PRODUCTION LOSSES FROM MASTITIS - CARRY-OVER FROM THE PREVIOUS LACTATION

The study examined whether elevation in SCC in the second lactation was associated with reduced milk production in the third lactation. Lactation records from 10,705 Holstein cows from 770 herds were taken from the Dairy Records Processing Center at Raleigh. Cows in the data set were selected so that no SCC test in the first lactation was elevated above a linear score of 4.5 (no mastitis in the first lactation). Using actual and mature equivalent milk production in the first lactation as a baseline, effects of elevated SCC on production in the second and third lactations were examined using linear regression. The effect of high SCC during a cow's current lactation was found to be essentially the same as previously reported by other investigators. An increase in the lactation average linear score of 1.0 was associated with a decrease of approximately 200 kg of milk per lactation. Limited carry-over effect of elevated SCC during the second lactation was found in the third lactation. For third lactation milk production, the effect of increased SCC during the preceding (second) lactation was only about 20 to 30% as much as the effect of SCC increases in the third lactation.