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Effects of Age, Parity, Season of Calving, and Sire on Milk Yield of Carora Cows in Venezuela¹

Department of Animal Science, Cornell University, Ithaca, NY 14853-4801

ABSTRACT

Age-parity-season of calving, mature equivalent factors were developed for the Carora breed of Venezuela from more than 13,000 244-d milk yield records from the Venezuelan milk recording program from 1975 to 1986. Age-parity-season interactions with parity-age were most important for young cows and seasonal effects most important for old cows. Multiplicative factors were verified as useful to adjust milk yields of Carora and Brown Swiss crossbred cows. Repeatabilities for mature equivalent adjusted milk were .47, .36, and .38 between pairs of repeated records through fourth lactation. Heritability of milk in first lactation by REML procedures was 12% based on 44 Carora sires with 14 effective daughters per sire. Small population size for Carora cattle hinders usefulness and cost effectiveness of progeny testing as the primary investment in genetic gain. Greater potential economy is likely from exploiting the dams of sires genetic pathway.

¹ Project 414, a continuing project to Southern Regional Project S49, Genetic Methods of Improving Dairy Cattle for the South.

² Universidad Nacional Experimental de los Llanos Occidentales Ezequiel Zamora, Guanare, Venezuela.

³ Facultad de Ciencias Veterinarias, Universidad Central de Venezuela, Maracay.