Abstract
Supplementation of 5 ppm of ractopamine, associated or not to feed restriction in diets with a high total lysine content (1.04%) was evaluated on performance and nitrogen balance. In experiment 1, 60 hybrid castrated male swine (76.2 ± 2.3 kg) were housed in pairs according to a randomized complete block design in a factorial treatment arrangement (2 ×2 + 1) with or without ractopamine supplementation, two forms of feeding, ad libitum and feed restriction with 1.04% lysine, and an additional treatment (control), with ad libitum feed without ractopamine with 0.8% lysine, amounting to five treatments and six replications. The final live weight, daily weight gain, daily feed intake and feed conversion for 28 days were evaluated. There were improvements in supplementation with ractopamine for final live weight, daily weight gain and feed conversion. The ad libitum feeding improved both final live weight and daily weight gain compared with ractopamine. Compared with the control, there was a decrease in feed conversion with ractopamine supplementation and improvement for final weight (FW) in the treatment with the ractopamine and ad libitum feed. In experiment 2, 30 hybrid castrated male swine (74.1 ± 2.5 kg) were housed in metabolism cages and fed the same experimental treatments to evaluate the percentages of absorbed nitrogen (Nabs), retained nitrogen (Nret), nitrogen retained from the absorbed nitrogen (Nret/Nabs) and the plasma urea concentration at 14 and 28 days. At 14 days, there was an increase in the Nret/Nabs and plasma urea concentration with ractopamine supplementation. Compared with the control, there was a decrease in the plasma urea concentration for feed restriction with ractopamine. At 28 days, there was an increase in the Nret/Nabs with ractopamine supplementation. Thus supplementation with 5 ppm ractopamine improved the performance and efficiency of swine nitrogen use. Feed restriction interfered negatively in weight gain, but it improved the efficiency of the nitrogen use of barrows.
Highlights
In swine production, the finishing phase shows higher feed:gain ratios than the other phases, with a higher feed intake needed to produce one unit of meat
In experiment 1, 60 hybrid castrated male swine (76.2 ± 2.3 kg) were housed in pairs according to a randomized complete block design in a factorial treatment arrangement (2 × 2 + 1) with or without ractopamine supplementation, two forms of feeding, ad libitum and feed restriction with 1.04% lysine, and an additional treatment, with ad libitum feed without ractopamine with 0.8% lysine, amounting to five treatments and six replications
The ad libitum feeding improved both final live weight and daily weight gain compared with ractopamine
Summary
The finishing phase shows higher feed:gain ratios than the other phases, with a higher feed intake needed to produce one unit of meat. Some nutritionists recommend the use of intake restriction in the finishing phase to improve the feed:gain ratio This restriction is based on the theory that lower energy intake will improve the feed:gain ratio and will decrease carcass fat (Campbell & King, 1982; Bellaver, 1992) and nutrient elimination by excrement (Marcato & Lima, 2005). This nutritional strategy is much utilized by integrated industries that aim for results with lower intake per quantity of meat produced.
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