Bioavailability determination of nutrients using linear and nonlinear models: DL-methionine vs. DL-methionine hydroxy analogue, copper sulfate vs. tribasic copper chloride

A series of studies were conducted to determine the bioavailability of nutrients in laying hens. Three studies including five experiments were conducted to determine the relative bioavailability value of DL-methionine hydroxy analogue (MHA-FA) compared to DL-methionine (DLM). One study with two experiments was conducted to compare the relative bioavailability in layers and preoxidant activity on phytase between copper sulfate and tribasic copper chloride (TBCC).; The most significant findings of the Study 1 were: (1) based on Experiment 1, the bioavailability of MHA-FA relative to DLM on a molar basis was 88.0 (egg production), 87.7 (egg mass) and 84.9% (egg weight) with the exponential model, and was 89.7 (egg production), 89.6 (egg mass) and 86.8% (egg weight) with the slope-ratio model; (2) based on Experiment 2, the bioavailability of MHA-FA relative to DLM was greater than 65% on a weight basis or 74% on a molar basis (P < 0.05). Based on the results of these two experiments, it can be concluded that the average bioavailability of MHA-FA relative to DLM was 88% on a molar basis and 78% on a weight basis.; The results of Study 2 indicated that it was difficult to detect the differences between DLM and MHA-FA because of less sensitivity of laying hens to supplemental methionine and a large variation in their response compared to broilers, and the bioavailability of MHA-FA relative to DLM was 88.9% on a molar basis or 78.2% on a weight basis based on the differences in egg weight between hens fed DLM and MHA-FA, but the relative value was not different (P > 0.05) from 100% on a molar basis or 88% on a weight basis.; The results of Study 3, in which milo-soybean diets were fed to laying hens, indicated that the average bioavailability was 122 (egg production), 109 (egg mass) and 89% (egg weight) on a weight basis, or 139 (egg production), 124 (egg mass) and 101 (egg weight) on a molar basis. All bioavailability values were not significantly different from 88% on a weight basis or 100% on a molar basis (P > 0.05), but were different ( P < 0.05) from 65% on a weight basis or 74% on a molar basis.; The main findings in Study 4 were that the bioavailability of TBCC was 134% compared to Cu sulfate and the optimal Cu supplemental level was 195 ppm for TBCC and 260 ppm for Cu sulfate based on egg weight; TBCC has less toxicity than Cu sulfate based on feed intake and TBCC is more effective than Cu sulfate at reducing losses of phytase activity during feed storage.