Comparative Size of Infective Larvae of Cooperia oncophora in Feces of Cattle and Sheep

Abstract

A cattle strain of Cooperia oncophora was used to infect a helminth-free calf and lamb. Sphagnum moss-feces cultures were made from the feces of the infected animals. In addition, eggs separated from the feces of each infected animal were incubated in cultures made from the feces of a helminth-free calf and lamb, respectively. The mean total length of larvae cultured in the feces of a parasite-free lamb was smaller, though not always significantly so, than the mean total length of larvae cultured in feces from any of the other sources. The mean total length of larvae cultured in the feces of a parasite-free calf was greater, though not always significantly so, than the mean total length of larvae cultured in feces from any other source. No consistent correlation could be made in either experiment between total length and other measurements such as distances between anus and tail tip, anus and sheath tip, tail tip and sheath tip, and total length of larvae minus sheath. These data indicate that a factor or factors operating within individual host animals are sufficient to affect significantly the size of the infective third-stage larvae developed from nematode eggs passed from the host. Various authors, working with nematodes parasitic in ruminants, have reported different average lengths and ranges of lengths for infective larvae of the same species. Several explanations of the causes of these differences have been advanced. Keith (1953) measured infective larvae of Ostertagia ostertagi, a parasite of cattle, and found the range of total length (784 to 928 [t) almost triple the range (850 to 900 A) noted by Threlkeld (1946). Infective third-stage larvae of 0. ostertagi, observed by Douvres (1956), were longer than those observed by either Threlkeld or Keith. In addition, Douvres noted that iodine-killed larvae were longer than those that had been heat killed, and that refrigerated larvae were longer than those that were nonrefrigerated. Shumard, Herrick, and Pope (1955) demonstrated that the nutrition of lambs parasitized with Haemonchus contortus influenced the size of infective larvae of a succeeding generation. These authors conjectured that differences between their measurements and those of Dikmans and Andrews (1933) might have been caused by the type of fluid in which the larvae were killed. Received for publication 30 August 1963. Keith (1953), working with Cooperia oncophora larvae cultured from eggs passed by infected cattle, found little difference in total length from that reported by Dikmans and Andrews (1933) for C. oncophora larvae cultured from eggs removed from worms recovered from sheep. Keith noted, however, that infective larvae of his study had longer tails than did those observed by Dikmans and Andrews and suggested that this was due to a strain difference. Isenstein (1963), working with C. oncophora from eggs passed by infected cattle, found the infective larvae considerably longer than those studied by either Dikmans and Andrews or Keith. In view of the foregoing, it was deemed desirable to compare the sizes of infective larvae of Cooperia oncophora cultured in cattle and sheep feces, wherein the diet of the host, strain of worms, and method of preparing the worms for measurement are kept constant. MATERIALS AND METHODS Thirty-two thousand infective third-stage larvae of Cooperia oncophora were administered per os to a parasite-free calf (1741). These larvae were of a cattle strain, having been passed through cattle for at least seven generations. A parasitefree lamb (102) was subsequently infected with 80,000 larvae cultured from the eggs passed in the feces of calf 1741.