hindgut parameters were in accordance with previous data. In blood, only L-lactate varied signiﬁcantly within time (P ¼ 0.008). No signiﬁcant diet effect was found on hindgut parameters when the 4 individuals were considered. This could be explained by a very strong individual effect. Two horses showed higher concentration of total lactate and one of total VFA with a peak between T2 and T6 during the B diet. Inter- estingly the fermentation proﬁles appeared similar in the cecum and the RV colon for each individual. In the blood BOHB (P ¼ 0.006) and L-lactate (P ¼ 0.007) concentrations were lower with B than with H diets, suggesting lower absorption of VFA and lactate when high-starch diets are fed. BOHB concentration was signiﬁcantly correlated with cecal C2 (r ¼ 0.34, P ¼ 0.03) and C4 (r ¼ 0.39, P ¼ 0.01) concentrations and with colonic D-lactate concentration (r ¼0.32, P ¼ 0.04). Blood D-lactate concentration was signiﬁcantly correlated with cecal C3 con- centration (r ¼ 0.32, P ¼ 0.04) and blood L-lactate concentration with colonic pH (r ¼ 0.35, P ¼ 0.02). This suggests that blood BOHB and lactate daily ﬂuctuations could indicate the state of hindgut fermentation for each individual. This will need further conﬁrmation. Key Words: hindgut, fermentation, blood markers 108 Effects of grazing system and season on glucose and insulin dynamics of the grazing horse C.A. Williams* 1 , L.B. Kenny 1 , A.O. Burk 2 1 Rutgers, The State University of New Jersey, New Brunswick, NJ, USA; 2 University of Maryland, College Park, MD, USA Rotational grazing has long been a recommended practice for grazing livestock, but less is known about with respect to grazing horses. The objective of this study was to investigate the effects of continuous and rotational grazing on forage soluble carbohydrates and whether those concentrations inﬂuenced circulating glucose and insulin concentrations in the grazing horse. Two 1.5 ha continuous grazing systems (CON) and 2 1.5 ha rotational grazing systems (ROT) seeded with cool-season grasses were established in 2013 at the Rutgers University Horse Farm. Twelve mature (14 ± 2 yr) Standardbred mares (535.8 ± 14.2 kg, body condition score 6.1 ± 0.3) were paired by age and weight and randomly assigned a pasture (n ¼ 3). Mares on CON had access to the full grazing area, hay feeders, water and shelter 24 h/d. Mares on ROT were given access to a 0.4 ha pasture section, stress lot, hay feeders, water and shelter; horses were restricted to the stress lot when forage was below 7.6 cm. Prior to each trial ROT horses were grazing at least 8 d contin- uously. Sampling of blood, feces, and forage was performed every 4 h over a 24-h period in June, August, and October 2015 starting at 0800; for 16 h prior horses were kept in stalls and fed a moderate quality grass hay. Forage was evaluated for nutritional composition including ethanol and water-soluble carbohydrates (ESC and WSC, respectively) and starch. Blood was assessed for plasma glucose and insulin, and pH was determined in feces. Data were analyzed by ANOVA with repeated measures with signiﬁcance set at P < 0.05. Forage starch, ESC and WSC varied with season, time of day, and grazing system. Overall, ESC and WSC was highest in June, whereas starch was highest in August (P < 0.002). Grazing system was only different in October for WSC (CON 9.9 ± 0.09; ROT 12.9 ± 0.09%; P ¼ 0.002) and ESC (CON 7.3 ± 0.09; ROT 10.2 ± 0.09%; P < 0.0001), while starch was different in August (CON 3.5 ± 0.06; ROT 1.8 ± 0.03%; P ¼ 0.012). Plasma glucose and insulin varied with season and time of day but not grazing system. Overall, plasma glucose was highest in August (105.6 ± 1.3 mg/dL) and insulin was highest in October (0.21 ± 0.02 ug/L; P < 0.0001). Fecal pH only varied by season and highest in August (7.06; P < 0.0001). In conclusion, the forage soluble carbohydrate concentrations within each grazing system did not signiﬁcantly affect glucose or insulin response in horses. This could be due to the differences in the soluble carbohydrate concentrations not being physiologically relevant enough to elicit a change. Key Words: rotational grazing, continuous grazing, carbohydrate 109 The effect of time- and space-restricted grazing on body weight, body condition score, resting insulin concentration, and activity in grazing horses J.C. Gill*, S.E. Pratt-Phillips, P.D. Siciliano North Carolina State University, Raleigh, NC, USA Excessive calorie intake from pasture contributes to obesity and increases the risk for laminitis. The objectives of this study were to determine if body weight (BW), body condition score (BCS), and serum insulin (INS) concentration could be signiﬁcantly reduced if the time and space allotment for grazing was limited, and to determine the effect of limited pasture access on volun- tary activity. Ten mature, idle geldings were randomly assigned to either a time- and space-restricted grazing group (RG; BW 584 ± 70 kg, Age 5 to12 yrs, n ¼ 5) or a 24-h grazing group (CTRL; BW 571 ± 51 kg, Age 5 to 12 yrs, n ¼ 5) for 35 d. The RG horses had access to pasture for 8 h/d in a grazing cell containing enough space to provide 80% of the mean maintenance digest- ible energy (DE) requirement for a 7-d grazing period. The remaining 15 h/d was spent in individual dry lot pens. All horses had continuous access to water and trace mineral salt. Horses in the RG group were moved to a new grazing cell every 7 d for 5 wks. The initial herbage mass (iHM) and residual herbage mass (rHM) were measured via falling plate meter, and the removal rate within each grazing cell was estimated as 1- (rHM/iHM) x 100. At the end of each week, all of the horses were brought inside overnight and at 0700 h the next day (d 7), scale BWs and BCSs were recorded and jugular venous blood samples were collected for resting serum INS. Horses alternated through 2, 3- d periods of heart rate (HR) monitoring/distance traveled (DT) assessments by Polar V800 activity monitors. Weekly repeated measurements of BW, BCS, INS, and activity were analyzed using a repeated measures ANOVA (PROC MIXED; TYPE ¼ AR(1)), while controlling for within-horse variance. Correlation between daily HR and DT was evaluated by Pearson correlation co- efﬁcients. Weekly herbage mass (HM) allowance and HM removal rate for RG over the 5 wks was 11,12, 10, 17,14, and 32 g DM,kg BW 1 ,d 1 and 71%, 40%, 71%, 59%, 66%, and 48%, respectively. The RG horses lost (P < 0.001) more BW and BCS over time than the CTRL horses. Weekly INS was unaffected by the treatment group (P ¼ 0.52) or the treatment by time inter- action (P ¼ 0.71), but was signiﬁcantly affected by time (P ¼ 0.01). There was a positive correlation (r ¼ 0.52; P < 0.001) be- tween HR and DT when all horses were considered; RG reduced overall activity by approximately 30%, but did not (P < 0.05) reduce daytime grazing activity. Limiting the time and space Abstracts / Journal of Equine Veterinary Science 52 (2017) 76e95 87