Susceptibility of 1- and 3-day-old chikks to infection with the coccidium, Eimeria acervulina.

Abstract

SYNOPSIS. One‐day‐old chicks were less susceptible to experimental infection with E. acervidina than were 3‐day‐old chicks. Chicks fed intact oocysts when 3 days old produced 5.3, 6.7, and 42.7 times as many oocysts and had more extensive lesions than did those fed a similar number of oocysts when 1 day old. When oocyst suspensions that contained both liberated sporocysts and intact oocysts were administered, chicks infected when 3 days old produced only 1.8, 1.3, and 2.6 times as many oocysts as did those infected when 1 day old.Examination of gizzard and intestinal contents of chicks killed 2–1½ hr after receiving massive numbers of intact oocysts showed that only a few sporocysts were liberated from oocysts in the gizzard of 1‐day‐old chicks, whereas more were liberated in the gizzard of 3‐day‐old chicks. Very few sporozoites were found in the duodenum of the 1‐day‐old chicks. but there was a linear increase in the percentages in samples from lower levels of the small intestine. In 3‐day‐old chicks, excystation in the duodenum was high and, instead of increasing, remained at about the same level in the jejunum.The far smaller number of liberated sporocysts in the gizzards of 1‐day‐old chicks is attributed to less musculature and an incompletely developed grinding surface The delayed excystation of sporozoites in the intestine of 1‐day‐old chicks is thought to be due to suboptimal concentrations of trypsin and/or other pancreatic enzymes effecting excystation.The lighter infections observed in 1‐day‐old chicks, as compared to those in chicks 3 days old, are attributed to (a) a smaller number of liberated sporocysts leaving the gizzard, (b) delayed excystation in the intestine, and (c) less opportunity for sporozoites to penetrate epithelial cells.