-The objectives of this study were to determine the chemical composition of vegetable and mixed crude glycerin and digestible energy to and evaluate different inclusion levels in rabbit feeding. A total of 108 rabbits were used in the digestibility assay, assigned in a completely randomized design into nine treatments, one reference diet plus eight test diets, where the glycerin types were included at levels of 4, 8, 12 and 16%, replacing the reference diet roughage. In the performance assay, 180 rabbits were assigned to a completely randomized design into a 2 × 4 factorial arrangement (two types of glycerin and four levels of inclusion: 3, 6, 9 and 12%) plus a reference diet and ten replications. The vegetable and mixed crude glycerin showed digestible energy of 5,099 and 4,953 kcal/kg of dry matter, respectively. Although feed intake decreased linearly with the growing inclusion of both kinds of glycerin during both evaluated periods (from 32 to 50 and 32 to 70 days), performance losses occurred only with the inclusion of vegetable crude glycerin. The inclusion of mixed crude glycerin up to 12% allowed similar animal performance to the reference diet up to 50 days, unlike vegetable crude glycerin, for which inclusions over 6% in the diet resulted in poorer performance compared with that obtained with the reference diet. In the total period, differences were not observed for live weight or weight gain of the animals fed both glycerin types. Carcass weight decreased linearly with the inclusion of both glycerin types, with lower values compared with the reference diet only for the two highest levels of glycerin inclusion. Mixed crude glycerin can be included up to the maximum level studied (12%), while vegetable glycerin can be added up to 6% in the diet of growing rabbits.
This study was designed to measure the responses of Dekalb laying hens to three amino acids such that the optimum economic amino acid intakes of these hens could be determined, taking into account variation in body weight and potential egg output in the population as well as changes in egg revenue and feed price. Three experiments were conducted with Dekalb White laying hens during the period from 33 to 48 weeks of age, with each trial being divided into four periods of 28 days. Responses were measured to intakes of lysine, methionine + cysteine and threonine. The laying hens were distributed in a completely randomized design among eight treatments and six replicates. The treatments consisted of increasing levels of each of the amino acids under test to obtain a response curve. These levels were obtained using a dilution technique, and a control treatment was included to confirm that responses were due to the test amino acid. Egg production (%), feed intake (g), body weight (kg), egg output (g/day) and egg weight (g) were measured. The control treatment confirmed that the amino acid under test was limiting in each assay. The Reading model was fitted to the data in each trial using the relevant amino acid intakes and egg outputs. The coefficients of response obtained were 8.58 mg/g, 7.96 mg/g and 6.73 mg/g egg output, and 36.6 mg/kg, 50.8 mg/kg and 37.2 mg/kg body weight for lysine, methionine + cysteine and threonine, respectively. Assuming a maximum egg output of 55±12.5 g/day, an average body weight of 1.45±0.2 kg and a cost ratio of the amino acid (c/mg) and egg (c/g) of 0.0023 (lysine), 0.0025 (methionine + cysteine) and 0.0034 (threonine), the optimum economic intakes of each amino acid under current Brazilian conditions were 746, 717 and 593 mg/bird/day for the three amino acids, respectively.
-Two experiments were carried out to evaluate, respectively, nitrogen balance (NB) and the productive performance of 31-to-50-day-old rabbits subjected to different levels of lysine and methionine+cystine (met+cys). Seventy-five animals were randomly distributed in 5 × 3 blocks (five levels of lysine: 5.5, 6.5, 7.5, 8.5 and 9.5 g/kg combined with three levels of met+cys: 5.0, 6.0 and 7.0 g/kg), with 15 treatments and five replications for the NB assay. The assay lasted 14 days: 10 days for acclimatization and four days for feces and urine collection. Increasing met+cys levels had a quadratic effect on the nitrogen excreted in urine (NU): the lowest excretion was found at the dietary level of 5.9 g/kg met+cys. Increasing lysine levels also affected NU and nitrogen retained daily (NR): the lowest NU was obtained at the dietary level of 7.28 g/kg lysine, and maximum NR was found at 7.24 g/kg lysine. Increases in met+cys levels in the diets affected neither performance nor carcass characteristics of rabbits up to 50 days of age. On the other hand, body weight at 50 days, daily weight gain and feed conversion of rabbits slaughtered at 50 days had a quadratic effect as the lysine levels increased. The best results were found at 7.5, 7.38 and 7.36 g/kg lysine. Lysine and met+cys levels of 7.4 and 5.0 g/kg in the diet are recommended for 31-to-50-day-old rabbits.
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