Introduction It may be easy to quickly say “Yes, I’m satisfied,” or “No, I’m not satisfied with the fertility of my Holstein heifers.” Nevertheless, to reasonably answer the question posed in the title of this article, we must first consider another question: What is the fertility level of Holstein heifers in the United States? Traditionally, reproductive research has focused on cow fertility. Consequently, it has been difficult to describe heifer fertility on a large scale, until now. An analysis of heifer fertility data by the Animal Improvement Programs Laboratory of the USDA was recently published in the Journal of Dairy Science. The paper may be accessed for free at http://aipl.arsusda.gov/publish/jds/2006/89_4907.pdf.

Records used were from Dairy Records Management System, Raleigh, NC, and AgSource, Verona, WI. These processing centers account for approximately 78% of the herds on DHI test, and 57% of the lactating cows on test. Although data from DHI Provo was not used in this study, it is noteworthy that the average age at first calving (and range) for herds in the northwestern and southwestern U.S. was 25.2 months (24.9 - 26.4 months), and 25.6 months (25.2 - 26.9 months), respectively, according to March 2007 DHI Provo data. Consequently, all dairy producers, regardless of geographic location, could benefit from this information and an analysis of their own heifer reproductive program.

Nutrition, growth and development
Although the focus of this article is heifer fertility, we must first discuss the importance of nutrition, growth and development, and puberty. All dairy producers should set realistic goals (see Table 1*) and monitor the growth of their heifers regularly.

To facilitate growth and development of your heifers, consult a nutritionist to provide expertise in ration balancing and growth monitoring.

Puberty
Puberty is defined as “the time at which reproduction by an individual animal becomes possible for the first time.” Simply stated, the first ovulation signals puberty. Holstein heifers will attain puberty at approximately 40 to 50% of mature weight (~ 550 to 650 lbs). In general, well-managed Holstein heifers should reach 550 to 650 lbs by 9 to 10 months of age. Monitoring growth of heifers is critical, as well-managed heifers fed a total mixed ration may grow faster and achieve puberty earlier than expected. Under poor management, heifers may grow slower and achieve puberty later than predicted.

How fertile are Holstein heifers?
Following 871,835 A.I. services, the average conception rate for Holstein heifers was 56.3% (Kuhn et al., 2006). In contrast to increased Jersey cow fertility as compared to Holstein cows (AIPL, 2005), Kuhn et al. (2006) reported that Jersey heifers actually had lower fertility (52.2%) than Holstein heifers.

Not surprisingly, Kuhn et al. (2006) also reported the conception rate decreased with increasing service number. This phenomenon is well-known to dairy producers, heifer ranch operators, and researchers, although the exact cause has not been determined. Chebel et al. (2006) also recently documented this trend in Holstein heifers in an Idaho feedlot (see Table 2*).

In recent years crossbreeding has become more popular, but what is the fertility of Holstein heifers mated to sires of another breed? As shown in Table 3*, Holstein heifers actually achieve a higher conception rate following A.I. with semen from Holstein bulls as compared to A.I. with semen from Brown Swiss or Jersey bulls (Kuhn et al., 2006). Although crossbreeding may have its merits, the results presented in Table 3* provide evidence that a decrease in conception rate may be incurred for at least the initial A.I. when Jersey or Brown Swiss bulls are used on Holstein heifers.

Lastly, Kuhn et al. (2006) reported the difference between the 6 major A.I. studs providing semen to the U.S. is relatively small at 2.8%, with the average heifer conception rate ranging between 50.3 and 53.1% across the studs. Each stud had greater than 20,000 services in the data set.

Now that you have an understanding of the fertility level of Holstein heifers in the U.S., are you satisfied will the fertility of your Holstein heifers? The following paragraphs contain brief information on reproductive management strategies to optimize heifer fertility.

Reproductive management strategies to optimize heifer fertility
1. Heifers should be bred based on size (weight) rather than age. If a Holstein heifer gains approximately 1.8 lbs per day, 800 lbs will be reached by 13 months of age. If heifers gain weight faster than expected and attain the proper size for breeding earlier, breeding should not be delayed, as the heifers will likely become over-conditioned.

2. Recognize that heat detection is the primary factor limiting reproductive performance. Heat detection aids (chalk, tail paint, visual pressure-sensitive devices) may be used to achieve greater efficiency and accuracy of heat detection. Know the limitations of heat detection aids, while keeping in mind the primary sign of heat is “standing to be mounted by a herdmate.” Secondary signs include clear mucus discharge, ruffled hair on the tailhead, increased activity, mounting other heifers, and chin resting.

3. When heat detection (visual observation or tail chalk application and reading) is performed infrequently (once or twice daily), heifers should be inseminated at the next most convenient time after first detection because the onset of heat is not known. Ovulation is physiologically tied to the start of the standing heat period. Consequently, there is a limited window of opportunity to breed the heifer and maximize the opportunity for conception. Using the HeatWatch system, Nebel et al. (2002) reported the average duration of heat (defined as the time interval from the first to last standing event) was 10.8 and 12.7 hours for Holstein and Jersey heifers, respectively. In another study using HeatWatch, conception rates of heifers were maximized when A.I. was performed within 16 hours of the onset of standing heat (see Table 4*). Keep in mind that the onset of standing heat is not known when visual observation and (or) tail chalk is used once or twice daily. Therefore, any heifer that is identified as being in heat has a “head start” towards ovulation, as the heifer has likely been in heat for at least a few hours. Consequently, the heifer should receive A.I. at the next most convenient time after first detection.

4. Synchronize heifers to ensure greater heat detection and A.I. labor efficiency. The greater the number of animals in heat simultaneously, the greater the opportunity for A.I. personnel to achieve success. Keep in mind that prostaglandin injections will only be effective in heifers that are cycling. Do not use Ovsynch (GnRH-7d-PGF2α-2d-GnRH-16 h-Timed A.I.) in heifers, as Ovsynch has been shown to produce unsatisfactory results (Pursley et al., 1997). Contact your veterinarian, semen salesman, or Cooperative Extension to help develop and implement an effective heifer synchronization program.

5. Check heifers for return to heat after A.I. and check pregnancy (or open) status before 40 days after A.I. This strategy focuses on identifying open heifers quickly, thus minimizing the potential increase in average age at first calving due to inefficient heat detection.

A few last thoughts
Hopefully, this article has provided a basis for which to evaluate your heifer reproduction program. The expense associated with raising a heifer from birth to calving is an investment in the future profitability of the dairy business. Sub-optimal heifer fertility will lead to an increased age at first calving, resulting in increased costs due to additional rearing expense. Furthermore, we all must realize the lost income opportunity from not having milk in the tank earlier in the animal’s life. There’s no better time than now to evaluate your heifer reproduction program, set goals for reproduction and age at first calving, and implement the necessary plans to achieve your goals. PD

References omitted but are available upon request.

Tables omitted but are available upon request to editor@progressivedairy.com.