Experimental production of fog fever by change to pasture free from Dictyocaulus viviparus infection
Selman, I.E.; Breeze, R.G.; Bogan, J.A.; Wiseman, A.; Pirie, H.M.
Veterinary Record 101(14): 278-283
1977
ISSN/ISBN: 0042-4900 PMID: 144350 Document Number: 122729
After almost five months of grazing relatively bare permanent pastures, a group of 11 clinically normal beef cows and heifers and their calves were introduced to a very lush, parasite-free field of new grass. Ten of the adult cattle developed mild transient respiratory signs after 3-11 days. The 11th, a fat Hereford heifer, had severe respiratory distress on day 14; this animal was slaughtered on the second day of illness and PM examination confirmed fog fever. The other ten adult cattle were slaughtered over the following three days; six had focal lesions resembling those found diffusely in the severely affected case. L-tryptophan was demonstrated in the new grass. At slaughter a rumen metabolite of this amino acid, 3 methyl indole, was found in the rumen liquor of all 11 cattle in concentrations comparable to those found after oral administration of L-tryptophan in amounts known to induce a proliferative alveolitis. It is concluded that, while Dictyocaulus viviparus cannot be excluded absolutely from playing a role in fog fever, the disease cannot arise as the result of recent larval invasion.