Effects of addition of benzoic acid in growing-finishing pig feed on performance and ammonia emission

An experiment was carried out with 120 fattening pigs (60 females and 60 castrated males) from 30 to 115 kg liveweight.They were shared into three groups of 40 pigs in order to evaluate the effect of the incorporation of benzoic acid in the diet on performance and ammonia emission. Two levels of incorporation were compared to a control diet, i.e. 0.5% and 1% of benzoic acid. The pigs were split up according to entry weight and sex. Individual weights were measured, at the beginning then each 6 weeks till slaughter. Feed composition was in accordance to CORPEN requirements i.e. 16.5% protein during the growing stage (under 65 kg weight) and 15% protein in the finishing period (from 65 kg to slaughter, close to 115 kg). The pen floor was made of concrete slats on the whole area and the slurry was stored in separate pits during the whole fattening period. The air entered through a perforated ceiling was extracted under the floor through a chimney. No significant effect of benzoic acid was observed on Average Daily Gain and on feed conversion ratio. But a significant effect of treatment was observed with the 1 % level on ammonia concentration in the air and on ammonia emission per pig per day. Adding 1% of benzoic acid to the feed of growing-finishing pigs led to a reduction of ammonia emission, i.e. 200 g per pig when compared to the control group. Urinary pH, measured during the whole fattening period, was also significantly affected : 1 point lower than for the control group. This decrease of urinary pH was assumed to be one of the reasons explaining the reduction of observed ammonia emission.