Breeding Soundness Evaluation and Surgical Sterilization of the Ram

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.



ECONOMIC SOUNDNESS EVALUATION


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.



Heritability


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.


Table 85-1 Heritability Estimates



















































Trait Heritability (%)
Reproductive
Ewe fertility 5
Prolificacy 10
Scrotal circumference 35
Age at puberty 25
Carcass
Carcass weight 35
Weight of trimmed retail cuts 45
Percent trimmed retail cuts 40
Loin eye area 50
Fleece
Grease fleece weight 35
Clean fleece weight 25
Percent yield 40
Staple length 55
Fiber diameter 40

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.



Cost of Ram Power


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.


Table 85-2 Annual Ram Costs*










































Example Purchase Price $350.00
Fixed Costs
Depreciation/3y 117.00
Interest on investment at 12% 42.00
Total Fixed Cost $159.00
Variable Costs
Feed and maintenance 60.00
Overhead 5.00
BSE 15.00
Death loss/15% 52.50
Total Variable Costs 132.50
Total Costs 291.50
Income from Wool 20.00
Annual Cost per Ram (exclusive of purchase price) 271.50

* These figures are representative of Colorado producers as reported by CSU farm management specialists Rod Sharp and Paul Gutierrez.





BREEDING SOUNDNESS EXAMINATION


The BSE is one of the most essential components of the overall economic soundness of a sheep operation. Reproductive efficiency is a key element of economic efficiency.




Brucella ovis


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.


Table 85-4 Semen Quality of a Brucella Ovis-Free and a Brucella Ovis-Infected Ram Flock

































  B. Ovis-Free B. Ovis-Infected
Rams, n 84 94
B. ovis ELISA positive, n 0 72
Grossly palpable epididymal lesions, n 0 23
Motility, % 66 29
Semen parameters, mean
Normal sperm, % 86.5 55.5
Detached heads, %* 6.9 25.5

* In an infected population, B. ovis infection is correlated with seminal leukocytes and detached spermatozoal heads.


Removed without semen evaluation.


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.



Sep 3, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Breeding Soundness Evaluation and Surgical Sterilization of the Ram
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