• Aucun résultat trouvé

Effects of live yeast on the fatty acid biohydrogenation by ruminal bacteria

N/A
N/A
Protected

Academic year: 2021

Partager "Effects of live yeast on the fatty acid biohydrogenation by ruminal bacteria"

Copied!
1
0
0

Texte intégral

(1)

EFFECTS OF LIVE YEASTS ON THE FATTY ACIDS BIOHYDROGENATION BY RUMINAL BACTERIA

Annabelle TROEGELER, Jean-Philippe MARDEN*, Corine BAYOURTHE*, Raymond MONCOULON*, Francis ENJALBERT

Ecole Nationale Vétérinaire de Toulouse, Département Elevage et Produits, Laboratoire d’Alimentation, BP 87614, 31076 Toulouse cedex 03, France. E-mail : a.troegeler@envt.fr *Ecole Nationale Agronomique de Toulouse, Laboratoire de Zootechnie, 31076 Toulouse cedex 03, France.

Ruminants only absorb a little part of dietary unsaturated fatty acids, because rumen microorganisms hydrolyse the dietary triacylglycerols and then hydrogenate the unsaturated fatty acids. Ruminal biohydrogenation (BH) of linoleic acid (C18:2) comprises three steps: isomerisation to conjugated linoleic acids (CLA), mainly cis9,trans11 (CLAc9t11) and

trans10,cis12 (CLAt10c12) isomers; hydrogenation of CLA to trans monoenoic acids

(C18:1t), mainly trans11 and trans10 isomers; and finally hydrogenation of C18:1t to stearic acid (C18:0) (Figure 1). Unsaturated fatty acids, and some intermediates of BH like CLA could have beneficial dietetic properties for consumer.

Addition of live yeasts in high concentrate diets for ruminants has proved to maintain the ruminal pH above 6, this pH favouring BH. Moreover, yeasts improve the growth of the

Megasphera elsdenii population in the rumen, which is able to isomerise C18:2 to CLAt10c12,

and so favour trans10 isomers.

The objective of this study was to examine the effects of live yeasts on ruminal BH in dairy cows receiving a low fibre diet without added fat.

Figure 1: Ruminal biohydrogenation of linoleic acid.

Materials and methods: Three ruminally fistulated dairy cows were given three diets based on

maize silage (control diet, control diet + 0.5g/d or control diet + 5.0g/d of Saccharomyces

cerevisiae NCYC SC47), according to a Latin Square design. Ruminal contents were sampled

and liquid and solid phases were separated through a 0.25mm sieve. Fatty acids profiles were obtained by gas chromatography.

Proportions of fatty acids (% of total fatty acids) in the rumen contents were statistically analysed with analysis of variance. Effects included diet, period, cow, and ruminal phase. Contrasts between control and both yeast diets, and between the two yeast diets were computed. Differences were considered significant at P < 0.10, and as a tendency when 0.10 < P < 0.15.

Results:

The addition of yeasts led to a greater pH than control diet, and maintained pH above 5.5 and 5.9 respectively for 0.5g and 5.0g added yeasts (Figure 2). With the added yeast diets, there was a significant decrease of the proportions of some saturated fatty acids: C14:0 (myristic acid), C15:0, C17:0, C18:0 (stearic acid), and C18:1c11 and C18:1t16 (Table 1). On the other hand the proportions of C18:2 and C18:1c9 (oleic acid) significantly increased (respectively by 32 % and 16 %), and that of CLAc9t11 tended to increase. No difference was observed between the two doses of yeasts.

5,00 5,20 5,40 5,60 5,80 6,00 6,20 6,40 6,60 6,80 -1 0 1 2 3 4 5 6 7 8 hours / meal pH Control 0,5g of yeasts 5,0g of yeasts

Figure 2: Effects of 0.5 or 5 g/d of live yeasts on the evolution of ruminal pH .

Liquid ruminal phase Solid ruminal phase P

Fatty acids control 0.5 g/d of yeasts 5.0 g/d of yeasts control 0.5 g/d of yeasts 5.0 g/d of yeasts SEM Control vs yeast diets 0.5 vs 5.0 g/d added yeasts C14:0 C15:0 C16:0 C17:0 C18:0 C18:1c9 C18:1c11 total C18:1t C18:1t9 C18:1t10 C18:1t11 C18:1t12 C18:1t13+14 C18:1t15 C18:1t16 C18:2 CLAt10c12 CLAc9t11 C18:3 2.94 1.11 15.24 0.50 39.35 4.67 1.81 11.42 0.45 1.72 4.23 0.90 1.92 0.62 0.62 6.66 0.07 0.09 1.01 1.81 1.02 15.00 0.47 37.54 5.44 1.33 11.49 0.49 1.59 4.44 0.99 1.80 0.63 0.57 7.52 0.12 0.14 1.06 1.49 0.98 14.96 0.44 35.68 5.62 1.18 12.16 0.49 1.74 4.61 1.04 1.96 0.68 0.59 7.74 0.08 0.13 1.04 1.21 0.74 14.66 0.43 31.83 9.55 1.42 8.77 0.35 1.30 3.72 0.66 1.36 0.46 0.27 17.68 0.16 0.21 2.65 1.05 0.71 15.06 0.39 25.82 12.49 1.44 7.38 0.30 0.85 3.61 0.55 1.07 0.39 0.11 23.50 0.16 0.24 2.85 0.87 0.68 15.09 0.38 25.00 12.57 1.44 7.96 0.34 0.90 3.99 0.60 1.15 0.44 0.00 23.52 0.17 0.26 3.03 0.27 0.05 0.16 0.01 1.95 0.46 0.16 0.80 0.03 0.21 0.57 0.06 0.11 0.04 0.07 1.23 0.04 0.03 0.13 0.011 0.097 0.607 0.050 0.027 0.001 0.089 0.627 0.937 0.225 0.715 0.789 0.154 0.872 0.053 0.013 0.568 0.154 0.165 0.387 0.467 0.995 0.323 0.512 0.789 0.644 0.451 0.535 0.664 0.641 0.427 0.279 0.284 0.499 0.923 0.764 0.978 0.539

Table 1: Effect of 0.5 or 5.0 g/d of live yeasts on the fatty acids profile (% of total fatty acids) of the liquid and solid ruminal phases.

Discussion:

Contrarily to what could be expected due to a higher pH and a possible increase of

Megasphera elsdenii activity, the addition of yeasts did not increase the extent of BH nor

favour trans10 isomers: the increase of C18:2 and C18:1c9 and the decrease of C18:0 proportions reflected an inhibition of the BH of unsaturated fatty acids, and no effect was noticed on CLAt10c12 and C18:1t10. Possible explanations are:

1. The diet used in this experiment did not provide enough long fibre to improve the growth of cellulolytic bacteria, which produce BH enzymes, so that the extent of BH was limited even if the pH was maintained near 6.

2. The trans10 isomers BH pathway needs both a competent Megasphera elsdenii population and a low pH in the rumen or/and a high starch supply.

Conclusions:

The addition of live yeasts in the ration of dairy cows can increase the proportion of unsaturated fatty acids in the rumen content by lowering the extent of fatty acids BH. This could be a way to increase their proportions in milk, without increasing trans10 isomers. However, more investigations are necessary to confirm this point and the effects on milk fat composition.

Références

Documents relatifs

The evolution of common bacterial PLFAs ( Table 3 , Fig. 3 ) showed high values of saturated and unsaturated fatty acids dur- ing the first month (phase I); their progressive

Heating leads to a lipid peroxidation, which could reduce the amount of fatty acids subjected to biohydrogenation and produce peroxides which could act directly on this reaction..

The use of olive cake, citrus pulp and wheat straw silage in dairy ewes feeding reduced the level of milk saturated fatty acids that are considered to raise plasma cholesterol,

The ratio between linoleic and linolenic acids was higher (P = 0.001) in milk from stall-fed ewes.These results indicate that the ewe feeding system strongly affects milk fatty

Post-prandial evolution of polysaccharidase activities in the rumen of dairy goats fed a high- concentrate diet was similar to previous observations, and yeast ruminal

Enriched n-3 polyunsaturated fatty acid diet modified oocyte lipid composition and may influence oocyte quality in Prim Holstein dairy cows.. Annual Meeting AETE, Sep 2018,

VA consumption was also associated with an accumulation of cis-9, trans-11 conjugated linoleic acid (rumenic acid; RA) in liver lipids (1.08 % total fatty acids compared with 0.28