Prenatal and postnatal maternal contributions to reproductive, maternal, and size-related traits of beef cattle.

Brown Swiss-Hereford (BS-H) reciprocal cross embryos were transferred to BS and H recipient cows and Red Poll-Angus (RP-A) reciprocal cross embryos were transferred to RP and A recipient cows to estimate the relative contributions of ovum cytoplasm and uterine influences to prenatal maternal effects. Calves resulting from embryo transfers (ET) were weaned early (3 to 5 d). Reciprocal cross mating also were made by natural service (NS) between BS and H and between RP and A breeds; part of the offspring were weaned at 3 to 5 d, and the remainder nursed their dams to an age of 150 to 180 d. This was done to estimate breed differences in prenatal and postnatal effects combined and to separate the effects of prenatal maternal influences from postnatal maternal influences of these breeds. Females produced in both ET and NS parts of the experiment were retained to produce three calf crops to an age of about 4.5 yr. The following traits were analyzed: percentage of conception rate; percentage of calf survival; percentage of calves produced per cow exposed; birth and weaning weights of calves produced; and periodic weights, heights, and condition scores of females to an age of 4.5 yr. Neither breed of donor (cytoplasmic influence) nor breed of recipient (uterine influence) had consistently important effects on the traits evaluated. In NS matings, differences between reciprocal crosses were small for most of the traits evaluated. Method of rearing (nursed vs weaned at 3 to 5 d) had no effect on reproductive and maternal traits for RP-A reciprocal cross females, but females that nursed generally were heavier, were taller, and had higher condition scores at most ages than early-weaned females. For the BS-H reciprocal cross, early-weaned females were favored over females reared by their dams in percentage of calves produced per cow exposed, but the method of rearing did not affect other reproductive or maternal traits. BS-H reciprocal cross females that nursed their dams were heavier at 550 d and were heavier and had higher condition scores at an age of 34 mo than early-weaned females.