Agricultural waterfowl have certain biological characteristics: intensive metabolism and rapid growth, early maturity and signifcant reproduction potential, high body temperature, and resistance to many infectious diseases. The article presents the results of an experimental study of the effect of the exogenous enzyme preparation Hemicell® HT (1 kg contains the active ingredient β-mannase - 160x106 units) on the productive qualities of young goslings of Shadryna and Italian breeds. To achieve this goal, four experimental groups of goslings were formed: Group 1 - control, 2, 3, 4 - experimental, which were fed the enzyme preparation Hemicell® HT as part of a complete feed mixture - 150 g for the second experimental group, 250 g for the third and 310 g for the fourth experimental group per 1 tonne of fodder. It was found that the introduction of the exogenous enzyme preparation Hemicell® in the above doses into the diet of young geese signifcantly affects the growth rate of young geese and metabolic processes in their bodies. If at the end of the frst decade the most positive effect on the body was found in low and high dos- age of the enzyme preparation (birds of the 2nd and 4th groups), as a result of which, compared to the analogues of the 1st control group, the difference in the average daily gain was 3.4 and 2.8 g (p<0.001), then the average dosage of the enzyme preparation in the analogues of the 3rd experimental group provided a difference of only 1.1 g (p<0.01). However, by the end of the frst rearing period (up to 21 days), the highest average daily weight gain was observed in geese of the 3rd experimental group compared to the analogues of the control, 2nd and 4th experimental groups. Thus, while the average daily weight gain in geese of the 1st control group was 43.1 g, this fgure was 2.6 g higher in the 2nd group (p<0.01), 5.1 g in the 3rd group and 3.6 g in the 4th group (p<0.001). This pattern was maintained until the end of the experiment, with signifcant differences in goslings of the 3rd experimental group compared to the control: at the age of 31 days - by 9.7 g (p<0.01), 41 days - by 10.1 g (p<0.05), 66 days - by 9.2 g (p<0.05). In geese of the 2nd and 4th groups, the average daily weight gain was higher than in the control group, but did not have significant differences during the same age period. As a result, in general, the average daily weight gain of goslings of the 1st control group was 59.9 g, in the 2nd experimental group it was 3.1 g (p<0.01), or 5.2%, in the 3rd - 6.6 g (p<0.001), or 11%, and in the 4th group - 4.2 g (p<0.001), or 7.0%, compared to the same indicator of the control. The use of the enzyme preparation had a positive effect on the goslings' organism, which made it possible to realise the genetic potential of goslings' productivity at a higher level in all experimental groups, but the highest growth rate was observed in the 3rd experimental group of geese. Key words: geese, Shadryna breed, Italian breed, enzyme preparation, Hemicell® HT, weight gain, live weight.