Comparative effect of Volvariella volvacea-treated rice straw and purple corn stover fed at different levels on predicted methane production and milk fatty acid profiles in tropical dairy cows

Abstract

The objective of this study was to determine the effect of different concentrations of rice straw (RS) and purple corn stover (PCS) treated with Volvariella volvacea fed in total mixed rations (TMR) on ruminal fermentation, blood metabolites, calculated methane (CH4) production, and milk fatty acid profile in mid-lactation crossbred Holstein Friesian cows. The experimental design was a 2 × 2 factorial arrangement of treatments in a 4 × 4 Latin square design. Factor A included roughage type (V. volvacea-treated RS and V. volvacea-treated PCS), and Factor B included roughage (R)-to-concentrate (C) ratio (R:C) (50:50 and 60:40). The four dietary treatment combinations were 1) RS with an R:C ratio of 50:50 (RS50); 2) RS with an R:C ratio of 60:40 (RS60); 3) PCS with an R:C ratio of 50:50 (PCS50); and 4) PCS with an R:C ratio of 60:40 (PCS60). Different roughage sources did not alter total tract digestibility of DM, OM, and NDF (P > 0.05), but PCS increased NDF digestibility by 4.6 percentage units and CP digestibility by 15.6 percentage units. Roughage types influenced rumen propionic acid (C3) concentration 4 h after feeding with PCA increasing higher C3 concentration compared to RS at both R:C ratios. There was no interaction between roughage types and the R:C ratio for CH4 emission calculated based on volatile fatty acid profiles. However, roughage type impacted CH4 emission. Calculated CH4 concentration was lower in PCS than RS. Changing the R:C ratio did not alter milk production, milk composition, or somatic cell count (SCC). Moreover, roughage type did not influence milk production and milk composition, except for SCC which was lower in PCS. Roughage type and the R:C ratio independently influenced milk fat arachidonic acid (C20:4n-6) concentration. Furthermore, the PCS group had higher conjugated linoleic acid (CLA) than the RS groups. The proportion of total C18:0 and cis-9 C18:1 in milk fat increased 10% with the feeding of PCS50 and PCS60. However, milk cis-9, trans-11 C18:2 increased by 61% in the PCS group (P < 0.01). In conclusion, PCS increased rumen C3 and milk fat CLA and arachidonic acid concentration and decreased CH4 production compared to the RS. The PCS treated with V. volvacea could be used for up to 60% of TMR for dairy cows.