The objective of an experiment in vitro was to determine the activity of proteolytic enzymes produced by Bacillus C.I.P. 5832, an active ingredient of probiotic preparation PACIFLOR, and by Bacillus subtilis CCM 2216, an active ingredient of probiotic preparation AVIBION. Proteolytic activity of Bacillus C.I.P. 5832 and Bacillus subtilis CCM 2216 microorganisms was determined in relation to cultivation time in acid, neutral and alkaline media. The highest proteolytic activity was recorded in medium with pH = 7.0 in both cases, the two time curves being linear from the 72nd hour of cultivation. Proteases produced by Bacillus C.I.P. 5832 tolerate alkaline medium better (pH = 8.2) than do the proteolytic enzymes produced by Bacillus subtilis CCM 2216, and their activity is higher in acid medium (pH = 5.8). The effects of both preparations used in diets with different protein contents were determined in a trial in vivo, as exerted on broiler performance with respect to N output in droppings. An extensive comparative feeding trial was conducted on 480 sexed chick broilers of ROSS hybrid. A metabolic trial included 48 cockerels in total, four individuals per balance cage from the 21st day of age. Chicks received BR1 feed mixtures (starters) from 1st to 21st days of age, and BR2 feed mixtures from 22nd to 42nd days of age. The comparative feeding trial was a three-factor one, with replications according to the design f A - probiotic preparations (3) x f B - diets with different protein contents (2) x f C - sex (2) x (40) for growth, f A(3) x f B (2) x f C (2) x (4) for feed consumption. The metabolic trial was a two-factor one according to the design f A (3) x f B (2) x (2). The effect of Bacillus C.I.P. 5832 bacteria (a(1) +4.47%) an chick weight at 21 days of age was highly significant (P < 0.01) while the effect of Bacillus subtilis CCM 2216 bacteria (a(2) +1.70%) was significant (P < 0.1) if compared with the control (a(0)) ;Chicks receiving BR1 feeds with a protein content of 24.31% (a(0)) had the live weight higher by 14.23% at 21 days of age (P < 0.01) than chicks receiving BR1 feeds with a protein content of 20.85%. Significantly higher live weight was recorded at 35 days of life in groups of chicks receiving BR2 feeds with Bacillus sp. based probiotic preparations. Higher live weight of chicks on average for the groups (a(1), a(2)) was determined at the end of trial (+2.47% and +2.00%, resp.), but the value was not at a significance level. Highly significantly higher live weight of chicks (P < 0.01) was also determined in the second period of feeding BR2 feeds with a higher content of proteins (a(0)) Substantial positive effects of Bacillus sp. bacteria application on chick weight were observed in chicks receiving BR1 and BR2 feeds with lower contents of proteins (groups a(1)b(1), a(2)b(1)). Bacillus sp. based probiotic preparations significantly (P < 0.1) decreased BR1 mash consumption in the production period from 1st to 21st days of chick age. The lower content of proteins in BR1 feeds resulted in the highly significantly higher feed consumption per 1 kg of weight gain (b(1) +9.18% against b(0)). There was no statistically significant difference between the groups of chicks receiving feeds containing Bacillus sp. based preparations and the control. On the contrary, chicks receiving BR2 feeds with lower contents of proteins (b(1)) had the significantly (P < 0.05) lower feed consumption per 1 kg of weight gain in the production period from 22nd to 42nd days to 42nd days in comparison with the groups of chicks receiving higher contents of proteins (b(0)). Total feed consumption did not show any statistically significant difference in any of the parameters under observation. Total feed consumption was found to be lower on average in chicks receiving diets containing Bacillus sp. based probiotic preparations, mainly in feeds with lower protein contents. Average nitrogen retention was insignificantly higher in diets containing Bacillus sp. based probiotic preparations (a(1), a(2)) if compared with the control group (a(0)) This difference was in the relative range of +5.5%. A slight decrease in average nitrogen retention was determined in diets with lower protein contents. A substantial increase in nitrogen retention was observed in groups of chicks receiving a higher content of proteins in BR2 feeds containing Bacillus sp. based probiotic preparations (a(1)b(0), a(2)b(0)). The lowest average nitrogen retention was determined in the control group (a(0)b(0))- higher content of proteins without any probiotic additives. The groups (a(0)b(1), a(1)b(1), a(2)b(2)) showed higher nitrogen retention than the control (a(0)b(0)) +3.50-+4.44%, but the probiotic preparations were not found to influence retention. The groups of chicks receiving Bacillus sp. based probiotic preparations (a(1), a(2)) had by 5.81-6.31% lower N output per 1 kg of weight gain. But this difference was just at a significance level. The groups of chicks receiving BR2 feeds with lower protein contents (b(1)) had by 13.31 % lower N output in droppings in comparison with the groups receiving feeds with higher protein contents (b(0)). The difference between the groups was statistically significant at (P < 0.05). The substantially lower N output than in the control (a(0)b(0)) in droppings of chicks receiving Bacillus sp. based probiotic preparations was determined in groups (a(1)b(0) and a(2)b(0)), in BR2 feeds with higher protein contents. The effect of Bacillus sp. applied to diets with lower protein contents on this parameter was much higher.
