The textbook recommendation for bull: In cows in which estrous synchronization is used, the recommendations are altered by necessity. One mature bull with 15 to 30 cows, confined to a small area, is a typical recommendation for a system where a majority of the cows are expected in estrus over a 5 day period. At least a 10 day rest between breeding periods is suggested with this type of breeding challenge. As might be anticipated, there is general disagreement with these recommendations among cattlemen.
Some feel these numbers are too low, while others feel that the recommendations are too high; especially for yearling bulls. An easy answer to the question of how many females a particular bull can service in a breeding season is not usually available. Perhaps the most fool-proof way to determine the mating capacity of a bull, or in other words the appropriate bull: After breeding seasons an observant manager would have a good idea of the potential of a given sire for mating capacity.
Unfortunately, by the time a sire has demonstrated his potential, he has often outlived his usefulness from a genetic standpoint for a given operation. What are the limits for the bull: Some information is available from research trials. Reports vary in regard to the limits. In some studies, performance for some bulls at ratios of 1: However, at these higher ratios, a few bulls failed and achieved unacceptable rates of conception. Thus, the problem still exists that general recommendations of bull: Rather, the mating capacity of an individual bull is more important to reproductive success than the bull: Two of the primary factors that affect mating are discussed here.
Determinants of mating capacity: Seminal Quality; a Semen quality and b. The importance of the bull in reproductive efficiency is often overlooked by producers, educators and research scientists. It is clear that the capacity of the bull to perform is limited by the fertility of the cowherd. Thus, a majority of efforts have and are placed upon ensuring that reproductive potential of the females in the herd is optimized.
In short, we have come to assume that the bull will do his job, if we make the correct management decisions regarding the cow herd. Even if the managerial and financial investments are made to ensure that the cow herd is reproductively competent, if reproductive failure occurs due to a defect in the bull, a tremendous loss in terms of reproductive efficiency is likely.
Unfortunately, a bull infertility problem is usually not detected until after the fact, or in the best cases, during the latter stages of the breeding season.
In the context of bull: Clearly, the more females that bull can effectively impregnate in a given season, the more optimal or efficient we are in the use of the capital invested in that sire. As one pushes the bull: At the risk of sounding like an economist, there is a point of diminishing returns, in terms of reproductive efficiency, uniformity of calf crop, etc.
Furthermore, the consequences of infertility of a given bull, when pastured with 60 cows, are much more serious than if exposed to only 25 females. Thus the risks increase as efficiency of bull utilization increases. There is no fool-proof way to ensure that a new bull is going to perform adequately in a natural breeding system.
However, there are some tools available, and management considerations that are important, to minimize the risk of reproductive failure. Factors affecting seminal quality: One definition of seminal quality for a given bull is the quality achieved as a result of the genetic composition of the bull, minus the detrimental effects of the environment in which the bull is reared and maintained.
Thus, seminal quality is a function of both genetic and environmental factors. Semen quality is usually defined as the number of abnormal sperm cells produced and the motility of the sperm cells, whereas, semen quantity refers to the number of sperm cells produced.
Also, a multitude of factors, such as health, nutrition, disorders, etc. I will only briefly highlight a few of these factors here to emphasize their importance in determining mating capacity of bulls.
Testicular Size — Scrotal Circumference: Scrotal circumference is controlled to a large extent by genetics of the animal. This trait is of moderate to high heritability and, as has been well documented, has an important influence on reproductive competence of the sire as well as his male progeny. What are the relationships of scrotal circumference to seminal quality? Bulls with small testicles are more likely to have reduced sperm output and increased numbers of morphologically abnormal spermatozoa.
Seminal quality increased up to a scrotal circumference of 38 cm, with no further improvement in bulls with larger testes. Thus, scrotal circumference can have major effects on seminal quality and, in turn, influence the mating capacity of an individual sire. It is important to mention the influence of scrotal circumference of a sire on age at puberty for female progeny. For each 1 cm deviation in scrotal circumference among sires, it has been estimated that age at puberty in daughters is influenced by days.
Thus 2 bulls with scrotal circumferences that differ by 10 cm, would sire daughters with a 40 day difference in age at puberty.
The benefits of assessing this trait, and including it in selection criteria for bulls are two-fold. Other genetic factors that can influence seminal quality are testicular consistency, some recessive trait, and scrotal shape.
Obviously age influences quality, with seminal quality shown to increase for about 4 months following the attainment of puberty in yearly bulls. Thus, careful consideration is necessary for evaluation of seminal quality of young bulls, and to the challenges we subject them to in terms of bull: Bulls used for natural service are exposed to a wide range of environmental and management conditions.
Typically, the factors in this category that effect seminal quality are most often associated with influences on hormonal mechanisms or on regulation of scrotal temperature. Only limited information is available regarding the effect of environment on the basic hormonal mechanisms that control seminal quality. More extensive information is available regarding the effects of various environmental and management factors on seminal quality.
Often, these influences are directed through their impact on regulation of testicular temperature. The influence of elevated testicular temperature on sperm production and quality have been well-documented and often include reduced sperm production and decreased semen quality. Optimal sperm production is achieved if the temperature of the testes is maintained a level below normal body temperature. The bull has 3 primary systems in place to ensure that the desirable testicular temperature is maintained.
Any environmental effect or management approach which alters the ability of the bull to regulate testes temperature, or increases testes temperature through other means, will negatively influence seminal quality. Nutrition is a key environmental influence that may alter seminal quality. Variable results have been obtained regarding the influence of nutrition on seminal quality. The most detrimental effects have been observed through the feeding of high energy diets to yearling bulls.
Some reports indicate substantial reductions in sperm production, storage, and motility and an increase in abnormalities in bulls fed high versus medium energy diets, while others have observed little effect of dietary energy on seminal quality.
Circumstantial evidence suggests that the mechanism for reduction in seminal quality with high energy feeding is the result of impaired thermoregulation of the testes. The impaired thermoregulation thought to be caused by increased fat deposition in key areas of the scrotum that are responsible for thermoregulation.
The practical implications are reflected in results from a field study in which bulls were evaluated for backfat and fertility. A significant negative relationship between backfat thickness and fertility were observed in the natural breeding season; as backfat thickness increased, bull fertility declined. Thus, nutrition, through its influence on body fatness, may contribute to reduced seminal quality thereby decreasing the bull: Other factors that can affect temperature of the testes also may influence seminal quality.
Elevated body temperature has clearly been shown to reduce seminal quality. An insult in the scrotal area such as frostbite or insect infestation can increase the local temperature, and influence seminal quality. Thus, maintenance of the thermoregulatory mechanisms of the testes are critical to defining the mating capacity of a bull.
In summary, seminal quality is the result of both the genetics of the sire and the environment in which he is reared and maintained.
Proper selection and management are critical to maintain high levels of seminal quality. This characteristic is most often assessed through the use of the BSE. Seminal quality is one of the primary factors that influences mating capacity. The influence of libido on mating capacity: In addition to seminal quality, the mating capacity of a bull is determined by his libido and mating capability.
In other words the willingness and competence of a bull to service a female is critical to his mating capacity. Several systems have been developed to evaluate and quantify libido of bulls. The basic premise of most tests is to expose a group of bulls to either females in heat or restrained females, and measure the willingness mounts and competence successful matings to mate in a set time period. Virgin bulls often require a learning period, and perhaps an offered sexual experience in order for them to demonstrate their true potential for libido.
In conclusion, libido tests can be used to accurately rank bulls according to libido score. However, the necessity for multiple tests, and providing the opportunities for young bulls to learn, increases the efforts necessary to successfully perform this type of evaluation. Effect of libido on mating capacity: The importance of adequate libido or serving capacity on the mating capacity of a bull, and the resultant fertility of the females serviced, has been demonstrated.
Some scientists have shown clear differences between bulls with high, medium, and low libido in terms of the conception rate of females to which they were exposed. However, others have demonstrated no difference between higher and lower libido bulls in terms of fertility, although usually the number of services was increased with increased libido. That factors other than libido are important can be easily assessed by comparing herd fertility among mature and yearling bulls that demonstrate equal mating activity.
Typically, herd fertility, at the same bull: The variations cited above for the effects of libido on herd fertility can be explained as follows. The largest effects of libido score on herd fertility can be detected when one compares bulls of different libido scores that have equal BSE scores i. Under these conditions, seminal quality is not an issue, and differences in libido are expressed due to the large number of females that are to be serviced.
If BSE scores are not considered, or if bull: In order to define the mating capacity of a bull, then, it is essential that both willingness and competence to mate libido and the ability to produce viable semen in effective quantities seminal quality-BSE are considered.