Science-Based Foal Weaning Strategies

As you consider ways you can help your foal—and his dam—through the weaning process, examine proven methods based on research findings to formulate a plan.

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As you consider ways you can help your foal--and his dam--through the weaning process, examine proven methods based on research findings to formulate a plan. | Photo: Anne M. Eberhardt/The Horse

Research-based recommendations that can improve your foal’s weaning experience

Barring a mare’s illness, injury, or death—which would necessitate separating her from her foal sooner than expected—you have the luxury of planning your foal’s weaning process. You can take steps to minimize potential negative effects of this stressful time and ensure your foal has the best possible outcome.

You also want your foal to become independent. Weaning him will allow you to begin his training without Mom’s ever-present influence and learn about and enjoy his personality as he develops into the horse you’ve dreamed about since you picked his sire.

Read on to learn about practical, proven tips and what recent research has revealed about how you can advocate for your foal’s optimum health and well-being during this typically tension-filled time.

Wipe Out Weaning Stress

Amanda Adams, PhD, an immunology researcher at the University of Kentucky’s Gluck Equine Research Center, in Lexington, says maternal separation and changes in environment, diet, and management are what makes weaning stressful for foals. This can result in increased vocalization, motor activity (locomotion), heart rate, and cortisol secretion (the horse’s body produces the hormone cortisol during times of stress, and it effectively decreases the body’s inflammatory and immune responses), as well as decreased appetite with subsequent slower daily weight gain post-weaning. Foals might also suffer from gastrointestinal (GI) and respiratory infections during this time.

Jill Mixer, DVM, owns Waterloo Animal Hospital, in Edmond, Oklahoma, breeds ­Quarter Horse runners, and, until recently, served as track veterinarian at Remington Park and other ovals. She shares advice from her years of raising foals, during which she’s seen very few clinical or behavioral problems.

“We start by administering plasma to all our foals within the first 24 hours of life to boost their immune systems and to help prevent future illness or infection,” she says.

Study: 'Nanny' Horses Reduce Weaning Stress for Foals
Related Content: Study: ‘Nanny’ Horses Reduce Weaning Stress for Foals

The weaning method Mixer says causes her youngsters the least stress involves keeping all mares and foals in one or two large groups by age, beginning when they’re about 1 month old. “When the foals are 5-6 months old, I’ll start to completely remove one or two mares at a time from the property so their foals can’t see or hear them,” she says. “The foals may nicker and run down the fenceline while we’re driving out of our property, but within a few minutes with their pasturemates they become calm again. We repeat the process over the course of one to two months until the last mare is removed.

“If a person only has one or two mares with foals,” she adds, “I’d recommend cross-fence weaning by putting mares next to foals in a paddock or pasture with safe fencing (board or V-mesh wire) or in stalls next to each other where they can see and hear each other. I don’t use companion animals because we have quite a few mares and foals, but for someone with one mare and foal, I believe it’s a good idea for the foal to have a gentle, preferably older companion.”

The most stressful form of weaning, she says, is putting two foals together in a stall and leaving the mares out in the pasture. “They can hear their dams, and studies have shown that when two foals are in the same stall, their cortisol levels are higher than when they’re by themselves in a stall. I’ve also found that the foal will bond with you when you enter the stall instead of bonding with the other foal.”

Dr. Jill Mixer says one of the most stressful forms of weaning is putting two foals together in a stall and leaving the mares out to pasture. | Photo: iStock

As far as your mares go, Mixer says she removes all grain from their diets for one week post-weaning and keeps them turned out for exercise, which helps reduce mammary swelling. “I monitor them closely and have had very few mares develop mastitis (mammary gland infection) over the years with this method,” she says.

Studying Immune Response

On the research side of weaning, Adams studies ways to support horses’ immune systems and thereby minimize their susceptibility to weaning-related health problems. Here are two recent investigations she conducted.

Study 1: PPVO

Adams examined the effects of the immunomodulator Parapoxvirus ovis (PPVO, a large double-stranded DNA virus that’s a commercially available intramuscular product) on cell-mediated immunity in abruptly weaned foals. ­Researchers have previously shown PPVO to enhance cell-mediated immune responses and dial down the severity of infectious disease outbreaks among horses and other ­species.

Adams and her colleagues administered PPVO (or a sterile diluent as a ­control) to—and took blood samples from—pony foals ages 3 to 4 months at set time points prior to weaning, at weaning, and post-weaning. The team weaned the foals abruptly and placed them out of their dams’ sight in a neighboring pasture.

“We were measuring cell-mediated immune responses, which are really important for combating viral infections and intracellular bacterial infections that often are causative agents to the respiratory and GI problems that foals can succumb to during weaning,” Adams says. Regardless of treatment, the foals’ immune responses declined significantly post-weaning and took up to 21 days to rebound to normal.

“We were hoping that the cell-mediated immune response in the foals that received PPVO would not be suppressed or that it would actually be enhanced a bit or supported through the time of weaning, but there was no treatment effect, in particular on the production of the lymphocyte (small white blood cell) interferon-gamma (IFN-γ), a key player in cell-mediated immune responses,” Adams says.

However, what the 21-day window of vulnerability revealed is that it’s particularly important to practice optimum biosecurity during this time. A bit of extra diligence could help prevent exposure to pathogens that might be introduced from outside your facility, so be sure to keep foals away from ingress and egress areas and new horses and to enforce good handler hygiene.

Also, monitor your weaned foals closely during this time frame. “We all hear about newly weaned foals with snotty noses,” Adams says. And be on the lookout for foals that are “off their feed” or develop diarrhea. These signs warrant a call to your veterinarian.

Study 2: P. acnes

Adams also studied pony foals ages 6 to 7 months under stress from abrupt weaning to determine the effects of Propionibacterium acnes on cell-mediated immunity and nasal shedding of respiratory pathogens. P. acnes bacteria exist naturally in skin flora and are commercially available as an intravenous ­immunostimulant.

Foals received P. acnes injections or saline (control group) at set time points before, during, and after weaning, at which time researchers also checked vital signs, plasma cortisol concentrations, immune function, and pathogen presence. They also watched for outward signs of disease, such as coughing and nasal discharge.

Adams and her colleagues hoped that P. acnes would boost cytokine (immune-cell-produced proteins that facilitate cell communication and orchestrate immune response) production in the foals, which in turn would activate T-cells (lymphocytes responsible for cell-mediated immune response) to amp up their defense during weaning.

They found that weaning, regardless of treatment, affected rectal temperature, nasal discharge, and one test’s detection of Streptococcus equi subsp. zooepidemicus. It increased serum cortisol levels and both decreased and increased cytokine ­production. 

“When analyzing the effects of P. acnes treatment on these parameters, treatment modulated rises in cortisol after weaning and affected production of IL-1β, which may indicate enhanced innate immunity,” says Adams.

“Looking back at both studies, though,” she continues, “foals in the P. acnes study were a bit older at weaning, almost starting to self-wean, and we didn’t see as drastic a decline in immune response as we did in that first study (PPVO) when the foals were a little bit younger when weaned. You have to be cautious in how you look at it, because they were two different crops of foals done in two different years, as well, but the results go along with studies that have shown behavioral differences for different weaning ages, and those behavioral differences—the increased vocalization and motor activity and decreased appetite—(negatively) influence the immune response.”

In other words, older foals might simply be able to cope with the stresses of weaning better and, thus, remain healthier through the process. 

“Of course we’d like to put this theory to the test,” she adds, “by conducting a study in which we wean foals during the same year but at different ages to really determine whether or not age impacts changes in immune response during the weaning period.”

In sum, while these two studies confirmed just how stressful weaning is on the body, the evidence isn’t strong enough at this time to recommend either of those treatments.

Other Considerations

Factors that might impact your selection of a weaning method and the subsequent amount of stress your foal experiences include:

  • The number of foals you’ll be weaning;
  • Facilities available (for example, pasture vs. stall);
  • How much time you can or want to devote to the process;
  • The mare and foal’s temperaments;
  • The foal’s age;
  • Feeding changes you’ve instituted prior to weaning (e.g., creep feeding);
  • Whether you prefer an abrupt or a gradual weaning process (e.g., removing one or two dams per day from a group or separating foals from dams for progressively longer periods each day); and
  • If you favor lone vs. group weaning, including using unrelated mares or geldings as companions.

Take-Home Message

As you consider ways you can help your foal—and his dam—through the weaning process, examine proven methods based on research findings to formulate a plan.


Written by:

Diane Rice earned her bachelor’s degree in agricultural journalism from the University of Wisconsin, then married her education with her lifelong passion for horses by working in editorial positions at Appaloosa Journal for 12 years. She has also served on the American Horse Publications’ board of directors. She now freelances in writing, editing, and proofreading. She lives in Middleton, Idaho, and spends her spare time gardening, reading, serving in her church, and spending time with her daughters, their families, and a myriad of her own and other people’s pets.

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