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Abstract

Additive genetic relationships between heifer pregnancy and scrotal circumference in Hereford cattle.

Abstract

An attempt was made to determine an appropriate method for using yearling scrotum circumference observations and heifer pregnancy observations to produce expected progeny differences (EPD) for heifer pregnancy. The additive genetic effects of and relationship between scrotal circumference and heifer pregnancy for a herd of ∼230 Hereford cattle in Solano (New Mexico, USA) were estimated. The binary trait of heifer pregnancy was defined as the probability of a mated heifer conceiving and remaining pregnant to 120 days. Estimates of heritability for heifer pregnancy and scrotum circumference were 0.138±0.08 and 0.714±0.132 respectively. Estimates of fixed effects for age of dam and age were significant for heifer pregnancy and bull scrotum circumference. The estimate of the additive genetic correlation between yearling heifer pregnancy and yearling bull scrotum circumference was 0.002±0.45. Additional analyses included models with additive genetic groups for scrotum circumference EPD for heifer pregnancy or heifer pregnancy EPD for scrotum circumference to account for a potential non-linear relationship between scrotum circumference and heifer pregnancy. It is concluded that the results support the development of a heifer pregnancy EPD because of a higher estimated heritability than previously reported.