Connection between Circadian Rhythm and Rumen Digestibility of Concentrate and Roughage in Sheep

This study investigated the effects of circadian rhythm on rumen nutrient digestibility using the nylon bag method and the digestibility characteristics of dietary nutrients during the daytime and at night. It also presents modification suggestions for evaluating the nutritional value of raw feed materials. The rumen nutrient digestibility was measured and investigated for correlation with circadian rhythm using the nylon bag method. We established a sheep-feeding program to determine the differences in rumen nutrient digestibility between the daytime and nighttime. The digestibility of 18 standard feed samples was investigated in 6 Hu sheep with ruminal fistulas (body weight: 33.59 ± 0.39 kg, 12 months old). Samples were incubated in the rumen for three periods: daytime (12 h, 6:00 AM to 6:00 PM), night (12 h, 6:00 PM to 6:00 AM), and the entire day (24 h, 6:00 AM to 6:00 AM). The activities of enzymes amylase, lipase and cellulase were higher during the day than at night. The rumen digestibility of organic matter was significantly higher during the daytime than at night compared to the digestibilities of dry matter (DM), crude protein (CP), and ether extract (EE). Among them, the rumen digestibility of DM and CP was higher, but the digestibility of EE was lower during the daytime than at night in cereal feed fed sheep. The rumen digestibility of DM was higher in roughage-fed sheep but lower in rice straw- and corn silage-fed sheep during the day than at night. Circadian rhythms correlate strongly with the activities of major digestive enzymes in the rumen and the rumen digestibility of nutrients. Moreover, the nylon bag method needs to be modified and improved to ascertain the appropriate time for placing the nylon bag in the rumen and thus establish a unified procedure.