In the rule “Workplaces”, at the beginning of the list of Workplaces, enter the following as a new first bullet point:

Pasture (Shepherd): If it is Spring and if at least a quarter of the Townspersons, rounded up, are Shepherds, each Townperson with at least 2 animals gains an animal.

In the same rule, right before “(The bracketed word after the name of each Workplace is the name given to any Townsperson who has that Workplace.)”, add

If there is no Shepherd when the Day of Observance is called, each Townsperson with at least 1 animal looses 1 animal.