Abstract
The aim of this thesis is to obtain basic information on the activity of carbohydrase enzymes over viscous cereals or conventional no viscous diets based on corn and soybean meal. The effects of enzymes supplementation in broiler chickens productive and digestive parameters will be also evaluated.In particular, in the case of the white cereals (barley and wheat), we have studied initially the effectiveness of b-glucanase and arabinoxylanase on the productive performances (Feed intake, bodyweight gain) and nutrient digestion in growing chicks; and the possible mechanisms involved, like the digesta kinetics and viscosity. Two experimental trials are presented.
Male chickens received 4 experimental diets based on 44% of barley + wheat (2 x 2; with or without enzymes, with or without 2% of sepiolite) during an experimental period of 36 days. Two balances of organic matter (OM), crude protein (CP) and fat (EE) were carried out on days 21-22 and 41-42 of age. The enzymes supplementation improved the daily weight gain of the animals and the food: gain ratios, mainly during the first phase (14%, P<0.001 and 10%, P<0.001; respectively). Productive results were simultaneous to significant increases of the whole-tract digestibility and retention of organic components, (5.6 and 1.7 percent units), especially the fatty fraction (13 and 3.5 percent units) on day 22 and 42, respectively.
The second experiment aimed to characterise the possible mechanisms involved. They were studied i/ the digesta mean retention time (MRT estimated from the faecal excretion of an indigestible marker or from its quantification in the animal digestive tract in steady state conditions) and ii / the jejunum and ileum digesta viscosity.
Productive results were similar to those of the first trial. Although, not significant differences were observed in food consumption, enzymes supplementation increased growth rates (+5%, P<0.05), and improved the FCR (7%, P<0.01). It was also observed a significant increase of the OM digestibility (CP, 6 percent units, P<0.001; EE, 6 percent units, P<0.05 and carbohydrates, 2.5 percent units, P<0.05) and metabolizable energy (EMAn: 5.4% from 3110 to 3280 Kcal / kg DM food). The enzymatic suplementación significantly reduced intestinal digesta viscosity (jejunum and ileum) and digesta MRT in the digestive tract.
Enzymatic supplementation in broilers feeding has expanded mainly as the b-glucanase and arabinoxylanase inclusion in «viscous» cereal diets. However, recently numerous expectations are being incorporated in poultry feeding, addressed by the search of enzymatic strategies to improve the nutritive value of leguminous in general, and soybean meal in particular. In this line, we planed to characterise «in vitro» and «in vivo» the effectiveness of different carbohydrase enzymes on the digestion of soluble and insoluble soybean meal polysaccharides.
We designed a first trial to characterise soybean meal carbohydrates (cotyledons and hulls). Fractionation (Water soluble and Water insoluble) of soybean hulls showed the existence of an insoluble structure mostly constituted by cellulose (b-1,4-D-glucose), while the soluble fraction contains a higher proportion of mannose and galactose (possibly b-manans of galacto- and gluco-manans type). Fractionation of cotyledons showed the existence of complex structures composed by a matrix of pectins, hemicellulose and cellulose. The "in vitro" incubation with pectinase, xylanase and cellulase enzymes released a low percentage of monosaccharides, but increased (until 20%) after cell wall fractionation.
Knowing the effect of toasting on SBM protein solubility and digestibility, the second experiment aimed to establish relationships between toasting (low and severe) and the "in vitro" enzymatic efficiency, especially of protease and different carbohydases. Effectively, toasting soybean caused gradual decreases in protein and carbohydrate solubility, indicating structural changes of the carbohydrate matrix in their relationship with proteins. Both, water-soluble and water-insoluble fractions were incubated with carbohydrases (pectinase, xylanase, mannanasa and cellulase) in combination or not with protease. Incubation of the soluble substrates with carbohydrases (especially cellulase and pectinase) reduced raffinose and stachyose. Similar results were not observed with mannanase. Incubations of the water-insoluble fractions released a low monosaccharide quantity, but sinergycally increased with the simultaneous incubation with protease.
However other aspects that cannot be simulated "in vitro" will affect efficiency of enzymes "in vivo" associated to the animal gastro-intestinal conditions. Then, we decided to check in "in vivo" trials the possibility of improving productive and digestive performances in broilers. In a first trial, we proved the effects of incorporating to a corn-soybean meal diet a mannanase enzyme (at two inclusion levels) associated or not with protease. Experimental design was similar to that described above for the b-glucanase and arabinoxylanase trial. Enzymes supplementation didn't cause significant modifications on productive or digestive results. However, mannanase incorporation significantly reduced the ileum microbial content (measured as purine bases concentration, during the first phase of chicken's growth). Although the experience was carried out in cages, and the not differences in the productivity observed, we think interesting to evaluate the productive and health impact of this effect on the microbial colonisation of small intestine digesta, especially under practical conditions.
| Date of Award | 26 Sept 2001 |
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| Original language | Spanish |
| Supervisor | Jose Francisco Perez Hernandez (Director) |