5.4. Food consumption and MEC responded to the change in diet

The change in diet lowered the food consumption immediately in grey partridges fed natural food (III). This may have reflected the natural suspiciousness of birds to new situations. During the feeding trial the food consumption in test group (III) was somewhat higher than in the control group based on the fresh weight of food. A similar response to natural food was found in the red grouse (Moss 1972), the mallard (Miller 1975) and the rock ptarmigan Lagopus mutus (Gasaway 1976b). Japanese quails adapted to the use of more fibrous food in about one week, and decreased food intake back to initial levels (Savory & Gentle 1976b), even though they initially increased food intake as a response to an increased fibre content in the food (Savory & Gentle 1976a).

The birds fed natural food ate more than the control birds by fresh weight, but the result was opposite when based on analyses of dry weight. This depended on the birds’ preference for barley shoots. The water content of shoots was about 90 %. Shoots might have been favoured because of the forthcoming breeding season, when they are very important for the breeding condition of female grey partridges (Siivonen 1957). However, it was of no interest to calculate food consumption on the basis of dry matter, because of the nature of the natural food in comparison to pelleted commercial food. Much information about the amounts of the consumed food would have been lost in that case.

Excreta production varied from week to week, which also affected assimilation efficiency, MEC (III). In the test group assimilation efficiency varied between 49–67 % and in the control group between 61–88 %. These values were within the normal range of the galliforms (30–86 %, for review, see Castro et al. 1989). The daily energy (GE) requirement of the rock ptarmigan (Gasaway 1976b), or the daily metabolised energy (ME) of the red grouse and the Japanese quail (Moss & Trenholm 1987, Starck & Kloss 1995) were not affected by the fibre content of food (but see Savory & Gentle 1976a). According to Duke et al. (1984) the preconditioning of turkeys to fibre-rich food quadrupled their ability to utilise food cellulose. In this study both GE and ME decreased when the diet was changed from commercial to natural. This was presumed to result to some extent from the high plant secondary compound concentration in the food (see Servello et al. 1987, Koenig 1991).

Tannin (6 %) added to the food did not lower food intake, which was in contrast to previous studies on chickens (Elkin & Rogler 1991, Helsper et al. 1996) and ruffed grouse (Hewitt et al. 1997). In the Canada geese (Buchsbaum et al. 1984) and the ruffed grouse, 8 % quebracho tannin (Hewitt et al. 1997) is known to decrease food intake, but this was not supported by our study. The commercial quebracho product used in this study included 73 % of condensed tannins, which means that the effective tannin content of this product was ca. 4.4 % (Robbins et al. 1991). On the other hand, it was reported by Chung-MacCoubrey et al. (1997) that quebracho had no dose-dependent effects on the captive eastern grey squirrels Sciurus carolinensis.