The resistance and carrier status of meat-type hens exposed to Mycoplasma synoviae.

Forty-eight 32-week-old meat-type females, free from Mycoplasma synoviae (Ms.) and Mycoplasma gallisepticum (Mg.) were aerosol exposed with a 24-hour broth culture of Ms. 1331 and placed in 3 pens. 16 birds per pen. Two males were placed in each of the 3 pens and used as contact birds. All birds were bled at 2, 4, 7, 10, 14, 24, 26, and 30 weeks post Ms. exposure. After the 24-week bleeding, the females were equally divided into 4 pens. All females in 2 of the pens were given a foot pad injection of 0.3 ml. of Ms. 1331 broth culture. Ms. isolation attempts were made from the trachea of all birds at 2, 14, and 24 weeks post Ms. exposure. Ms. isolation attempts were made from all eggs produced, either from the allantoic fluid and egg yolk of 17- or 18-day-old embryos, dead embryos, and infertile eggs, or from the tracheas of day-old progenies. Each day-old progeny was bled. Ms. and Mg. serum plate tests were conducted on the serums from the progeny and adult birds from each bleeding. Ms. hemagglutination-inhibition (HI) tests were conducted on the serums of the adult birds. In the Ms.-exposed birds, the geometric mean HI titer of the serums from each bleeding rose significantly over the previous bleeding. The percentages of Ms. serum plate reactions increased with length of time after Ms. exposure. There were false Mg. serum plate reactions in the early stages of Ms. infection. A foot pad challenge with a broth culture of Ms. 1331 24 weeks after Ms. exposure did not significantly increase the geometric mean HI titer over the Ms. exposed birds that did not have a Ms. foot pad challenge. Ms. was isolated from the trachea of 91.6%, 100%, and 100% of the Ms.-exposed birds at 2, 14, and 24 weeks after Ms. exposure, respectively. There were 35 Ms. isolates from 575 attempts from 17- or 18-day embryos, dead embryos, or infertile eggs, and 7 Ms. isolates from 67 attempts from the trachea of day-old progenies. All isolates were made from eggs collected from 6 through 31 days afer Ms. exposure. No isolations were made from 1760 attempts made from eggs collected from 32 through 210 days after Ms. exposure, including eggs collected from Ms. foot pad-challenged birds at 168 days after Ms. exposure. There were 312 broilers reared from eggs collected from the 22 through 24 weeks after Ms. exposure. The broilers were marketed at a federally inspected poultry processing plant. Their records showed 3 birds condemned for septicemia-toxemia, but none were condemned for air-sacculitis or synovitis. Twenty-four serums from the broilers that were positive to Ms. or Mg. serum plate tests were all negative to the Ms. and Mg. HI tests. Ms. serum plate reactors began to show up in the day-old progeny from eggs collected beginning on the 76th day after Ms. exposure. There were 16.0% (80/500) positive to the Ms. serum plate test from eggs collected from the 76 through 126 days after Ms. exposure and 14.0% (52/372) from eggs collected from the 169 through 210 days after Ms. exposure.