Nutrition for Health Dietary Copper Influences Reproductive Efficiency of Queens

Copper, an essential trace element for all animals, functions as a component of metalloenzymes that catalyze electron transfer reactions involving molecular oxygen (Linder 1996). Cuproproteins have several nonenzymatic functions including copper transport, temporary storage and coagulation (Linder 1996). Before the initiation of this project, there was only one published report concerning the copper requirements of cats (Doong et al. 1983). On the basis of that study and the requirement of rats, the National Research Council (NRC 1986) proposed a copper requirement of 5 mg Cu/kg diet for kittens for growth. However, while testing commercial diets in Association of American Feed Control Officials (AAFCO) protocols, we found that queens fed three different diets produced offspring with signs compatible with clinical copper deficiency in other species, including neonatal death, premature kittens, hypochromatricia and collagen abnormalities. All of these diets contained supplemental copper supplied as copper oxide, a form demonstrated to be unavailable in other species (Baker et al. 1991, Cromwell et al. 1989). The objectives of this study were to determine the copper requirement of queens for gestation and the extent to which cupric oxide is an available form of copper for queens for reproduction. Materials and methods. The experimental protocol adhered to the NRC guidelines (NRC 1985) and was approved by the Animal Use and Care Administrative Advisory Committee of the University of California at Davis. Animals and their management. Thirty-eight 2to 3-y-old specific-pathogen–free domestic short-hair queens from the Feline Nutrition and Pet Care Center of the University of California at Davis were used. Queens were group housed in large wire cages (2.5 3 2.5 3 2.5 m) in rooms with controlled temperature (21 6 2°C) and a light:dark cycle of 14 h:10 h. Queens were transferred to queening cages (76 3 76 3 76 cm) before giving birth and remained there until the kittens were weaned. Queens had free access to the experimental diets and water. Diets. Experimental diets were prepared by adding varied amounts of copper as copper sulfate (CuSO4 z 5H2O) or cupric oxide (CuO), (both obtained from Fisher Scientific, Fair Lawn, NJ) to a casein/lactalbumin-based diet composed of the following constant ingredients (g/kg diet): casein (New Zealand Milk Products, Petaluma, CA), 220; lactalbumin (see casein), 220; rendered animal tallow (Florin Tallow, Dixon, CA), 270; sucrose, 75.5; starch (cornstarch, Melojel, Bridgewater, NJ), 144; taurine (Taisho Pharmaceutical, Torrance, CA), 1.5; choline chloride (International Mineral and Chemical, Terre Haute, IN), 3; vitamin mixture (Williams et al. 1987), 10; L-methionine (Ajinomoto USA, Raleigh, NC), 3; L-arginine (Ajinomoto USA), 3; mineral mixture, 50 (containing CaHPO4, 28.1; MgSO4, 2.25; NaCl, 5.11; KCl, 13.85; MnSO4 z H2O, 0.153; ZnSO4 z 7H2O, 0.178; FeSO4 z 7H2O, 0.318; pentacalcium orthoperiodate, 0.00316; SnSO4, 0.038; Na2SeO3, 0.0012; (NH4)6Mo7O24 z 4H2O, 0.0016; CrCl3 z 6H2O, 0.0104; NiCl2 z 6H2O, 0.012; NaF, 0.0056; NH4VO3 z 4H2O, 0.00008). The purified diet exceeded NRC recommended levels of all ingredients other than copper and has been demonstrated to support adequate growth and reproduction in cats at the Feline Nutrition and Pet Care Center. Copper concentrations in the experimental diets were confirmed by using an atomic absorption spectrophotometer (model 3030B, Perkin-Elmer, Clay Adams, NJ). Diets were stored at 4°C between preparation and feeding. Design. A depletion-repletion study design was used. Queens were trained to eat a purified diet containing copper. When weight maintenance was satisfactory, they were fed a copper-depletion purified diet (0.8 mg Cu/kg diet) for 4 mo after which they were randomly allocated into one of four dietary treatment groups. Dietary copper additions to the purified diet were 3, 6 or 10 mg Cu/kg diet as copper sulfate, or 10 mg Cu/kg diet as cupric oxide. Plasma samples were collected every other week throughout the study. Five of the 38 queens underwent exploratory laparotomies for liver biopsies before and after the depletion and repletion periods. Plasma and liver samples were analyzed for copper concentration by using atomic absorption spectrophotometry (model 3030B, Perkin-Elmer). After the introduction of a tom into each Presented as part of the Waltham International Symposium on Pet Nutrition and Health in the 21st Century, Orlando, FL, May 26–29, 1997. Guest editors for the symposium publication were Ivan Burger, Waltham Centre for Pet Nutrition, Leicestershire, UK and D’Ann Finley, University of California, Davis. To whom correspondence should be addressed.