Effects of the In ovo Administration of the 6/85 Mycoplasma gallisepticum Vaccine on Layer Chicken Embryo Hatchability and Early Posthatch Performance †

SIMPLE SUMMARY: Mycoplasma gallisepticum (MG) has reduced egg production and caused other economic losses in the poultry sector. This study studied the potential use of in ovo vaccination of the 6/85 MG vaccine in layer embryos for subsequent early protection as well as live performance of pullets. The use of various dosages of live attenuated 6/85 MG vaccine in either the air cell or amnion, ranging from 1.73 to 1.73 × 10(4) CFU was evaluated after 18 days of incubation. In the current study it was found that the in ovo vaccination of the high dosage of 6/85 MG (1.73 × 10(4) CFU), when administered in the amnion (AM), resulted in detrimental impacts to the hatchling process as well as post-hatch live performance but increased three-week-old antibody titers. Additionally, as compared with the air cell (AC), the in ovo administration of the medium dosage of the 6/85 MG vaccine (1.73 × 10(2)) in the AM had promising results in terms of the hatchability, live performance and antibody titer of early posthatch pullets. Therefore, it is suggested that the 1.73 × 10(2) CFU treatment injected in the AM may be an appropriate candidate for the pragmatic and commercial application of 6/85 MG vaccine because it did not result in embryo or posthatch chick mortalities while eliciting a humoral response. ABSTRACT: In ovo administration as a possible alternative method of 6/85 MG vaccination was assessed. After 18 days of incubation (doi), the eggs were administered a particular dosage of a live attenuated 6/85 MG vaccine in either the air cell (AC) or amnion (AM). The treatments included non-injected eggs and eggs injected into the AC or AM with diluent alone as controls. Treatments also included eggs injected with diluent, which contained 1.73 × 10(2), or 1.73 × 10(4) CFU of 6/85 MG. Hatchability of viable injected eggs (HI) and residual embryonic mortality were determined at 22 doi. At hatch and at three weeks posthatch, one hatched chick per treatment replicate was bled and swabbed for the detection of 6/85 MG in the choanal cleft using PCR, serum plate agglutination (SPA), and ELISA methods. The results show that AC in ovo injection of 6/85 MG had no negative impacts on HI or on the live performance of pullets, but that it failed to provide adequate protection (p ≤ 0.0001) in hatchlings or three-week-old pullets. The 1.73 × 10(4) 6/85 MG CFU dosage injected into the AM decreased the hatchability of injected eggs containing viable embryos (HI; p = 0.009) and was associated with a significant increase in late dead mortality (p = 0.001). Hatchling and three-week-old chick mortalities (p = 0.008) were significantly greater in the 1.73 × 10(4) CFU-AM treatment group in comparison with the other treatment groups. In addition, the 1.73 and 1.73 × 10(2) 6/85 MG-AM treatments had no negative effects on the hatching process or on posthatch growth, and the 1.73 × 10(2) 6/85 MG-AM treatment was more effective in the protection of pullets against MG (p ≤ 0.0001) as compared with the low dosage and non-injected treatment groups. Further research is needed to examine the influence of the 6/85 MG in ovo vaccine on layer immune competence.