Effect of aflatoxin B1 on in vitro ruminal fermentation of rations high in alfalfa hay or ryegrass hay

A 2 × 4 factorial experiment was conducted to determine the effect of aflatoxin B1 (AFB1) at dose rates of 0, 320, 640, 960 ng/ml on ruminal fermentation of substrates high in alfalfa hay (HA, alfalfa hay: maize meal = 4:1) and ryegrass hay (HR, ryegrass hay: maize meal = 4:1). In vitro dry matter disappearance was not affected by AFB1 dosage. The asymptotic gas production numerically declined by increase in AFB1 dosage for HA and HR. AFB1 dosage decreased gas production rate (P<0.05), and the rate for HR was lower for HA (P<0.05). Ammonia N concentration declined with the increase in AFB1 dosage for HA (P<0.05), and was higher for HA than HR (P<0.01). The highest AFB1 dosage decreased total VFA concentration by 12.7% for HA and 9.6% for HR (P<0.05), compared with that of the zero dosage. The molar proportions of propionate and butyrate did not differ between HA and HR, but molar proportions of isobutyrate, valerate and isovalerate were distinctly greater in HA than in HR (P<0.01). After 72 h incubation, 0.831 (HA) and 0.842 (HR) of included AFB1 (960 ng/ml) was degraded. The results implicate that rumen microbes have high ability to degrade AFB1.