Research conducted by the Western College of Veterinary Medicine shows severe infections can impact the function of the hypothalamus and pituitary and thyroid glands resulting in hypothyroidism. The Western College of Veterinary Medicine is studying the impact of hypothyroidism associated with PRRS and other diseases on the growth performance of the pig.
Dr. Glenn Hamonic, a Post Doctoral Fellow working in PRRS research at the Western College of Veterinary Medicine, explains hypothyroidism isn't typically associated with disease but, during severe infections, there's a significant suppression of the thyroid hormone and, in the case of PRRS, thyroid hormone levels can drop to 50 percent of normal.
Clip-Dr. Glenn Hamonic-Western College of Veterinary Medicine:
So far we've found there is a clear association with growth performance and the level of hypothyroidism they hit during infection. Just looking within the typically 42ish day window of these challenge studies, if you look at their growth performance and then their thyroid hormone levels throughout that same period, there is a clear association where the animals that are not performing are absolutely the ones that are hypothyroid.
Additionally to that, when we're talking about looking into the mechanisms or why these animals are going hypothyroid, there is several points in the animal's control system in that hypothalamus, pituitary, thyroid access that are not correctly responding. We can see right from the hypothalamus and the pituitary, which will typically single the thyroid to produce more thyroid hormone, those two tissues are not able to detect that the animal is hypothyroid so they're not able to tell the thyroid gland to produce more thyroid hormone.
Then we've actually found the thyroid gland itself is not responding to signals and is kind of shutting down it's own production of thyroid hormone. So it's really the entire system that is disreguated in these significant infections.
Source : Farmscape