|Nutritional and genetic adaptation of galliform birds: implications for hand-rearing and restocking|
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The most significant difference between the ”browsing” Tetraonidae and the ”seed-eating” Phasianidae birds is in the relative size of their caeca. The caeca of the browsers may be over twice as long (per unit body mass) as those of the seed eaters. Grouse in the 500-gram weight class (ruffed grouse Bonasa umbellus, spruce grouse, ptarmigans) have a mean caecal length of 44 cm, whereas in partridges of same size (the grey partridge, the chukar partridge Alectoris chukar) the caecal length is less than 20 cm (Leopold 1953). The length of the caeca seems to reflect the selection of coarse, fibre-rich food (McLelland 1989) and also digestive efficiency (Barton & Houston 1993).
Natural food is fibre-rich compared with commercial poultry food (III). Increased fibre content in food increases the length of the intestine and the weight of the gizzard in hand-reared red grouse (Moss 1972), mallard Anas platyrhynchos (Miller 1975), Japanese quail Coturnix coturnix japonica (Savory & Gentle 1976a, Starck & Kloss 1995), rock partridge Alectoris graeca (Paganin & Meneguz 1992), and also in some diving ducks Aythya spp. (Kehoe & Ankney 1985). Similar results on European starlings Sturnus vulgaris were reported by Geluso and Hayes (1999). The weight of the gizzard increased as a result from changing the diet to coarse, fibre rich natural food (III, V). Further, the gizzards were heavier in wild than in captive capercaillies (I). This probably reflected the need for a more effective grinding ability when feeding on fibre-rich diet. Tannin had no effect on the gizzard mass (V).
There was no difference in the length of small intestine and caeca between grey partridges fed natural or commercial foods (III, V). However, wild capercaillies had longer intestines and caeca than captive birds (I), which was in agreement with the studies of Pendergast and Boag (1973), Hanssen (1979a), Majewska et al. (1979), Paganin and Meneguz (1992), and Putaala and Hissa (1995). It was noticeable that grey partridges (III, V) had shorter intestines and lighter gizzards, as well as livers, than wild grey partridges or birds that were of wild origin and had spent only 1–2 generations in captivity (Putaala & Hissa 1995). Moss (1972) showed that the caeca shortened in the red grouse in captivity from generation to generation.
The length of the GI tract is known to vary seasonally (Pendergast & Boag 1973, Pulliainen & Tunkkari 1983). The adjustment time to changed food varies from a couple of weeks in the Japanese quail (Starck & Kloss 1995) to 4–6 weeks in the red grouse (Moss & Trenholm 1987) or it may take even longer (Duke et al. 1984). Since no differences in the length of small intestine and caeca in the grey partridge were found, this may reflect their feeding habits; grey partridges have a similar diet throughout the year. Therefore, it is possible that they do not have a similar need for adaptation to changing diets as do Tetraonid birds. It is also possible that feeding four (V) or six (III) weeks on natural diet was insufficient to cause any visible changes in the gut length of grey partridges. However, the effect of tannin on the length of the small intestines of the grey partridge was obvious even though the feeding trial lasted only for four weeks (V). Tannin-fed birds had longer small intestines than control birds, which may reflect the increased enzyme activity or increased need for absorptive surface in the gut. Short-term fasting or food restriction, as well as switching to a totally different diet may cause partial atrophy of the gut, which may limit utilisation of ingested food energy and nutrients (McWilliams & Karasov 2001).
Caeca play an important role in the digestion of cellulose (Suomalainen & Arhimo 1945, Fenna & Boag 1974, Thompson & Boag 1975, Moss 1989, but see Andreev 1988, Remington 1989), and water absorption (Gasaway et al. 1976, Chaplin 1989, Thomas & Skadhauge 1988, 1989, Williams & Braun 1996) in galliform birds. Therefore, watery composition of the excreta of the birds fed natural food after the change in the diet may indicate disturbed caecal function (III, V). The excreta became dry (”normal”) by the time a bird’s body mass reached the initial level (III). The caeca take part in balancing nitrogen levels (Gasaway et al. 1976, Mortensen & Tindall 1981, Björnhag 1989, Karasawa 1989, Karasawa et al. 1997), since galliform birds are able to recycle uric acid through caeca by microbial activity (Mortensen & Tindall 1981, Karasawa 1989, Karasawa et al. 1997). If hand-rearing shortens the caeca, this may reduce effective decomposition and absorption activities in them. Also tannin-fed birds had high water content in their excreta, which may reflect the need to keep tannin concentration low, or to facilitate the removal of tannins dissolved in water.
Wild capercaillies had heavier livers than hand-reared birds (I). The liver’s capacity to store glycogen may partly affect its size. The assumption was, that heavier livers would partly reflect the quantity of detoxication enzyme activity. However, the results obtained in grey partridges (V) did not support this, because tannin fed birds did not have significantly larger livers than the control birds. The liver fat, protein, and ash content was higher and the water content lower in hand-reared than in wild capercaillies (I). This result is in agreement with the results of Putaala and Hissa (1995) on grey partridges. Because in the willow grouse the size of the liver shows diet-dependent seasonal variation (Pulliainen & Tunkkari 1984), the difference in the liver composition found in this study may result from the different food of wild and captive capercaillies. The effect of food on liver composition has also been reported in geese Anser sp. (Benard & Labie 1992).