THE EFFECT OF IN OVO OOCYST OR SPOROCYST INOCULATION ON RESPONSE TO SUBSEQUENT COCCIDIAL CHALLENGE

A trial was conducted to investigate the effects of in ovo Eimeria max ima inoculation on response to subsequent posthatch challenge with E. maxima. The in ovo treatments were arranged in a 4 x 2 factorial with four in ovo inoculation sites (air cell, amnion, yolk sac, and allanto is) and two parasite forms (oocyst and sporocyst). Four control treatm ents included an uninoculated (naive) unchallenged group, a naive chal lenged group, and two posthatch inoculated challenged groups. Chicks w ere challenged by crop intubation with 50,000 sporulated E. maxima ooc ysts 10 d posthatch. On Day 8 postchallenge, feed intake was determine d and birds were weighed and lesions scored. During the brooding perio d, oocysts were isolated from the fecal material of chicks receiving i n ovo administration of sporocysts in the amnion and sporocysts or ooc ysts in the yolk sac. Posthatch inoculated chicks had gain and feed:ga in ratios similar to those of naive unchallenged chicks. Gain, feed:ga in ratio, lesion scores, and oocyst shedding of chicks inoculated in o vo were similar to those of naive, challenged chicks. Although there w as some indication that parasites introduced in ovo may complete their life-cycle within the developing chick, this experiment provided no e vidence that in ovo administration of either E. maxima oocysts or spor ocysts will protect birds from subsequent coccidial challenge. Contrar ily, inoculating chicks on day of hatch with a single oral dose of E. maxima oocysts provided significant protection against subsequent cocc idial challenge.