Methionine and cystine requirements for kittens

Despite the carnivorous origin of the domestic cats, little is known about the protein and amino acids requirements of these animals. Additionally, the most of experiments were performed with purified and semi-purified diets that could produce different results from practical diets. The aim of this study was to determine the nitrogen and methionine+cystine (M+C) requirements of kittens from 150-240 days-old. Thirty-six kittens (150 days-old) were divided in six treatments (n=6 per treatment). The study was in a block design with repeated measurements. The nitrogen balance and fur collection were performed at 150, 195 and 240 days-old. For the Nitrogen balance, kittens were adapted for 5 days and after, the total collection of feces and urine were performed for 6 consecutive days. At the start of the study, the lumbar area of the kittens was shaving and the hair growing was measured at 195 and 240 days-old with micrometer. Six isoenergetics diets (4.000 kcal/kg) were formulated, with increasing protein concentration (22, 29, 35, 42, 50 % CP and counter proof diet with 22 % CP plus M+C) but constant ratio of amino acids, by using of dilution technique (Fisher and Morris, 1970). The diets were relatively deficient in M+C (0.65, 0.88, 1.13, 1.36, 1.60% M+C) in order to determine the requirements of these amino acids. The amount of food was calculated individually to meet the recommended nutrient requirements for growing cats (NRC, 2006). Protein and M+C requirements were determined according to G?ttingen approach, by using of an exponential model and mathematical relationships between nitrogen intake (NI), nitrogen excreted (NEX), nitrogen deposition (ND) obtained in the nitrogen balance trials (Liebert et al., 2000). The nitrogen requirements for maintenance (NMR) of the kittens were 565, 558 and 457 mg/BWkg^0.67/day, respectively at 150, 195 and 240 days-old. Considering 60% of NR_maxT (according to optimal weight gain and growth fur, the M+C requirements were 1.15, 1.20 and 1.08% for each period, respectively, at 150, 195 and 240 days-old. The M+C requirements were higher than NRC (2006), probably due to cats need more sulphur amino acids to fur growth.