Reproduction in Cattle:

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Diseases Affecting Reproduction in Beef Cattle
By Ron Parker, Extension Beef Cattle Specialist, College of Agriculture and Home Economics New Mexico State University.

 Infertility and abortions in cattle are two of the greatest problems the cattle breeder faces. The causes are complex and difficult to identify. This publication discusses and briefly outlines some of the more common diseases and control measures.

In case of abortion, call your veterinarian immediately and have the following information or material available.


Identify aborting cows and isolate them from the rest of the herd. This helps prevent spread of infection and makes them available for examination.
Save fetuses and fresh placentas. Refrigerate them at 38 to 45°F. Do not freeze it unless specimen is frozen when found; then keep it frozen.
Wrap in plastic or other waterproof material. Do not cut or wash the fetus or placenta.
Maintain a history of herd vaccinations, movement of cattle to and from other premises, and management and origin of bulls.
Keep a reproductive history records of cows, including number of abortions, conception rate, and approximate breeding dates.
Caution:
Some diseases that cause abortions in cattle can be easily transmitted to humans. Follow aseptic procedures in handling aborted fetuses and associated tissues, or when examining the animal's reproductive system. Use of disposable plastic gloves protects both the technician and cow from contamination.

This is a rough guide to help determine age of an aborted fetus:

Guide to help determine age of an aborted fetus
Length of gestation (months) Description of fetus
2 Size of a mouse
3 Size of a rat
4 Size of a small cat
5 Size of a large cat
6 Size of a small dog (hair around eyes, tail, muzzle)
7 Fine hair on body and legs
8 Hair coat complete, incisor teeth slightly erupted
9 Incisor teeth erupted


Brucellosis
Bovine brucellosis, or Bang's disease, is perhaps the best known and most controversial infection of the bovine reproductive system. Brucellosis generally has been thought of as a cattle disease, but it is also seen in swine, sheep, goats, dogs, horses, and wildlife, and can be readily transmitted to humans. The disease in humans is referred to as undulant fever and is one of the reasons for a national eradication program to remove the threat from cattle and human populations. The disease represents a real occupational hazard for veterinarians, slaughtermen, and cattle producers.

Brucellosis is caused by the bacterium Brucella abortus. The organism has an affinity for certain body tissues such as the udder, uterus, lymph nodes, testicles, and accessory sex glands. Because of its affinity for the uterus, abortion is the usual sign of the disease. However, other symptoms, primarily reduced milk production and reduced weight gain, are often seen. In bulls the most obvious clinical sign of this disease is epididymitis.

Brucellosis is a particularly difficult disease to work with for several reasons. First, there is no sure way to identify infected cattle by their appearance. All infected cattle do not abort. In addition, the incubation period for brucellosis is variable, ranging from 3 weeks to as much as 90 days and more. These characteristics all contribute to the problem of eradicating the disease.

Brucellosis is primarily transmitted to susceptible animals by direct contact with infected animals. Essentially, the only time an infected cow transmits the organism is at or around calving or abortion. Aborted fetuses, placental membranes, placental fluids, and the vaginal discharges that persist for several weeks after an infected cow has calved or aborted all abound with virulent Brucella organisms. The organism may be transmitted to other animals that contact the environment that has been contaminated with discharges from infected animals. Milk and colostrum from infected cows is a readily available source of infection for calves and the human population.

Infected cows seldom abort more than once, but calves born from later pregnancies may be weak and unhealthy. Such cows will probably continue to harbor and discharge infectious organisms, and have reduced conception rates.

Abortion is apparently associated with stage of pregnancy at the time of exposure to the disease. Cows that conceive soon after exposure, or in the first trimester of pregnancy after exposure, have a high abortion rate. Chances of abortion decrease in later stages of pregnancy, with cows in the third trimester of pregnancy at time of exposure rarely aborting.

Because brucellosis can easily be transmitted to people, aseptic procedures such as using disposable gloves when examining or assisting cows at calving are highly recommended.

A cooperative state-federal brucellosis eradication program has been in effect for many years. Although much maligned and often changed, this program has undoubtedly done much to finally near eradication of the disease in this country. States are classified as free, class A, class B, or class C. New Mexico became a free state in 1996.

Cattle can generally be moved interstate from free states without testing. However, cattle moved from non-free states must be tested before moving across state lines.

The old saying that "brucellosis is usually bought and paid for" is true more often than not. Just because an animal or group of animals has been tested and declared free of infection does not ensure that some are not in the incubation stage of the disease. Therefore, any newly purchased cattle should be quarantined and retested in 45-120 days. This may be the most important part of a preventive program, and one over which the buyer has complete control.

A relatively new RB51 vaccine has replaced the old Strain 19, the only vaccine available for many years. The biggest advantage of the RB51 vaccine is the almost total elimination of false positives observed with use of Strain 19. Use of Strain 19 often resulted in antibody titers that were difficult to differentiate from actual infection titers. Heifer calves can be vaccinated between the ages of 4 and 12 month; about 6 months of age is best. Brucellosis vaccine only can be administered by licensed veterinarians.

A small percentage of heifer calves born to brucellosis-infected cows will harbor the organism until they are mature. Serological tests may be negative during the heifer's developmental period. However, once the heifer becomes pregnant, she may abort or she may become seropositive and a source of infection at calving time. Therefore, unknowing cattle producers may be buying the disease via serologically negative heifers carrying a latent infection. Calfhood vaccination of heifers will not prevent this from happening. Anyone buying replacement heifers should keep this in mind. Buying heifers in areas of high brucellosis incidence may be a risky venture, whether or not they were calfhood vaccinates.

Leptospirosis
Leptospirosis is a contagious, bacterial disease of animals and humans. In cattle, horses, pigs, sheep, goats, and dogs, it has been characterized by a wide variety of conditions including fever, icterus (jaundice), hemoglobinuria (bloody urine), abortion, and death. However, our concept of the disease has recently changed. It used to be considered a highly fatal disease, but is now thought to be a widespread, mostly subclinical infection of many species of wild and domestic animals.

Originally, Leptospira pomona was identified as the principal cause of the disease in cattle. However, in recent years, an increased incidence of other serotypes has been observed, including L. hardjo, L. icterohaemorrhagia, and L. grippotyphosa. Other serotypes, including L. canicola and L. szawajizak, have been isolated from cases of bovine leptospirosis.

Signs of leptospirosis in cattle range from mild, unapparent infections to acute infections that end in death. Clinical signs that precede abortions may suggest leptospirosis, but owners of beef herds often do not recognize any signs of disease until they find aborted fetuses. The highest abortion rate occurs in the last 3 months of gestation. High abortion rates have been observed among beef herds during the winter feeding period in herds utilizing seasonal breeding for spring calving. Hemoglobinuria (bloody urine) in either bulls or cows, or blood-tinged milk in lactating cows, may be observed. Milk production may nearly cease.

The acute form of the disease usually occurs in calves. Calves will have fevers from 104 to 107°F, and may have diarrhea followed by constipation, then again by diarrhea. Hemoglobinuria and a yellowing of the mucous membranes and tissues are common. Death may occur in a short time.

The only certain way to diagnose leptospirosis is through laboratory testing of serum, or cultural isolation of the organism. Generally, serum testing is used to diagnose lepto in a herd. Significant titers against a certain serotype indicate the disease is active in the herd, assuming the herd has not been vaccinated for the disease. Paired serum samples may be needed to demonstrate active infections. Rapidly rising or falling titers in paired samples probably indicate active infections. Antibodies first appear in the serum of infected animals by the sixth or seventh day, and titers rise rapidly to a high level. Titers then decline to a more or less constant level and may persist for months. Samples sent to the laboratory for culture must be collected and shipped as rapidly as possible because leptospires do not survive long in dead tissue.

Vaccination with killed bacterins protects against clinical leptospirosis for up to a year, but the bacterin must contain the antigens of the strain to which the cattle are exposed. An annual vaccination program with vaccine containing bacterins against L. pomona, hardjo, and gripotyphosa should be considered for most New Mexico cattle herds.

Campylobacteriosis, Vibriosis
Campylobacteriosis (vibriosis) is a venereal disease of cattle caused by the organism Campylobacter fetus subspecies fetus. Before 1973, this organism was known as Vibrio fetus subspecies venerealis, but was reclassified into the Campylobacter genus in 1973.

Campylobacteriosis is characterized by infertility with an increased number of services necessary for conception. Early embryonic deaths are common and late abortions from 4 months gestation to term are occasionally observed. Presence of the disease is often unsuspected until many nonpregnant females are found during fall pregnancy examination. Also, considerable differences in fetal age may be noticed, indicating reduced fertility and delayed conception in some females.

In a herd that has never been exposed, and where no immunity exists, an acute type of infertility problem develops. In this case, infertility caused by endometritis results in early embryonic death and a prolonged period (up to 120+ days) passes before successful conception occurs. Within this time, the female develops a local immunity and the organism clears from the uterus so conception can take place. Some heifers have a natural immunity, or develop immunity quickly, and conceive within 2 months. Others may conceive early but remain carriers of the organism for months, while still others remain infected for months, require many services, and may even abort after conception.

The subacute or chronic form of the disease is expressed as a vague or intermittent infertility problem in older cows, but susceptible females added to the herd develop the more acute form.

Under natural breeding conditions, bulls transmit Campylobacter fetus from one female to another. Before the advent of properly handled and antibiotic-treated semen, the disease also could be spread by means of artificial insemination. Direct female-to-female spread is highly unlikely, but bull-to-bull transmission can occur among groups of bulls penned together where riding behavior is active. The organism establishes itself in the prepuce of the male, but does not interfere with semen quality or breeding ability.

Spread of the organism to the male is primarily by way of copulation with an infected female. Bulls can remain carriers for up to 18 weeks after infection. Older bulls tend to retain the infection more permanently than younger bulls, possibly because of the increase in number and size of the crypts in the epithelium of the penis.

A definite diagnosis of genital campylobacteriosis can be difficult and laboratory test results are often disappointing. Although blood tests are available, they are not reliable because it is not a systemic disease and antibodies are rarely found in the blood stream.

Most infected heifers rid themselves of the organism within 6 months of sexual rest, thus a reduction of demonstrable antibodies occurs. Therefore, at pregnancy evaluation or at calving time, when the owner first becomes aware of a problem, only a limited number of females may be infected and antibodies may have disappeared.

Bacteriological examination of aborted fetuses appears to be the only practical method of confirming the diagnosis later in gestation. Cultures of vaginal or cervical mucus from aborting females, or samples taken from the sheath of bulls, may be used, although diagnosis by this method is difficult because of the organism's fragile nature.

Without vaccination, control and prevention of this disease can be difficult. Use of artificial insemination that is successful in dairy herds and small farm beef herds may be impractical on larger ranches. Maintaining a clean, unexposed herd is possible only if virgin bulls are used, and if only clean, uninfected females are introduced. Serum antibody titers tend to decrease rapidly after vaccination; therefore, a corresponding reduction in immunity can be expected.

Maximum immunity in heifers can only be established if they are vaccinated twice before breeding. In one study, a vaccination given 4 1/2 months before the breeding season, followed by a booster injection 10 days before breeding, gave satisfactory immunity in heifers. However, the single injection given 4 1/2 months before breeding did not. In most New Mexico herds, satisfactory protection can be obtained with single vaccinations before the breeding season followed by yearly booster injections.

Both killed and modified-live vaccines are available. Modified-live vaccines may cause abortions and should not be used in pregnant cows. Combination vibri-lepto vaccines are available.

Vaccination of bulls has been reported to be effective for both prevention and also as a cure for C. fetus infection. Initial vaccination should consist of two injections before breeding time. Annual booster vaccinations close to breeding time will help assure high immunity during the breeding season.


Trichomoniasis
Trichomoniasis, like vibriosis, is a venereal disease of cattle. It was formerly thought to be a relatively rare disease. However, in recent years, frequency of diagnosis of this disease in western beef herds has increased dramatically. Whether this increase is the result of an actual increase in the incidence of the disease, or better test procedures and increased awareness, can only be speculated.

Trichomoniasis is caused by the protozoan, Trichomonas fetus. These organisms are harbored in the reproductive systems of infected cows and bulls, and are transmitted from cow to cow by chronically infected bulls. Cows will generally rid themselves of the disease after 60 to 90 days of sexual rest, but infected bulls appear to be unable to develop immunity. Unless they are extremely valuable animals, they should probably be slaughtered because treatment can be a long and laborious procedure.

Infertility is the most common clinical sign of a trichomoniasis infection. Abortion generally occurs early in gestation (first 3 months). Because little tissue is shed during these early abortions, they often go undetected. The usual evidence that a problem exists is a lower percentage of pregnant cows in the fall, or a reduced calf crop or prolonged calving season. Protecting the beef herd from exposure to the disease is the recommended management approach. Like many other diseases, trichomoniasis is usually introduced into the herd by purchase of infected cows or bulls. Maintaining a quarantined herd, adding only young bulls and heifers of prepuberal age, can greatly reduce the risk of infection. Diagnosis of the disease may be difficult, and one screening test of newly purchased animals will not guarantee they are clean.

Older bulls (4 years and older) are more likely to carry the disease. The disease is rarely diagnosed in younger bulls and they are apparently less likely to become permanent carriers. The practice of purchasing older, used bulls should be used with much discretion. If there is any question about the origin and health status of such bulls, they should not be used.

Commercial vaccines are now available. Proper immunization requires two injections, usually administered two to four weeks apart. Annual revaccination may be recommended. The vaccine is given to cows only. As with any vaccination program, consult your veterinarian before beginning a trichomoniasis vaccination program.


Other Diseases
Several other diseases can cause abortion or lowered fertility in cattle. Infectious bovine rhinotracheitis (IBR, rednose) and bovine viral diarrhea (BVD) are viral diseases that can cause abortion. However, other symptoms of these diseases will generally be observed before abortion occurs. Foothill abortion (EBA) and Listeriosis also may cause abortion, but are rarely seen in New Mexico.

Poisonous plants are another common cause of abortion and must be considered when abortions are observed.

[mikey]

Boosting Births
By Jeromy Ten Hag - Milk Quality Assurance Program Lead/OMAFRA. Mastitis in your herd may be costing you more money than you think, suggests a study linking mastitis and poor reproductive performance in dairy cows.

 
The average clinical mastitis case costs you, the producer, an estimated $150. This figure accounts for economic losses from discarded milk, antibiotic treatment, decreased lactation production and your time managing the treated animal. However, mastitis costs may go deeper than these obvious losses. Udder infections may be hampering your herd's reproductive success.

University of Tennessee researchers have investigated how clinical and subclinical mastitis affect reproduction measures. They analysed data gathered over a 10-year period from 758 Jersey cows in their research herd. The microbiological data was from quarter milk samples collected from lactating cows every four to eight weeks. Researchers defined subclinical mastitis as a cow with two consecutive milk cultures containing the same organism. Milking personnel identified clinical cases. Milkers practised teat dipping and used antibiotic therapy at dryoff and to treat clinical cases. Personnel measured reproductive performance by days to first service, days open and services per conception.

Researchers divided data into groups. The cows with mastitis before first service (374) showed a significant increase in days to first service, days open and services per conception compared with cows with no mastitis or a case developing after pregnancy (326). The result was the same for clinical and subclinical mastitis.

The 35 cows with clinical mastitis between first service and confirmation of pregnancy had a significant increase in days open and services per conception compared with cows with subclinical cases or no mastitis (see Table 1). Cows with prolonged udder infections (subclinical infections that eventually became clinical cases during the breeding period) were most severely affected for the three reproduction parameters. The reliability of the results may be questionable because this group had only six cows. Nonetheless, the impact on reproduction was large and deserves attention.

Table 1. Effect of mastitis in cows between first service and confirmed pregnancy on reproductive parameters.
Mastitis case group  Number of Cows Days to 1st service Days open Services per conception
No mastitis or mastitis after pregnant 326 67.8 85.4 1.6
Subclinical  11 61.2 90.9 2.1
Subclinical progressed to clinical  6  93.9  196.0  4.3
Clinical  35  70.6  143.6  3.0


Research often provides answers while leading to more questions. Scientists don't fully understand the link between mastitis and reproductive performance. Some work has shown a cow's response to mastitis caused by gram-negative pathogens (like E. coli and Klebsiella) has a negative effect on its hormonal profile and follicular development. Other studies suggest that prostaglandins are released in the inflammatory response to gram-negative infections. This prostaglandin increase acts similar to a prostaglandin injection, which can change the length of a cow's heat cycle and may cause the loss of a developing embryo in a bred cow. In the Tennessee study, gram negative and gram positive bacteria caused clinical mastitis equally-here, the type of bacteria had no bearing on results.

These suggested mechanisms of mastitis affecting reproduction seem plausible for cows contracting an udder infection during the breeding period. However, researchers are more skeptical about mastitis' negative effects on reproductive performance for the cows that develop mastitis early in lactation. More research is needed to understand this relationship.

Some aspects of the Tennessee study may affect its relevance for Ontario producers. Ontario's dairy population is over 90 per cent Holstein, so a Jersey herd study's relevance may be questioned. Nevertheless, a study conducted on the University of Florida Holstein herd to evaluate clinical mastitis and reproduction reported similar results. However, the warmer climate and different feeding programs used in the southern U.S. may decrease the relevance of this study to Ontario dairy herds.

Nonetheless, study results stress the importance of striving to control udder infections in your herd. There are the obvious direct costs of clinical or subclinical mastitis, but there's growing evidence of the indirect cost of reproductive inefficiency. Three U.S. research studies have reported that the estimated cost of each day open after 90 days ranged between 50 cents and $4.00 US. The importance of managing your herd to prevent mastitis in the first 60 days of lactation is obvious, but mastitis control needs to remain a top priority right through a cow's breeding period and beyond.

Given the potential economic importance of these research findings, following a mastitis control program would benefit your bottom line. One program, recommended by the National Mastitis Council (NMC), includes 10 steps that involve all areas that may affect mastitis in your herd. (see Table 2 below)

Setting udder health goals and monitoring them regularly basis is an important first step. Proper stall maintenance and adequate bedding will keep teats clean and dry in between milkings. Keeping the maternity area clean and well bedded will protect fresh cows from udder infection during their most vulnerable period. Good udder preparation practices prior to milker attachment are important. Applying the milker to clean and dry teats is a must.

Record keeping is extremely important for monitoring clinical mastitis trends in your herd. Prior to treating a clinical mastitis case, collect a milk sample of the infected quarter and submit it for bacteria identification. This information can be used to determine a bacteria profile for your herd, which can help identify management practices that may need attention. With the help of your veterinarian develop treatment strategies that are appropriate for the mastitis cases in your herd.

Using dry cow antibiotic therapy after the last milking is important to help cure existing udder infections and prevent new infections in the early dry period. Using alcohol swabs to prepare teats prior to dry cow treatment is important to avoid contaminating the udder with bacteria from the outside of the teat. Enrolling in an individual cow somatic cell count program can help detect subclinical mastitis before it becomes a clinical mastitis problem.

Your veterinarian and DFO's udder health specialists are excellent resources who can advise you on developing and implementing a mastitis control program for your farm. The benefits of implementing sound practices to control mastitis go further than a decreased incidence of the disease. Increased reproductive performance in your herd is another benefit that is becoming more evident.
Table 2. NMC recommended 10-step mastitis control program
Establish udder health goals for your herd

Maintain a clean, comfortable environment

Use proper milking procedures

Properly use and maintain your milking equipment

Keep good records

Manage clinical mastitis appropriately during lactation

Use effective dry cow management

Use biosecurity protocols to prevent the spread of contagious pathogens and when marketing chronically infected cows

Monitor your herd's udder health status regularly

Periodically review your mastitis control program

[mikey]

Growth Implants on Beef Heifer Reproduction
By Gene H. Deutscher, Extension Beef Specialist. This guide discusses the benefits and concerns in the use of growth implants with beef heifers.

Contents

Implants Available
Effect of Implants on Growth Rate
Effect of Implants on Puberty
Effect of Implant on Pregnancy
Effect of Implants on Pelvic Area and Calving difficulty
Economics of Implant Use
Summary of Implant Research
Recommendations on Using Implants

Growth promoting implants are used extensively in beef cattle finishing programs and in suckling and growing steer programs. Implants are one of the most economical means of improving performance. However, producers are concerned with implanting suckling and growing heifers because of the possible negative effects on subsequent reproduction of heifers selected as replacements.

Replacement heifers need to grow rapidly, reach puberty early, conceive early, and increase in skeletal structure to reduce calving difficulty. If implants could be used to increase growth and skeletal structure and not affect fertility, they could be very advantageous.

Over 40 research studies have been reported on the effects of implants on growth rate, pelvic size, reproduction, and calving difficulty of replacement heifers. This research was summarized to provide the following recommendations on the use of implants for heifers. Economic considerations are also provided to help producers determine their risk/benefit ratio.
Implants Available
Table I shows the various implants available for suckling and/or growing heifers. The Food and Drug Administration (FDA) regulates the use of these implants so producers need to read and follow the label directions. Only Ralgro and Synovex-C implants have been approved by the FDA for use in heifers to be saved for breeding. Ralgro can be used in heifers that are at least 1 month of age and Synovex-C can be used in heifers that are 45 days of age or older. The other implants are not approved for use in replacement heifers; although Calf-oid and Heifer-oid have similar chemical makeup to Synovex-C and Synovex-H, respectively. Therefore, the following discussion will cover only the effects of Ralgro and Synovex-C implants.

Table I. Growth promoting implants for heifers
Trade name Company Ingredients Use
Ralgro Pitman-Moore Inc. Zeranol (estrogenic) Suckling and growing
Synovex-C Syntex Agr. Bus. Inc. Estradiol and progesterone Suckling
Synovex-H Syntex Agr. Bus. Inc. Estradiol and testosterone Growing
Compudose Elanco Anim. Health Estradiol Growing
Calf-oid Cell Estradiol and progesterone Suckling
Heifer-oid Boehringer Ingleheim Estradiol and testosterone Growing


Implants on Growth Rate
In general, these implants given at 1 to 2 months of age will increase weaning weights of heifer calves by 2 to 6 percent or 10 to 30 pounds. The Synovex-C implant appears to have a longer lasting effect than Ralgro and may continue to increase growth rate up to 12 months of age. Implants given at 1 to 2 months of age and again at weaning will yield heavier yearling weights.
Effect of Implants on Puberty
Puberty in heifers is the first behavioral estrus followed by ovulation and development of a corpus luteum. Heifers implanted at one to two months of age with either Ralgro or Synovex-C will show a greater incidence of non-ovulatory estrus periods (false heats) after weaning than non-implanted heifers. Multiple implanted heifers may show up to 50 percent non-ovulatory estrus periods. This means heifers show riding activity and stand to be ridden but have not reached puberty. In general, research shows that the implants have little effect on the onset of puberty when heifers receive an adequate level of nutrition.
Effect of Implants on Pregnancy
Ralgro - A Ralgro implant given at birth (or one day old) can decrease yearling pregnancy rates considerably. Five research studies show an average reduction of pregnancy of 35 percentage points. Thus, heifers should not be implanted with Ralgro at birth if they will be kept for breeding. Label directions indicate that heifers should be at least one month of age before Ralgro is given if heifers are to be saved for breeding.

Research shows a Ralgro implant given to heifers between one and 10 months of age can have variable effects on yearling pregnancy rates (Table II). Of 24 studies, about 40 percent showed a positive effect, 24 percent showed no effect, and 36 percent showed a negative effect on yearling pregnancy rates. The results ranged from a negative 14 percent to a positive seven percent, with an average of a negative one percent. When results of the studies were pooled and interpreted, the implant had little or no effect on yearling pregnancy rates if heifers were fed to gain at least 1.1 pounds per day to reach breeding weights.

Research on multiple (2 or more) Ralgro implants given between one and 11 months of age showed a decrease in pregnancy rates in yearling heifers in 55 percent of the studies, while 45 percent showed no effects or an increase in pregnancy. However, several studies found a considerable negative effect (from -16 percent to -42 percent), while the positive effects were quite small. Most studies reporting negative effects had heifers on a low nutritional level. Studies in Montana and Nebraska found that increasing nutrition level to heifers overcame the adverse effects of multiple implants on fertility. In Nebraska, heifers implanted at one, six, and nine months of age and fed to gain one pound per day from weaning to breeding had a 12 percent decrease in pregnancy rate, while similar heifers fed to gain 1.3 pounds per day showed no decrease.

Synovex-C - Research is limited on the effects of Synovex-C given at or near birth on pregnancy rates; however, it is not recommended if heifers are to be retained for breeding. The label directions indicate heifers should be at least 45 days of age before implanting.

When Synovex-C implants were given to heifers between two and three months of age, effects on yearling pregnancy rates varied from +2 percent to -9 percent in seven studies, with an average of -2 percent (Table III). When heifers were implanted at six months of age, two studies showed an average decrease of three percent in pregnancy rates. In a Nebraska study, heifers implanted at both two and six months of age had pregnancy rates five percent lower than non-implanted heifers (Table IV). Early pregnancy rates (in first 21 days of breeding) tended to be lower for all groups of implanted heifers. Therefore, a slight decrease in early fertility and pregnancy rate may occur if heifers are implanted at either two or six months of age. Heifers that did not gain adequately to reach breeding weights had the greatest decrease in fertility.

Table II. Effects of single Ralgro implant on yearling heifer pregnancy rates. 
    Ylg. preg. rate,a %
Location of study  Age at implant (months) Cont. Imp. Diff.
NE 1 96 96 0
OK 1.5 46 50 +4
TX 1.5 77 70 -7
KS 1.5 76 81 -4
KS 1.5 85 81 -4
KS 2 100 100 0
WY 2 83 73 -10
KS 2 86 90 +4
KS 2-3 78 79 +1
KS 2-5 98 98 0
MO 3 90 84 -6
FL 3 52 50 -2
CO 3 86 86 0
CO 6 86 93 +7
TX 5 77 76 -1
NE 6 96 96 0
IN 6 100 86 -14
KS 6 85 90 +5
FL 8 82 86 -14
NM 8 35 37 +2
LA 9 85 86 +1
NE 9 96 100 +4
KS 9-10 96 89 -7
OR 10 85 91 -6
      Average -1


aCont. = non-implanted, Imp. = implanted, Diff. = difference between groups.

[mikey]

Table III. Effects of single Synovex C implant on yearling heifer pregnancy rates
      Ylg. preg. rate,a %
Location of study  Age at implant (months) Length of breeding season (days) Cont. Imp. Diff.
IN 2 90 96 94 -2
TX 2 90 77 79 +2
CAN 2 70 93 95 +2
CAN 2 70 97 91 -6
MO 2-3 45 81 77 -4
CO 3 95 99 90 -9
NE 2 63 93 92 -1
        Average -2


aCont. = non-implanted, Imp. = implanted, Diff. = difference between groups.


Effect of Implants on Pelvic Area and Calving Difficulty
Research has shown that calving difficulty in two-year-old heifers is inversely related to pelvic area. Therefore, increasing pelvic area should help reduce calving difficulty. Many studies on both Ralgro and Synovex-C show implants increase yearling pelvic area substantially. However, this advantage must be present at calving to reduce calving difficulty. Studies on Ralgro have shown variable calving results; thus, the effects on precalving pelvic area and calving difficulty are inconclusive. The studies on Synovex-C implants showed precalving pelvic areas of heifers were slightly larger due to the implants; however, only a slight reduction in calving difficulty was found. An exception to this occurred in a Nebraska study (Table IV) when heifers given Synovex-C implants at both two and six months of age had only half the calving difficulty (14 versus 32%) as the non-implanted heifers, although the implanted heifers had a 5 percent decrease in yearling pregnancy rate.
Table IV. Synovex C implants on heifer calves in Nebraska, 1988-1992
  Treatment groups a
Item Cont. 2 mo 6 mo 2 and 6 mo
Number of heifers 94 94 93 88
12 month weight, lb 651 669 649 682
Precalving weight, lb 937 944 939 953
12 month pelvic area, cm2 158 168 164 171
Precalving pelvic area, cm2 240 243 250 248
Puberal before breeding season, % 83 84 77 78
First service conception, % 68 65 57 61
Pregnancy in breeding 21 days, % 67 60 61 55
Pregnancy in breeding 63 days, % 93 92 89 88
Calf birth weight, lb 73 74 77 71
Calving difficulty, % 32 29 23 14

aCont. = non-implanted, 2 mo = implanted at 2 months of age,
6 mo = implanted at 6 months of age,
2 and 6 mo = implanted at both 2 and 6 months.

Summary of Implant Research
Heifer calves implanted at birth (especially with Ralgro) may have substantially lower fertility, thus, potential replacements should not be implanted at birth.
Implants should be given according to label directions when calves are at least 30 days old (Ralgro) or 45 days old (Synovex-C). These implants are very economical and will increase weaning weights by 10 to 30 pounds.
Heifer calves implanted once during the suckling period may experience a small decrease in early fertility, but yearling pregnancy rates are only slightly affected if adequate nutrition is provided.
Multiple implants can cause adverse effects on reproduction but may be overcome with high levels of nutrition.
Implants will increase yearling pelvic area, but the advantage decreases by calving time and effects on reducing calving difficulty are minimal.
Implanting replacement heifers probably won't affect their future milk production as two-year-olds or their calf weaning weights.
Implanting pregnant heifers may cause abortions.
Economics of Implant Use
Because research studies have shown both advantages and disadvantages of implants on heifers, producers need an economic evaluation before using implants. Many factors can be considered in an eco-nomic analysis, such as the increase in weaning weight, price of calves at weaning, replacement heifer rate, change in yearling pregnancy rate, value of bred heifers, and any long-term effects on calf production. An economic analysis using these factors was reported by Gutierrez et al. at Colorado State University. The assumptions used were: calf weaning weights of 450 pounds, selling price of $.90 per pound, heifer replacement rate of 15 percent, and bred heifer value of $800.

Table V shows that the net return per heifer implanted when all heifer calves were implanted at two to three months of age compared to no heifers implanted.
Table V shows three different weight gains (increases in weaning weight) and three possible changes in yearling pregnancy rates due to the implants. For example, if the heifers sold at weaning gained an additional 21 pounds due to the implants and the heifers saved for breeding had a five percent decrease in yearling pregnancy rate, the return is $4.12 per implant. In general, the returns to implants are positive unless fertility is decreased more than five percent. Producers can use this table to help estimate the return they could expect under their management.

Table V. Economics of implanting heifer calves 
  Weaning weight gain (lb)
Pregnancy rate change 15 21 25
  Net return per implant ($)
0% 4.37 7.27 9.20
-5% 1.22 4.12 6.05
-10% -6.17 -3.29 -1.34

(Gutierrez et. al, 1993)


Recommendations on Using Implants
Both advantages and disadvantages of implants need to be considered and weighed on an economic basis before implanting heifer calves.
If heifers to be saved for breeding can be identified early (before two months of age or at processing), DO NOT IMPLANT THEM.
If replacement heifers cannot be identified until weaning time or later and economic returns to implants appear positive, all heifers can be implanted at about two months of age. Implants will increase weaning weights and market value. Heifers kept as replacements should be fed to reach breeding weights before the breeding season.
If heifers are implanted at both two and six months of age or later, additional replacement heifers should be saved to compensate for lower yearling pregnancy rates. High nutrition levels may help overcome the negative effects of implants.