2.2. Animals and experimental design
The protocol of this study was approved by the Institu- tion Animal Care and Use Committee at Zhejiang Univer- sity. And, the animal trial was conducted in accordance with the National Institutes of Health guidelines for the care and use of experimental animals.
A total of 160 crossbred barrows (Duroc Landrace Yorkshire) with an average body weight of 66.107 1.01kg were selected (Anji Zhengxin Breeding Farm, Zhejiang,China). The pigs were blocked by initial BW and assigned to pens with 10 pigs per pen. Pens were randomly assigned within block to 4 dietary treatments with 4 replicates per treatment. The pigs were housed in 3.25 5.25 m pens with concrete floors. Feed was pro- vided ad libitum and water was provided by nipple water- ers. The duration of the feeding trial was 35 d. The ADG, ADFI, and G:F were determined throughout the experi- mental period. Pigs received the basal diet (Table 1) supplemented with 0, 100, 200, or 400 μg/kg of Cr from CNP-Cr. The basal diet, which consisted primarily of corn, soybean meal, and wheat bran, was supplemented with minerals and vitamins to meet or exceed NRC (1998) requirement estimates. To minimize potential variation that can occur with multiple diet mixings, a single batch of basal diet was prepared. Approximately the first 5