Selection and evaluation of beef heifers (Proceedings)
Productivity for beef cattle herds has been shown to be increased when a high percentage of heifers become pregnant early in the first breeding season. A producer's heifer selection and development program should result in most heifers in the replacement pool reaching puberty at least 42 days prior to the start of breeding because the conception success to first service is lower on the puberal estrus compared to the third estrus. In addition, profitability is improved in herds with excellent cow longevity because of lower costs due to fewer replacement heifers maintained and less dystocia, as well as increased income (heavier weaning weights) due to fewer young cows. Both onset of puberty and cow longevity are largely determined by which females are selected as replacement heifers.
Selection begins at birth. Heifer calves from early maturing cows requiring minimal nutritional supplementation to conceive early in the calving season should be identified as possible replacements. These heifers should be from dams that have excellent udder, foot, and leg conformation.Determining that udder conformation will be acceptable as an adult is difficult, if not impossible when examining a heifer. Therefore, heifers should be selected from dams that have udders with a wide rear attachment and a fore attachment that extends as far forward as possible. Teats should be small enough to be easily grasped by a newborn calf.
Pigeon toes, long toes, and straight hocks are examples of some common structural problems in adult beef cows. Heifers identified as potential replacements should have feet of adequate size relative to her frame, with evenly sized toes. The heel should have adequate depth and the pastern and foot should have a correct degree of slope as viewed from the side. The hind leg should have an acceptable set to the hock as viewed from the side. The range of acceptability is 120° to 155° with the ideal of 140°. When evaluating front limb structure, heifers should have an adequate slope to the shoulder (45°-50°) and the legs should be acceptably straight when viewed from the side and front. A straight shoulder reduces the shock-absorbing function of the front limb and reduces the ability of the mature animal to move long distances in range situations, and front legs that bow outward even slightly make a heifer unacceptable. If a heifer or her dam fails any of these criteria, the calf is identified as unsuitable as a replacement. In addition, heifer calves from bulls that have been identified as producing early-maturing, high fertility females with low nutritional maintenance requirement should be identified as potential replacements. If, however, a bull's offspring have a tendency toward any structural unsoundness or delay in reaching puberty, heifers from those individuals are unacceptable.
A valuable objective measurement of a bull's ability to produce daughters that reach puberty at a young age is the bull's yearling scrotal circumference. Scrotal circumference is a moderately to highly heritable trait. Scrotal circumference at 1 year of age has a high correlation with puberty in bulls and in the percentage of that bull's daughters that are pubertal by 1 year of age. A minimum standard for the sires of replacement heifers is a yearling scrotal circumference of 32 cm.