Study supports hormone-based foal grafting in nurse mares

A newly published study in the Journal of Veterinary Internal Medicine suggests that medical induction of maternal behavior can work in a substantial share of mares used for foal grafting, with a 71% overall success rate across 140 cases. The retrospective series, published July 6, 2026, evaluated a Swedish protocol using an NSAID, dinoprost tromethamine, and oxytocin in both nurse mares and mares that had rejected their own foals. (academic.oup.com)

The paper addresses a familiar challenge in equine practice: how to safely and quickly place an orphan foal, or salvage a mare-foal pair after rejection, without prolonged physical restraint or repeated high-stress handling. Traditional approaches can involve scent transfer, repeated supervised nursing, sedation, and mechanical restraint. Earlier literature has shown that maternal behavior in mares can sometimes be triggered through hormonal manipulation, prostaglandin use, or vaginal-cervical stimulation, but published evidence has generally been limited to smaller case series or procedural descriptions. (pubmed.ncbi.nlm.nih.gov)

In the new study, investigators reviewed records from a nationwide veterinary field practice and an equine referral hospital in Sweden from 2015 through 2025. The final dataset included 113 nurse mares and 27 mares that had rejected their own foals, for 140 cases and 144 treatments. Overall success was 71%, with better outcomes in nurse mares, at 76%, than in mares rejecting their own foals, at 52%. The authors also noted that, in most successful cases, acceptance was immediate and required only minimal restraint. Their conclusion was that the protocol was time-efficient, safe, effective, and potentially beneficial for animal welfare because it reduced the need for restraint. (academic.oup.com)

That result is directionally consistent with earlier reports. A 2019 Equine Veterinary Journal retrospective case series described prostaglandin F2 alpha-induced maternal behavior for fostering orphan foals and for mares showing foal rejection, supporting the idea that pharmacologic induction can shorten time to acceptance and improve welfare. Older work has also shown that non-parturient mares can develop effective maternal behavior after hormonal manipulation, although those protocols often still required close supervision and, at times, human intervention to prevent early aggression. (beva.onlinelibrary.wiley.com)

Industry and expert commentary over the years has framed this as both a welfare and logistics issue. In equine clinical commentary, Katherine Houpt and Karen Wolfsdorf have described the practical tradeoffs among restraining a rejecting mare, using drugs to support bonding, inducing lactation in a surrogate, or finding a nurse mare. Those experts have also emphasized that aggressive mares can seriously injure foals, making any method that reduces confrontation meaningful in practice. At the same time, older behavior literature cautions that foal rejection is heterogeneous, with causes ranging from fear and pain to disrupted early imprinting, which helps explain why mares rejecting their own foals may be less responsive than experienced nurse mares. (dvm360.com)

Why it matters: For veterinary professionals, the main value of this paper is that it moves the discussion from anecdote toward a more usable evidence base. A 71% success rate will not eliminate the need for fallback plans, but it gives clinicians and breeding operations a more concrete expectation when discussing options with pet parents and farm clients. The split between nurse mares and foal-rejecting mares is especially useful for case selection and counseling. In practical terms, the study supports considering medical induction earlier in the decision tree when the goal is to reduce handling stress, staff time, and risk to the foal, while preserving the developmental advantages of mare-reared rather than hand-reared foals. (academic.oup.com)

The study also highlights a gap that still matters in the field: predicting which mares will respond. Prior endocrine research in foal-rejecting mares has not identified a simple hormonal explanation, suggesting behavior, pain, parity, prior maternal history, and management factors may all influence outcome. Because this was a retrospective case series, it can describe results and associations, but it can't settle causation or define the optimal protocol for every setting. (academic.oup.com)

What to watch: The next step is likely prospective validation, including clearer selection criteria, standardized outcome definitions, and direct comparisons with traditional grafting methods or other induction techniques. If those studies confirm similar success with less restraint and lower risk, this protocol could become a more routine part of equine neonatal and reproductive practice. (academic.oup.com)