Analysis of the Reingestion Rhythm in Confined Cottontails

Abstract

Reingestion in caged cottontails occurs as a well—synchronized diel rhythm coinciding with or following sunrise. On a reversed lighting regimen rabbits slowly adjust their rhythmic functions so that reingestion is closely fixed to the light time. When they are exposed to sunlight the relationship between the onset of reingestion and sunrise differs during the seasons. As the days become longer reingestion begins later in the morning. This daily and seasonal relationship appears to follow very closely the condition found in unconfined populations. A gastrocolic reflex appears to govern the rate of hard pellet defecation, but another answer apparently must be found to explain the cyclic production of soft feces. The transition from soft feces to hard pellets occurs previous to and is independent of the evening feeding activity. If rabbits are not allowed to feed in the evening a second period of reingestion occurs, at least in some animals.

The entrainment of the circadian caecotrophy rhythm with different light‐dark time ratios

“…This accords well with the observation of Heisinger (1965) in another Lagomorphe, the cottontail. Exposed to natural lighting conditions caged cottontails reingested caecotrophe in summer several hours after dawn, whereas during fall and winter reingestion was started one hour after sunrise.…”

Caecotrophy in caged Mountain hares (Lepus timidus)

“…Seasonal trends in caecotrophy have also been found in rabbits by Watson (1954) and Myers (1955) and in cottontails by Heisinger (1962Heisinger ( , 1965, while Lechleitner (1957) in his material on the Black-tailed jackrabbit could not detect any seasonal periodicity. Pehrson (198 1) showed that dry matter digestibility did not change with different amounts consumed.…”

“…The main work, so far, has been centred on the periodicity of the excretion of the two types of faeces, whether it is induced by an endogenous clock, or by external factors such as food intake or day-length (Watson, 1954;Heisinger, 1962Heisinger, , 1965Hornicke & Batsch, 1977;Jilge, 1976Jilge, , 1979a. The origin of hard and soft faeces and the mechanism behind 0022-5460i83/040563 + I2 503.00iO 0 1983 The Zoological Society of London 563 their production has also been the object of much research (Thacker & Brandt, 1955;Bjornhag, 1972;Pickard & Stevens, 1972;Leng & Hornicke, 1976;Leng, et al, 1977).…”

Coprophagy in the Japanese hare (Lepus brachyurus): reingestion of all the hard and soft faeces during the daytime stay in the form

“…For example, Lockley (1964) notes that he never saw the wild rabbits discard faeces in the burrows in the course of a four-year observation period. Heisinger (1962Heisinger ( , 1965 regarded the 4-or 5-h period after the reingestion of the last soft faeces until the evening, during which fresh food was not eaten and only hard pellets were in the rectum, as a fasting period. This interpretation is based on the assumption that hard faeces are not reingested and it may be unjustifiable.…”

“…A mechanism at the proximal colon has been shown to be involved in the alternate production of hard and soft faeces (Cheeke, 1987). The reingestion rhythm is regulated by photoperiod and feeding activities (Heisinger, 1965;Jilge, 1974;Hornicke et al, 1984).…”