Approximately half of all reported laminitis cases are the result of “grass founder” (laminitis associated with long-term over consumption of lush, early spring pastures). Elevated body weights (BW), body condition scores (BCS), and blood glucose concentrations have all been associated with the onset of grass founder. Plasma fructosamine concentrations (PFC) have recently been used as an indicator of long-term (14–21 d), mean blood glucose concentrations in horses and numerous authors have reported that elevated PFC were observed in laminitic horses (Murphy et al., 1997; Keen et al., 2004; Knowles et al., 2012). This study was conducted to evaluate the long-term effects of transitioning from an ad-libitum tall fescue hay diet in late winter to an adlibitum tall fescue pasture diet in early spring on parameters associated with grass founder in horses. Five mature stock horse mares were given free choice access to good quality tall fescue hay for 18 weeks before initiation of data collection. Each horse acted as their own control. PFC were determined on day 1, day 128, and then monitored at 14 d intervals for the following 84 d (February 26th through May 21st). Three trained lab technicians evaluated BW and BCS on day 1, 128, 170 and 212 of the trial. The horses were placed in a 20 acre field where their diets consisted of free choice access to hay only for 156 days (DTP1) followed by free choice access to tall fescue hay with minimal access to some early emerging tall fescue pasture for 14 days (DTP2), and finally to free choice access to lush spring tall fescue pasture only for the final 42 days (DTP 3) when the animals refused to eat offered hay. Mean PFC were highest (P < 0.01) for DTP1 and decreased with each successive transition to DTP2 and DTP3. This may have been due to increased insulin secretion associated with the pasture only diet. Mean BCS at the beginning of the trial was 5.7 and increased throughout the trial (P < 0.001) to a value of 7.8. BCS associated with the pasture only diet were higher (P < 0.001) than those associated with the free choice hay and hay plus pasture diets. Mean BW increased (P < 0.05) from 1199 lbs. to 1268.3 lbs. during the 12-week trial. Mean weight gain was 113 lbs. with an average daily gain of 1.35 lbs./day. No incidence of laminitis was observed.