The mean lactation number in Table 1 shows that on
average, cows are older in organically managed herds
(mean lactation number was 2.97 in organic and 2.35 in conventional herds). Average culling age also differed between the two management systems. Cows from organic herds were culled at a mean age of 5 yr and 4 mo, compared with 4 yr and 6mofor conventional herds.
The EA305 for cows that had completed 305 d of lactation was 22% lower in organic than in conventional herds. When this comparison was done by lactation, organic herds were consistently lower. Differences ranged from 19 (in the fourth lactation) to 28% (in the first lactation). All these differences were significant at a P value less than 0.01