SERUM CONSTITUENT PROFILES OF BEEF HEIFERS INFESTED WITH HORN FLIES (DIPTERA, MUSCIDAE)

Nine yearling crossbred beef heifers, Bos taurus L., were used to exam ine physiological responses to horn fly, Haematobia irritans (L.), inf estation. Heifers were stanchioned indoors in individual environmental ly controlled rooms. On day 0, each animal received 0, 500, or 1,000 h orn flies. Fly numbers were adjusted daily to maintain an appropriate infestation for each heifer. Feed intake, respiration rate, and rectal temperature was recorded daily. In addition, blood samples were colle cted from each animal on days 0, 12, and 33 for serum constituent anal ysis. To monitor metabolic hormone status, intensive blood samples wer e also collected hourly for 6 h on days 0, 12, and 33. Throughout the period of treatment, feed intake values were similar among treatments resulting in comparable body weight at the end of the trial. Respirati on rates on each day were similar among groups. Rectal temperature was also unaffected by horn fly infestations. Serum electrolyte analysis revealed that neither Na, K, Cl, Ca, P, nor Fe differed among treatmen ts. Likewise, HCO3/CO2, ratio, anion gap, and serum osmolality did not differ among treatment groups. Major indicators of nutrient status (g lucose, cholesterol, triglycerides, urea N, creatinine, uric acid, alb umin, globulin) and insulin, growth hormone, and prolactin were also u naffected. Serum bilirubin and enzyme (alkaline phosphatase, creatine phosphokinase, gamma-glutamyl transpeptidase, lactic dehydrogenase, as partate amino transferase, alanine amino transferase) concentrations w ere similar in control heifers and those infested with horn flies. Res ults of this trial indicate that horn fly infestations up to 1,000 fli es per animal had little adverse physiological influence on the physio logy of beef heifers housed under laboratory conditions in which they were well fed and not exposed to external environmental conditions. Da ta suggest that adverse effects on production traits of cattle due to horn flies are not likely to result in alteration of constituents meas ured in chemistry or hormone profiles.