Circadian Ingestion Behaviors: Animal Models Outlooks

Abstract

Submit Manuscript | http://medcraveonline.com Grazing occurs mainly around sunrise and sunset. In grazing sheep, the maximum jaw movement occurs in the late afternoon before sunset. Dairy cows exhibit three main grazing bouts of dawn, afternoon, and dusk. However, the diurnal patterns in grazing appear to vary across seasons. In Western Australia with hot summers and mild winters, the main summer grazing activity occurs during early morning and late afternoon with a smaller activity around midnight. Sheep and cattle likely have comparable grazing patterns in summer. In winter, however, the cattle show intensive grazing activities not only in the morning and afternoon but also during the period from 2000-0100 h. Unlike in summer, in winter, sheep has a progressive grazing activity from 0600 through 1700 with low activity in the evening. Under intensive feeding systems, dairy cows and finishing bulls fed only once daily in the morning exhibit two peaks in eating activity. The greatest one is right after feeding and another around dusk. The eating/ grazing pattern has circadian patterns [1]. Cows seem to stop the morning eating before reaching the maximum rumen capacity. The observation that rumen capacity peaks at dusk but not during the morning and afternoon grazing has implications. It is found that time spent eating during the dusk grazing bout is longer than that during the dawn and afternoon bouts. Moreover, during dawn and afternoon bouts, the cows finish eating before reaching a rumen capacity which was reached during the dusk bout. Therefore, the rumen fill has probably a more significant role in regulating the dusk feed intake compared to dawn and afternoon feed intakes [2,3]. Despite feeding adequate coarse corn silage as 45% of diet dry matter (DM), finishing bulls select the coarse particles for as long as 16-h post-feeding. Such a late selection of the more structured total mixed ration particles is an effort to optimize the intake of long roughage particles. In beef cattle, the herbage allocation time (e.g., 0700 h vs. 1500 h) alters daily patterns in eating, ruminating, and idling behaviors in heifers. The heifers turned unto the ungrazed strip at 0700 h have more intense evening grazing with faster bite rates compared with the heifers allotted the herbage at 1500 h. The morning grazing is 36-39% of total daily grazing time in the latter group but only 25-28% in the former group. The nutritional status of the animal before feeding can affect the postfeeding eating intensity. Fasting, for instance, hastens eating by increasing the bite rate and enlarging the bite mass. However, the data on the effects of feeding strategies on diurnal patterns in feed intake of non-grazing ruminants is scarce [3-5]. The large evening meals in grazing cows are partly linked to an optimal foraging strategy. The plant content of DM and water soluble carbohydrates rises and NDF decreases as day progresses. The accumulation of highly-digestible nutrients in the evening is due to the daylight photosynthesis in plant leaves. This may partly explain why cattle, sheep, and goats prefer the fresh forage grass and legumes harvested at sunset compared to that harvested at sunrise. A higher in vitro true DM digestibility for PM-cut than for AM-cut alfalfa hay is known. Ruminants may have greater feed intake and greater total tract DM digestibility when they are offered the sunset-cut alfalfa hay instead of the sunrise-cut alfalfa hay. The grazing ruminants appear to learn the time of maximum plant nutrient quality, leading to a more intensive eating in the evening than in the morning [4-6].