The Modern Dairy Bull

Health Programs and Bull Management Issues

by Donald R. Monke, DVM

Welcome to this web site containing comprehensive management information about health programs for the modern dairy bull.

   The genetically superior adult dairy bull in the 21st century resides in an environmentally controlled barn, receives 3 or 4 nutritious meals a day, and is regularly monitored for its physical condition and health.  These animals receive extensive attention because their genetic product, that is their semen, is regularly collected, processed, and sold to dairymen around the world.  Because there are numerous domestic and international regulatory policies that govern the health of such animals, a series of preventive medicine and animal management programs must be implemented to achieve and maintain international marketing compliance.  This web site describes important aspects of these programs for different stages in the life of a dairy bull.

The life stages of a modern dairy bull

    The modern dairy bull is typically the result of a contract mating wherein a geneticist will select a dairy cow with specific milk production and conformational characteristics and mate her with a genetically elite bull.  The cows are bred by artificial insemination.  The genetic dam of the bull may carry the fetus for a complete gestational interval and give birth to a calf.  However, it is more common for an embryo resulting from the planned mating to be transferred to a surrogate dam, or recipient heifer, on day 7 or 8 following the insemination.  In either case, dairymen must recognize that the health of the animal performing the "gestational duties" is important to the health of the fetus. 

    Following a normal gestation, the calf is born and is raised by the dairyman for several months.  The calf is usually evaluated at 5 to 8 months of age by a veterinarian for its suitability to enter a semen collection center (SCC).  Bull calves meeting the necessary criteria are transported to the admittance facility.  During the admittance isolation interval the bulls are regularly monitored for their physical and reproductive health and repeatedly tested to determine their freedom from specific diseases.  Bulls that comply with the stated requirements are permitted to enter a resident herd of the SCC. 

    When the bull reaches 10.5 to 12 months of age, collection of semen will commence.  The semen is carefully evaluated for the quantity of spermatozoa as well as for its motility and morphology.  Bulls with satisfactory seminal parameters are recognized as sire candidates for artificial insemination (AI).  The bulls enter the progeny test program wherein semen is distributed to cooperating dairy farms, cows are randomly mated with a test bull's semen, and the female progeny are eventually evaluated for their milk producing capabilities.  The progeny test interval lasts about 3.5 years.  Bulls that have sired daughters with above average milk production and conformational characteristics are considered for "graduation" from the progeny test program.  About 10% of the dairy bulls tested graduate into the marketing lineup.  The adult stage of a dairy bull's life is sometimes the longest stage because it may last 2 to 9 years. Semen is regularly collected from most adult bulls. 

    Details regarding preventive medicine and bull management programs are discussed in the following sections.

• The gestation interval: Protecting the fetus

• Raising the bull calf (0 to 6 months)

• Admittance to the bull herd (6 to 11 months)

• Semen collection (11 to 16 months)

• Progeny test interval (17 to 60 months)

• The adult dairy bull (61 to 168 months)

The gestation interval: Protecting the fetus

    A complete bull health program begins by preventing transplacental transmission of disease to the fetus.  This segment of the bull's life is typically managed by the dairyman and not by the SCC.  The dam of a contract mated bull should be clinically healthy and in good physical condition.  Semen should be from a bull residing in a SCC that complies with the health requirements of Certified Semen Services.  If embryo transfer technique is used, the health of the recipient heifer should be considered.  Basically, the health of the "uterine dam" (the cow or heifer that performs the "gestational duties") is important because several diseases can be transmitted in utero, or across the placenta, and infect the developing fetus.  A bull infected during gestation is not permitted entry to a SCC if it tests positive to required pre-entry diagnostic criteria.

    The disease of greatest concern during the gestation interval is bovine viral diarrhea virus (BVDV).  It can be transmitted in utero when the cow is acutely infected during gestation or if the cow is persistently infected (PI) with BVDV.  When infection of the fetus occurs during the early part of pregnancy, that is between days 30 and 125 of gestation, the developing fetus will become PI.  Persistent infection occurs because the immune system of the fetus has not yet developed, the fetus does not recognize the BVDV as an infectious agent, and does not mount an immune response against it.  A BVDV-PI calf may die, be physically unthrifty, or be healthy and reach breeding age.  A bull that is PI with BVDV will shed the virus in all its secretions and excretions, including semen.  It is, therefore, important that the uterine dam be tested for BVDV to determine she is not PI.  It is also important to test the bulls for BVDV to determine if they are PI.  About 0.5 to 1.0% of dairy bull calves are found positive for BVDV and are rejected from entering a SCC. 

    Another virus that can be transmitted in utero is bovine leukosis virus (BLV).  If the uterine dam is infected with BLV, the fetus has a low (< 20%) risk of acquiring the infection.  In utero transmission occurs late in gestation and a calf infected in this manner will test positive for the virus.  Diagnostic tests for BLV antibodies, such as the enzyme linked immunosorbent assay (ELISA) or the agar gel immunodiffusion (AGID) test, are generally accurate and reliable. It is suggested, therefore, that the uterine dams be tested negative for BLV.  Most dairy bull calves infected with BLV will be rejected by a SCC because they will not comply with many international health protocols.

    A bacterial disease agent that may be transmitted in utero is Mycobacterium avium subsp. paratuberculosis, the organism that causes Johnes Disease.  The frequency of transplacental transmission is thought to be about 25%.  A cow that has tested positive to M. paratuberulosis by ELISA or fecal culture should not be the uterine dam of a bull intended for artificial insemination service.

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Raising the bull calf (0 to 6 months of age)

   This web site does not describe the numerous methods by which cattle may be competently managed during the calving and neonatal periods other than to state that proper hygiene should be conducted and the calf should receive a good first meal of colostrum.  Bull calves should be properly dehorned at an early age.

    A bull calf contracted to enter a SCC should be raised in its own pen or calf hutch.  Individual housing assures that it receives proper nutrition.  If the bull is raised with other animals that will remain at the farm-of-origin, it may be inadvertently vaccinated or exposed to a modified-live virus vaccine from other recently vaccinated animals.  Such exposure or vaccination may cause diagnostic tests to be positive and cause the bull to be rejected.

    Bulls contracted to enter a semen collection center should NOT be vaccinated for the following diseases:

• Brucella abortus

• Leptospirosis

• Infectious bovine rhinotracheitis virus (IBR)

• M. paratuberculosis

    Large breed dairy bull calves should be fed so they weigh about 2 to 2.3 pounds per day of age (or 1.1 kg per day of age) when they are 5 to 6 months old.

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Admittance to the bull herd (6 to 11 months of age)

    Within 30 days prior to a bull being transported to the admittance facility of a SCC, a physical examination is conducted by a veterinarian.  The bull's identification is checked as well as its size and physical condition.  The bull should have two normally developed testicles and should not have an umbilical hernia, a heart murmur, nor a history of chronic pneumonia.  Bulls with these problems or an incompletely descended testicle will be rejected.  

    The basic health test program for semen collection centers in the U.S. is the Certified Semen Services Requirements for the Health of Bulls Producing Semen for Artificial Insemination.  To qualify a bull for entry to a SCC, a test for tuberculosis is conducted within 60 days prior to scheduled transportation and a blood sample is collected within 30 days to evaluate if the bull has been exposed to or infected with several specific diseases.  Personnel at the SCC will have the blood serum sent to a state or federal veterinary diagnostic laboratory to be tested for at least bovine viral diarrhea virus (BVDV), brucellosis, and leptospirosis.  Additional tests for bovine leukosis virus (BLV), bluetongue virus, infectious bovine rhinotracheitis (IBR) virus, and M. paratuberculosis may also be conducted.  

    Bulls that satisfactorily comply with the pre-entry criteria are transported to the SCC.  Upon arrival they are weighed and shortly thereafter are examined by a veterinarian.  The above diagnostic tests  are repeated at least once during the isolation interval; however, there should be minimum 60-day interval between the two tuberculosis tests.  In addition, a series of 3 or 6 weekly tests for venereal diseases of cattle (Tritrichomonas fetus and Campylobacter fetus subsp. venerealis) are conducted.  Tests for tuberculosis and brucellosis are usually repeated after the bulls have completed at least 60 days in admittance isolation, especially if the resident herds are tuberculosis accredited-free and brucellosis certified-free by the U.S. Department of Agriculture (USDA).  An example admittance health test program, as administered by Select Sires in 2002,  is shown below.

    Evaluation of the bull's genital health is another important component of the admittance criteria.  The testicles and epididymides of each bull are carefully evaluated and the scrotal circumference (SC) may be measured at about monthly intervals to assess each bull's readiness for semen collection.  The SC measurement is a meaningful predictor of sperm production capabilities for yearling bulls and is also correlated with a bull's future SC as an adult.  Accordingly, a yearling bull with a small SC measure (i.e., two or more standard deviations below average) or a bull that has an immature epididymis (i.e., the cauda epididymis is much smaller than normal) will be rejected from the progeny test program.  

Average scrotal circumference data for young Holstein bulls

Age (months)	Scrotal circumference (cm)
5	18.9 + 1.6
6	21.9 + 2.5
7	24.3 + 2.4
8	26.6 + 2.4
9	28.6 + 2.3
10	30.5 + 2.1
11	31.7 + 2.2
12	32.7 + 2.0

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Semen collection (11 to 16 months of age)

    A competent semen collection program has the goals of optimizing seminal quality while maximizing the quantity of sperm collected.  The collection room should have good lighting and the floor should provide good footing for the bull, the stimulus animal, and the technician collecting the bull.  The bulls should be handled to reduce the risk of injury.  Following adequate stimulation of the bull, semen is collected in a clean and properly prepared seminal collection device.  To prevent cold shock to the spermatozoa, an insulated jacket is applied over the semen collection liner.  After the collection, the sterile tube with 5 to 12 ml of semen is removed from the collection device, is labeled with the bull's identification name and number, and transferred to the laboratory for evaluation and further processing if the spermatozoal characteristics are satisfactory. 

    Large breed dairy bulls may be successfully collected when their scrotal circumference (SC) measurement is greater than 31 cm.  Jersey bulls may begin collection when their SC measures about 29.5 to 30 cm.  Bulls with unacceptable spermatozoal quantity or quality parameters are again evaluated to assess their prognosis as a AI sire candidate.  If seminal problems continue, the yearling bulls are culled from the progeny test program.

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Progeny test interval (17 to 60 months of age)

    After the yearling dairy bull has produced satisfactory semen for artificial insemination (AI) and it has also passed the required health test protocol, the bull enters the progeny test interval. About 70% of the bulls that were initially evaluated on the farm-of-origin successfully complete the required protocol to be an AI sire.   During this time, semen of each progeny test bull is distributed to cooperating dairy farms, cows are randomly mated with its semen, and the female progeny are evaluated for their milk production capabilities about 24 months later.  Most dairy bulls do not have semen collected during this time, but are housed in small groups with several other bulls or in individual stalls.  The bulls are regularly evaluated for growth and physical condition; diagnostic tests to monitor the health of the bulls and the herd are continued at semi-annual intervals. 

    When the bulls reach 55 to 60 months of age, early lactation data from their daughters is received from the regional dairy records processing centers and is statistically analyzed by the Animal Improvement Production Laboratory (AIPL), a division of the USDA.  Bulls that have sired daughters with above average lactation records will be returned to the production herd for additional semen collections.

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The adult dairy bull (61 to 168 months of age)

    The genetically superior adult dairy bull is the result of a considerable investment in time and money by the bovine genetics company or dairymen that conducted the progeny test.  Genetic improvement is the result of a rigorous animal selection program.  Biotechnology methods may be employed but only in the context of using molecular-based tests for detecting chromosomal markers for either genetic diseases or lactation production traits.  Direct manipulations of the animals' genome are not conducted.

    The adult stage of a dairy bull's life commences with receipt of the USDA-AIPL data, which is received when the bull is about 60 months old.  The term of a bull's residence in a SCC is dependent on marketing factors and on the bull's physical condition and musculoskeletal health.  The average lifespan for an adult dairy bull is 9  to 12 years; a few bulls will remain productive until 13 or 14 years of age, but few go much beyond that time. 

    To promote longevity in these genetically superior bulls, they are fed a nutritious diet with recommended levels of protein and energy; the calcium/phosphorus levels are also appropriately balanced.  The bulls' hooves are regularly evaluated and trimmed as necessary.  The bulls are monitored by barn personnel and any indication of illness or lameness are reasons for requesting a veterinary examination.  Bulls showing signs of illness may be further evaluated with hematological and serum biochemical tests.  

    Evaluation of hematology and serum biochemical variables can be helpful in monitoring adult bulls that have developed a chronic respiratory tract infection.  While many affected animals may cough or have nasal discharge, others show few clinical signs other than perhaps a fetid breath.  However, most bulls with a chronic infection will have decreased albumin levels, elevated globulin levels, and a lower than normal albumin/globulin ratio.  The bulls may also be moderately anemic.  The clinician should also recognize that the bull's normal creatinine level is higher than that typically observed in cows; this is thought to be associated with the bull's larger muscle mass.

    Reproductive examinations should also continue during the bull's adult stage of life.  Although most of its testicular growth, as measured by SC, has occurred by the time the bull is 3 to 4 years old, testicular health and tone need to be monitored at about semi-annual intervals.

    For the bulls to comply with domestic and international regulations governing the movement of bovine semen, the diagnostic tests mentioned earlier to monitor the bulls and the herd for freedom from infectious disease are continued at semi-annual intervals.  A few bulls may be tested more frequently to comply with the requirements of selected countries.

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Summary

    This web site has provided information about preventive medicine and management programs for dairy bulls, from conception to their geriatric stage of life.  The programs are intended to provide dairymen and management personnel at semen collection centers an opportunity to develop and maintain bulls that are productive and can comply with numerous domestic and international health regulations.  It is not appropriate, however, that all segments of these programs be included in international regulatory documents.  For example, veterinarians issue export health certificates to accompany semen being traded internationally based on health tests conducted under their supervision at the semen collection center.  Statements pertaining to the management of a bull prior to its admittance to the semen collection center, or to its uterine dam, are not appropriate for international regulations. 

    For additional information or inquiries regarding dairy bull management issues, contact Dr. Don Monke at Select Sires, Inc., Plain City, Ohio.

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Bibliography

Howard, T.H., Bean, B., Hillman, R., & Monke, D.R. (1990). Surveillance for persistent bovine viral diarrhea  virus infection in four artificial insemination centers. Journal of the American Veterinary Medical Association, 196, 1951-1955.

Hueston, W.D., Monke, D.R., & Milburn, R.J. (1988). Scrotal circumference measurements on young Holstein bulls. Journal of the American Veterinary Medical Association, 192, 766-768.

Monke, D.R. (1986). Noninfectivity of semen from bulls infected with bovine leukosis virus. Journal of the American Veterinary Medical Association, 188, 823-826.

Monke, D.R., (1987). Examination of the bovine scrotum, testicles, and epididymides - Part I.  Compendium on Continuing Education for the Practicing Veterinarian, 9, F252-255.

Monke, D.R. (1987). Examination of the bovine scrotum, testicles, and epididymides - Part II.  Compendium on Continuing Education for the Practicing Veterinarian, 9, F277-283.

Monke, D.R. (1988). On-farm management of bulls intended for AI service.  Proceedings of the Technical Conference on Artificial Insemination and Reproduction, 12, 68-79.

Monke, D.R. (in press). Bull Management: Artificial Insemination Centres. In H. Roginski, J.W. Fuquay, & P.F. Fox (Eds.), Encyclopedia of Dairy Sciences. London: Academic Press.

Monke, D.R., Kociba, G.J., DeJarnette, M., Anderson, D.E., & Ayars, W.H. (1998). Reference values for selected hematologic and biochemical variables in Holstein bulls of various ages. American Journal of Veterinary Research, 59,1386-1391.

Monke, D.R., Parker W.G., Milburn, R.J. (1986). Examination and management of the bull's foot.  Proceedings of the Technical Conference on Artificial Insemination and Reproduction, 11, 59-70.