Apparent ileal digestibility of amino acids in protein feedstuffs and diet formulation based on total vs digestible lysine for poultry

Abstract

A digestibility experiment was carried out with 140 Ross-broiler chickens (age 24 days) to determine coefficient of ileal apparent digestibility (CIAD) of amino acids in meat and bone meal (MBM), full-fat soyabeans (FFSs), soyabean cake and meal, full-fat rapeseeds, and rapeseed cake and meal. The birds were fed semi-purified diets which contained protein feedstuffs as a sole protein source and chromium mordanted straw as an indigestible marker. The CIAD of nutrients were assessed using the slaughter technique. A 37-day growth experiment was carried out with 2880 Ross-broiler chickens to compare feed formulation systems based on apparent ileal digestible or total lysine content. Three barley based diets were formulated to be similar in total lysine content (9.5 g/kg feed). Diet 1 contained soyabean meal (SBM) (280 g/kg DM), Diet 2 SBM (180 g/kg DM) and rapeseed meal (RSM) (171 g/kg DM) and Diet 3 a combination of SBM (78 g/kg DM), RSM (172 g/kg DM) and MBM (87 g/kg DM). The composition of Diets 4 and 5 was similar to that of diets 3 and 4, respectively, except that they were supplemented with l-lysine–HCl to obtain a similar apparent ileal digestible lysine content as in Diet 1 (7.9 g/kg feed). The total lysine content of Diets 4 and 5 was 10 g/kg feed. Furthermore, Diet 1 was supplemented with l-lysine–HCl to obtain Diet 6, in which the total and apparent ileal lysine contents were 10 and 8.5 g/kg feed, respectively. CIAD of lysine, methionine, threonine and cystine were respectively 0.60, 0.66, 0.48 and 0.34 for MBM; respectively 0.81, 0.75, 0.68 and 0.67 for FFSs; respectively 0.86, 0.86, 0.76 and 0.62 for soyabean cake; respectively 0.85, 0.84, 0.74 and 0.63 for SBM; respectively 0.59, 0.59, 0.43 and 0.53 for full-fat rapeseeds; respectively 0.68, 0.81, 0.64 and 0.53 for rapeseed cake; and respectively 0.63, 0.75, 0.54 and 0.43 for RSM. Final weight and growth rate were highest when digestible lysine based feed formulation was used compared to that based on total lysine ( P<0.001). The increase in final weight was largest for diet containing MBM and formulated based on digestible lysine ( P<0.001). In addition, the proportion of breast muscle of total live-weight and weight of breast muscle increased ( P<0.05) in animals fed diets formulated on the basis of digestible compared to total lysine. However, diet formulation based on digestible lysine impaired feed conversion ratio compared to that of total lysine for birds fed SBM as the sole source of supplementary protein compared to diets containing rapeseed or MBM ( P<0.01). Growth rate and final weight were higher in birds fed diets containing SBM alone compared to those also containing RSM and MBM ( P<0.001). In addition, the effect of diet formulation based on digestible lysine on performance results of broilers was more obvious in males than females ( P<0.05). The results indicated that formulation of diets based on a digestible lysine was better than that based on total lysine when diets contained protein sources of low amino acid digestibility such as meat and bone and RSMs.