What is the average iodine content (say in mg) in a pig (or cow) thyroid?

In a large and well-documented study, the iodine content of whole,
fresh bovine thyroid glands was as follows:

Bulls                             19.38 mg
Steers                            19.73 mg
Pregnant cows                     18.50 mg
Non-pregnant cows and heifers     16.98 mg

The number of animals used in this investigation: Bulls, 470; steers,
1068; pregnant cows, 1123; non-pregnant cows, 1021.

THE INFLUENCE OF PREGNANCY AND CASTRATION ON
THE IODINE AND PHOSPHORUS METABOLISM OF THE THYROID GLAND
http://www.jbc.org/cgi/reprint/17/1/23.pdf

Bovine thyroids contain from 0 to 3.5 micrograms of iodine per
milligram. The weight and iodine content of the thyroid gland depends
on several factors, including body weight, gender, and diet.

"While performing activation analytical investigations on the actual
concentration of the long-lived radioactive 129iodine in human and
bovine thyroid glands the absolute natural nonradioactive 127 iodine
content was determined. In all thyroid glands an uneven distribution
of 127I was found (in human thyroids from 0 to 0.75 micrograms 127I
/mg, in bovine thyroids from 0 to 3.5 micrograms 127I /mg)."

Medscape: Content and heterogeneity of distribution of iodine in human
and bovine thyroid glands...
http://www.medscape.com/medline/abstract/6725871

My Google search strategy:

Google Web Search: "iodine content" thyroid cows OR bovine OR pigs OR porcine
://www.google.com/search?hl=en&q=%22iodine+content%22+thyroid+cows+OR+bovine+OR+pigs+OR+porcine

Google Web Search: "bovine OR porcine OR cow OR pig thyroid" "of iodine"
://www.google.com/search?hl=en&q=%22bovine+OR+porcine+OR+cow+OR+pig+thyroid%22+%22of+iodine

I hope this is precisely what you need. If anything is unclear or
incomplete, or if a link doesn't work for you, please request
clarification; I'll be glad to offer further assistance before you
rate my answer.

Best regards,
pinkfreud

Nice job!