Effect of Sodium Caseinate on Equine Hindgut Fermentation and Fiber Digestion

Supplementing protein to cattle consuming low quality forages has shown to increase DMI, DM digestibility, and VFA production. Given similarities between the rumen and cecum, it can be hypothesized the same would be true in the equine. Eight cecally cannulated Quarter Horses were used in replicated 4 x 4 Latin square design conducted in 4, 14-d periods to determine effects of sodium caseinate on equine hindgut fermentation and fiber digestion. Horses were assigned to 1 of 4 treatments during each period, consisting of control (water; CON), 0.125 g casein/kg BW (LOW), 0.25 g casein/kg BW (MED), or 0.5 g casein/kg BW (HI). Casein was solubilized in 800 mL of water and dosed directly into the cecum at 0700 and 1900 each day using a metal dosing syringe. Smooth Bromegrass hay (CP 8.50%) and water were available ad libitum. New hay was fed at 0700 and 1900 and orts were recorded at 1900 each day. During the final 3 d of each period, cecal digesta were collected every 6 h. Digesta pH was measured immediately after sampling, and samples were then frozen for subsequent analyses of VFA and NH3 concentrations. Feed intake during the final 4-d of each period was recorded, and feces were collected over the 3-d sampling period, pooled, subsampled, and analyzed to determine pH, and digestibilities of DM, OM, NDF, and ADF. Digestibilities of DM, OM, NDF, and ADF were unaffected by treatment (P > 0.40). Cecal digesta pH was greater for horses dosed with CON and MED compared to horses receiving the LOW and HI treatments (P < 0.01). Cecal NH3 concentrations increased linearly in response to the amount of casein administered (P < 0.01), and decreased 6 h after dosing and addition of new hay regardless of treatment (P < 0.01). Concentrations of VFA were unaffected by treatment, but VFA concentrations did change over time with the greatest concentrations observed 6 h after treatment and introduction of new hay (P < 0.01). Treatment did not affect DMI (P ≥ 0.17). In this experiment, cecal infusions of sodium caseinate had no effect on fermentation parameters or fiber degradation. While a type II error may have occurred due to the small population size, it is more likely that the medium quality hay fed to these horses provided sufficient protein for microbial fermentation.