CHAPTER 85 Breeding Soundness Evaluation and Surgical Sterilization of the Ram
Breeding soundness evaluation (BSE) is an overall assessment of the ram’s capacity for serving and impregnating a number of ewes during a breeding season. An overall physical examination is performed with special emphasis on the reproductive system. The BSE includes anatomic and structural correctness, freedom of disease, body condition, scrotal circumference, and semen quality. The ram accounts for the major genetic changes in a flock. An economic soundness evaluation (ESE) is an assessment of the ram’s potential contribution to the profitability of a sheep enterprise. An ESE includes an evaluation of ram management and an assessment of the potential genetic contribution of the ram.
The ram genotype influences not only the quality but also the quantity of production per ewe exposed. A highly fertile ram can increase lamb crops by impregnating more ewes and by producing more multiple births per ewe.1 Research has shown that over three generations the ram is responsible for approximately 87.5% of the genetic influence on a flock.2 Therefore, specific criteria should be established for both production and reproductive traits.
The estimated heritability of different traits varies greatly. Although many production traits, such as carcass, dairy, and wool characteristics, are highly heritable, most reproductive traits are not (Table 85-1).3 Selection pressure for traits with low heritabilities must be intense over several generations for progress to be noted. Genetic progress is generally slower when selecting for multiple traits. It is also important to be aware that selection for some traits may have a negative impact on others. For example, many carcass characteristics and wool characteristics are negatively heritable.
|Age at puberty||25|
|Weight of trimmed retail cuts||45|
|Percent trimmed retail cuts||40|
|Loin eye area||50|
|Grease fleece weight||35|
|Clean fleece weight||25|
Scrotal circumference (SC) is probably the most important genetic trait associated with reproduction efficiency. The heritability of SC is estimated at 35%. SC is correlated with sperm output, age at puberty of the female offspring, ovulation rate, and the number of multiple births produced. In addition, some British researchers have reported a positive correlation between SC and the ratio of muscle to fat in the offspring. Failure to properly select for SC has the potential to reduce reproductive performance and production, thereby reducing the potential profitability of subsequent generations.
The cost of ram power per lamb produced is an important component of the ESE. The cost of ram power is determined by purchase price and by the number of lambs sired by an individual ram. Table 85-2 gives an example of annual costs per ram, exclusive of purchase price. Based on this example, Table 85-3 shows how the ram-to-ewe ratio and lambing percentage affect the annual cost of a ram per lamb produced.
|Example Purchase Price $350.00|
|Interest on investment at 12%||42.00|
|Total Fixed Cost||$159.00|
|Feed and maintenance||60.00|
|Total Variable Costs||132.50|
|Income from Wool||20.00|
|Annual Cost per Ram (exclusive of purchase price)||271.50|
The breeding capacity of a ram is determined by sperm production, semen quality, and libido. The breeding capacity of a highly fertile ram is one of the most difficult concepts for many sheep producers to accept. Under most range and semiconfinement conditions, a ram in good physical condition, with high libido, can successfully serve 100 or more ewes during a 17-day breeding cycle. For example, one 5200-ewe western range operation using 1.5 rams per 100 ewes consistently lambs over 90% of the bred ewes during the first 17 days of the lambing period and averages a 140% lamb crop.4 In this type of an operation, a higher ram-to-ewe ratio cannot be economically justified.
Brucella ovis is the primary cause of lowered fertility in multi-sire breeding systems in the western United States. B. ovis is also a major concern in Australia and New Zealand. B. ovis infection in a flock can have a devastating effect on the level of production by decreasing the number of ewes bred, decreasing the number of multiple births, and increasing the lambing interval. B. ovis ram epididymitis is a contagious venereal disease generally affecting mature rams in multi-sire breeding systems. The disease is transmitted via homosexual activities or via the ewe during the breeding season. The ewe does not become permanently infected, but serves as a mechanical vector for the spread of the disease.
The B. ovis organism enters the blood through the mucous membranes and infects the reproductive tract. Clinical signs include enlargement and fibrosis of the epididymis with wasting of testicular tissue. In some cases, infection of the secondary sex organs occurs without involvement of the epididymis. In these instances, no palpable lesions are evident, and diagnosis must be made by microscopic examination of the semen, semen culture, or serology. Table 85-4 shows a comparison between the semen qualities of a B. ovis–free and a B. ovis–infected ram population.
|B. Ovis-Free||B. Ovis-Infected|
|B. ovis ELISA positive, n||0||72|
|Grossly palpable epididymal lesions, n||0||23†|
|Semen parameters, mean|
|Normal sperm, %||86.5||55.5|
|Detached heads, %*||6.9||25.5|
Data from Ram Breeding Soundness Evaluation Records, Fort Collins, CO: Department of Clinical Sciences, Colorado State University, 1990.
Antibiotic treatment of B. ovis is disappointing, as about half of the cases do not respond. Vaccination interferes with the enzyme-linked immunosorbent assay (ELISA) serologic test, and is strongly discouraged. It is recommended that all rams in a multi-sire flock have an annual ELISA test, preferably during the period of lowest sexual activity. In single-sire flocks, the ram should be tested at purchase and retested 30 days later. All rams that test positive should be immediately culled. With the potential of B. ovis being in a latent stage and not showing a positive test in a multi-sire flock, the entire group of rams should also be retested at the end of the breeding season/shearing, once again culling all positive rams.
Libido refers to the willingness of a ram to breed ewes. A serving capacity test or direct observation of a ram with ewes is an important component of the BSE, but is frequently neglected. It has been estimated that approximately 10% of all rams have no interest in breeding ewes. In addition to not siring lambs, these rams can interfere with other working rams and should be removed from the breeding population. The behavioral evaluation of a ram should be conducted before the evaluation of the reproductive tract and the semen evaluation. Rams with inadequate libido should be culled without incurring further expense.
Restraint can vary, depending on the number of animals being tested and the number of people available to assist. The most important factor in restraint is that it should allow for a complete examination of both structural and physical characteristics. An adequate examination can be conducted on a standing ram restrained by a halter and pushed against a wall or fence. However, a calf table or sheep cradle makes restraining a ram for proper examination much easier.
Structural soundness refers to the capacity of a ram to remain sound during the breeding season under normal environmental stresses. The feet, legs, and teeth should be examined for structural soundness. Physical soundness refers to the health of the ram. The ram should be examined for conditions that may prevent optimal performance, or that can be transmitted to the ewes, such as foot rot, lip and leg ulcerations (ulcerative dermatitis), and pizzle rot. Body condition should also be noted during the physical examination. A body condition score of 2.5 to 3.5 is recommended for rams entering the breeding season. Structural and physical conditions should be noted at the time blood is collected for the B. ovis ELISA test, in conjunction with libido testing, and before examination of the reproductive tract and semen evaluation. If there are structural or physical conditions that cannot be corrected, the ram should be culled before incurring further expense.