The effects of different vaccination dosing and timing protocols on porcine circovirus type 2 viremia and post vaccination serologic responses

Mycoplasma hyopneumoniae (Mhyo) and PCV2 cause significant economic losses to the U.S. swine industry. Circumvent® PCV-M G2 (Merck AH, USA) protects against both pathogens using two dosing options: single, 2mL intramuscular (IM) dose at 3 weeks of age (WOA) or older, or 1 mL IM as early as 3 days of age followed by 1mL dose 3 weeks later. The objective was to evaluate different vaccination dosing and timing protocols on PCV2 viremia and post vaccination serologic responses.

This study was conducted in four separate flows in a large production system. One flow was a parity 0 to 1 sow farm that provided sows for the three other sow farms. Pigs (n=521) were randomly assigned by weight within litter to treatment groups just prior to weaning at 21-28 days of age: A) 2mL, 3 WOA; B) 1mL 3&7 WOA; C) 1mL 3&9 WOA. In the finisher, pigs were evenly dispersed throughout the barn by treatment and mixed with non-study pigs. Pigs were weighed at allocation, 9 WOA, and prior to marketing at 24 WOA. Blood samples were collected at allocation and 7, 9, 16, and 24 WOA. Serum was tested for PCV2 viremia by PCR in pools of five at ISU Veterinary Diagnostic Lab. Environmental challenge was assessed by monitoring oral fluids for PCV2 by PCR at each blood sampling. Serum was tested for PCV2 antibodies by IFA, reported as the reciprocal of the geometric mean (GM) titer and Mhyo antibodies by ELISA performed at 3, 7, and 9 WOA.

No pigs were viremic at 3, 7, 9, 16, and 24 WOA. Oral fluid rope samples at 7, 9, 16, and 24 WOA were PCV2 PCR low positive. Group B seroconverted to Mhyo at a high rate in the presence of Mhyo maternal antibody at 3 WOA. PCV2 maternal antibody at 3 WOA reduced IFA titers at 9 WOA. Group B pigs with titers < 640 at 3 WOA had a GM of 3,044 at 9 WOA while pigs with GM> 1,280 had 1,428. Average daily gain (ADG) for A, B, and C was 0.827, 0.842, and 0.834 pounds in nursery and 1.991, 2.012, and 2.029 pounds in finisher, respectively and was not significantly different. Mortality rates were A 4.6%, B 5.7%, and C 5.2% and did not differ significantly.

No viremia was detected in any pigs, possibly due to the low challenge level as assessed by oral fluid samples. The reason for the low challenge level is unknown. Previous testing of these flows indicated that active PCV2 infection was occurring. However, potential variability in endogenous challenge level is a limitation in field studies. Serologic testing shows that B pigs are able to mount an immune response to both Mhyo and PCV2 in the presence of maternal antibody. Additional handling for a second vaccination did not negatively impact ADG.

Disclosure of Interest: None Declared.