| Nutritional and genetic adaptation of galliform birds: implications for hand-rearing and restocking | ||
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Certain blood parameters were used to describe the nutritional status of birds (I, III, V). Grey partridges did not show any response in analysed blood parameters to the change in diet from commercial to natural (III). Perhaps the analysed parameters were not sufficiently sensitive to indicate nutritional stress in grey partridges, although some of them have been successfully used in the study of starvation (Jeffrey et al. 1985, Robin et al. 1987, Totzke et al. 1999). Plasma total protein and thyroid hormones are shown to decrease as a response to food deprivation in herring gulls Larus argentatus (Totzke et al. 1999). However, birds fed natural food had higher alanine concentration (V) in plasma in comparison to control birds. This may have been a sign of catabolism of nutrient reserves, because the birds fed natural food were lighter in weight (III, V) than birds on other diets.
Hand-reared grey partridges had lower Hb and Hcr than hand-reared or wild capercaillies, but the values varied in a range of flight-restrainted birds of several other species (Balasch et al. 1974). Flight – or in this case flightlessness as a result of limited exercise ability in test cages, may have had an impact on plasma composition.
Glycine takes part in some detoxication reactions (Stevens 1996), which may explain the somewhat elevated glycine (V) level in the birds fed natural food. Tannin had no significant effects on the blood parameters, but methionine should be mentioned. Methionine level seemed to be somewhat elevated in the tannin group. Added methionine in the diet is known to decrease the effects of tannin (Elkin & Rogler 1991). In birds, phenolic compounds may be conjugated with ornithine (Jakubas et al. 1993), but no elevated ornithine levels were observed. The last sampling was conducted simultaneously with decapitation, which affected plasma consistency.
Hand-reared capercaillies had higher uric acid and T4 levels than wild birds (I). Results obtained from grey partridges (III) were in agreement with this, but the difference between test and control groups was not significant. High uric acid levels may have resulted from the high protein concentration in the commercial poultry food, or from the reduced ability of the caecum to recycle uric acid (Karasawa 1989). Plasma uric acid is assumed to indicate protein breakdown in starving Svalbard ptarmigan Lagopus mutus hyperboreus (Lindgård et al. 1992).
Hand-reared grey partridges (Putaala et al. 1993) and turkeys Meleagris gallopavo (Burke et al. 1977b) have significantly higher T3 concentration in plasma than wild birds. This may reflect a higher metabolic rate in hand-reared birds when compared with the wild birds (Warkentin & West 1990). According to Bishop et al. (1995) T4 may be important in birds in affecting the aerobic capacity of certain muscles, as T4–treated tufted ducks (Aythya fuligula) have higher cytochrome oxidase activity in the pectoral muscle than control birds. The high plasma T4 level of hand-reared birds (I) may reflect a lower level of metabolism in comparison to wild birds, expressing the unnecessity of the hormone in low level activity. This may be linked to the flightlessness of birds in aviaries.
Serum total protein is known to be higher in adult than in juvenile hand-reared capercaillies (Cuenca et al. 1995). The somewhat higher total protein level of captive birds (I) may be explained by the higher number of adult birds among them. In general, the results of the blood characteristics in captive capercaillies were in agreement with those obtained from a wide sampling of captive birds of several species (Polo et al. 1994). Birds are generally able to maintain a high and relatively constant plasma glucose level, even during fasting (Langslow 1978, Groscolas & Rodriguez 1981).
No statistically significant effects could be seen in the nitrogenous compounds of plasma in the grey partridges fed tannin or natural food. However, potential short-term effects, that the change in diet had, coincide with the period of body mass loss, and also with the high mortality rate after release into the wild.