PROC GLM with a Tukey-Kramer adjustment with days to ovulation as a covariable. Estrous data were evaluated with Proc GENMOD using a Poisson distribution. It was noted that the average follicle size before ovulation was smaller (P < 0.05) in both the BMP-15 (15.5 ± 2.3 mm) and GDF-9 (23.2 ± 3.3 mm) mares as compared with the control (39.8 ± 3.8mm) group. Fol- licle size at ovulation did not differ between treatments. Estrous behavior did not differ in treatment groups compared with con- trols. Further research will be needed to fully understand the effects of these 2 growth factors on ovulation, but these results support the potential for BMP-15 and GDF-9 being used as con- traceptives for mares in the future. Key Words: contraception, behavior 181 Relationship between insulin dysregulation and morphometric neck measurements in the non-obese stock-type horse C.P. Heaton a , C.A. Cavinder a , E.N. McClure *a , T. Smith a , P. Harris b , N. Liburt c , A. Krotky c a Mississippi State University, Mississippi State, MS, USA; b WALTHAM Centre for Pet Nutrition, Melton Mowbray, UK; c Mars Horsecare U.S. Inc., Dalton, OH, USA Recently it has been suggested that the main feature of equine metabolic syndrome (EMS) is insulin dysregulation (ID) associ- ated with an increased risk of laminitis, with or without other metabolic alterations and/or obesity (regional or generalized). This new definition acknowledges that animals that are non- obese may have ID and suffer from EMS. Insulin dysregulation can be defined as any combination of fasting hyperinsulinemia, postprandial hyperinsulinemia, or tissue insulin resistance and is typically evaluated in the field using the oral sugar test (OST). Regional adiposity, particularly over the neck, has been linked with ID and an increased risk of laminitis in ponies. Limited work, however, has been done to evaluate regional neck adiposity and the prevalence of ID in non-obese, stock-type breeds such as Quarter, Paint, and Appaloosa horses. Various neck morphometric measurements were taken in 62, non-obese (BCS 4.95 ± 0.62) stock-type horses (n ¼ 36 mares, n ¼ 26 geldings; 16.24 ± 1.06 yr): total neck length from poll to the cranial aspect of the wither, neck circumference at 1/4, 1/2, and 3/4 along the neck length (25% NLC, 50% NLC, and 75% NLC, respectively), and neck crest height (NCH) from the nuchal ligament to mane hairline at 50% NLC. An OST was carried out (Karo light syrup, 0.15 mL/kg BW) after a 12 h fast. Insulin (RIA, Cornell Animal Health Diagnostic Center) and glucose (hand- held glucometer) were measured pre- and 60 min post-syrup administration. Insulin dysregulation was defined as an animal having a pre-insulin >20 uIU/mL and/or >60 uIU/mL at 60 min post. Post insulin was described as equivocal if between 45 and 60 uIU/mL. Correlations were analyzed with PROC CORR in SAS 9.4 with significance set at P  0.05. Mean neck crest mea- surement was 4.71 ± 0.21 cm (range 0.50e8.00 cm). Fifty-seven (89%) animals were defined as non-ID (4.00 ± 0.19 cm); 4 as equivocal (NCH 4.5 ± 0.66 cm) and only one as ID (post insulin ¼ 81.37 uIU/mL; NCH 8 cm). Pre-OST glucose concentrations had a tendency to be correlated with pre-insulin (P ¼ 0.10, r ¼ 0.21) but were significantly correlated with post-insulin con- centrations (P ¼ 0.01, r ¼ 0.33). Interestingly, the post-glucose concentration was significantly correlated (P ¼ 0.02, r ¼ 0.29) with both 50% NLC and 75% NLC and there was a tendency for the NCH to be correlated with the post-insulin concentration (P ¼ 0.07, r ¼ 0.23). Reassuringly, ID was not prevalent in most non-obese stock-type horses. An increase in neck crest height, even in non-obese stock-type horses, may indicate a greater risk of ID but further research is warrented. Key Words: insulin dysregulation, neck crest, obesity 182 Effect of short stem forage mixed with grain to promote mastication in horses V.L. Sorrentino *b , C.L. Wickens a , L.K. Warren a , C.W. Knight b , B.F. Goff b , R.C. Causey b a University of Florida, Gainesville, FL, USA; b University of Maine, Orono, ME, USA Gastric ulceration has a prevalence of up to 80% in some horse populations, especially those fed high grain diets. Saliva produced during mastication may help reduce the incidence of gastric ul- cers through buffering gastric acid and providing additional mucus to protect the gastric epithelium. Short stem (7.62 cm chop length) forage mixed with grain may provide a way to increase salivation through increased mastication. We therefore hypoth- esized that adding chopped forage will increase mastication during grain consumption. In a replicated 3  3 Latin Square design, 6 Standardbred mares were randomly assigned to 3 amounts of forage (0 kg, 0.68 kg, and 1.36 kg of chopped timothy) added to each horse’s grain ration, 2 horses receiving each forage amount. After a 12-d adjustment, and data collection on d 13 and 14, each pair of horses was transitioned to one of the other forage amounts and data collected on d 13 and 14. Horse pairs were then transitioned to the third and final forage amount and data again collected on d 13 and 14. During evening feeding on d 13 and 14, video recordings (5 min) of each horse consuming each diet were obtained using a Go-Pro camera attached to the halter, and the number of “chews” counted by 3 observers reviewing the re- cordings. Counts were analyzed as a 3 way ANOVA using the GLM procedure of SAS with forage amount as the main effect. The mean number of chews counted over 5 min at 0 kg, 0.68 kg, and 1.36 kg of added forage were 85, 262, and 268 respectively, with significant differences between 0 and 0.68 but not between 0.68 and 1.36 kg of forage added. Observer was not an effect (mean counts 203, 207, 198, P > 0.05). In addition, rate of intake over the 5 min observation decreased with increasing forage (P ¼ 0.0234). Overall, these data support the hypothesis that addition of chopped forage to grain increases mastication and reduces rate of feed intake. Subjective observations indicate that prehension is more noticeable than mastication when consuming grain. In contrast, when consuming forage, lateral jaw movements were pronounced. Further studies are necessary to measure saliva production when horses are fed forage mixed with grain, and to determine if addition of chopped forage to grain reduces the incidence of gastric ulcers. Key Words: forage, grain, mastication 183 Effects of level of bedding on lying behavior in stalled horses K. Guay a , M. Fuentes a , R. Trice a , S. Elmore *a , M. Attal a , A. Christie a , J. Baker a , T. Garcia b a Tarleton State University, Stephenville, TX, USA; b Oklahoma State University, Stillwater, OK, USA Most riding horses are housed in stalls or runs with limited space for movement and activity. There have been numerous studies conducted evaluating the effects of bedding material on the behavior and physiology of horses, but little investigation into the Abstracts / Journal of Equine Veterinary Science 76 (2017) 36e129 122