|Nutritional and genetic adaptation of galliform birds: implications for hand-rearing and restocking|
|Prev||Chapter 5. Discussion||Next|
Hand-reared capercaillie males had somewhat heavier pectoral muscles than wild males, whereas the result obtained from females showed the opposite (I). This probably resulted from the different growth strategies of males and females (Lindén et al. 1984): males usually gain mass already during autumn and winter in preparation for the breeding season and ad libitum feeding of hand-reared birds could have facilitated the mass gain of pectoral muscle. Low locomotive activity was reported to cause pectoral muscle atrophy in pheasants (Majewska et al. 1979), pigeons (Chaplin et al. 1997), great crested grebes Podiceps cristatus (Piersma 1988) and black-necked grebes Podiceps nigricollis (Gaunt et al. 1990). In contrast, Lindström et al. (2000) suggested that avian muscles do not need power-training as do mammalian muscles, and that in their windtunnel experiment, repeatedly flown red knots (Calidris canutus) did not have any thicker pectoral muscles than their unflown counterparts.
The size of the heart is positively correlating with flying ability (Thomas 1985, Viscor et al. 1985); good flyers tend to have bigger hearts than moderate flyers. Hand-reared capercaillies had smaller hearts than wild ones (Hissa et al. 1990, I), which probably was a result of limited flying possibilities in rearing aviaries. Domingo et al. (1991) reported heart burst in capercaillies as a consequence of handling stress. In Nappée’s study (1982) heart failure caused death in released capercaillies. Thus, untrained heart may be more vulnerable to the impact of sudden stress effects.
The oxidative capacity of a muscle may be expressed in cytochrome-c oxidase activity. Enzyme activity in the pectoral muscle of the wild capercaillies was over three times that of the hand-reared birds. Also, the heart enzyme activity was higher in the wild birds compared with the hand-reared birds (I). The concentrations of mitochondrial protein in the pectoral muscle and the heart were higher in wild capercaillies compared with the hand-reared birds, which most probably was connected to the higher cytochrome-c oxidase activity in the wild birds. The low tissue enzyme activity indicated a poor ability for long-term flight performance in hand-reared birds. Additionally, it may have indicated an adaptation to low energy demands of living in captivity (I). However, Warkentin and West (1990) suggested that the basal metabolic rate (BMR) is significantly higher in captive than in wild, freshly caught merlins Falco columbarius.
In short term power production (take-off), hand-reared grey partridges are weaker than wild birds (Putaala et al. 1997). Cytochrome-c oxidase activity plays an important role in long-term power production (flight), which in hand-reared grey partridges (Putaala & Hissa 1995) and capercaillies (I) is lower than in their wild counterparts. Wild grey partridges (Pyörnilä et al. 1998) and capercaillies (Mäkinen et al. 1997) have more muscle cells, which are needed in long-term exercise (red, fast-oxidative-glycolytic fibres = FOG) than hand-reared bird. In contrast, captive birds have more muscle cells for short-term exercise or short spurts (white, fast-glycolytic fibres = FG). This could at least partly explain the difference in the COX activity. According to Kaiser and George (1973) and Rosser and George (1986) FG fibres are rich in glycolytic enzymes, and adapted to anaerobic metabolism using glycogen as their main fuel. FOG fibres are rich in oxidative enzymes, adapted to aerobic metabolism, and mainly use fat as fuel for long-lasting activities. In relatively poor flyers, like the chicken or the pheasant, the pectoral muscle comprises mainly FG fibres, whereas in good flyers like the pigeon, FOG fibres dominate (see Hissa 1988 and references therein). According to Rome et al. (1988) FG cells are needed for maximal movement, because FOG cells do not shorten fast enough.
Glycogen is metabolised anaerobically and used predominantly during take-off and landing (Parker & George 1975). The glycogen content of a tissue is a labile parameter, depending on the bird’s previous activity. This probably affected the results. No difference was found in the glycogen content of tissues between wild and hand-reared birds, although the glycogen content in the liver of wild birds was somewhat higher than that in hand-reared birds (I). According to Hissa et al. (1990), wild capercaillies stored more glycogen in the pectoral muscles than hand-reared birds. Putaala and Hissa (1995) reported for wild grey partridges that the glycogen content of the pectoral muscle was almost ten times that of hand-reared birds. Wild pheasants had higher glycogen content in both pectoral muscle and liver in comparison to captive birds (Majewska et al. 1979), and seasonal variation in the glycogen content of the liver was also reported (Pulliainen & Tunkkari 1984).
|Added dietary tannin expressed in excreted nitrogen and tannin content||Up||Primary growth and temperature regulation|