Continuous Culture Fermentation of Wild-Type Endophyte-Infected, Endophyte-Free, and Non-Toxic Endophyte-Infected (MaxQ[TM]) Tall Fescue Supplemented at Four Energy Levels

Abstract

Eight dual-flow continuous culture vessels (700 ml) were used to compare in vitro effects of wild-type, endophyte-infected (E+), endophyte-free (E-), and non-toxic, endophyte-infected (EN) (MaxQ™) Jessup tall fescue on ruminal fermentation in a grazing simulation at four levels of concentrate supplementation (ground corn). For each of the fescues (E+, E-, and EN), forage to concentrate ratios of 100:0, 85:15, 70:30, and 55:45 were used for a total of 12 experimental diets in a randomized incomplete block design with two replicates. Vegetative grasses were used with compositions as follows: E+ (12.3 % CP, 59.9 % NDF, 29.2 % ADF); E- (13.4 % CP, 60.7 % NDF, 29.4 % ADF); and EN (10.4 % CP, 63.2 % NDF, 31.4 % ADF).

Ruminal cultures were adapted for 48 h before experimental diets were fed and then gradually adjusted to the final diets. Each culture vessel was offered a total of 15 g of DM per day including four equal portions of grass (fed at 0300, 0900, 1500, and 2100 h); and two equal portions of corn (fed at 0900 and 2100 h). Ruminal fluid passage rate was set at 6.25% per h. Headspace gas and liquid samples were analyzed for methane (CH4), ruminal culture pH, volatile fatty acids (VFA), and ammonia N (NH3 N) production to assess the ruminal environment from the pasture-based diets.

Forages had no effect on molar proportion or total VFA production (58.8 mmoles/d). Methane production (24.7 mmoles/d) and ruminal culture pH (6.11) also remained unaffected by forages. Ammonia N output (g/d) varied by grass: EN had lower (P < 0.05) values compared to those of E+ and E-.

Increasing the level of grain linearly decreased (P < 0.05) ruminal culture pH, ammonia N, acetate production, and the acetate to propionate ratio, whereas propionate and butyrate production increased (P < 0.1) with higher grain supplementation. Overall, ruminal fermentation was minimally altered by the presence or absence of the endophyte. However, forage by grain interactions for methane and ammonia N production were reported. The grain-induced culture pH drop for the highest level of grain (45%) changed the methane production pattern for all three grasses. At that supplementation level, EN was the most energetically efficient forage.