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Effects of subcutaneous (s.c.) administration of 50 micrograms/kg body weight of recombinant bovine growth hormone (rbGH) or saline were studied for 11 weeks in 40 intact male veal calves supplied 50 mg or 10 mg of iron (Fe)/kg of milk replacer (MR). Feed intake, average daily gain and growth: feed ratio were reduced in Fe-deficient calves, but not significantly influenced by rbGH. Plasma Fe and haemoglobin concentration, red-cell number and packed cell volume were decreased in Fe-deficient calves (P < 0.05) and rbGH further reduced red-cell number in Fe-deficient calves (P < 0.05). The age-dependent increase of total Fe binding capacity was greater in Fe-deficient calves and enhanced by rbGH (P < 0.05). Plasma urea concentrations increased, whereas glucose (G) and triiodothyronine (T3) levels decreased in Fe-deficient calves. rbGH significantly increased G in calves fed MR containing 50 mg/kg (P < 0.05) and influenced urea concentrations (P < 0.05). Plasma insulin (I) and IGF-I concentrations were lower in Fe-deficient calves (P < 0.05). Plasma GH in the first hours after rbGH injections increased (P < 0.05) to higher levels in calves fed 10 than in those fed 50 mg Fe/kg MR, but incremental changes were comparable. In conclusion, low Fe intake caused haematologic, metabolic and endocrine changes. Plasma IGF-I, I and T3 concentrations after rbGH administration and effects of rbGH on IGF-I in Fe-deficient calves were reduced, even though plasma GH levels were increased.
Ceppi et al. (Sat,) studied this question.