PSII-16 Physiological response of grazing horses to seasonal fluctuations in pasture nonstructural carbohydrates.

摘要

High intakes of pasture non-structural carbohydrates (pNSC) can cause digestive and metabolic disturbances. This study aimed to investigate the influence of seasonal patterns of pNSC content on grazing horses. Twelve sporthorse mares (15 ± 3.4 yrs) were maintained together on 8.5-ha mixed-grass pasture (free-choice mineral supplementation) for 12 mo beginning October 2016. Horses were grouped according to their baseline cresty neck score (CNS); CNS≥2.5 (C; n=5) or CNS<2.5 (NC; n=7). Weekly pasture samples (200g wet weight) were clipped at random, 2.5 cm from plant base. Samples were weighed, dried at 70ºC and analyzed to determine monthly pNSC content (Equi-analytical, Ithaca, NY). Monthly fecal grab samples were collected from the rectum to measure pH and D-lactate concentrations. Monthly body weight (BW), body condition score (BCS), and CNS were evaluated. Blood glucose and insulin dynamics (%∆ change) were assessed using an oral sugar test (pre and 75min post 0.3ml/kgBW Karo syrup). All sample analyses were performed in duplicate. Data were analyzed using PROC Corr and ANOVA in PROC Mixed (SAS v9.4) with P≤0.05 considered statistically significant. pNSC was highest in April (17.13 ± 3.18 %DM) and varied by mo (P<0.0001). Fecal pH and D-lactate differed by mo (both P<0.0001) with pH lowest in April (6.65 ± 0.05) and D-lactate highest in April (4177.51 ± 190.59 µM); however, there were no differences between C and NC. pNSC was associated with D-lactate (r=0.36, P=0.008) and there was a trend with pH (r=-0.26, P=0.07). Throughout, C had higher BW and BCS than NC (P<0.0001 and P=0.0009, respectively) with no effect of mo. Mo influenced glucose (P<0.0001), but there was no treatment effect. Insulin differed by mo in both groups (P=0.01), but C had higher insulin compared to NC across all mo (P<0.0002). These results highlight seasonal changes in pNSC and its potential effect on grazing horses which will help direct grazing management strategies.