Fertility and Infertility in Male Animals

Fertility and infertility in male animals

EXAMINATION FOR BREEDING SOUNDNESS

Examinations of male animals are made fortwo main purposes: either to ascertain whethernormal fertility can be expected from the animal,or for the diagnosis of infertility. In either situation,the requirements are a history of the animal,a general examination, a detailed examination ofthe genital tract, observation of copulation, andcollection and evaluation of semen.

History-taking is an important part of theexamination of a suspected infertile male animal.Many of the causes of infertility do not manifestthemselves until aconsiderable period of time haselapsed from the original insult, so that careful

questioning of the owner, often over matters thatmay have been considered trivial at the time oftheir occurrence, may be needed to elucidate suchcauses.

History-taking is also a useful way ofassessing owners’ expectations of their animals,

for many cases of so-called ‘infertility’ result fromno more than an unrealistic expectation of a sire’scapabilities.

The history must establish whether or not thesire is likely to be the cause of the infertility, theduration of infertility and the circumstances ofits onset. The number of females with whichthe sire’s infertility has been manifest must bedetermined, as must the conditions under whichmating has occurred. For example, it is not uncommonfor dogs to be presented for infertility examinationafter failure to achieve pregnancy on nomore than one or two occasions, with bitches thatwere scarcely in oestrus. Clearly, under such circumstances,the probability of a pathological cause

of infertility is minimal. Amongst agriculturalanimals, the sizes of groups of females and thesystem under which mating was taking place mustbe determined.

A common cause of apparent infertilityin rams derives from no more than using

groups of too many ewes, especially if these haveundergone synchronisation of oestrus or are beingused in out-of-season breeding regimens.

The time of year when the infertility wasnoticed may give helpful clues as to its cause, andmay help to determine whether female factors arelikely to have been of importance. Similarly, informationregarding the previous achievements of the

animal is of great importance in differentiatingbetween congenital and acquired conditions, orbetween managemental and pathological causes.

The general examination of the sire must takeinto consideration its age and likely sexual experience,body condition, the possibility of intercurrentillness and the animal’s temperament.

Considerable importance can be attached to thebody condition and general degree of maturityof young animals; on one hand, puberty can bedelayed in poorly grown animals, while, on theother hand, animals that have achieved very highgrowth rates during rearing may have a body conformationthat belies their sexual immaturity. It is

also noticeable that young bulls of some latermaturing breeds, notably the Charolais andHolstein, may remain relatively subfertile forlonger than their earlier-maturing counterpartsThus, the assessmentof young sires can present some difficulty, for

allowance has to be made for the maturity characteristics of the breed, yet the use of young bulls inwhich puberty is excessively delayed is bestavoided in view of the evidence that the age ofpuberty in a sire is highly correlated with the ageof puberty in his daughters. This problem isfurther compounded by the pressure of timeimposed by the requirements of progeny testing,

particularly of dairy bulls. In a seasonally calvingnational herd, semen from young bulls has to beavailable roughly 12 months after their birth, ifprogeny testing is to be carried out successfully.

For Friesians, this target presented little difficulty,but a significant proportion of young Holsteinbulls do not produce consistently usable semenuntil beyond this age. By the time they reach thisage, the majority of cows in the national herd willalready be pregnant, so progeny testing is delayeduntil the following season.

When young sires are used in natural-mating regimensfurther difficulties may be encountered.Firstly, it must be ascertained that they have learntto mount and successfully copulate. Similarly, itmust be determined that copulation is feasible,since, where young sires are running with fullymature females, copulation may not be physicallyachievable. Furthermore, it is not uncommon forthose young boars or rams that are run with large,mature females to be bullied by these females, toachieve no pregnancies and to lose a great deal ofbody condition. Secondly, young sires are mostunlikely to achieve high pregnancy rates amongstlarge groups of females and are generally unsuitablefor use with groups of oestrus-synchronisedfemales.

Body condition is also important in adult males.Spermatogenesis tends to be limited when bodycondition is poor, and can also be limited by specificmicronutrient deficiencies. In general, chronicand continuing deficiencies of protein and energy

are likely to be of greater overall importance thanmicronutrient deficiencies, although the effectsupon fertility can be severe when these occur simultaneously(Salisbury et al., 1978). For most agriculturalspecies, sires should be maintained inmoderate condition, although rams should start thebreeding season in a high condition score, due tothe considerable weight loss they experience duringthe season. Conversely, ruminants that are fed onvery poor-quality roughage can develop such greatrumen fill that normal copulation can be physicallydifficult to achieve. Moreover, as excess weight canlead to damage to females during mounting, it isimportant to determine that the sizes of sire andfemales are compatible.

Whereas any systemic illness can affect reproductiveperformance, three groups of conditions can benoted as of particular importance: namely, diseasesof the locomotor system, conditions causing pain inthe caudal abdomen and conditions that result inprolonged pyrexia. Specific conditions will be consideredunder the first two headings later in thechapter but, in principle, it is important to note thathindleg, hindfoot or back pain are incompatiblewith normal mating behaviour. Furthermore, notonly does locomotor pain limit mating directly, butalso the stress of prolonged, unresolved pain maycause corticosteroid-mediated impairment of spermatogenesis.

Systemic illness causing prolongedpyrexia can result in increased temperatures withinthe testis, thereby causing temperature-limitedimpairment of spermatogenesis.

REPRODUCTIVE EXAMINATION

A complete examination of the reproductivesystem requires physical examination of thegenital system, observation of the response of theanimal to an oestrous female, observation ofmating and the collection of semen. In practice,which of these procedures are actually carried outand the order in which they are undertakendepend upon the species and the nature of theowner’s complaint. For example, it is requently

desirable to observe mating or to collect semenbefore the animal has undergone the stress of aphysical examination. Thus, for a bull, collectionof semen by an artificial vagina (AV) is oftenbetter undertaken before palpation of the genitalia(especially before examination of the internal genitaliaper rectum), whereas collection by electroejaculationis probably best left until the rest ofthe examination has been completed. Also,observing mating (or collecting semen by an AVor with a judiciously placed electroejaculator) isthe easiest way of observing the penis of a bull.Conversely, in the ram, it is generally best toexamine the external genitalia first, as this frequentlyobviates the need for causing the animalstress by collecting of semen by electroejaculation.

Choosing the conditions for the observation ofmating behaviour is important. Where the inherentlibido of the animal is high, such as in boarsand dairy bulls, it will often be willing to mountfemales that are not in oestrus, or even to mountother males, castrates or dummy animals. Indeed,the willingness of a cow to be haltered and tied isoften a more important criterion for her use thanwhether or not she is in oestrus; few bulls arewilling even to attempt to mount a fractious cowthat is fighting against unfamiliar restraint! Ramsand beef bulls, although usually of high inherentlibido, commonly refuse to mount an oestrousfemale in the presence of a human observer, andconsiderable tenacity and patience are oftenrequired before mounting occurs. Animals thatare stressed by recent transport are also oftenunwilling to mount straight away.Taken together,these many caveats mean that, although theresults of observations of mating are valuable andoften provide diagnostic information in infertilityexaminations, one should be most cautious aboutcondemning an animal that does not performunder observation.During examination of the genital tract, all

parts of the genitalia that are accessible externallyshould be palpated.When xamining the contentsof the scrotum, the temperature, size, texture,resilience and evenness of the testes and epididymesshould be determined. The testes shouldbe freely movable within the scrotum. It is generallypossible to palpate the head and tail of theepididymis, but the body is often difficult to feel,due to its medial site. The vasa deferentia shouldbe palpated throughout the scrotal neck and (particularlyin rams) the presence or absence ofvasectomy scars confirmed. The spermatic cordshould be palpated up to the level of the inguinalring for the presence of abdominal contents

(scrotal hernia) or abnormalities of spermatic vasculature.

Measurement of scrotal circumference isuseful in animals with a pendulous scrotum

(Figure 30.2), while, in the stallion, measurementof the width of the testes by calipers or ultrasonographyis similarly valuable. Likewise, ultrasonography of the testes of stallions and dogs tovisualise fluid-filled structures within their substanceis proving to be a valuable additional examination

Scrotal circumference ofyearling bulls should exceed 30 cm, while maturebulls should be over 36 cm for British beef breedsand over 38 cm for most other breeds. Scrotalcircumference of mature rams depends uponbody weight; values over 28 cm are acceptable forsmaller breeds, and over 34 cm for larger breeds.

Scrotal circumference of rams is highly dependentupon season, with a 25–35% change in size occurringbetween the non-breeding and breeding seasons.The texture of the testes and the turgor ofthe cauda epididymes undergo parallel changes.

It should also be noted that, although rams continueto produce sperm during the non-breedingseason, they often fail to respond to electroejaculationduring that period. Hence, much care mustbe exercised in interpretation of clinical findingsin rams during the non-breeding season.

After palpation of the preputial part of thepenis, exteriorisation of its free part where possible,palpation of the sigmoid flexures and palpationof the prepuce and preputial orifice, such ofthe internal genitalia as are within reach should bepalpated per rectum. In the bull and stallion, allaccessory glands can be palpated thus, but they

are generally out of reach to a digital examinationof the ram. In large boars, rectal examination ispotentially feasible, but digital examination ofsmaller boars will only reveal the bulbourethralglands. In smaller dogs, digital examination ofthe prostate is possible, but radiography, whichis essential when prostatic disease is suspected,

is required in any case for examination of theprostate in larger dogs.

Libido testing

Assessment of libido and serving ability is widelyused in the examination of bulls for breedingsoundness (Chenowith, 1986, 1997). Observationsof bulls’ mating ehaviour (Blockey, 1976a, b) suggestedthat serving capacity tests might be a predictorof bulls’ fertility (Blockey, 1978). Moreover,libido is considered to be highly heritable incattle, so early selection of animals for high libidois likely to result in an overall increase in thisaspect of reproductive performance (Boyd andCorah, 1988). A number of tests have been devisedthat attempt to assess libido and serving capacity

(Chenowith, 1986), utilising either females inoestrogen-induced oestrus or non-oestrousfemales, and scoring the number and vigour ofmatings or mating attempts. A number of reportshave shown that high test scores are associated withgood reproductive performance (e.g. Makarechianand Farid, 1985; Blockey, 1989). However, otherreports have been more cautious, giving only qualifiedsupport for libido testing (Chenowith et al.,1984) or suggesting that moderate numbers of mounts were superior to high or low numbers(Coulter and Kozub, 1989).Yet other workers havefailed to demonstrate a relationship between testscores and fertility (Crichton et al., 1987; Farinet al., 1989). Finally, the repeatability of individual

libido scores is not high, although rankings of libidoscore are much more consistent (Chenowith,1997). In consequence, the American Society ofTheriogenologists advocated clinical examination,rather than libido testing, in their recent guidelines

for breeding soundness examination of bulls(Hopkins and Spitzer, 1997).

Many of the factors that have been mentionedpreviously, such as age, sexual experience andsocial dominance, can affect libido and so leadto unreliability of tests. Nevertheless, whenChenowith (1986) discussed the reasons for thevariability of the relationship between libido andfertility, he noted that bulls with high libido arethe most efficient at detecting oestrous cows, andin multiple mating systems, bulls of high socialranking mate more cows than low-rank animals.

However, even with bulls with a high intrinsicsemen quality, an excessively high number of servicesis likely to deplete sperm numbers, resultingin a reduced chance of conception occurring to anindividual service. A bull of high libido but withmore mediocre semen quality would undergosuch a decline in conception rates more readily.

Moreover, since clinical findings, especiallyscrotal circumference and the presence of abnormalsperm (Coulter and Kozub, 1989), are poorlycorrelated with measures of libido (Chenowithet al., 1988), it is quite feasible that a bull of highlibido might have inadequate semen quality toachieve an acceptable number of pregnancies.

Hence, Chenowith (1986, 1997) concluded thatneither clinical examination nor libido testing canbe used in isolation for the evaluation of breedingsoundness but, if the findings from both examinationsare taken into consideration, subfertile bulls

are most unlikely to avoid detection. Conversely,where range and beef bulls are examined, a combinationof clinical examination and libido testinggives good results. Morris (1998), for example,suggests that a low serving capacity test score or alow scrotal circumference should preclude a bullfrom use, but that, if minimum criteria for bothare met, the number of cows with which a bull canbe run will be dictated by a combination of bothscrotal circumference and service capacity test

score.