Infertility in Sheep: Causes of Poor Fertility in Ewes and Rams

Infertility in sheep means a ewe, ram, or larger breeding group is not producing the expected number of pregnancies or lambs. In practice, this may show up as open ewes after breeding, repeat returns to heat, a low lambing percentage, or a long, spread-out lambing season. The problem can start before conception, during early pregnancy, or later if embryos or fetuses are lost.

Infertility is not one single disease. It is a reproductive performance problem with many possible causes. Some are management-related, such as poor nutrition, low body condition, heat stress, or too few fertile rams. Others involve infection, reproductive tract damage, congenital defects, or seasonal breeding patterns.

Both sexes matter. A flock can have disappointing conception rates because ewes are not cycling well, but one subfertile ram can also affect many ewes in a short breeding season. That is why your vet will usually look at the whole breeding system rather than focusing on one animal alone.

Poor fertility in sheep usually has more than one contributor. Nutrition is a major factor. Ewes that are too thin or losing condition may cycle poorly, ovulate less reliably, or struggle to maintain early pregnancy. Body condition around breeding matters, and strategic nutrition changes before breeding can improve results in some flocks. Rams also need adequate body condition and sound feet, eyes, and teeth so they can find and breed ewes effectively.

Seasonality also matters. Many sheep breeds are short-day breeders, so fertility drops outside the normal breeding season. If breeding is attempted too early, too late, or out of season, ewes may be in anestrus and rams may have lower semen quality. Heat stress can reduce ram fertility for weeks to months after exposure because sperm production takes time to recover.

Infectious disease is another important category. Rams may develop contagious epididymitis, including infection associated with Brucella ovis, which can lower semen quality and fertility. In ewes, reproductive losses may be linked to organisms such as Campylobacter, Chlamydia abortus, and other abortion-related pathogens. Some infections show up as infertility or early embryonic loss before obvious abortion is noticed.

Management problems can look like infertility too. Examples include too few rams, poor ram-to-ewe ratios during synchronization or out-of-season breeding, short breeding exposure, lameness, poor libido, reproductive tract defects, mineral imbalances, toxins, and inaccurate breeding records. Your vet may help sort out whether the main issue is ewe-related, ram-related, infectious, nutritional, or management-based.

Diagnosis starts with flock history. Your vet will want to know breeding dates, ram numbers, body condition, nutrition changes, vaccination history, abortion history, lambing percentage, and whether the problem affects one group or the whole flock. Good records often shorten the workup and help separate a true fertility problem from a timing or management issue.

A hands-on exam is usually next. Ewes may need body condition scoring and reproductive evaluation, while rams should have a full breeding soundness exam. That exam commonly includes a physical exam, scrotal measurement, palpation of the testes and epididymides, and semen evaluation. A ram is generally considered satisfactory only if he meets minimum standards for health, scrotal circumference, and semen quality.

Your vet may also recommend pregnancy diagnosis by ultrasound, especially if the breeding season has ended and you need to identify open ewes quickly. Lab testing may include serology, culture, PCR, or submission of aborted fetuses and placentas when infectious disease is suspected. In flock problems, testing several animals often gives more useful answers than testing one individual.

Because infertility can be multifactorial, diagnosis is often a stepwise process. Conservative care may focus on records, body condition, and ram exams first. Standard or advanced workups may add ultrasound, semen testing, and targeted infectious disease panels based on your flock's risks and region.

Prevention starts before breeding season. Keep ewes and rams in appropriate body condition, and review forage, energy intake, and mineral balance well ahead of ram turnout. Many flocks benefit from checking body condition scores and making nutrition changes several weeks before breeding rather than waiting until animals are already thin.

Rams deserve special attention because one ram can affect many ewes. Have your vet examine breeding rams before the season, especially if they are new, older, recovering from illness, or expected to breed large groups. Watch for lameness, heat stress, poor feet, eye problems, and abnormal testes. A breeding soundness exam before breeding can prevent major losses.

Good flock management also helps. Use appropriate ram-to-ewe ratios, avoid overcrowding, and keep accurate breeding and lambing records. If you use synchronization or breed out of season, planning becomes even more important because fertility can drop if timing and ram coverage are not adjusted.

Biosecurity matters too. Isolate new additions, work with your vet on vaccination plans where indicated, and investigate abortions promptly. Submitting placentas and fetuses for testing can protect the rest of the flock and guide future prevention. In many cases, infertility prevention is less about one product and more about steady nutrition, sound rams, clean records, and early veterinary input.