Effects Of Dietary Cottonseed Meal Level On Growth Performance, Health And Gossypol Residues In Meat Ducks Of 15 To 35-day-old

The study was conducted to investigate the effects of graded levels of dietary CSM on growth performance, health and gossypol residues in meat ducks of 15 to 35 day-old. Nine hundreds of 15-d old Cherry Valley male ducks were randomly allocated into 5 groups with 10 replicates per groups and 18 birds per replicates. The 5 experimental diets were formulated based on digestible amino acid to produce diets in which 0%,25%,50%,75% and 100% of protein from soybean meal were replaced with that from cottonseed meal, and the corresponding analyzed free gossypol (FG) concentration in 5 diets were 0,36.4,75.2, 110.7 and 152.9 mg/kg, respectively. On 21,28 and 35d, one bird of each replicate was chosen to blood via the jugular vein, and then euthanized by cervical dislocation to sample. Two digestible trials were conducted after growth experiment to determine the effect of dietary FG concentration on nutritent digestibility.The results showed that 1) body weight (BW), and ADG (except for d 29 to 35) linearly decreased (P<0.01) with the increase of dietary FG concentration, and the maximum limit of dietary FG based on BW at 21d,28d and 35d was 96.9,107.2 and 107.5 mg/kg, respectively, and based on ADG during 15-21d,21-28d and 15-35d was 97.8,108.9 and 107.8 mg/kg, respectively. Feed to gain ration linearly increased (P<0.01) with increasing of dietary FG content. Average daily feed intake (ADFI) of ducks fed diets containing 36.4,75,2.110.7 mg FG/kg during 15-21d,22-28d and 15-35d were significantly (P<0.01) higher than ducks fed control diet and diet containing 152.9 mg FG/kg, Using 2-slope broken-line analysis, the maximum limit of dietary FG based on ADFI (d 15 to 35) was 41.7 mg/kg (the first breakpoint) and 117mg/kg (the second breakpoint) (R2= 0.9993, P=0.0004), respectively.2) The breast meat yield of ducks fed diet containing 152.9 mg FG/kg was significantly lower than ducks fed the other 4 diets (P<0.05), and the maximum limit of dietary FG concentration based on breast meat yield was 116.9 mg/kg.3) Villus height of duodenum and jejunum at 21 and 28d of age (P<0.05), villus height of ileum and crypt depth of jejunum at 28d of age (P<0.05), and the ratio of villus height to crypt depth of duodenum at 21 d (P<0.05) and jejunum at 21 d and 28d (P<0.05) and ileum at 35d (P<0.05) linearly decreased (P<0.05) with the increase of dietary FG concentration.4) As the level of dietary FG increased, the ileal energy, crude protein, lipid, and DM digestibility of ducks from different treatments fed their corresponding diets linearly decreased (P<0.05), and the maximum limit of dietary FG content were 60.2,44.4, and 98.9 mg/kg based on ileal energy, lipid and DM digestibility. Healthy ducks from control group fed the 4 diets containing FG had a lower ileal DM digestibility than ducks fed control diet (P<0.05).5) Blood HGB, MCV and MCH content were significantly (P<0.01) affected by dietary FG concentration at 35d, and presented (P<0.01) in linear decrease. Serum alanine aminotransferase (ALT) activity and creatine content linearly increased (P< 0.05), and the ratio of aspartate aminotransferase to ALT linearly decreased (P< 0.05) with the increasing of dietary FG at 28 d of age. Serum total protein, albumin and globulin linearly decreased (P< 0.05), and the ratio of albumin to globulin linearly increased (P< 0.01) with increasing of dietary FG at 35 d of age. The maximum limit of dietary FG content based on RBC, HB, and CR were 43.1,104.3, and 109.0 mg/kg, respectively6) The total score of hepatic histopathology increased with increasing of dietary FG content.7) As the FG concentrations of the diets increased, the concentrations of gossypol in liver, kidney, heart, leg, and breast muscle linearly increased (P< 0.01), with the liver having the highest accumulation of gossypol followed by kidney, breast muscle, heart, and leg muscle. With increasing CSM-fed time, the accumulation of gossypol in liver inearly increased (P< 0.01). There was a significant interaction (P< 0.01) between dietary FG concentration and the length of gossypol intake on liver gossypol accumulation.These results suggested that the maximum limits varied from 36 to 121 mg free gossypol/kg diet depending on the parameter evaluated. However, according to ADFI, food safety and bird welfare, the safety limits of dietary FG concentration in meat ducks of 15 to 35d were 36 mg/kg.