Management of natural service bulls on large dairies Management of natural service bulls on large dairies

Natural service (NS) bulls are widely used on large dairy farms despite the wellproven genetic progress achievable through AI. Producers may choose to use NS bulls for a variety of reasons that are discussed below. In this presentation, problems encountered with the use of NS bulls on a large dairy in Kansas are described in relation to reduced reproductive performance on that dairy. Lameness in bulls was considered to be a major contributing factor to reduced herd reproductive performance, with seminal vesiculitis also possibly playing a role. Possible contributing factors for the occurrence of these problems in the bull population are discussed. A number of recommendations are made for optimal selection, use, and management of NS bulls. These include the following. Natural service bulls should preferably be younger bulls (< 2.5 years of age) and t ractable. Facilities should be adequate for the safe handling of bulls and people. Attention should be paid to minimizing heat stress during the summer. An environment should be created where reproductive behavior can be fully expressed. Appropriate considerations include: sufficient space for courtship and breeding; minimizing distractions, such as people and noise; and the provision of suitable flooring for breeding (i.e., provision of secure footing). Natural service bulls should pass a breeding soundness evaluation prior to purchase and/or first use and this should be repeated at least annually. Bulls should undergo the same herd health procedures as the cow herd (except for brucella, trichomoniasis and MLV IBR vaccination). Particular attention should be paid to the prevention of venereal disease (vibriosis and trichomoniasis) transmission. Monitoring and record keeping for cows exposed to bulls should be similar to that for cows in AI groups and include regular pregnancy checks.


Summary
Natural service (NS) bulls are widely used on large dairy farms despite the wellproven gene tic pro gre ss ac hievable through AI.Producers may choose to use NS bulls for a variety of reasons that are discussed below.In this presentation, problems encountered with the use of NS bulls on a large dairy in Kansas are described in relation to reduced reproductive performance on that dairy.Lameness in bulls was considered to be a major contributing factor to reduced herd reproductive performance, with seminal vesiculitis also possibly playing a role.Possible contributing factors for the occurrence of these pro blems in the bull population are discussed.A number of recommendations are made for optimal selection, use, and management of NS bulls.These include the following.Natural service bu lls sho uld pre fera bly be younger bulls (< 2.5 years of age) and t rac table.Facilities should be adequate for the safe handling of bulls and people.Att ent ion shou ld be p aid t o minimizing heat stress during the summer.An environment shou ld be created where reproductive behavior can be fully expressed.Appropriate considerations include: sufficient space fo r co urt ship a nd br eeding; minimizing distractions, such as people and noise; and the pr ovision of suitable floo ring for breeding (i.e., provision of secure footing).Nat ura l service bulls should pass a breeding soundness evaluation prior to purchase and/or first use and t his should be repeated at least annually.Bulls s hou ld undergo the same herd health procedures as the cow herd (except for brucella, trichomoniasis and MLV IBR vaccination).Particular attention should be paid to the prevention of venereal disease (vibr iosis and trichomoniasis) transmission.Monito ring and record keeping for cows exposed to bulls should be similar to that for cows in AI groups and include regular pregnancy checks.

Introduction
Bulls are co mmonly used on United States dairies; particularly on newly established large dairies.Natural service (NS) bulls may be exclus ively employed initially, and the n less as increa sing e mphas is is placed upon improving t he herd's genet ic base, including raising replacement heifers.With the latter consideration, a number of producers using NS bulls consider that they can purchase replacement heifers with acceptable genetics.Dairy bulls are often not subjected to close scrutiny or monitoring.As a consequence, many dairies fail to adequa tely explo it the potential for improved reproductive performance with NS bulls.NS bulls pro vide the "default" o ption when the effective implementa tio n of AI is difficult or costly.Bulls are used in breeding management schemes to eliminate perceived obstacles to AI including costs and the lack of qualified personnel to perform tasks such as heat detection.A common perception is that a motivated bull will generally detect more heats than will humans, particularly if the latter are poorly trained.Bulls also should be able to deposit semen at the most advantageous time for female fertility because they work 24 hr per day, 7 da ys per we ek .Bulls often service recept ive females a number of times during the period of female receptivity.Thus, bulls continue to be used in dairy herds because they provide an alternative to managing a heat detection or an est rus synchr onization program and the appropriate personnel to manage a successful AI progra m.This report describes pro blems observed with NS bulls on a large dairy in southwest Kansas.

Procedures
Bulls were examined in January 2000 on a large, newly established, 2,500-cow dairy in southwest Kansas.This was a new facility where management procedures and personnel were still evolving as the dairy grew in size and a tt empted to achieve production goals.All breeding was exclusively performed by NS bulls.It was evident, however, tha t na tural breeding was not as successful as it sho uld be, with a large number of cows (more than 500) remaining open after more than 200 DIM.
Natural service bulls were obtained under contract by a supplier and varied in age.The bull to female ratio was approximately 1:40.Female groups consisted of several hundred cows.The cow groups included varying numbers of open and preg nant females at any given time.Bulls spent much of t heir time in free-stalls, on concrete, although access had recent ly been provided to outside dirt lots.In the free-stalls, the "working" area consisted of t he conc ret e alle y-way behind the stalls, which was periodically flushed with water.Bull groups comprised mixed ages of bulls that were generally kept intact, although they were rotated between cow groups at approximately 1-week intervals.Bulls were fed the same diets as their respective cow group.Both cows and bulls were vacc inated agains t leptosp irosis (5-way) and vibriosis.A total of 98 bulls were subjected to a physical examination, 66 of which were electro-ejaculated for semen evaluation.Appr oximately 30 bulls were sampled to test for trichomonosis.An additional 20 young bulls were subjected to visua l appraisal only.

Results and Discussion
During examination it was observed that many of the bulls were "tenta tive" in their foot ing on concrete.Twenty-one of the 98 bulls were classified as poor breeding prospects and were recommended to be culled.An add itio nal 7 bulls ha d pr oblems that might compromise breeding success, but which could improve with time.Screening for trichomoniasis wa s neg ative for all samples.No obvious pro blems were det ect ed in the young replacement bulls that were subjected to a visu al appra isal o nly.A summation of the problems encountered in bulls is presented in Table 1.
The most common bu ll problem encountered was lameness.Lame bulls were recommended to be culled only if the problem was severe and probably irreversible.Lameness in the hind limbs was regar ded as being more detrimental to reproduct ive success than lameness in the fore limbs.S ever ely lame bull problems included a dislocated hip, a dislocated patellar (knee cap), a number of swollen joints (particularly of the lower limbs), and acute foot sor enes s.Litt le evidence of severe laminitis was evident , although it is probable that subclinical laminitis was present.With bulls being fed the same rations as lact ating dair y cow s, it is pro bable that some bull lameness pr oblems would be caused by excessive energy and calcium in their rations.However, it was considered that a large number of the lameness problems observed in this herd were due to trauma (i.e. , loss o f footing or fighting with other bulls).
The relatively high prevalence of seminal vesiculitis or accessory genital disease observed (17.3%) was of concern, although only two bulls were severely affected.Active vesiculitis will adversely affect semen quality.Often the infection will spread to other parts of the genital tract where it may lead to irre versible problems.The factors leading to increased seminal vesiculitis in a group of bulls are not all kno wn.This p roblem is often encountered in young beef bulls on performance test , when t here is a combination of high energy rations and intensive rearing (and pe rhaps inc rea sed homo sexual behavior).Without further observations and tests, it would be d ifficult to determine the cause in this case.However, managerial opt ions such as rotating bulls, red ucing cat tle density in pens, and perhaps feeding chlort etracycline should he lp to redu ce t his pro blem.

Conclusions
The practice of running bulls in mixedage groups with large numbers o f females in free-sta lls facilities with concrete floors seems to be a major contribut or to the "bull pro blem" encountered at this dairy.Bu lls are particularly susceptible to injury during mounting and mating when they are often off-balance, with their weight being supported by th e hind feet.Whe n foo ting is insecure, especially in confined spaces, injuries easily occur.Bulls with injuries are less likely to mount and serve.In addit ion, the fear of injury will lead to loss of confidence and reduced sexual activity.In this case, running older bulls with younger bulls, par ticular ly in confined spaces, also could contribute to lowered activity by the latter group beca use older bulls t end t o be dominant, more aggressive, and prevent other bulls from accessing females, even if they themselves are infertile.Older bulls also pose a human safety risk as well as tend ing to outgrow free-stalls.In the present case, lameness also was a concern with cows at the dairy, with factors such as concrete texture and free-stall design p robably playing roles.

Recommendations
The follo wing reco mmenda tio ns sho uld be followed when using bulls on commercial dairies: • All virgin bulls should be subjected to a breeding soundness evaluation (BSE) before admittance to the herd.
• All bulls should be given a physical exam e very 6 months and a full breeding soundness exam every 12 months.• Adequate handling facilities should be provided for the working and handling of bulls to reduce t he risk of injur y to both animals and p ersonnel.• Bulls in freest all housing should be given access to dirt lots.• All working bulls should be monitored daily.• A worka ble system is to maintain bulls in breeding groups that will be rotated into the bree ding herd for 1-2 weeks, followed by 1-2 weeks of rest.• Bulls ideally should be less than 2.5 years of age.Aggressive, older and large, heavy bulls should not be sold.• A suit able bull to female rat io is a ppr oximately 1 bull to 15-25 open cows.• If a dairy has large p ens it may be beneficial to distribute open cows over more pens to reduce the number of bulls in any given pen.• Avoid dra stic changes in diets fed to bulls.Don't put bu lls abruptly onto the same diet s as la ctating co ws without slow ly increasing intake and energy in steps • Minimize the effects of heat stress by providing shade and cooling systems.
• Bulls should be s ubjec ted to t he sa me vaccination and preventive health program as the cows (with the exception of vaccinations for brucello sis, trichomoniasis and MLV IBR).
It is important for personnel to be especially alert for signs of lamenes s.E arly detection of lame bulls is critical and employees should be trained t o o bser ve co mmon lameness signs, as well as ot her problems associated with breeding bulls.Lame or otherwise injured bulls should be treated and/or replaced as soon as possible.