Use of modified cages attached to growing calves to measure the effect of stable flies on dry matter intake and digestibility, and defensive movements

Abstract

The effects of stable flies on growing calves were examined using fly cages attached to the animals. Dry matter intake, DM digestibility (DMD), and behavioral responses of calves were monitored. Nine Holstein calves were exposed to 3 levels of stable flies (0, 10, 100 flies/animal) 3 times daily for 30 min. The study consisted of a 4-period crossover design; each period included 5-d adaptation, 7-d exposure, and 5-d postexposure. Calves were weighed at the beginning and end of each period. Feed consumption was continuously recorded. Fecal samples taken during and after exposure were used to determine DMD. Three calves were monitored for activity and defensive behavior during exposure. Caged stable flies successfully fed on the calves and invoked defensive behaviors similar to those observed in field studies. Defensive behaviors were proportionate to exposure level, and calves became more proficient at interfering with fly feeding over time. Stable fly exposure increased DMI relative to calf weight and decreased ADG/DMI. Calves initially exposed to 100 flies exhibited more defensive behaviors and lower relative DMI and ADG across all exposure levels relative to calves initially exposed to 10 flies. Stable fly exposure did not affect DMD, number of meals, time eating, or amount eaten per meal. Host defensive behavior, not reduced DMI or DMD, appears to be reducing ADG of calves exposed to stable flies. Results indicate that cages placed on calves may be used to study the effects of stable flies, but host exposure history and behavioral variables must be considered.