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Med. Weter. 73 (12), 770-773, 2017

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Małgorzata P. Majewska, Renata Miltko, Jacek Skomiał, Barbara Kowalik
Influence of humic acid supplemented to sheep diets on rumen enzymatic activity
The objective of the present study was to investigate how different levels of natural humic acid in the diet affect the hydrolases activity in the rumen of sheep. The experiment was carried out on three rumen-fistulated adult sheep. The control animals were fed a diet (K) containing 59.7% meadow hay, 28.4% crushed barley, 9.8% soybean oil meal and 2.1% vitamin mineral mixture. The experimental diets were composed of the control ration supplemented with humic acid (HUMAC natur AFM® containing 65% humic acid in dry matter) and supplied at doses of 10 g · d–1 (diet H10) or 20 g · d–1 (diet H20). Samples of rumen digesta were collected just before the morning feeding, as well as 2, 4, and 8 h afterwards. In the present study, the cellulolytic activity in the rumen digesta was higher (P < 0.01) in sheep fed the K diet than it was in animals fed the H20 ration 2 h after feeding. However, the effect of humic acid on the cellulose degradation rate depended on the content of humic acid in the diet. The cellulolytic activity was increased 2 h after feeding in sheep fed the H10 diet as compared with animals fed the H20 ration (P < 0.05). Sampling time had significant influence on the hydrolases activity in the rumen of sheep. In sheep fed the H10 ration, the cellulolytic activity was higher 8 h after feeding than it was before feeding and 4 h after feeding (P < 0.05). In the H10 and H20 groups, the xylnalolytic activity was higher before feeding, but lower than it was in the control group K. The degradation rates of xylan were decreased 2 and 4 h after feeding in sheep fed the H10 and H20 rations and then increased 8 h after feeding (P < 0.05). In sheep fed the H20 diet, the amylolitic activity 8 h after feeding was higher than it was 2 h after feeding (P < 0.05). The effect of humic acid on the hydrolases activity in the rumen of sheep is not uniform and depends on the quantity of humic acid in the diet and on sampling time. Humic acid present in commercial HUMAC natur AFM® product enhances the initial rate of cellulose degradation in the rumen at a dose of 10 g · d-1. Thus, it may suggest that humic acid stimulates the growth of fibrolytic microorganisms in the rumen. On the other hand, the present results suggest that humic acid may reduce the rate of carbohydrate degradation in the rumen, since a higher hydrolases activity was observed before morning feeding and 8 h afterwards....
Key words: humic acid, hydrolases, rumen, sheep