Performances of Brahman-crossbred and English x Exotic-crossbred feeder heifers when exposed to stable flies

Brahman-crossbred and English x Exotic-crossbred feeder heifers were simultaneously exposed to low, medium and high stable fly population levels to test their relative resistance to stable fly bites. The Brahman-crossbred heifers showed resistance to stable flies only when they were 12-13 months old. At this age, the English x Exotic heifers sustained reductions in average daily gain (ADG) at low, medium and high stable fly levels by a similar magnitude of about 11%. At 14-15 months of age, both breeds were equally susceptible to the highest stable fly level. An 11% reduction in ADG was observed on both breeds. Low and medium stable fly levels did not affect the 14-15 month-old heifers. Long-term exposure of Brahman-crossbred and English x Exotic heifers to a medium stable fly population level indicated that continuous declines in ADG of both breeds occurred from the first until the 84th day of exposure. The greatest declines in ADG were recorded between the 29th and 84th days of exposure to stable flies, when the heifers were 13-14 months old. Fifteen-month-old heifers of both breeds were not affected by stable flies. Overall reduction in ADG was about 9% for both breeds, indicating that the Brahman-crossbred heifers were not resistant to long-term exposure to a medium stable fly population level. Feed conversion ratios were not affected by stable flies but showed that Brahman-crossbred heifers were less efficient in converting feed to body weight. An assumption was made that both breeds consumed equal amounts of feed. Stable fly counts on the heifers varied with time of day as well as the level of stable fly population present in the pens. Both breeds appeared equally attractive to stable flies. With or without stable flies, the Brahman-crossbred heifers were consistently outperformed by the English x Exotic heifers by about 16%, in terms of ADG, during the 3-year experiment.