Interaction effects of concentrate level and duration of fattening period in lambs on in vitro gas production, fermentation parameters, and volatile fatty acid concentration

The aim of this study was to investigate the effects of levels of concentrate and duration of fattening period in lambs on in vitro gas production (GP), fermentation parameters, protozoa number, and volatile fatty acid (VFA) concentration. Twenty-seven Lori male lambs (26±5 kg BW) were fed with three experimental diets (55, 70 and 85% concentrate) for 100 days (9 lambs for each). At 70 and 100 days of fattening period, ruminal fluids from lambs in each group were collected by the esophagus tube. The mixed ruminal fluids were used for In vitro GP test. Results showed that potential (b) and rate (c) of GP were affected neither by level of concentrate nor by duration of consumption of diets (P>0.05). Organic matter digestibility of diets increased (P<0.05) by increasing concentrate level; however it was decreased (P<0.05) by duration of fattening period. The NH3-N concentration increased (P<0.05) by increasing the concentration level and duration of the fattening period of the diets. Number of protozoa and total VFA concentration in diet containing 85% concentrate was higher (P<0.05) than those with 55 and 75% concentrate. With the extension of fattening period, propionic acid, and iso-butyric acid decreased (P<0.05), while the acetic acid, iso-valeric acid decreased (P<0.05). Interaction effects of concentrate level and duration of fattening on GP after 24 h of incubation, propionic acid, and butyric acid were observed (P<0.05) In conclusion, reducing the fattening period when lambs fed a high concentrate diet may exert beneficial effects on rumen fermentation parameters.