77 In vitro true digestibility of hempseed meal using equine fecal inoculum

Abstract

Digestibility of hempseed meal (Cannabis sativa L.; HSM) has been previously investigated in several livestock species as a protein source; however, data is lacking in horses. The study objective was to determine in vitro true digestibility (IVTD) of HSM compared with soybean meal (SBM), rice bran pellets (RBP), alfalfa hay (Medicago sativa; ALF), Coastal Bermudagrass hay (Cynodon dactylon; CBH), and a commercial concentrate (Bluebonnet® Equilene® Pellets; EQU). Four mature stock-type geldings (8.5 ± 3.9yr; 558.4 ± 31.0kg; 6.0 ± 0.4 BCS) were used in a duplicated 4 × 6 Factorial Design. Horses were acclimated to a basal diet of 1.8% BW as-fed of CBH and 0.2% BW as-fed of EQU for 21d. Fresh feces (400g) were collected on d22 via rectal-grab for use as incubation inoculum. Dried, ground feed samples (0.5g), sealed in ANKOM filter bags, were placed in duplicate within 2 DaisyII incubators for 48hr in fecal inoculum. After incubation, fiber bags were removed, dried (100°C for 2hr), then analyzed for neutral detergent fiber (NDF) composition to determine IVTD. Split samples were analyzed to determine pre-incubation NDF composition of feedstuffs. Data (mean ± SEM) were analyzed using a repeated measures ANOVA within R Statistical Program©. Significance was set at P ≤ 0.05. Hempseed meal NDF (440.2 ± 6.82 g/kg DM) was greater than ALF(330.8 ± 5.07; P < 0.001), RBP (219.0 ± 12.15; P < 0.001), and SBM (109.4 ± 6.17 g/kg DM; P < 0.001), yet lower than CBH (715.4 ± 10.77; P < 0.001) and tended to be higher than EQU (400.2 ± 8.29; P = 0.077). Feedstuff IVTD (g/kg DM) was greatest in SBM (962.9 ± 4.47) followed by RBP (857.8 ± 5.88) (P < 0.001). Alfalfa hay (742.6 ± 9.34) and EQU (757.2 ± 33.91) IVTD were similar (P = 0.962). Both ALF and EQU were decreased compared with RBP (P < 0.001) and greater than HSM (567.1 ± 4.93; P < 0.001) which was higher than CBH (401.4 ± 14.04; P < 0.001). These results indicate that HSM has an NDF content and IVTD between ALF and CBH, indicative of a lower digestibility compared with other proteinaceous feeds. This suggests potential for HSM to partially replace fiber sources in equine rations. High fat content in feedstuffs limits microbial fermentation of fiber, thus the fat content of HSM (107.0 g/kg DM), assumed to be digested in the foregut, may have limited microbial fiber digestion during in vitro incubation. Modified methods may be necessary to further assess IVTD of HSM in horses.