Although it's difficult to calculate the exact age of farm animals -- including pigs -- with precision, farmers, veterinarians and biology students are able to provide a reasonable estimate by following general guidelines related to length and weight of an animal. These estimates help farmers know a fair price to offer for livestock based on how long it takes the pig to reach maturity for breeding or slaughter and pork processing; assist high school or college students to obtain data during dissection labs; or help veterinarians who need to determine the cause of a sow's spontaneous termination of pregnancy.

Measure the length of the pig from snout to rump, and record it.

Download the length/age chart from http://www.ideas4ag-ed.com/uploads/3/7/0/4/3704787/fetal_pig_dissection_guide_day_1.pdf.

Consult the length/age chart to determine the appropriate number of days into gestation the pig was at the point of pregnancy termination.

Examine the pig's mouth. Determine how many teeth are present.

Identify whether the teeth are incisors, canines or pre-molars and where they're located along the upper or lower jawline.

Consult your veterinarian or the dental X-rays displayed at http://www.portec.com.au/thepig/disorders/head/anatomy/agingpigsteeth.htm to determine your pig's approximate age.

Measure the length of teeth in a pig whose teeth are all in. Determine the average incisor, canine and molar lengths. Consult your veterinarian to get a reasonable age estimate based on tooth size.