PSII-16 Comparison of Two Methods of Inoculation of Continuous Culture Fermentors Fed Different Diets

Abstract

Abstract This study assessed how methods of inoculating continuous culture fermentors with rumen particulate digesta affected in vitro fermentation. A 4-unit, single-flow fermentor system was used in a 4x4 Latin Square with treatments arranged in a 2x2 factorial design. Dietary treatments were 1) a corn-silage-based total mixed ration (TMR) diet; and 2) an orchardgrass (Dactylis glomerata L.) and ground corn-based (ORG) diet balanced to support similar levels of milk production. Within each diet, two inoculation methods were used 1) direct addition of particulate digesta (32 g) into the fermentor vessel (-S); or 2) blending an equivalent quantity of particulate digesta with 0.5 L of rumen liquid for 2 minutes, straining through two layers of cheesecloth, and adding only the strained liquid to the vessel (-B). All fermentors were inoculated with identical total quantities of rumen liquid (1.5 L). This resulted in four treatments, ORG-S, ORG-B, TMR-S, and TMR-B, which were randomly assigned to fermentors with 7 d of treatment adaptation and 3 d of sample collection. Effluent samples (24-h composite) were collected on d 8-10, composited by fermentor within period, and analyzed for volatile fatty acids (VFA), and organic matter (OM) and crude protein (CP) for determination of nutrient digestibilities. Data were analyzed using a mixed model with period and treatment as fixed effects, and fermentor as a random effect. Preplanned contrasts were used to compare the effect of inoculation method within each diet, and the interaction between inoculation method and diet. Apparent OM digestibility was 16% greater in ORG-S compared with ORG-B (P < 0.01), whereas no effect of inoculation method was observed in the TMR diet (P = 0.36), which resulted in an interaction of diet and inoculation method (P < 0.01). Concentration of total VFA was greater with direct addition of particulate digesta in both diets, though there was a significant interaction of diet and inoculation method (P < 0.01) due to a greater increase in VFA in the ORG diet (34%; P < 0.01) compared with TMR (10%; P = 0.01). Crude protein digestibility tended (P = 0.06) to be greater in ORG-S vs. ORG-B, whereas inoculation method did not affect CP digestibility in the TMR diet (P = 0.58). Inoculation method affected methane production (mmol/d) only in the ORG diet; total methane production was 58% greater in ORG-S compared with ORG-B (P < 0.01), whereas methane production was not different in TMR-S vs. TMR-B (P = 0.76), leading again to an interaction of diet and inoculation method (P = 0.04). In general, adding particulate digesta directly to fermentor vessels increased feed degradation and methane production in the ORG diet, but had a lesser effect in the TMR diet.