Reproductive Efficiency of Purebred and Crossbred Dairy Cattle

Nine measures related to breeding efficiency were used for comparisons among purebred Ayrshires, Brown Swiss, Holsteins, and Jerseys and between purebreds and 32 crossbred groups representing 2-breed, 3-breed, 5/8, and backcrosses by purebred sires and progeny of crossbred sires. There were four herds wi th Holsteins common to all, Brown Swiss and Jerseys in three herds and Ayrshires in one herd. Four 2-breed, two 3-breed, and two backcross groups were common to two or more herds. Among purebreds, breed effects were significant in 16 of 72 tests, but there was no consistent trend favoring one breed. Generally, Jerseys were better than Holsteins, and Brown Swiss were poorer than Holsteins. Purebred females bred to their breed required similar services for conception (1.77 versus 1.79) as when bred to a different breed of sire. Least squares estimates of differences between purebreds and crossbreds favored crossbreds in 86 of 144 tests suggesting advantages for breeding efficiency; however, few were significant. Standard errors frequently exceeded estimates of differences. Parity was not associated with superiority in the crosses. Received June 29, 1973. This work was part of the Southern Regional Dairy Cattle Breeding Project, S-49 (Genetic Methods of Improving Dairy Cattle for the South). *Present address: Veterinary Institute, Tropical and High Altitude Research, Universidad Nacional, Mayor de San Marcos, Lima, Peru. ~Present address: Dairy Experiment Station, Lewisburg, Tennessee 37091. 4Present address: Department of Animal Science, North Carolina State University, Raleigh 27607. Average heterosis in % was (2.0) for days from calving to first heat, (11.1) days first breeding to conception, (1.7) days open, (.8) calving interval, (6.4) percent pregnant <90, (8.4) <120, (-.2) <145, (1.6) <200 days postpartum, and ( 1 . 3 ) in services for conception. The average overall was 3.2%. Numbers of sterile heifers were similar for crosses and purebreds, but fewer crosses completed two gestations. Crosses by purebred sires were poorer than the mean of parent breeds in percentage of reproductive disorders (7.8 versus 5.5), calving troubles (6.2 versus 5.0), and termination of lactation for health (10.1 versus 9.6), sterility (6.6 versus 5.7), and death (2.2 versus 2.0). Daughters of crossbred sires had slightly fewer reproductive disorders than crosses by purebred sires. Progeny of crossbred sires were similar to other crosses in death losses but had higher frequencies than crosses by purebred sires in the other traits.