Magnesium proteinate is more protective than magnesium oxide in heat-stressed quail.

We evaluated the effects of dietary supplementation with Mg-oxide and Mg-proteinate on perfor- mance; nutrient digestibilities; malondialdehyde (MDA) concentrations in serum, liver, and thigh meat; and serum cholesterol and triacylglycerol concentrations in Japanese quail (Coturnix coturnix japonica) exposed to high ambient temperature. The birds (n 360; 10 d old) were randomly assigned to 12 treatment groups consisting of 6 replicates of 5 birds each in a 2 2 3 factorial arrangement (temperature, Mg source, Mg level). Birds were maintained in temperature-controlled rooms at 22°C for 24 h/d or 34°C for 8 h/d (0900 -1700 h) and fed a basal diet or that diet supplemented with 1 or 2 g Mg-oxide or Mg-proteinate/kg of diet. Heat exposure decreased (P 0.0001) live weight gain, feed intake, feed efficiency, and carcass weight in quail fed the basal diet. A linear increase in feed intake (P 0.008) and body weight (P 0.001), and improvements in feed efficiency (P 0.001), carcass weight (P 0.0001), digestibility of dry matter, organic matter, crude protein, and ether extract were found in Mg-supplemented, heat-stressed quail. The effects of Mg-proteinate were greater than those of Mg-oxide (P 0.0001). Serum Mg (P 0.001) concentration increased, whereas the concentration of MDA in serum (P 0.0001), liver (P 0.04), and thigh meat (P 0.0001) and serum triglyceride and cholesterol concentrations decreased linearly (P 0.001) with the level of Mg in the diet. Interactions between dietary Mg source, temperature, and level of supplementation (P 0.05) were found for several variables. Results of the present study suggest that supplementation with Mg-proteinate is more protective than Mg-oxide in reducing the negative effects of heat stress in quail. J. Nutr. 135: 1732-1737, 2005. High ambient temperature has adverse effects including decreased feed intake, egg production, live weight gain, nutri- ent digestibility, and feed efficiency in poultry (1-3). Increased mineral excretion is one of the major consequences of heat distress. Belay and Teeter (4) reported lower rates of phospho- rus, potassium, sodium, magnesium, sulfur, manganese, copper, and zinc retention in broilers raised at high cycling ambient temperatures (24-35°C) compared with those housed at 24°C. Stress causes secretion of epinephrine and corticosteroids and results in Mg loss in animals and humans (5,6). Donoghue et al. (7) reported that Mg-aspartate supplementation increased the body weight of broilers during heat stress (HS). 2 Magnesium plays a role in 300 fundamental enzymatic reactions, including the transfer of phosphate groups, the acylation of coenzyme A in the initiation of fatty acid oxida- tion, and the hydrolysis of phosphate and pyrophosphate. In addition, it functions in the activation of amino acids, the synthesis and degradation of DNA, and has a key role in