Infection and immunity in broiler chicken breeders vaccinated with a temperature-sensitive mutant of Mycoplasma gallisepticum and impact on performance of offspring

A comparison of infection and immunity to Mycoplasma gallisepticum (MG) in broiler chicken breeders vaccinated with a temperature-sensitive mutant of MG versus nonvaccinated chickens, and the impact on the performance of thei r offspring was conducted. Infection and immunity in breeders were assessed by culture and enzyme-linked immunoassay, respectively. However, performan ce in their offspring was assessed by studying MG infection in embryos, occ urrence of infection titers to MG in relation to mortality, and feed conver sion in the broilers. Five out of 10 broiler chicken breeder flocks raised on the same multiple-age farm with a long history of mycoplasmosis were vac cinated intraocularly once with a temperature-sensitive MG mutant vaccine ( ts-11(R)) at an average age of 7.5 wk; another five breeder flocks were lef t as unvaccinated controls exposed to field MG. The average recoveries of t s-11(R) organisms from tracheas and infraorbital sinuses of 41-wk-old vacci nates were 88 and 84%, respectively. No field MG organisms were recovered f rom vaccinates between 15 and 41 wk of age. The recovery of field MG organi sms from tracheas and sinuses of nonvaccinated chickens increased to an ave rage of 100% at 41 wk of age. A significant decrease (P < 0.05) in the aver age percentage of MG-seroconverted breeders occurred in ts-11(R)-vaccinated flocks in comparison with nonvaccinated, MG-infected flocks at 15, 20, 23, 29, 32, 36, and 41 wk of age. The average infection prevalence by MG in the vitelline membrane of 7-d-old embryos produced by the five unvaccinated breeder flocks peaked at 79% whe n their respective hatching eggs were collected at 36 wk of breeder's age. Embryos of ts-11(R)-vaccinated flocks had zero prevalence of MG infection a t all times between 29 and 57 wk of breeder's age. Seroconversion to MG (average of 17.7%) at 42 d of age was only present in sera of 10 offspring broiler flocks of the nonvaccinated breeders. However, a lack of seroconversion to MG occurred in 10, 42-d-old offspring broiler flocks of the five ts-11(R)-vaccinated breeder flocks. This lack was associ ated with a lower, better average feed-conversion ratio (2.05) (P < 0.05) a nd a lower average mortality percentage (5.3%) (P < 0.05) in comparison wit h those obtained in the offspring of the five unvaccinated, MG-infected bre eder flocks. The results indicate that vaccination of broiler chicken breeders with a te mperature-sensitive mutant of MG prevented infection by field MG in trachea s and infraorbital sinuses of these breeders and in the vitelline membranes of their embryos. In addition, the broiler offspring of the vaccinated bre eders had a better production performance.