Effects of feed deprivation on Standardbred horses fed a forage-only diet and a 50:50 forage-oats diet

P>Reasons for performing study:A higher forage allowance to athletic horses might be an alternative to increase health and the gut fluid reservoir. However, more forage might increase bodyweight (bwt) and could therefore be a limitation during competition.Objectives:To investigate the effect of a forage-only diet (FD) compared to a 50:50 (dry matter basis) forage:oats diet (OD) on bwt, plasma protein concentration and some metabolic plasma parameters during 12 h of feed deprivation.Methods:Twelve adult Standardbred horses in training were used. The 2 diets were fed in 2 experimental periods of 3 weeks each in a crossover design. The last day of each period the horses were fasted for 12 h. The horses were weighed and their water intake measured every day during the trial and every hour during the 12 h feed deprivation. During feed deprivation total plasma protein (TPP), insulin, nonesterified fatty acids (NEFA), urea, glucose and acetate concentrations were analysed.Results:Bwt and water intake was higher on FD compared to OD. Bwt loss was higher during feed deprivation on FD compared to OD. TPP was lower before and during the last 8 h of feed deprivation on FD compared to OD. Plasma insulin was lower on FD than on OD at feeding and for 5 h during feed deprivation. Plasma NEFA and urea increased on both diets during feed deprivation. Plasma glucose was not affected by diet or feed deprivation.Conclusion:High energy forage diets could be an alternative to high grain diets for athletic horses. The small increase in bwt on FD diminished with feed deprivation and the low TPP concentration indicate a greater potential to use an internal fluid compartment to maintain plasma volume.