The presence of Salmonella was investigated in transport boxes of newly hatched chicks in the moment they were received in the farms. 1,611 boxes, delivered to 15 farms (one broiler grand-parent farm, four broiler parent farms, two commercial broiler chick farms and seven laying hens farms) were tested.

Foram examinadas caixas de transporte de pintos de um dia com o objetivo de investigar a presença de Salmonella no momento em que chegaram à granja. 1611 caixas foram amostradas em 15 propriedades, sendo uma granja de avós, quatro granjas de matrizes, duas de frangos de corte e seis de aves de postura comercial.

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1517...

There are very few hits for "broiler grandparent" or "grandparent farms" so I am not very convinced of this answer.