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Single and Multiple Trait Sire Selection. First Lactation Milk Yield and Composition, Conformation, Feed Intake, Efficiency, and Net Income^1,2,

USDA, SEA-AR, Animal Science Institute, Milk Secretion and Mastitis Laboratory, BARC, Beltsville, MD 20705

ABSTRACT

Daughters of sires selected on Predicted Difference milk of first lactations (yield) were compared with daughters of sires selected on an udder index from among artificial insemination bulls with less than 10% of their daughters culled and with a Predicted Difference fat-corrected milk greater than 181 kg (merit). On latest proofs yield bulls were 425 kg higher than merit bulls for Predicted Differences of first lactations, whereas merit bulls had an average Predicted Difference Type, which was 1 point higher than yield bulls. Data were from first calving interval.

Yield daughters produced 685 and 51 kg more milk and solids-not-fat but were .28% and .12% lower in fat and protein percentages than merit daughters. Energy intake of the ad libitum mix rations was nearly identical, but gross feed efficiency was significantly higher (.73 vs. .69) for yield daughters. Mammary conformation score was significantly higher for the merit group. A significantly higher number of merit daughters were coded acceptable for descriptive udder traits in the udder index. Net income per day was significantly higher for the yield group than for the merit group ($.25 vs. $.15). Much of this difference was due to the higher expense associated with a 21 day longer calving interval of merit heifers.

¹ Contribution to the NC-2 Regional Project, Improving Cattle through Breeding with Special Emphasis on Selection.

² Scientific Article No. A2736, Contribution No. 5786 of the Maryland Agricultural Experiment Station, Department of Dairy Science.

³ Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061.

⁴ Department of Dairy Science, University of Maryland, College Park 20742. Present address: Department of Animal Science, Iowa State University Ames 50010.

⁵ Department of Dairy Science, University of Maryland, College Park 20742. Present address: College of Animal Science, Haryana Agricultural University, Hissar 125004, India.