EFFECTS OF LEFT DISPLACED ABOMASUM ON TEST DAY MILK YIELDS OF HOLSTEIN COWS

A linear model was used to estimate the effects of left displaced abom asum on 57,383 test day milk yields collected between January 1, 1992 and December 31, 1993 in New York State from 12,572 Holstein cows in p arity less than or equal to 6. Twenty-five index categories were creat ed to differentiate among milk collected between calving and up to 60 d after diagnosis of left displaced abomasum, milk collected >60 d aft er diagnosis of left displaced abomasum, milk collected before or afte r diagnosis of cows with any diseases other than left displaced abomas um, and milk collected from cows that remained healthy for the entire lactation. For each parity, the statistical model included fixed effec ts (management, age at calving, length of dry period, previous 305-d m ilk yield, stage of lactation, year and season of sampling date, disea se index, and DHIA SCS at milk sampling) and random effects (permanent and temporary environments) on test day milk yields. From calving to 60 d after diagnosis, cows with left displaced abomasum yielded on ave rage 557 kg less milk than did cows without left displaced abomasum; 3 0% of losses occurred before diagnosis. Milk loss increased as parity and productivity increased. Cows with left displaced abomasum were nea rly twice as likely to have another disease than were cows without lef t displaced abomasum.