A fifth-grade science experiment made 50 students sick last month, the Massachusetts Department of Public Health said last week.

The students were asked to dissect owl pellets, a form of feces, at Jefferson Elementary School. According to DPH spokeswoman Donna Rheaume, 28 were infected with salmonella bacteria.

Because of the outbreak, the state plans to update its guidelines for handling the pellets for the upcoming 2006-7 school year. The new DPH guidelines will instruct teachers and students to wear protective gloves and to wash their hands and work areas following the experiments.

A similar 2005 salmonella outbreak in Minnesota was linked to owl pellets when 40 students fell ill after dissecting them on a cafeteria table, according to the Minnesota DPH’s Acute Disease Investigation and Control Section.

Since tens of thousands of students perform similar experiments each year across the country, Franklin School Superintendent Wayne Ogde said he believes the official results could have national implications.