Influence of L-lactic acid on the efficacy of microbial phytase in broiler chickens

Two growth trials and a short-term metabolism trial were conducted in broiler chickens in the period of 22 to 42 days of age in order to evaluate the effects of two dietary levels of L-lactic acid (1.03 or 2.06 g/kg) and microbial 6-phytase (750 U/kg), added either separately or in combination, on growth rate, feed conversion, dressing percentage and utilization of selected nutrients. In the first growth trial, six different dietary treatments were added to a basal grower diet containing 19.4% crude protein and a reduced level of dietary phosphorus (P) (5.9 g total and 2.9 g non-phytate P per kg). Single administration of L-lactic acid did not show any positive effect on the growth rate or feed conversion. In contrast, phytase addition to a low-P grower diet resulted in the increased final weight of birds and higher feed conversion. This beneficial effect was markedly stronger when the microbial phytase was added to the diets containing L-lactic acid. Based on two-factor analysis of variance, microbial phytase significantly increased the mean final weight by 6.5% (P < 0.01) and significantly improved feed conversion from 1.877 to 1.829 (P < 0.05). In the second growth trial, the same six dietary treatments were added to a basal diet containing a standard level of dietary P (6.7 g total and 4.0 g non-phytate P per kg), but the level of crude protein was reduced to 17.0%. L-lactic acid alone did not show any positive effects on performance. Phytase supplementation alone resulted in numerical improvement of the final weight (+1.1-2.4%), but a higher effect was observed in the diets containing L-lactic acid. In agreement with the reduced final weights of broilers fed the low-protein diets, markedly higher values of feed/gain ratio were noted. In the metabolism trial, selected dietary treatments were involved to evaluate the effects of L-lactic acid and microbial phytase, added either separately or in combination, on the digestibility of nitrogen (N) and fat as well as on the retention and excretion of N and P. Apparent digestibility of N and fat in the low-P diets was not affected by dietary treatments. Retention and utilization of N were numerically higher in all treatments fed low-P diets when compared to the treatment fed a standard diet, but the differences were not significant. Retention of P was numerically higher in all treatments fed low-P diets. When compared to the standard diet, the combination of phytase and L-lactic acid increased daily P retention by 37.6%. P excretion was significantly (P < 0.05) reduced in all treatments fed low-P diets supplemented by both test products, either separately or in combination. A numerical decrease in N excretion was noted in both treatments fed low-protein diets.