Achieving a Sound Reproductive Health Management Program

Jack H. Britt

College of Veterinary Medicine,
N.C. State University,
4700 Hillsborough Street,
Raleigh, NC, U.S.A. 27606 E-mail: jack_britt@ncsu.edu

Take Home Messages

Simple, achievable goals are important for a strategic herd reproductive health plan.

Preventing disease and health problems during the early postpartum period is the most important factor for maintaining good reproductive performance.

Strategic treatment of early postpartum reproductive disorders can enhance reproductive performance.

Controlled breeding programs can decrease days open and percentage of open cows.

Introduction

In order to have a sound reproductive management program, one must have definable goals for herd reproductive performance. Simple, achievable goals should provide the basis for the strategic herd health plan, and these goals should be consistent with profitable dairying. Simple achievable goals include the following:

Calve AI-sired heifers at approximately 24 months of age.

Aim for a calving interval of 12 to 13 months.

Make sure that at least 90% of the cows are bred back to produce another calf.

Keep cows in the herd as long as they are profitable.

With these goals in mind, one should plan a herd-health program that focuses on:

preventing disease and limiting health problems, particularly during the early postpartum period,

incorporating management practices to get cows bred back promptly after the voluntary waiting period, and

implementing a strategy for dealing with problem breeders.

Such a program should focus on prevention of problems through dry cow management, administering appropriate treatments in the early postpartum period, minimizing weight loss in the postpartum cow, using controlled breeding programs after the voluntary waiting period, and treating repeat breeders with appropriate therapy.

Healthy Cows Reproduce Well

Cows that are healthy during the first two months after calving have better reproductive performance than those that experience health problems (Table 1). For example, we (13) compared reproductive performance of cows that experienced no health problems during lactation (healthy) with those that required treatment by herd personnel (minor) and those that required treatment by a veterinarian (severe) in eight commercial herds (Table 1). Conception rate at first service for multiparous cows that were healthy was nearly 30% higher than that in cows that had severe health problems (71% versus 44%), and culling rate was three times greater among older cows with severe health problems than among healthy older cows (31.7% versus 11.2%). Moreover, culling caused by infertility was four times greater in unhealthy older cows than in healthy herdmates (19.0% versus 4.7%).

Keeping cows healthy after calving requires a management program during late-lactation and a dry cow program that focuses on maintaining appropriate body condition, preventing common diseases associated with the dry period and calving, and promoting a smooth transition from the dry period to lactation.

Management During the Dry Period

During the dry period, the management strategy should be to group and manage cows according to the stage of pregnancy and to prevent the occurrence of health or metabolic conditions that might affect the cow after calving (2, 11). A sixty-day dry period is optimal, and should be divided into two to three phases, depending on herd size. Early dry cows need to be managed and fed differently than late dry cows, and an intermediate group may be appropriate in many herds. The goal should be to have cows calve with a body condition score of approximately 3.5 (5-point scale) and to be consuming enough energy to minimize the decline in energy balance that occurs during the last week of pregnancy. Management practices that are important during the dry period include the following:

Maintain two to four dry cow groups so that cows are managed alike at the same stage of pregnancy.

Prevent new intramammary infections and trim feet during the early dry period to enhance the health and vigour of fresh cows.

Feed a dry forage-based diet during the early dry period to promote rumen and gastrointestinal function and to control body condition.

Provide selenium and vitamin E to enhance postpartum health by preventing mastitis and postpartum disorders.

Avoid over-conditioning or excessive weight gain.

Provide a transition ration one to two weeks before the due date, with special attention to calcium intake and the cation-anion balance.

Prevent excess weight loss and onset of a negative energy balance during the last week before calving.

Calve cows in the driest, cleanest location available on the farm, and force-feed colostrum to the newborn calf.

Making the Nutritional Transition

Cows voluntarily reduce their feed intake by about 40% during the last week before calving (19), so it is important to pay close attention to feeding during this period to avoid adverse metabolic conditions associated with onset of a negative energy balance. Feeding grass hay ad libitum with 3 kg of grain supplementation per day prior to calving resulted in less depression in feed intake than feeding an all-forage (50% alfalfa silage, 50% corn silage) diet (19). Fatty infiltration of the liver occurs when cows experience a more negative energy balance prepartum, and this can lead to lower intake after calving, ketosis, and poorer health (19).

Dry cows should be offered some of the fresh cow ration before calving to enhance DMI postpartum. Fresh cows should be fed a ration to stimulate appetite. The goal should be to have the fresh cow consume as much DM as possible as soon as possible after calving. This prevents excessive body weight loss which delays resumption of postpartum cycles (5, 6) and lowers fertility during the breeding period (3, 4). Hutjens recommends that fresh cows be fed slightly differently than cows that are beyond the fifth week of lactation (Table 2), and he recommends the following practices for feeding fresh cows (11):

Feed a total mixed ration.

Provide forage energy >1.32 Mcal/kg of DM.

Balance degradable protein and non-fiber carbohydrate.

Avoid rumen acidosis by using buffers.

Limit fat intake during the first three to five weeks postpartum to stimulate appetite.

Provide fresh free-choice feed.

Notice that the fat levels (Table 2) are lower in the fresh cow diet than in the diet to be fed after the third to fifth week of lactation. Although addition of fat to rations increases energy density, it also depresses appetite, and for fresh cows, intake is greater if fat supplementation is limited. Once cows are eating more vigorously, then addition of fat is recommended for high producers. Balancing degradable protein with non-fiber carbohydrate and energy will maximize intake.

Reproductive Management Around Calving

From the standpoint of reproductive health, the most critical period in a cow's life is the period from four weeks before to four weeks after calving. Health disorders during this period seem to occur as a complex. One disorder tends to lead to another, so that eventually the cow may experience several problems before regaining her health (Table 3). For example, difficult births are often followed by retained fetal membranes which lead to higher levels of metritis or endometritis, lower feed intake and milk production, and increased incidence of metabolic disorders. The ultimate outcome is poorer performance in terms of calf survival, milk yield, reproductive performance, and survival of the cow in the herd.

Regardless of how well cows are managed during the dry period, if they are not provided with a good environment at the time of calving, they are likely to experience postpartum health problems that will lower milk yield and reproductive performance. Cows should be calved outside in a dry area if weather permits. Otherwise, cows should calve in a well-bedded box stall or on a bedding pack. Straw is the preferred bedding in the calving area because it absorbs more moisture than other bedding materials and because its larger particle size minimizes its potential uptake into the reproductive tract.

Calving problems, abnormal discharges after calving, and poor health in general during the periparturient period prevent the reproductive tract from involuting properly. Poor uterine involution leads to reduced long-term reproductive performance. For example, we (12) noted that cows with abnormal discharges during the first two to three weeks after calving were more likely to have a medium or large cervix at the postpartum exam than cows that were normal (Table 4) . When the process of involution was slowed, the consequences were manifested as poor reproductive performance several weeks later during the breeding period (Table 5).

Getting Cows Off to a Good Start After Calving

Most well managed cows will start cycling during the second to fourth week after calving (9). Cows that experience health problems at calving and cows that are in a severe negative energy balance after calving will be slower to cycle. Researchers at Cornell University in New York (6) reported a negative relationship between energy balance during the first 20 days after calving and first ovulation. They determined that cows ovulated shortly after energy balance had reached a nadir and began returning to zero. A good indicator of whether a herd is being fed properly is the proportion of cows that has not started to cycle by six weeks after calving. If this exceeds about 25%, then the feeding program needs to be examined carefully to improve energy intake and reduce the duration of negative energy balance.

Cows that experience severe substantial losses in body condition during the postpartum period may begin to cycle normally, but still experience low fertility during the breeding period (3, 5, 6). There is evidence that ovarian follicles in early stages of development (50 to 80 days prior to ovulation) may be impaired by development during a period when negative energy balance leads to an alteration in the levels of growth factors (3, 4).

Treating Postpartum Disorders

Traditional intrauterine antibiotic treatments for postpartum metritis are of questionable efficacy (8). Improper use of antibiotics during lactation may lead to residues in milk and meat, therefore, alternative methods for treating metritis are valuable. There is experimental evidence that some reproductive hormones, particularly prostaglandins and GnRH, may be useful for improving postpartum reproductive performance, particularly in cows that experience dystocia or metritis. The veterinary practitioner's use of hormones should be consistent with regulations within the governmental jurisdiction where the hormone is to be used.

Retained Placenta

There is some evidence that long-acting prostaglandin agonists will reduce the duration of placental retention if administered during the first few hours after calving (10). The mechanism of such action is unclear, particularly when one considers that uterine levels of prostaglandin are high during this period of time. Potentially, the prostaglandin could eliminate residual progesterone from a CL that had not completely regressed prior to delivery, but if this was the mechanism, then one would expect shorter-acting prostaglandins to be effective. In general, the literature in this area is too inconsistent to recommend the routine use of prostaglandin agonists after calving, except in certain situations such as with induced calving, where the incidence of retained placenta would be expected to be high.

Dystocia and Metritis

Administration of prostaglandin F analogues at one or two weeks postpartum or GnRH at two weeks postpartum may be beneficial for initiating estrous cycles and reducing interval to first service and days open (7, 14). This benefit has been seen in field trials when cows were treated routinely (Table 6), but such treatments may be most beneficial for cows that experienced dystocia or other problems at calving (Table 7). Recent field trials have indicated that prostaglandins alone are probably as effective as the GnRH-prostaglandin combination (Table 7). In general, cows that have more cycles by the beginning of the postpartum breeding period are more likely to conceive at first service and require fewer services per conception than anestrous cows (18). So the effect of PGF and GnRH in cows with dystocia and retained placenta may be primarily through the earlier cyclicity and better uterine involution associated with recurring estrous cycles.

Cystic Follicles

GnRH or human chorionic gonadotropin (hCG) are the accepted treatments for ovarian follicular cysts, and there does not appear to be a major difference in their efficacy. Luteinized cysts will regress in response to PGF, but the ability to detect whether a cyst is luteinized or not based on palpation alone varies considerably. Cowside progesterone tests may be useful for determining whether a cow is likely to be responsive (1).

Repeat Breeders and Early Embryonic Death

Quite a number of studies have shown that conception rate in repeat-breeder cows (third or later service) can be enhanced by treatment with GnRH at insemination (17). The mechanism through which GnRH induces its effect is probably associated with altering progesterone secretion by the corpus luteum rather than by stimulating ovulation, because treatment with GnRH consistently improves fertility in repeat breeders whereas double insemination does not (17). If delayed ovulation was a problem in repeat breeders, then double insemination should be beneficial. One must determine whether the increase in conception rate (about 15% overall) associated with GnRH treatment of repeat breeders is worth the extra investment. There also is evidence that treatment of repeat breeders with low doses of hCG to increase progesterone level my be beneficial and the cost of the latter treatment may be more favorable.

Embryos that die after the second week of pregnancy cause cows to show a delayed return to estrus (4). It is estimated that 7 to 12% of embryos die after the second week of pregnancy (4), and typically these cows will have return intervals of 28 to 35 days (4). This return interval is not a multiple of that which would be expected from missed heats, but a careful examination of heat detection records is needed to distinguish between errors in heat detection and embryonic death. Little is known about causes of early embryonic death, but factors such as excess intake of degradable protein and ingestion of mycotoxins may be involved. There are no clearly effective procedures for preventing early embryonic death except in cases where dietary or environmental conditions are the cause.

Programmed Breeding

In normal healthy cows that have experienced two to three estrous cycles before the breeding period, programmed breeding may be useful for reducing labour required for detection of estrus and increasing the number of opportunities to get cows bred during the optimal postpartum target window. In general, programmed breeding involves using sequential injections of prostaglandins to set cows up for breeding during a specified time. For example, "Monday morning programs" are focused on getting cows inseminated during mid-week rather than on weekends (15, 16). These programs generally involve giving cows their two injections of prostaglandin about 14 days apart with the second injection given at the end of the voluntary waiting period. Thus, treated cows experience the first breeding heat at about 60 to 70 days postpartum. These programs reduce the percentage of cows that go for long periods without being inseminated. Conception rates may be slightly lower in programmed cows than in cows bred to natural heats, but this is offset by an increase in the number of opportunities to get cows inseminated. Days open can be reduced substantially by use of programmed breeding, leading to a higher retention rate of cows in the herd.

Another programmed breeding strategy is to batch cows so that breeding occurs during one week out of three (2). In this scenario, cows that do not conceive at first service exhibit there repeat heat at the time of first service for the next batch. This can substantially reduce the effort devoted to heat detection and insemination without lowering herd reproductive performance.

There is a high correlation between days to first service and days open. Thus, the best way to reduce days open is to breed cows as soon as possible after the end of the voluntary waiting period. While there is a modest increase in conception rate up to about 100 to 120 days postpartum, the higher conception rate does not offset the days lost because of failure to inseminate cows. Even at highest levels of production, it is still recommended to aim for calving intervals of 12 to 13 months.

References

1. Bajema, D.H., M.P. Hoffman, T.E. Aitchison and S.P. Ford. 1994. Use of cow-side progesterone tests to improve reproductive performance of high-producing dairy cows. Theriogenology 42: 765-771.
2. Britt, J.H. 1977. Strategies for managing reproduction and controlling health problems in groups of cows. J. Dairy Sci. 60:1345.
3. Britt, J.H. 1991. Impacts of early postpartum metabolism on follicular development and fertility. The Bovine Practitioner Proc. 24: 39.
4. Britt, J.H. 1992. Influence of nutrition and weight loss on reproduction and early embryonic death in cattle. In: Proc. Vol 2, 25th Ann. Meeting Am. Assoc. Bovine Practitioners. St. Paul, MN. pp 143-148.
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