Incidence and importance of subclinical mastitis in sheep.

The incidence of positive CMT, indicative of subclinical mastitis, was studied in a flock of purebred Targhee ewes from four selection lines. The incidence of positive CMT was found to be random at lambing with respect to age and line of ewe, number of lambs born and weaned and sex of lambs, but at docking (3 to 7 weeks after lambing) increased with increasing age of ewe and number of lambs born. The effect of CMT score on total weight of lamb weaned was examined in the Targhee ewes and in a flock consisting of purebred and crossbred ewes of several types mated to Suffolk rams. CMT score of the ewe at lambing was not a significant source of variation in total weight weaned, but variation in score at docking approached significance in both flocks. There were indications that positive CMT scores were associated with lamb losses, although it was not possible to tell if mastitis was a cause or an effect of the lamb loss. l.ine and age of ewe (selection experiment), number of Iambs born and weaned and sex of lambs were all significant sources of variation in total weight of lamb weaned. (