Sheep Industry News September 2025

Optimizing Ram Fertility: Breeding Soundness Exams and Brucella Ovis Control

Dr. Rosie Busch Dr. Bret McNabb UC Davis School of Veterinary Medicine A s we prepare for the upcoming breeding season, the health and fertility of our rams deserve careful attention. Rams may make up a small fraction of the flock, but they carry the weight of its reproductive success. A single infertile or infected ram can quietly derail a lambing season, making proactive health management essential. At the heart of this effort are two tools that work together: the breeding soundness exam (BSE) and Brucella ovis testing. To gether, they offer a reliable way to ensure your ram battery is ready for the work ahead. Beyond Looks: What a Breeding Soundness Exam Tells You A breeding soundness exam is more than a quick glance at body condition or a confident gait across the pasture. It’s a thorough assessment designed to answer one critical question: Can this ram settle ewes? Ideally performed six to eight weeks before breeding turnout, a BSE begins with a full physical exam. The veterinarian will evaluate the ram’s general health, musculoskeletal soundness, body condition, vision, and even his teeth. Healthy rams should have a body condi tion score between 3 and 4 on a 5-point scale and be free of lameness or injury, particularly to the head and neck—common trouble spots in group-housed rams prone to fighting. Special attention is given to the reproductive tract. The external geni talia are examined for abnormalities like scrotal hernias, pizzle rot, or abscesses. The testes, epididymis, and spermatic cords are palpated for symmetry, tone, and the presence of granulomas or masses. A scrotal circumference measurement gives insight into sperm produc tion potential—mature rams should measure at least 33 centimeters. Mature rams with a small scrotal circumference, or an abnormal scrotal palpation, should be removed from the breeding flock. Semen is collected either by electroejaculation or artificial vagina and analyzed under a microscope. Both the sperm motility and sperm morphology (sperm shape) are important for fertility. Good fertility is marked by at least 30% progressive motility and fewer than 30% abnormal sperm cells. While libido—the ram’s actual desire to breed—is not measured directly, factors like age, nutrition, and social hierarchy all influence this critical trait. Keeping detailed records on previous breeding performance can help fill in the gaps. It’s worth noting that young rams are often sold before reaching sexual maturity. While they may not yet produce semen for analysis,

a physical exam can still reveal congenital defects such as penile or scrotal abnormalities that could affect future fertility. The Silent Threat: Brucella ovis While structural soundness and semen quality are essential, infectious disease status is just as critical—and Brucella ovis is one of the most important pathogens to rule out. This bacterium causes epididymitis in rams, causing poor quality semen and, in some cases, can lead to abortion, stillbirth, or weak lambs in ewes. It is a significant cause of reduced conception rates and decreased lambing percentages, especially in multi-sire flocks. Brucella ovis spreads primarily through venereal transmission. Rams become infected when they breed ewes that were previously covered by another infected ram, often during the same heat cycle. Ram-to-ram transmission is also common during the non-breeding season through mounting behavior and preputial licking. Infected rams may not show clinical signs for weeks, and fewer than half will develop palpable lesions in the epididymis. That means palpation alone is a poor screening tool. Thankfully, there is a reliable diagnostic test. A blood-based ELISA developed by the National Veterinary Services Laboratories detects antibodies with approximately 97% sensitivity. It is most useful when performed on the entire ram battery before breeding season. Rams that test positive should be isolated immediately and either culled, castrated, or, in very limited cases, retested and to con firm infection status using semen PCR. If fewer than five percent of rams test positive, these animals can be reevaluated in two to four weeks. All rams that were exposed to positives should be retested after 30 to 45 days to ensure they haven’t seroconverted during the incubation period. Repeat testing after the breeding season is also advisable, particularly in flocks that are actively managing this disease. One often overlooked aspect of B. ovis control is the role of teaser rams. These animals, commonly used to stimulate estrus in ewes, may be vasectomized but still retain their accessory sex glands. If these glands become infected, teaser rams can shed the bacteria in their seminal fluid during mounting. While they may not cause pregnancy, they can absolutely transmit disease. For that reason, teaser rams should be tested and managed just as carefully as intact breeders. Feeding and Other Keys to Success Ram fertility is also dependent on good nutrition. Trace miner als like selenium, zinc, and copper are essential for spermatogenesis and hormone production. Diets that are too heavy in grain or alfalfa See Optimizing Ram Fertility story on Page 20

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