Relationship between early postpartum blood composition and reproductive performance in dairy cattle.

Blood samples were collected over 1 year from 115 postpartum Holstein cows to determine the relationship between blood composition and reproductive performance. Blood samples were collected from each cow at 14 to 21 days (sample 1) and 38 to 45 days (sample 2) postpartum. These samples were analyzed for packed cell volume, hemoglobin, total protein, calcium, phosphorus, magnesium, copper, zinc, and selenium. Blood composition varied little with lactation number and season, and relationships were not consistent for the two collection periods. Hemoglobin, packed cell volume, total protein and zinc were associated negatively and calcium and magnesium associated positively with at least one measure of milk yield. None of the blood components examined at the two collection periods had a consistent relationship to reproductive performance. The most important relationship was the positive relationship of selenium concentration at first collection period with services per conception and days open.