Two experiments were conducted to investigate the effects of various standard ilealdigestible (SID) lysine (Lys) levels and SID threonine (Thr) to Lys ratios on the performanceand carcass characteristics of finishing gilts receiving low crude protein (CP) diets supplementedwith crystalline amino acids (CAA). In Exp. 1, 108 gilts (87.8 ± 5.9 kg) were randomlyallotted to one of six diets which consisted of a high CP (135 g/kg) diet with 6.1 g/kg SIDLys or five low CP (100 g/kg) diets providing SID Lys levels of 4.9, 5.5, 6.1, 6.7 and 7.3 g/kg,respectively. Gilts were housed in three pigs per pen with six pens per treatment. At theend of the 28 days experiment, 36 gilts (one pig per pen) with average body weight (BW)of 116 kg were killed to evaluate carcass traits. The SID Lys levels required to maximizeaverage daily gain (ADG) and optimize feed conversion ratio (FCR) as well as to minimizeserum urea nitrogen (SUN) levels were 5.7, 5.8 and 6.1 g/kg using a linear-break point modeland 6.5, 6.5 and 6.6 g/kg using a quadratic model. The fat-free lean gain tended to increaselinearly with the increase in dietary SID Lys levels from 4.9 to 7.3 g/kg when gilts receiving alow CP diet (linear effect, P=0.06). In Exp. 2, 90 gilts (90.6 ± 5.7 kg) were utilized in anotherdose–response study. Based on the Lys requirement estimated in Exp. 1, dietary treatmentswere formulated to contain 5.1 g/kg SID Lys to ensure the dietary Lys level was marginallydeficient for late finishing gilts. Graded levels of crystalline Thr (0, 0.3, 0.6, 0.9 or 1.2 g/kg)were added to the basal diet providing SID Thr to Lys ratios of 0.54, 0.60, 0.66, 0.72 or 0.78,respectively. Each diet was fed to six pens with three gilts per pen. At the end of Exp. 2, 30gilts (one pig per pen) were slaughtered to evaluate carcass traits (average BW = 118 kg).The optimum SID Thr to Lys ratios to maximize ADG and FCR as well as to minimize SUNlevels were 0.61, 0.63 and 0.64 using a linear-break point model and 0.70, 0.75 and 0.74using a quadratic model. With the exception of L* light (linear effect, P<0.05), no effect oncarcass characteristics was observed with increasing dietary SID Thr to Lys ratio
การแปล กรุณารอสักครู่..
