in the first 21 days and should have 95% or greater by Day 45." Goehl notes that this is on optimally managed heifers. They will have been tract scored to remove free martins, marginally mature heifers, etc.
In order to reach those goals, Larson and Goehl offer these 12 ways to help clients improve beef heifer fertility:
1. Select cross-bred heifers from dams with sound feet, legs, and udders that conceive early in the breeding season with minimal supplementation, and have producers by-pass heifers from cows that have had vaginal prolapses and other health issues.
It is important when retaining heifers from within your herd to select animals that are from parentage with the traits you wish to propagate. This can be done with computer records, a notebook or any system that identifies these animals. "Ideally we would have records of conformation, reproductive performance and growth/ performance potential," Goehl says. Recording birthdates or at least birth week is useful because heifers born early in the calving season will have an age advantage relative to females born at the tail end of the season.
Larson suggests also having producers mark dams (with an ear notch, special colored ear tag, etc.) from which heifers should not be retained.
2. Select heifers that will be at least 13 months of age at the start of the breeding season.
Larson notes that both age and weight are important for reaching puberty. "A tight calving season will result in a high percentage of heifer calves that will meet the target age."
Tightening the calving season will increase age and weight of the calves, Goehl says. "This is beneficial because it will increase the number of heifers available that meet the criteria needed for early breeding. It will also increase the age/weight of the entire calf crop, improving profitability."
3. Provide adequate nutrients post-weaning to reach 60% of mature weight by a month prior to the start of the breeding season for Bos taurus breeds and 65% for Brahma or Brahma-cross heifers.
Goehl says traditionally we have always thought of protein as the limiting factor in most rations, but with the use of new feedstuffs, "we now see energy being the limiting factor more often."
Larson agrees that energy is probably the most likely to be deficient in post-weaned heifers. "Energy or protein deficiencies are most likely to be associated with poor fertility, but a diet that provides sufficient energy, protein, and minerals is necessary for best reproductive performance."
4. At about yearling age, vaccinate the heifers against diseases that can cause abortion or infertility such as IBR (infectious bovine rhinotracheitis), BVD (bovine viral diarrhea), vibriosis, and leptospirosis. Some herds may elect to vaccinate against trichomoniasis.
A BVD biosecurity plan needs to be in place, Goehl states. This can vary depending on the ongoing herd health plan of a herd. "Purchased animals need to be tested unless coming from a herd that previously tested or that you have total confidence in their BVD biosecurity plan. In herds that we work with our biosecurity plan may not always include a test of every replacement if we are confident in our level of security."
Larson adds that PI testing of home-raised replacement heifers prior to the start of the breeding season may be beneficial in some herds and should always be done with purchased heifers.
5. Start the heifer breeding season approximately one month prior to the adult cow breeding season.
Heifers are more likely to have calving difficulty than adult cows, therefore by breeding heifers before the mature cows, attention and labor can be concentrated on the population with the largest risk of dystocia. "Heifers need extra TLC," Goehl says. "Also, nutritional requirements are different from that of mature cattle and these animals need to be segregated from each other both leading up to, during and after calving."
In addition, the second pregnancy is the most difficult to conceive. "These heifers are growing, milking and trying to breed back, and reproduction is the lowest priority for the animal," Goehl explains. "A heifer that calves late in the calving season will have a very difficult time breeding back on time to be in the calving season the following year. Managing heifers to breed with the second calf is one of the biggest if not the biggest challenge of heifer management."
Because heifers take longer after calving to resume fertile cycles than mature cows, by calving heifers ahead of cows, it is more likely that they will have resumed cycling by the start of the next breeding season, Larson adds.
And finally, because calves from heifers are at greater risk of developing calf scours, by having heifers calve early in the calving season while environmental contamination with scours-causing pathogens is minimal, disease risk is reduced.
6. Utilize estrous synchronization and artificial insemination (AI) to high-accuracy calving ease bulls if possible.
Having heifers calve early in the calving season allows them more time to resume fertile cycles before the start of the next breeding season. Estrous synchronization and AI allows producers to breed more heifers during the first week of the breeding season and increases the number of heifers that have had two chances to conceive by the 25th day of the breeding season.
7. Palpate the heifers approximately six weeks prior to breeding to determine breeding soundness (reproductive tract score) particularly if utilizing AI.
Finding freemartins, very immature heifers, or pregnant heifers prior to the start of the breeding season will increase the success of an estrous synchronization and AI program as well as allow more appropriate management of these non-breeding animals. "The expense of a non-breeding heifer is exaggerated when AI is used, but these animals need to be culled no matter if you are utilizing AI or natural service," Goehl says.
Eliminating non-breeders as early as possible will help the bottom line. "Nothing is more frustrating than managing a heifer all the way through until calving to find out she is a non-breeder," Goehl states.
8. Breed heifers to bulls with high calving ease EPDs (or low birthweight EPDs).
Successful heifer management does not end until the heifers have a live calf at side and are re-bred early in the breeding season for their second pregnancy. Larson explains that calving difficulty is a greater risk for heifers than for adult cattle because heifers have not reached their full skeletal size; therefore selection of bulls that are not likely to contribute to calving difficulties is more likely to result in the birth of a live calf, a short postpartum period until fertile cycles are resumed, and heifers becoming pregnant early in next breeding season.
9. Limit heifer breeding season to no more than 70 days (many producers prefer a 50-day heifer breeding season).
Heifers that calve late in the calving season are often not able to resume fertile cycles in time to have two or more opportunities to be mated in the subsequent breeding season. To prevent heifers from having one calf and then being culled from the herd for being open after their second breeding season, they should ideally calve in the first 50 days or less of the calving season and no later than by day 70.
10. If utilizing AI, palpate about 100 days after breeding to accurately determine if heifers settled to AI mating.
It is easier to accurately determine the approximate length of gestation if the heifers are palpated when the fetus is 40 to 100 days of age. By palpating early and identifying those heifers that became pregnant to an AI mating, the success of the synchronization and AI breeding can be determined (and any problems investigated), early calving heifers can be identified for close observation as the calving season starts, and breeding success of the natural service bulls can be easily distinguished from the AI success.
Goehl notes to remind producers that even if they have 100 heifers AI bred on one day, there is still a bell-shaped curve calving distribution over approximately 14–21 days (10 days either side of date conceived).
11. Maintain heifers on a plane of nutrition that allows them to reach 80% of mature weight by the start of calving.
In order for heifers to calve in good body condition so that they are less likely to have calving difficulty and can resume fertile cycles by the start of the next breeding season they need to be gaining enough weight to reach 80% of their mature weight by calving. Body condition at calving has a strong influence on the length of time it takes for heifers to resume cycling. "Heifers that are thin at calving are less likely to be cycling at the start of the next breeding season than heifers in good body condition," Larson says.
12. Do not allow heifers to lose weight between calving and the start of the next breeding season.
Heifers that lose excessive weight after calving are much less likely to become pregnant early in the next breeding season. If available forage is not adequate to maintain body condition, harvested forage or supplement will be necessary to achieve satisfactory reproductive performance.