Factors Affecting Milk Yield and Reproductive Performance

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Abstract
Dairy Herd Improvement testing records of 201 dairy herds of sizes from under 100-over 1000 cows and herd average milk yields from under 5000-over 10,000 kg were studied. Average days to 1st postpartum breeding tended to be less in herds of over 500 cows. Herds of 300-600 cows had highest production per cow. Herds with higher average yields averaged shorter intervals to 1st postpartum breeding and fewer days open. Days open included farrow cows arbitrarily assigned 305 days open. Number of breedings changed little as herd yield increased, but days open for highest producing herds averaged 1 estrous period shorter than for low producing herds, suggesting better detection of estrus.For the individual cow, high yield or associated factors have a small but real antagonistic association with reproductive efficiency. Days to 1st breeding, to last breeding and days open increased 0.27, 0.80 and 0.61 and number of breedings increased 0.014 for each 100 kg increase in 180-day yield of fat-corrected milk. The record averages of high-producing herds indicate this antagonism may be overshadowed by good management: effective estrus detection probably is a major factor.