Changes occurring in the breed composition of U.S. dairy herds
The breed composition of Dairy Herd Improvement (DHI) herds from 1990-2018 was examined to determine what changes have occurred in the U.S. population. Breed was characterized by the animal’s recorded breed code. Animals with breed code ‘XX’ or ‘XD’ were considered crossbred. The number of animals obtaining genetic evaluations increased by 66.9% since 1990 even though number of DHI herds declined by 64.2%. This confirms a substantial increase of recorded pedigrees in the national database since 2006. Breed composition was examined on a herd and year of calving basis. Ayrshire (AY), Brown Swiss (BS), Guernsey (GU), Holstein (HO), Jersey (JE), Milking Shorthorn (MS), and ‘other breeds’ were documented as was crossbred composition. An investigation was conducted to determine total cows assigned to each breed by year. All lactation records entering the database were examined. Trends were substantiated on a cow basis. From 1990 to 2018, the number of cows increased from 2,386,473 to 3,983,909. HO increased from 2,161,579 to 3,243,490; JE increased from 135,374 to 485,849. Crossbreds experienced the greatest percentage increase going from 2,971 to 207,368. Sires and dams of all cows were examined also. HO and JE sires comprised 83.3% and 14.8% of DHI cows in 2018 respectively. The percentage of HO has been gradually decreasing (90.8 to 83.3%) while the percentage of JE has been increasing (5.7 to 14.8%). The parentage of crossbreds was examined to determine the background of the growing crossbred population (5.2% in 2018). Any breeds having representation of ≥0.1% were shown. A majority of dams of crossbreds were coded as crossbreds also (54.6%); 51.3% of the sires of crossbreds were HO. The breed of the maternal grandparents when the dam was a crossbred was assessed also. Similarly, 60.6% of their maternal granddams were crossbreds and 57.7% of their maternal grandsires were HO. The parents and grandparents of XX or XD cows display a significant reduction in the number of currently unknown breed codes. Reporting thresholds for breeds presence in individual herds were 1 cow, 10%, 25%, 50%, 75% and 90%. The number and percentage of herds meeting each threshold within each breed was determined. The number of herds that had at least 75% crossbreds increased from 18 to 189 from 1990 to 2018, while herds with 75% HO declined from 34,977 to 11,604 herds and those with 75% JE declined from 2,323 to 859.
Key words: breed composition; United States; dairy herds; crossbreds;
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