Effects of different protein levels and starch-to-fat ratios in diets on growth performance, slaughter performance, and nutrient digestibility of geese

The study was performed to explore the impacts of varying protein levels and starch-to-fat ratios (SFR) in diets on the growth performance, slaughter performance, and nutrient digestibility of geese. Three hundred sixty healthy 28-day-old geese with similar weight were selected and divided into 6 groups, with 6 replicates of 10 geese in each group. A 2 × 3 two-factor complete randomized design was applied, and the geese were fed diets with the same apparent metabolizable energy, two protein levels, and three starch-to-fat ratios. The protein levels were 16.5% (HP) and 14.5% (LP), and starch-to-fat ratios were 20:1, 11:1, and 5:1 respectively. The findings reveal the following: 1) The body weight (BW) of 63-day-old geese in the SFR_5:1 group was significantly higher than in the other two groups (P < 0.05). The average daily gain (ADG) from 28 to 63 days in the SFR_5:1 and SFR_11:1 groups was significantly higher than that in the SFR_20:1 group, and the average daily feed intake (ADFI) was notably lower than that in the SFR_20:1 group (P < 0.05). The feed-to-gain ratio (F/G) from 28 to 63 days in the SFR_5:1 group was significantly lower than in the other two groups (P < 0.05). 2) The skin and subcutaneous fat thickness (SSFT) was increased significantly in the SFR_5:1 group compared to SFR_20:1 and SFR_11:1 groups (P < 0.05). 3) The digestibility of phosphorus was significantly higher in the 14.5% protein level group than that in the 16.5% protein level group, while crude ash digestibility showed the opposite trend. The digestibility of crude fat was significantly higher in the SFR_11:1 and SFR_5:1 groups compared to SFR_20:1 group (P < 0.05). Moreover, the SFR_5:1 group significantly reduced the digestibility of crude ash, calcium, energy, and dry matter (P < 0.05). In conclusion, a diet with a starch-to-fat ratio of 11:1 and a protein level of 14.5% is recommended for formulating feed for geese aged 28-63 days.