Effect of Exogenous Enzymes on Feed Digestion and Anaerobic Digestion of Holstein Cow Faeces

This study aimed to evaluate the effect of exogenous enzymes (ExE) on feeding behaviour, feed intake, nutrient digestibility and rumen disappearance rate of Holstein cows, as well as methane production from faeces of these cows by means of anaerobic digestion. Five cannulated Holstein cows were distributed in a 5 x 5 Latin square design (5 periods of 21 days each) and received five treatments which differed in inclusion of different ExE in the diet (control: diet without enzymes; amylase: basal diet with 7.5 g of amylase/cow/day; xylanase: basal diet with 15 g of xylanase/cow/day; cellulase + protease: basal diet with 7.5 g cellulase + protease/cow/day; and pool: basal diet with 30 g enzyme mixture (all enzymes added at the same dose of individual treatments). Therefore, feeding behaviour, dry matter intake (DMI), nutrient digestibility and rumen disappearance rate were evaluated. Representative pools of faeces from each cow were collected in each period to perform anaerobic digestion. Afterwards, 25 experimental batch-type biodigesters were filled with faece substrates and were subsequently arranged in a completely randomised design of 5 treatments with 5 replicates. Then, evaluations of total gas, methane production, total solid (TS) and volatile solid (VS) removal efficiency were performed. No effect of ExE was observed (P>0.05) on feeding behaviour (number of daily meals; total daily time spent eating, ruminating or masticating), DIAL nutrient digestibility (although enzyme pool and cellulase + protease tended to increase crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) digestibility) or on rumen disappearance rate. No effect of ExE was observed on total gas and methane production or on the efficiency of removal of TS and VS from faeces. Exogenous enzymes did not increase efficiency of nutrient utilisation by the animals and, accordingly, did not affect the potential of methane emission from faeces of Holstein cows by means of anaerobic digestion.