Seasons of Calving: Age, Management, and Genetic Differences for Milk

Differences between six seasons of calving (January-February, March-April, etc.), three ages (~2, 3, ~4 years), dry lot and pasture management, quartiles of herds on average production, and their interactions were measured by maximum likelihood in 37,247 305-day-2X-mature equivalent records of milk by 15,507 Holstein cows in 198 herds on test in Michigan Dairy Herd Improvement Association from 1958 to 1964. The largest yields of January-February declined 352 kg to the least for July-August calvings. Threeyear-Dials yielded most milk, but yield by two-year-Dials was 25.4 kg more than the weighted average of older cows. The 4,195 records by 2~719 drylot cows were 338 kg more than 3,566 records by 2,318 cows in matching pasture herds.