In vitro evaluation of aflatoxin B1 effect on gas production and ruminal fermentation parameters.

BACKGROUND: Aflatoxins are fungal secondary metabolites negatively affecting ruminant performance; however, little information is available on their impact on rumen fermentation. AIMS: This study aimed at determining the effects of different concentrations of aflatoxin B1 (AFB1) from Aspergillus flavus on in vitro gas production and ruminal fermentation parameters using two experiments (Exp.). METHODS: In Exp. 1, two concentration ranges (0, 0.5, 1, and 1.5 µg/ml of rumen inoculum as low and 0, 5, and 10 µg/ml as high concentration ranges) were used to evaluate AFB1 effect on gas production kinetics using 96-h incubations. In Exp. 2, only the high concentration range was used to investigate AFB1 effects on ruminal fermentation parameters using 24-h incubations. RESULTS: In the low concentration range, the half-time of asymptotic gas production (T1/2) increased and the fractional rate of gas production (µ) decreased linearly with AFB1 dosage (P<0.05). However, in the high concentration range, the asymptotic gas production (A) and T1/2 decreased; and the lag time (L) and "µ" increased linearly (P<0.001) by increasing the concentrations of AFB1. In Exp. 2, dry matter (DM) and organic matter (OM) disappearance, microbial biomass (MB) and total volatile fatty acids (TVFA) concentrations were depressed, but pH and ammonia-N concentration increased (P<0.01) by increasing the concentrations of AFB1. The pattern of rumen volatile fatty acids (VFAs) was also modified by AFB1, as the propionate proportion increased at the expense of acetate. CONCLUSION: Aflatoxin B1 had an adverse effect on in vitro ruminal fermentation parameters in high concentration ranges (5 and 10 µg/ml).

Degradation of terpenes and terpenoids from Mediterranean rangelands by mixed rumen bacteria in vitro.

This in vitro study aimed at estimating the disappearance rates of 14 terpenes and terpenoids after 24-h incubation with mixed bacteria from caprine rumens. These compounds comprised nine monoterpene hydrocarbons (δ-3-carene, p-cymene, ß-myrcene, (E)- and (Z)-ß-ocimene, α-phellandrene, α-terpinene, γ-terpinene and α-terpinolene), four oxygenated monoterpenes ((E)- and (Z)-linalool oxide, 4-terpinenol, α + γ terpineol) and one sesquiterpene hydrocarbon (ß-cedrene). They were individually exposed to goat rumen microflora for 24 h in 70 ml culture tubes at an input level of 0.5 ml/l. Terpenoids were the least degraded, 100% of (E)-linalool oxide, 95% of (Z)-linalool oxide, 91% of 4-terpinenol and 75% of terpineol remained intact after 24-h incubation. In contrast, α-terpinolene concentration in fermentation broth extracts was below quantification limit, thus indicating an extensive, if not complete, degradation by rumen bacteria. Only 2% of the initial amounts of α-phellandrene were recovered. The other monoterpenes and ß-cedrene were partly degraded, with losses ranging from 67% for δ-3-carene to 90% for (E)-ß-ocimene. The corresponding rates of disappearance were between 2.67 and 4.08 µmol/ml inoculum per day.

Disappearance of nine monoterpenes exposed in vitro to the rumen microflora of dairy goats: effects of inoculum source, redox potential, and vancomycin.

This in vitro study evaluated the roles of diet type and redox potential in the degradation of linalool, (E)- and (Z)-beta-ocimene, alpha-phellandrene, (-)-beta-pinene, (-)-alpha-pinene, (+)-alpha-pinene, sabinene, and alpha-terpinene when incubated with rumen microflora, and it provided information on the time course of their disappearance. The 9 monoterpenes are found in the winter and spring diets of dairy goats in northwestern Mediterranean grazing systems. The diets were individually exposed to rumen microflora for 3 h in 17-mL culture tubes at a concentration of 4 microL/L. The mixed flora of the inoculum was controlled by the use of vancomycin (eliminating gram-positive bacteria) and by the energy source (starch vs. structural polysaccharides) on which rumen microflora had been grown. Redox potential was controlled by addition of L-cysteine-hydrochloride. The preliminary adaptation of microbial inoculum to a diet rich in structural carbohydrates reduced the recovery yields of (E)- and (Z)-beta-ocimene, (-)-beta-pinene, (-)-alpha-pinene, (+)-alpha-pinene, and sabinene (P<0.01), whereas vancomycin was without effect. The effect of carbohydrate source likely stems from the specific composition of the microbial community rather than from its acidogenic capacity. Reducing the culture redox potential by 50 mV reduced the recovery yields of linear and monocyclic terpenes (P<0.02), and the culture redox potential interacted with the inoculum source for (E)- and (Z)-beta-ocimene and for alpha-phellandrene. The time course of terpene disappearance was studied by exposing terpenes to a rumen microflora adapted either to starch or to fiber for 3, 6, or 24 h. The degraded fraction reached a plateau within 3 h for alpha-phellandrene and for all the isomers of beta-ocimene and pinene with the fiber-adapted microflora as well as with both inocula for alpha-terpinene. With the starch-adapted microflora, this steady state was reached for most other terpenes within 6 h of incubation. Sabinene was the only compound still disappearing after an incubation period of 6 h. Biotic and environmental variables in the rumen affected terpene degradation in a way that can alter the dietary terpene profile and possibly its influence on animal product characteristics.