Profiles of strongyle EPG values for Thoroughbred mares on 14 farms in Kentucky (2012-2013).

The main purpose of the research was to determine if three weekly samplings would produce consistent results for low strongyle egg shedders, generally associated with older horses. Strongyle egg counts per gram of feces (EPG) were done for 661 Thoroughbred mares on 14 farms in 2012-2013 once a week for three consecutive weeks. None of the mares had been treated with ivermectin or moxidectin for more than 90 days and with fenbendazole, oxibendazole, or pyrantel pamoate for more than 60 days. Strongyle EPG count data indicated that 38.3% of the mares were positive at first and second sampling, and 37.8%--at third sampling. There were 5.6-63.3% of horses positive per farm. Correlations between EPG count data in all three weeks are quite high (Rs = 0.84, p<0.001). Level of horse infection was found to be dependent on horse age, type of farm and individual characters of horse. This study documented that strongyle egg counts (EPGs) from individual horses did not differ significantly between weeks. Thus, a single strongyle EPG count can be interpreted as indicative of the level of egg shedding for a given horse. These data support the current trend of not deworming all adult horses on a farm, so that high shedders can be identified and treated. This saves horse owners money and reduces development of potential drug resistance of parasites because of less frequent usage of antiparasitic compounds. Information from this study helps to conclude recommendations for parasite control in horses globally.

Pregnancy without progesterone in horses defines a second endogenous biopotent progesterone receptor agonist, 5α-dihydroprogesterone.

One of the most widely accepted axioms of mammalian reproductive biology is that pregnancy requires the (sole) support of progesterone, acting in large measure through nuclear progesterone receptors (PRs) in uterine and cervical tissues, without which pregnancy cannot be established or maintained. However, mares lack detectable progesterone in the latter half of pregnancy. Instead of progesterone, several (mainly 5α-reduced) pregnanes are elevated and have long been speculated to provide progestational support in lieu of progesterone itself. To the authors' knowledge, evidence for the bioactivity of a second potent endogenously synthesized pregnane able to support pregnancy in the absence of progesterone has never before been reported. The 5α-reduced progesterone metabolite dihydroprogesterone (DHP) was shown in vivo to stimulate endometrial growth and progesterone-dependent gene expression in the horse at subphysiological concentrations and to maintain equine pregnancy in the absence of luteal progesterone in the third and fourth weeks postbreeding. Results of in vitro studies indicate that DHP is an equally potent and efficacious endogenous progestin in the horse but that the PR evolved with increased agonistic potency for DHP at the expense of potency toward progesterone based on comparisons with human PR responses. Sequence analysis and available literature indicate that the enzyme responsible for DHP synthesis, 5α-reductase type 1, also adapted primarily to metabolize progesterone and thereby to serve diverse roles in the physiology of pregnancy in mammals. Our confirmation that endogenously synthesized DHP is a biopotent progestin in the horse ends decades of speculation, explaining how equine pregnancies survive without measurable circulating progesterone in the last 4 to 5 mo of gestation.

Eastern tent caterpillars (Malacosoma americanum) cause mare reproductive loss syndrome.

A new equine abortigenic disease, mare reproductive loss syndrome (MRLS), was recognized and significantly impacted the Ohio Valley in the springs of 2001 and 2002. MRLS caused approximately 330 million US dollars in losses in 2001. An epidemiological investigation of MRLS associated occurrence of the disease with exposure to eastern tent caterpillars (M. americanum). This work investigates the epidemiological association between M. americanum and MRLS to determine if this association was correlative or causative. A pilot study and simulated exposure to M. americanum and their excreta on pasture grasses. The pilot study advanced exposure of pregnant mares to M. americanum materials and 18 of the 29 mares in the study aborted with symptoms of MRLS before other cases were reported in the region. In, three of seven mares exposed to M. americanum aborted, while mares in control (n=6) and M. americanum frass (n=7) treatments had no losses. In, mares were fed frozen insect larvae in feed buckets mixed with oats. Abortions occurred in three of five mares receiving frozen M. americanum, while mares that were fed autoclaved M. americanum (n=5) or frozen gypsy moth larvae (n=4) had no abortions due to MRLS. In, M. americanum larvae were dissected and fractionated. Statistically significant numbers of abortions occurred only in the positive control group and in association with the M. americanum exoskeleton. All abortions induced by exposure to M. americanum exhibited changes in echogenicity of fetal fluids and bacteriological findings post abortion that were consistent with MRLS. These studies support the hypothesis that ingestion of M. americanum larvae induces the MRLS-type equine abortions, and provide experimental evidence that this lepidopteran larva can cause an abortigenic disease in a vertebrate host.