Effect of Dietary Soy Galactooligosaccharides on Performance, AME, Nitrogen Retention and Excreta Moisture of Broiler Chickens

Introduction. The indigestible soy galactooligosaccharides (GOS) stachyose and raffinose are considered anti-nutritional factors in poultry because they decrease the metabolizable energy of soy protein (Leske et al., 1993) and decrease performance (Jiang et al., 2006). The objective was to investigate if there was a dose-response effect of increasing levels of the soy GOS raffinose and stachyose in feed on performance and gastrointestinal health including AMEn, nitrogen retention and excreta moisture in young chickens. It was hypothesized that increasing levels of GOS would negatively impact performance, AMEn, nitrogen retention and excreta moisture. Results of intestinal morphology and permeability, ceca microbiome and cell immunology have been published previously.

Material and methods. 400 d-old Cobb 500 male chickens were placed in 50 battery cages (8 birds/cage; 0.04 m2/bird) and enrolled in a 21-d trial utilizing a randomized complete block design. Replicate cages were assigned to one of five treatments: a control diet based on soy protein isolate (SPI) devoid of soy GOS or the same SPI diet with 0.9, 1.8, 2.7 or 3.6% added GOS (a 4:1 ratio of stachyose and raffinose, as found in soybean meal). Birds had ad libitum access to feed and water. Body weight (BW) and feed consumption were recorded on d0, 7, 14 and 21 of trial for calculation of body weight gain (BWG, feed intake (FI) and feed conversion ratio (FCR). FI and excreta output were measured from d12-14 and d18-21 and homogenous excreta samples were collected to determine nitrogen retention and AMEn. The d14 excreta sample were also submitted for moisture analysis. Data were analyzed by one-way ANOVA. Means were compared by Tukey’s multiple comparison test. Linear and quadratic regressions were used to investigate the dose-response of GOS in diets. Differences considered significant at P< 0.05.

Results and discussion. From d0-21, BWG increased quadratically (P< 0.05) as dietary GOS increased, with maximum value of 1.264 kg at 2.27% GOS. Feed intake and FCR increased linearly (P< 0.01), with a 3-point increase from birds fed SPI to 3.6% GOS. At d14, excreta moisture increased linearly (P< 0.01) with increased dietary GOS. AMEn increased quadratically (P< 0.05) with increased dietary GOS, with maximum value of 4,073 kcal/kg DM at 1.61% GOS and both linear (P< 0.01) and quadratic effects (P< 0.01) were observed for nitrogen retention (maximum value: 70.20% at 1.24% GOS). At d21, AMEn increased according to a quadratic regression (P< 0.01) with maximum value of 3,911 kcal/kg DM at 1.44% GOS, whereas nitrogen retention decreased linearly (P< 0.01) with increased dietary GOS.

Conclusions. In conclusion, results from this trial indicate that soy GOS have dose-dependent effects on the performance, nitrogen retention, AMEn and excreta moisture in broiler chickens from d0-21.

Implications. This is the first dose-response study in chickens with stachyose and raffinose together. Its main application will be in young chick feeding, since these findings will help nutritionists ascertain the maximum level of soy GOS that they should ideally have in starter diets.

Keywords. Soy galactooligosaccharides; AMEn; nitrogen retention; excreta moisture; broilers.

References. Leske, K et al. 1990. Poult. Sci. 69:787–793; Jiang H et al. 2006. Br. Poult. Sci. 47:516–522.