Impact of Ractopamine on Whole-Body and Carcass Growth and Efficiency in Pigs Reared Under Moderate Heat Stress

Abstract Text:

Paylean® (PLN, Ractopamine) is one of the most important dietary tools available to counteract the growth depressing effect of heat stress in pigs. This study was conducted to provide quantitative data for financial evaluation of PLN in growing pigs reared under moderate heat stress. A total of 2170 PIC terminal castrate and female pigs (91.5 ± 0.5 kg) were used in a growth assay to approx. 123 kg (±.6 kg).  Pigs were placed in a commercial research facility (May/June), blocked by gender, stratified by weight and allocated (22 pigs/pen, with 0.74 m²/pig) to diets either devoid of PLN (CON) or with 5 ppm PLN for the first 21 d followed by 8.8 ppm of PLN for the last 18 d on feed (50 pens/treatment). Environmental controls were manipulated to establish upper and lower temperature limits of 30.1 C and 25.6 C respectively. Acclimatization began 10 d prior to initiation by elevating temperature 0.56 C/d from an initial set point of 21 C.   Temperature tended to be at or near maximum 16-18 h/d. Diets were composed of corn, soybean meal, corn ddgs (18.0%) and cwg fat (2.5%). SID lysine content of CON and PLN diets was 0.76 and 1.01% respectively; days on test averaged 39.3 d for CON and PLN pigs (range of 27-44 d).  Average feed intake was greater for CON pigs (2.644, 2.595 kg/d; P=0.062), but whole-body (WB) ADG and G:F ratio were greater (P<0.001) for the PLN group (0.871 kg/d, 0.336 kg/kg) as compared to CON pigs (0.789, 0.298).  Final WB weight (124.9 vs 121.6 kg, P<0.001) and carcass dressing %, based on farm WB weight, was improved by PLN (75.0 vs 73.8 %, P<0.001). This resulted in a carcass gain of 4.0 kg/pig (26.3 vs 22.3 kg, P<0.001), on a time constant basis. Carcass ADG and G:F ratio was computed as the difference between estimated initial carcass weight (0.74 x WB weight) and plant carcass weight.  PLN improved (P<0.001) ADG and G:F ratio respectively (0.669 kg/d, 0.268 kg/kg), compared to the CON group (0.568, 0.215). PLN also improved (P<0.001) FOM lean (53.1 vs 51.7%), which was the result of improvements in both FOM fat and FOM loin depth (-2.1, +3.4 mm), thereby suggesting improved saleable meat.    Thus, PLN improved carcass growth (4 kg/pig), under conditions of moderate heat stress, to an extent that is unparalleled by any reported nutritional technology.

Keywords:

Heat stress, growth, ractopamine