Peppermint (Mentha piperita Huds.) and basil (Ocimum basilicum L.) etheric oil by-products as roughages for sheep feeding

Whole plants of peppermint and basil after etheric oil distillation were tested for in situ degradability and in vitro gas production. Digestibility of these by-products was also determined in in vivo trials with nine wethers using 3 × 3 Latin square design. Three diets were tested: 900 g dry matter (DM) meadow hay (diet H), 450 g DM meadow hay plus 450 g DM peppermint (diet P), and 450 g DM meadow hay plus 450 g DM basil (diet B). Peppermint, after etheric oil distillation, contained more crude protein (130 vs. 72 g kg−1 DM), and less neutral detergent fibre (NDF) (583 vs. 828 g kg−1 DM) and acid detergent fibre (ADF) (425 vs. 680 g kg−1 DM) than basil. High acid detergent insoluble nitrogen concentration was obtained in both peppermint and basil (19.7% and 23.4% of total N, respectively) which resulted in low ruminal crude protein degradability (42% and 36%, respectively). Results of in vitro gas production indicated less extensive and slower fermentation of basil compared to peppermint. Organic matter digestibility (OMD) of basil was 0.51, while OMD of peppermint (0.54) was slightly less than that of meadow hay (0.56). No differences between the treatments were found in pH, ammonia and volatile fatty acid concentrations of rumen liquor sampled 3 h after the morning meal. Feeding diet B led to the highest proportion (75%) of acetic acid in the rumen liquor which corresponded to the highest intake of structural carbohydrates (NDF: 683 g day−1 and ADF: 504 g day−1) when diet contained basil. The lowest total protozoa number was counted in the rumen liquor of sheep fed diet B: 151 × 103 m−1 vs. 195 – 197 × 103 ml−1 for diets H and P.