Excerpts from Beef Improvement Federation Weaning Weight Guide.
Weaning weights are used to evaluate differences in growth potential of calves and the milking ability of dams. In order to evaluate differences in weaning weights, individual calf records must be adjusted to a standard basis. It is recommended that weaning weights be standardized to 205 days of age and a mature age of dam basis. Weaning weights should be taken when a contemporary group of calves averages about 205 days of age. Adjusted weaning weights should be calculated for calves within an age range of 160 to 250 days of age. Records on calves weaned outside this range should be given a special management code and handled as a separate management group. They should not be adjusted for age of dam, because appropriate correction factors are not available.
Adjusted 205-day weaning weight is computed on the basis of average daily gain from birth to weaning, using the formula:
Adj. 205-Day Wean Wt. = (Wean Wt. – Birth Wt.) Divided by (Weaning Age in days) X 205 + Birth Wt. + Age of dam Adj.
Individual animal records for adjusted 205-day weaning weight and adjusted 205-day weaning weight ratio should be calculated and reported separately for bulls, steers and heifers. The ratio should be calculated with the following formula.
Adj. 205-Day Weaning Wt. Ratio = (Individual Adj. 205-day Weaning Wt.) Divided by (Group Average Adj. 205-day Weaning Wt.) X 100
Adjusted 205-day weaning weight ratios document each animal’s percentage deviation from the average of its contemporaries and are useful in ranking individuals within each sex. For weight ratios to be of value, contemporaries should be herd mates, similar in age, and raised under the same management and environmental conditions.
Excerpts from Beef Improvement Federation guidelines
on Selection Practices related to replacement animals.
A well marked British White Calf
Sire Selection.
To make sustained contributions to the breeding program, bulls should be structurally and reproductively sound. Sound feet and legs are essential in order for a bull to cover many acres of pasture, both for obtaining adequate nutrition and mating cows. Structural soundness is not an all-or-none phenomenon; rather it is expressed in various degrees. Bad feet, pigeon toes, excessively straight or sickle hocks, and loose or pendulous sheaths are examples of some of the more common structural problems of bulls. Because many structural problems become worse as bulls grow older and heavier, it is particularly important to critically evaluate young bulls.
Structural soundness of bulls that are candidates for selection should be evaluated in a systematic manner. Inspect each bull‘s feet, toes, heels, pasterns, knees, hocks, and sheath. When viewed from the front, the feet should point straight ahead, both when the bull is standing and walking. The feet should be large and round with a deep heel and with toes that are similarly sized. When viewed from the rear, the legs should be equally far apart at the hocks and pasterns and then toe out slightly from the pasterns to the ground. The bull should move freely with each hoof striking the ground evenly.
Many structural problems are partially heritable and should be particularly discriminated against when daughters will be kept for replacements. However, structural problems that do not compromise longevity or ability to service cows are of little consequence in the selection of terminal sires.
Evaluating bulls for structural soundness also provides an opportunity to gauge a bull‘s temperament or disposition, a moderately heritable trait. A bull with poor disposition may be dangerous or difficult to work, and his daughters may be difficult to manage as well.
Replacement Female Selection. Many of the concepts involved in the selection of sires are equally appropriate to selection of replacement females. In general, female selection is less intense than selection of males and accuracy is usually greater for proved bulls. Therefore, most genetic progress results from sire selection. From an economic perspective, selected replacement females should calve first at two years of age, reproduce annually thereafter, and remain in the herd for an extended period of time.
Beyond the ability to reproduce annually, replacement females should remain functionally sound to advanced ages. Proper foot, leg, and udder structure is important. A cow’s udder should be well attached, level across the bottom, and have small to moderate sized teats that are not excessively long. In general, soundness of the udder deteriorates with age.
Cow Culling Decisions. Removal of cows from the herd is largely an economic decision, because it has limited influence on genetic improvement. In most cases, it has been recommended that nonpregnant cows routinely should be culled. Functionally unsound cows should almost always be culled. Cows with impaired mobility or unsound mouths are unlikely to harvest sufficient nutrients to maintain body condition and be productive.
Heifer Selection. Seedstock breeders typically select replacement heifers from within their own herds as opposed to purchasing heifers from other breeders. This has the advantage of utilizing the same genetic resources that produce their marketable bulls. Selection of replacements is a multi-stage process and is similar to any other selection scheme for females. However, it is important to note that the quality of sires used to produce the heifers will greatly impact the genetic potential of future calf crops.
Heifers should be culled for structural problems that may interfere with their ability to raise a calf, breed back, and have a long productive life.
