Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 6/22/2003
Publication Date: N/A
Technical Abstract: To determine usefulness of current and previous test-day somatic cell score (SCS) in predicting test-day milk yield, test-day records from Holstein first and second calvings between 1995 and 2002 were examined. Initial selection required that cows have at least the first four test days with recorded milk yield and SCS for both parities 1 and 2. Least-squares analyses were conducted for milk yield on test days 2 through 10 within herd and cow. The model included regressions on both current test-day SCS and mean SCS of all previous test days with separate estimates by parity; effects for parity and calving year also were included as well as a regression on days in milk on test day 1. Error degrees of freedom ranged from 143,748 to 214,526. Highest SCS was most often on test day 1 (20%) followed by test day 10 (14%). Effect of current SCS on test-day milk yield was much greater for parity 2 than for parity 1 but only slightly greater than effect of mean of previous test-day SCS on milk yield for parity 1. Milk loss from elevated SCS likely results both from mammary status on test day and from direct and residual influences of elevated SCS earlier in lactation. Mastitis in early lactation appears to have a carryover effect on milk yield for the remainder of the lactation.