by: Lee Jones DVM, MS
University of Georgia College of Veterinary Medicine

Without a doubt reproductive efficiency is crucial for cow-calf herd production and profitability. Without pregnancies, calves aren't born or weaned and sold. Pregnancy has four times greater economic impact than any other production trait (per Dr. Cliff Lamb) and reproductive efficiency is more important than growth or carcass traits for the cow-calf producer.

For a cow or heifer to get pregnant, the following events have to successfully occur: she needs to cycle and ovulate, conceive, recognize the presence of the embryo, and the embryo needs to attach and develop the placenta and maintain pregnancy to birth. While those events are critical for pregnancy, reproduction doesn't actually end until the calf is weaned. Any loss of the embryo, fetus or nursing calf is a failure of reproduction. Reproduction, then, is an all or nothing event and can fail at several points along the way.

While the challenges to getting cows pregnant change slightly each year. They fall into two categories: non-infectious and infectious. Noninfectious causes are further divided into environment and management. Infectious causes of reproductive failure include viruses, bacteria, fungi or protozoa or parasites that infect the reproductive tract of cattle. Noninfectious causes are everything else including nutrition, bull fertility, cow body condition, etc.

The term infectious doesn't necessarily mean contagious. Cattle are exposed to infectious agents from the environment or from things like vectors (insects that transmit disease agents) not just directly from each other. The contagious agents like viruses include Bovine Viral Diarrhea virus (BVD) and Infectious Bovine Rhinotracheitis (IBR) and can spread rapidly through a herd causing severe problems in naive cattle. Some bacteria can be spread through direct contact but spread slower than viruses, while others require some other means of transmission like needles or sexual contact. Some can be ingested orally like Lysteria spp in spoiled feeds or spread through breeding like Campylobacter foetus (that causes vibriosis). Protozoa like Tritrichomonas fetus are transmitted by infected bulls to cows at breeding.

Other parasites like Neospora may be transmitted directly to a cow's calf during pregnancy or acquired by consuming feed contaminated by Neospora oocysts. This happens when cattle feed is contaminated by the feces of infected dogs. Leptospora spp bacteria can be picked up from the environment as the bacteria also inhabit wildlife, but also can be transmitted during breeding from infected bulls.

Anaplasmosis is rapidly becoming a leading cause of late-term abortions in cows in the Southeast and is transmitted by ticks or through use of contaminated needles. There are numerous other pathogens (disease-causing agents) that, though they aren't specific reproductive concerns, can cause reproductive problems like infertility and abortion under the right stressful conditions.

Understandably, infectious agents get a lot of attention from producers and veterinarians. After all, they interfere with conception and fertility and cause abortions or weak, stillborn or deformed calves. So the attention makes sense. Some things we can do to protect our herds from these problems include vaccinations, testing and biosecurity or biocontainment as part of a comprehensive herd health program.

Though vaccinating our herds to boost resistance to common reproductive disease agents can be an effective tool, the protection is limited to a few pathogens. And even then resistance may be weakened due to stress or restricted nutrition or other factors. For instance, some strains of BVD can be found in vaccinated herds. Trichomoniasis, neospora and anaplasmosis may reside in herds for extended periods of time. Strategic testing helps owners know what they are dealing with and how to control or rid the herd of the problem.

Chronically low production or periodic, random abortions or even dead cows could be a sign of an endemic problem that requires testing to discover the cause and help determine a plan for control.

Though infectious diseases often get the most attention, non-infectious causes of poor reproductive performance are more common. Managing body condition of the cow herd is the best practice to maintain reproductive performance in herds. Selecting heifers for fertility and longevity are essential for lifetime productivity. Heifers that calve early their first year and maintain early calving can produce 100 lbs. more calf each year than heifers that calve two cycles later.

Traditional methods of heifer selection rely on physical traits such as weight, age and pregnancy status to determine who to keep. Though genetic tools show potential to improve our ability to identify the most productive heifers earlier than traditional tools, selecting heifers by physical traits and overall phenotype is still a valuable tool to build a fertile cow herd.

Managing our bulls is another important part of reproductive efficiency of the herd. Selecting fertile bulls will get more cows bred earlier than subfertile bulls. Several studies show the benefits of a thorough annual breeding soundness exam consisting of a physical examination, thorough reproductive tract examination and semen evaluation including checking motility and morphology of the sperm. Some sub-fertile bulls can take two or more services to get cows bred. Fertile bulls get more cows bred in the first service. Every cycle a cow goes open is 40 to 50lbs. lost at weaning, so testing bulls and only using fertile bulls helps keep more cows bred and bred early.

Other practices like a controlled breeding season and pregnancy checking also contribute to an efficient, productive herd. There are a lot of things that challenge reproduction in our cow herds. Fertility is the single most significant factor for cow herd productivity. The other side of the coin is infertility and is six times more costly than calf respiratory disease or other non-fatal disease. Infertility can be defined as a cow failing to breed, breeding but not delivering a live calf or breeding late. The fact is that if the calf born alive and healthy and weaned, we don't have anything to sell. Managing for reproduction pays dividends and the reward is lots of healthy, heavy calves.

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