Use of the in vitro gas production technique to study feed digestibility in domesticated ostriches (Struthio camelus var. domesticus)

In order to enhance knowledge of the nutritive value of ostrich feeds, the in vitro gas production technique was used. Five feeds (corn silage, CS; alfalfa hay, AH; barley, BG; soybean meal, SM; beet pulp, BP) were weighed (~ 1g) in quadruplicate in 120 ml serum flasks and incubated at 39 °C with 75 ml of anaerobic medium and 4 ml of reducing solution. A pool of caecal contents obtained at slaughter from 4 male ostriches was diluted 1:2 with the medium and used as inoculum (10 ml/flask). Gas production was recorded at regular intervals up to 120 h from inoculation. At the end of incubation, pH and organic matter digestibility (OMd) were measured. The gas produced at each time was fitted to a mathematical model to obtain the kinetics fermentation parameters (e.g. maximum fermentation rate, Rmax and time at which it occurs, Tmax). On the basis of OMd, the substrates were classified as: AH (55.5 %) < CS (63.82 %) < BG (79.98 %) < BP (80.78 %) < SM (88.51 %). BG and BP showed the same pH (6.36) and similar gas production (OMCV, 321.9 ml/g vs 317.0, respectively for BG and BP). However, BG showed higher Rmax (9.83ml gas/h vs 7.23, respectively for BG and BP, P < 0.0001) and lower Tmax (17.51 h vs 22.36, respectively for BG and BP, P<0.0001). SM, also showing the highest OMd, showed a low gas production (OMCV, 258.2 ml/g), confirming that not all fermented organic matter produces gas. The OMd of AH and BG was in agreement with the findings of another study in which the dry matter digestibility in ostrich of alfalfa (50.1 %) and barley (82.6 %) was determined by in vivo trials. Our results suggest that the in vitro gas production technique can be used successfully to estimate the organic matter digestibility of ostrich feed and study the fermentation characteristics of ostrich caecal content.