Effects of soybean meal source and dietary lysine level on productive performance and nutrient digestibility in broilers

Resumen

Soybean meal (SBM) is a high protein source with a good balance for amino acids (AA) and because of its high nutritive value, is usually incorporated at levels of up to 30% in broiler diets. However, although the feed industry accepts that the nutrient content of SBM is constant, these depends on variables such as origin and the conditions applied during heat processing (HP) of the beans. Therefore, 3 experiments were conducted to study the effects of SBM source and dietary lysine (Lys) level inclusion in the diet on growth performance and nutrient digestibility in broilers. In experiment 1, the objective was to compare 2 methodologies to determine acid insoluble ash (AIA) content to evaluate the total tract apparent retention (TTAR) of nutrients and metabolizable energy (ME) in broiler diets. The analytical procedures used to determine AIA were described by Vogtmann et al. (1975) and González-Alvarado et al. (2007) (coded VO and GA). The AIA contents of excretas and the TTAR of nutrients were lower with the GA than with the VO methodology. However, no interactions between diets and methodology were detected for any of the parameters studied. The GA methodology has several advantages in relation to VO methodology such as less sample size to determine the same number of analytical measurements. Therefore, GA technique may be more convenient for nutrient ileal digestibility determinations than that described by VO. The experiment 2 was designed to study the influence of the source SBM on apparent ileal digestibility of energy, nitrogen (N), and AA in broiler diets. Moreover, in vitro digestibility of dry matter (DM) and N was also determined. Therefore, 6 treatments were used, with the SBM tested as the only source of protein added. Three of the batches of SBM tested were imported from Brazil (ILH, SAN, and PAR) and 1 from Argentina (ROS). Other SBM sample, was obtained directly from the US supplier, with a previous adequate dehulling and reduce antinutritional factors processing of beans (OWE). The other SBM was obtained from soybeans from US origin but dehulled and processed in Spain (SPA). The diets were formulated to have similar energy and crude protein (CP). The CP content ranged from 50.6% for the SBM SPA to 45.2% for the SBM collected from Santos port (SAN). The AA profile varied also among SBM samples, with the highest Lys content per unit of protein for Owensboro meal (OWE, 6.26%) and the lowest for SAN meal (5.51%). The neutral detergent fiber varied from 10.8% (SAN and Ilheus, ILH) to 7.0% (SPA and OWE). The oligosaccharide content varied from 6.38% (SAN) to 4.81% (SPA) and that of sucrose from 6.70% (OWE) to 5.26% (SAN). The trypsin inhibitor activity differed among samples and was highest for ROS SBM and lowest for SPA and OWE. The inclusion of SBM with less trypsin inhibitor, oligosaccharides, and neutral detergent fiber, and more sucrose (OWE and SPA vs. SAN), improves the chicks coefficient of apparent ileal digestibility of nutrients from at 21 days of age. The in vitro assays may be used to predict successfully the in vivo digestibility of DM and CP in SBM. The experiment 3, designed to evaluate the influence of 2 SBM sources (regular from Argentina and high-protein from US) and the total Lys content in the diet on performance and TTAR of nutrients in broilers, corroborated the results showed in experiment 2. The beneficial effects of this SBM source inclusion, with high ME and AA digestibility, have consistent effects on growth performance broilers from 1 to 36 days of age and in the TTAR of DM and gross energy at 21 days of age. On the other hand, an increase in the level of Lys:ME ratio, improved the average daily gain (ADG) and the feed:gain ratio (F:G) in broilers from 1 to 36 days of age, although these effects were less evident with the age. Moreover, an interaction between SBM source and Lys:ME ratio was detected for ADG and F:G in broilers from 1 to 21 days of age, detecting that the beneficial effects of increasing the Lys:ME ratio were more evident with the regular SBM diets than with the high-protein SBM diets. From 22 to 36 days of age, it was observed higher ADG and better F:G with the medium level of Lys:ME; however, no interactions were observed between SBM source and Lys:ME ratio in this period.