Original Research
Insulin resistance and laminitis in broodmares

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Anatomy

As shown in Fig. 1, the delicate structure of the epidermal and dermal lamellae of the normal equine foot greatly increases the surface area of dermal-epidermal attachment and forms the suspensory apparatus of the distal phalanx (DP), facilitating the transfer of the horse's weight from the skeletal elements of the digit to the hoof wall [1]. Each foot has 550–600 parallel primary epidermal lamellae (PELs), each of which has 150–200 secondary epidermal lamellae (SELs), giving an estimated total

RFM and Laminitis: “Organ Failure” of the Equine Foot

Retained placenta, or more accurately, retained fetal membranes (RFM), and subsequent septic metritis are commonly associated with laminitis in broodmares [27], [28], [29]. Retention of the fetal membranes is more likely following abortion, dystocia, severe placentitis, fetotomy, and Caesarian section, and may be more common in Draft mares than in light breeds [27], [30]. Dystocia and severe placentitis are believed to result in delayed uterine involution, increased autolysis of the placenta,

Obesity and IR

Many cases of equine laminitis are associated with IR and a metabolic syndrome that has many parallels to human prediabetic metabolic syndrome [15], [39]. Human metabolic syndrome, or syndrome X, is characterized by central obesity, atherogenic dyslipidemia (low high-density lipoprotein-cholesterol (HDL-C), elevated low-density lipoprotein-cholesterol (LDL-C), and serum triglycerides), a prothrombotic state, a proinflammatory state, hypertension, and IR, often culminating in pancreatic β-cell

IR During Pregnancy

Broodmares might be at particular risk for EL due to the physiological effects of pregnancy on glucose and insulin dynamics. Mares with pre-existing IR or lamellar damage due to prior episodes of laminitis might be at or near the hypothetical HI threshold for induction of laminitis [12].

Pregnancy in women and dogs is associated with a 60% and 43%, respectively, decrease in insulin sensitivity and an increased insulin response to glucose [42], [81]. This physiological IR of pregnancy facilitates

Hypothyroidism vs. EMS

Until relatively recently, it was common practice to treat any overweight mare with perceived subfertility for hypothyroidism. The actual prevalence of hypothyroidism in adult horses is now considered to be very low [82]. Many of the clinical signs previously attributed to hypothyroidism, which included obesity, regional adiposity, and weight gain on little feed, are now associated with EMS [57], [82]. In fact, horses that were made hypothyroid by surgical thyroidectomy or pharmacological

RFM and Septic Metritis

Expulsion of fetal membranes typically occurs 30 min to 3 hrs after parturition. The membranes are considered to be retained if not expelled by the end of this period [29]. Mares with RFM may display signs of abdominal pain and/or straining, recumbency, and have fetal membranes present at the vulvar lips. Retention of the fetal membrane at the tip of the nongravid uterine horn is most common, although retention may occur in any region [28], [29]. It is therefore critical to routinely perform a

Acknowledgments

The authors gratefully acknowledge financial support from The Fund for Laminitis Research at the University of Pennsylvania, School of Veterinary Medicine, and the Bernice Barbour Foundation. The authors have no conflicts of interest to report.

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