Research has shown that very hot temperatures can suppress production levels and also reproductive ability, if temperatures are sustained over a period of time. One of the genetic traits was heat stress, also generated as a normal distribution, but converted to a ratio, and then used as a probability to determine if the animal is stressed by the weather.
Daily weather data were collected for this area of Ontario for a 10 year period. The minimum, maximum, and average temperatures, precipitation plus a THI (temperature-humidity index value) were available. They are read into the simulation program one day at a time (as needed), and used as the temperature variables for that day. When the end of the file is reached, the file is re-opened from the beginning and figures are re-used. Thus, the trend in global warming is not really taken into account.