Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2005
Publication Date: May 1, 2005
Citation: Grings, E.E., Waterman, R.C. 2005. Inoculum source effects on in vitro gas production of forages. American Society of Animal Science 83(Suppl 1):148. Technical Abstract: Buffer N concentration and forage protein fermentability can both influence in vitro gas production profiles. Therefore, we tested the impact of using inoculum from cattle fed grass or grass and alfalfa on in vitro gas production profiles of forages and ruminal extrusa. Four ruminally cannulated beef cows were used in a 2 x 2 Latin Square design experiment. Dietary treatments consisted of grass hay or grass hay plus 1.4 kg/cow of alfalfa pellets fed once daily. Ruminal fluid was used to inoculate an in vitro gas production system using 100 ml glass syringes. Twenty ml of media were placed in each syringe containing from 200 to 250 mg substrate. All substrates were run in media containing ruminal fluid at concentrations of 24, 29 or 34%. Substrates tested included two alfalfa hays, one grass hay, Agropyron smithii harvested in either June or December, and lyophilized ruminal extrusa collected from cattle grazing native range in May, August, or December. Gas production was read manually at 0, 2, 4, 6, 8, 10, 12, 14, 24, 30, 34, 36, 48, 54, 72, and 96 h of incubation. Net gas production was calculated on an OM basis. Rate, maximal gas production, and lag time were evaluated using a Gompertz model. Gas production at each time point, the relative standard deviation of duplicate readings, rate, maximal gas production, and lag time were subjected to analysis of variance procedures using a model containing the terms diet, cow group, gas run, ruminal fluid concentration, and the ruminal fluid concentration by diet interaction. The residual error term was used to test effects. Relative standard deviations were less (P < 0.05) for many individual gas production measures when only grass was fed to inoculum donors. Grass inoculum resulted in increased (P < 0.05) gas production at all time points earlier than 48 h, faster (P < 0.05) rates of gas production, and decreased (P < 0.05) lag times compared to inoculum from cows fed grass plus alfalfa. Addition of alfalfa into the diet of inoculum donors to increase dietary protein did not improve the precision of in vitro gas measures.