Effect of type and inclusion level of cold-pressed oilseed cakes on in vitro rumen fermentation

The current study was conducted to explore the impact of inclusion of different types and levels of cold-pressed oilseed cakes on in vitro rumen fermentation and gas production parameters. Two batch fermentation trials (24 and 96 h) were conducted using the in vitro gas production technique. In each trial, three types of lipid sources [palm fat (PF), cold-pressed rapeseed cake (CPRC) and cold-pressed sunflower cake (CPSC)] two levels of total fat (30 and 60 g/kg DM) were evaluated. Incubated substrates were made from iso-energetic and isoproteic basal mixtures of barley straw and concentrate (ratio 10 : 90). During the 24-h incubation trial, samples were collected 24 h post-incubation to measure volatile fatty acids (VFA) and methane production. The 96-h incubation was used to assess the rate and extent of in vitro gas production. CPSC showed lower total VFA (P < 0.001) and methane (P < 0.001) production, compared with PF and CPRC. High fat level decreased total VFA (P < 0.001) and methane (P < 0.001) production compared with low level of inclusion. Molar proportions of individual VFA and acetate to propionate ratio were not affected by lipid supplementation. CPSC reduced (P = 0.006) asymptotic gas production at high fat level, compared with PF and CPRC. Neither supplementation level nor type of lipid affected the fractional gas production rate or lag time. In conclusion, there was no difference in ruminal fermentation when either CPRC or PF were added but CPSC altered microbial fermentation in vitro at a total fat level of 60 g/kg DM.