Some bitter compounds show potential for decreasing feed intake and fat deposition while others improve growth and feed conversion ratio in finishing pigs

Immunocastration (IC) of pigs has often been related to increased appetite. In addition, finishing pigs divert a significant part of the dietary net energy into lipid stores resulting in excess fat deposition, poor feed efficiency and carcass downgrades. Recent findings of the physiological mechanisms around bitter taste perception have shown the potential of bitter compounds to suppress appetite (Janssen et al. 2011; Roura 2011). The current study tested the hypothesis that bitter compounds can reduce feed intake and fat deposition while improving feed conversion in IC finishing pigs.

A total of 175 Improvac^®-treated male pigs with a body weight (BW) of 65.2 ± 5.54 kg (mean ± SD) were selected and housed in individual pens. Animals were weighed and randomly assigned to one of the seven experimental diets (25 pigs per treatment). The trial was conducted over two consecutive blocks (13 and 12 pigs per treatment in blocks one and two, respectively). Animals were offered water and experimental feeds ad libitum. The seven experimental feeds consisted of a reference diet (14.6 MJ digestible energy (DE)/kg and 0.58 g available lysine/MJ DE) without (Control) or with one of the six bitter supplements: caffeine (at 0.05% inclusion) and the aqueous extracts of rhubarb (Rheum rhabarbarum L.), brassica (Sinapis alba L.), gentian (Gentiana lutea L.), quassia (Quassia amara L.) and artemisia (Artemisia absinthium L.), all of them at 0.1% inclusion. Average daily feed intake (ADFI) and average daily gain (ADG) were measured over a 5-week test period. Carcass weight, back fat depth, loin muscle depth and carcass yield were measured at slaughter. The results were analysed using the least significant difference test of the GLM procedure (SAS^®; USA).

Overall (d 0 to 35), pigs fed the diet with 0.05% caffeine had a lower (P < 0.01) ADFI and backfat deposition and tended (P < 0.1) to have a lower ADG compared to Control pigs (Table 1). Gentian and artemisia extracts resulted in a higher (P < 0.05) ADG without affecting (P > 0.1) ADFI. Similarly, rhubarb and quassia tended (P < 0.1) to increase ADG. The FCR of the pigs fed with 0.1% rhubarb, gentian and quassia extract was lower (P < 0.05) than the Control pigs. None of the treatments with significantly heavier carcass weights showed more back fat than the Control pigs. Furthermore, feeding quassia tended (P < 0.1) to increase loin muscle depth relative to the Control group. In summary, the hypothesis that bitter compounds would decrease feed intake was confirmed in the case of caffeine but not the other compounds tested. However, gentian, quassia and rhubarb extracts increased ADG and feed efficiency, a result that warrants further investigation.

Table 1.  Effects of bitter taste compounds on performance and carcass traits of finishing pigs