GPS documentation, stress days: introduction. Stress days are defined as those days when calves experience heat or cold stress. The number of days are tallied and reported in the stress days report on the GPS homepage, shown here. Calculating stress days, GPS uses the 2021 NASEM nutrient requirements of dairy cattle approach, to calculate upper critical temperature or UCT and lower critical temperature or LCT.

When the effective ambient temperature is above UCT, calves will use energy to dissipate heat. Similarly when the temperature is below the LCT, calves experience cold stress and use energy to stay warm. This was shown in a 1981 NRC report, that shows the relationship between heat stress, cold stress, and the effective ambient temperature. Younger calves are more susceptible to cold, presumably due to a lack of rumen development, and the heat produced by rumen fermentation. Therefore the LCT or lower critical temperature depends on the age of the calves. Calves less than 21 days of age have an LCT of 15°C and greater than 21 days, an LCT of 5°C. The UCT or upper critical temperature for all calves is set at 25° C. Above, the UCT and below the LCT capsule used 2.01 kilocalories of kilogram per kilogram of empty body weight raised to the .75 power for each degree above or below the critical temperature, as shown here.

The additional energy required is then added to the unadjusted net energy for maintenance requirement to adjust the NEM. The calculations are shown here. Adjusting the temperature, the effective ambient temperature is set at the farm and calf menu here shown at the upper part of the screen. We select the farm and calf and then change the farm and calf info to set the temperature for the effective ambient temperature.

We have only one temperature for the entire simulation, so be careful. We can select anywhere from -35°C to a +35. There is no provision for entering units of fahrenheit. As we change the temperature effective ambient temperature, the simulation will recalculate the nutrient requirements based on the calculations shown. Well, that will do it for this video. Feel free to visit other parts of the GPS knowledge base to learn more about using the program.