Effect of pesticides applied in cowpea production on rumen microbial fermentation of cowpea haulms as reflected in in vitro gas production

Abstract

The present study assessed the effect of lambda cyhalothrin, cypermethrin and dimethoate residues in cowpea haulm on microbial fermentation using gas syringes as incubators. The lambda cyhalothrin, cypermethrin and dimethoate were applied at the vegetative, flowering and podding stages of the cowpea at the rate of 2.66 mg/L, 5.14 mg/L and 6.68 mg/L of water, respectively. Dimethoate was detected in the cowpea haulm at the highest concentration of 1.38 mg/kg. The haulm with no pesticide treatment was incubated with media containing rumen fluid, and pesticides were added at concentrations of 40 mg/kg, 80 mg/kg and 120 mg/kg. In vitro gas production was measured at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h and 96 h to estimate the rate of gas evolution. Gas production in general was influenced by pesticide application. In general, gas evolution was reduced by increasing levels of lambda cyhalothrin up to 80 mg/kg. However, an increase in gas accumulation was observed with increasing levels of dimethoate, while the application of cypermethrin yielded no noticeable change in gas production. The study indicates that pesticide residues may function as toxins at concentrations greater than those encountered in the field or lethal dose (LD50) and may inhibit the growth of rumen microbes.