Hypergastrinaemia, abomasal bacterial population densities and pH in sheep infected with Ostertagia circumcincta.

Serum gastrin and pepsinogen concentrations, food intake, abomasal pH and abomasal aerotolerant and anaerobic bacterial populations were measured in sheep infected with Ostertagia circumcincta to search for links between hypergastrinaemia, food intake and changes in the abomasal environment. Abomasal pH and serum gastrin and pepsinogen concentrations were elevated in each of five sheep infected via abomasal cannulae with 150000 exsheathed larval stage three, followed 11 days later by 100000 sheathed larvae given intraruminally. Unparasitised abomasa contained aerotolerant bacterial population densities of between 10(3) and 10(6) cells ml(-1) and these did not change significantly following parasitism. In contrast, anaerobic bacterial population densities increased markedly by about 10(4)-fold following parasitism. Anaerobic numbers changed rapidly when abomasal pH increased from 2.5 to 3.5. At pH 4 and above, anaerobic bacterial numbers approached levels expected in rumen contents but parameters other than pH did not relate to bacterial numbers. Brief periods when serum gastrin was lower than expected, coinciding with raised abomasal pH, were not explicable by increased bacterial numbers. Food intake, which decreased for a variable period from around Day 5 p.i., correlated poorly with serum gastrin concentration, suggesting hypergastrinaemia is not the sole cause of anorexia in parasitised animals. The survival of substantial numbers of rumen bacteria in the abomasum at only slightly raised pH may significantly lower the bacterial protein available to the sheep.

Experimental concurrent infection of cattle with Ostertagia ostertagi and Salmonella dublin.

Six seven-month-old Friesian steers were given 8.1 X 10(9) Salmonella dublin orally. Four had been infected with third stage larvae of Ostertagia ostertagi on four occasions over the previous three months. All became pyrexic and excreted S dublin in the faeces for eight to 15 days. Intravenous injection of 8.7 X 10(8) S dublin six weeks later produced similarly mild effects in parasitised and control animals alike. Two parasitised animals stopped excreting S dublin after three and five weeks respectively; the other four were still excreting regularly when killed eight weeks after intravenous infection. S dublin was recovered from the carcases of all six. O ostertagi, unlike Fasciola hepatica, did not increase susceptibility to S dublin or predispose to prolonged infection.