Effects of fiber type, particle size, and soak time on water hydration and estimated potential water releasing capacities of roughages fed to horses

s / Journal of Equine Veterinary Science 31 (2011) 230-356 261 [4] Xiong Y, Bartle LJ, Preston RL. Improved enzymatic method to measure processing effects and starch avaliability in sorghum grain. J. Anim. Sci 1990;63:3861-70. [5] National Research Council. Nutrient Requirements of Horses. 6th Ed. Washington, DC: National Academy Press; 2007. [6] SAS. SAS User's Guide. SAS Inst. Inc.: Cary, N.C.; 2008. Effects of fiber type, particle size, and soak time on water hydration and estimated potential water releasing capacities of roughages fed to horses A.M. Parsons , B.D. Nielsen , H.C. Schott , R. Geor , M. Yokoyama , and P. Harris 2 Michigan State University, East Lansing, MI, USA, WALTHAM Centre for Pet Nutrition, Leics, UK Introduction: Horses consume the majority of their diet in the form of roughage, with voluntary intakes from pasture grazing horses reported as high as approximately 5 percent of their body weight [1]. The insoluble fibers in roughage have the ability to bind water due to the hydrophilic nature of non-starch polysaccharides. The measure of a fiber's ability to trap water within its matrix is known as its water hydration capacity (WHC). Water binds to polysaccharides with differing strengths and amounts based on its chemical structure, hydrophilic balance, and particle size [2]. WHC also increases with particle size [3] and decreases following fermentation due to bacterial access to polysaccharide and protein bonds [4]. An increase in hind-gut fiber may act as a reservoir for water and electrolytes, possibly assisting in maintaining hydration during exercise. Studies conducted inponies have shown thatwatermay be absorbed from the gastrointestinal tract during endurance exercise [5]. However, this water needs to be available for uptake and not too tightly bound to the fiber. While some data exists regarding the WHC of varying fibers [3,4], there are limited data on the estimated potential water releasing capacity (EPWRC). If fiber sources are unable to release significant amounts of boundwater, the additional fiber in the hind-gut could potentially be detrimental to performance due to an increase in the weight of the GIT contents [6]. This study investigated the WHC and EPWRC of four roughages commonly fed to horses under conditions of simulated fermentation, with evaluation of the effects of particle size, fiber type, and soak time on outcome variables. Materials and Methods: Alfalfa hay (AH), grass hay (GH), beet pulp (BP), and a fiber mix (FM) of chopped hays and soy hulls were tested. Samples were ground to particle sizes of 1 mm and 5 mm and tested for 24 h and 72 h soak times. For undigested fiber WHC determination, 0.5 g sample was soaked in 20 ml di water at 37 C, centrifuged at 6,000 x g for 20 min, decanted, drained for 1 h, then dried to a constant weight [7]. The equation provided by Sowbhagya et al. [8] was used to determine WHC. To determine EPWRC, the digestive process of equids was simulated and in vitro dry matter digestibility was determined using a modified predigestion method, with a 48 h incubation to simulate hind gut digestion time [9]. Next, 20 ml of actively growing equine cecal culture in late exponential growth phase was inoculated into the predigested sample [10], sparged with CO 2, and incubated at 37 C for 48 h. The samples were then centrifuged, decanted, drained for 1 h, then dried to a constant weight. The dried digested samples were then rehydrated using the previously described method for determining WHC. The EPWRC of the samples were calculated by determining the difference in the WHC of undigested samples and the digested samples. Samples were run in triplicate and were analyzed using PROC MIXED in SAS 9.2 (SAS Inst. Inc., Cary, NC) with significance declared at P < .05. Results and Discussion: WHC of non-digested fiber samples was different between fiber types (P < .0001), with GH having the highest WHC (11.32 .47 g water/g sample), followed by BP (10.14 . 0.4 g water/g sample), AH (8.53 .60 g water/g sample), and FM (4.89 .47 g water/g sample). 5 mm particle size samples (9.29 .35 g water/g sample) had a higher WHC (P 1⁄4 .05) than 1 mm samples (8.14 .38 g water/g sample). In-vitro digestibility also differed between fiber types (P< .0001) and particle size (P1⁄4 .03). Post digestion WHC showed differences between fiber type (P < .05), but not particle size (P 1⁄4 .14). EPWRC differed between fiber type (P < .0001), with GH having the highest EPWRC (10.03 .46 g water/g sample), followed by BP (6.79 .47 g water/ g sample), AH (5.99 .48 g water/g sample), and FM (3.35 .47 g water/g sample). 5 mm particle size (7.27 .33 g water/g sample) had higher EPWRC (P 1⁄4 .01) than 1 mm particles (5.80 .32 g water/ g sample). Roughages commonly fed to horses vary in WHC, likely due to differences in fiber and protein conformation in the forage. Larger particle sizes have greater WHC and EPWRC, likely due to differences in pore size and structure. Fibers were completely saturated at 24 h as shown by no difference according to soak time (P1⁄4 .73). TheWHC of digested forages was lower (P < .0001) than undigested forages, likely due to polysaccharide bond hydrolysis during digestion [4]. Although digestibility differed for each forage, ranking of WHC post digestion remained identical to undigested WHC, consequently resulting in GH having the highest EPWRC and FM having the lowest. Conclusion: Results from this study demonstrate that the type and processing method of roughage appear to play a role in both WHC and EPWRC.