Cattle Today

Cattle Today

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by: F. David Kirkpatrick
Professor Animal Science, University of Tennessee

Sire selection is an important decision made in cow/calf operations. In a single-sire herd, the bull is responsible for one-half of the genetics of the entire calf crop. Almost 87 percent of the genetic makeup of a herd, where replacement heifers are retained, will be represented by the last three sires used in the operation. The first requirement before selecting a new herd sire is to determine your herd's present level of production and decide what traits need improvement. Several considerations should be evaluated in sire selection.

What Breed Do I Need?

Many breeds are available from which to make a selection. Select a breed with a market demand for the offspring in your marketing area. Also, select a breed that has a performance program and can document expected performance of future progeny. No one breed exceeds all others in all traits of economic importance. Within the breed you select, make sure that the prospective sire has the genetic potential to make positive directional changes in economically important traits. If color of the offspring is an important factor, you need to understand the inheritance of coat color in cattle.

Do I Save Replacement Heifers?

If heifers are to be retained from the herd, then the bull's EPD for milk needs to be considered. A bull with a milk EPD that is below the breed average will likely sire daughters that will not have excellent milk production, and consequently will wean lighter calves. If feed resources are limited, selecting a bull with a milk EPD that is well above the average of the breed could drastically affect future reproduction of his daughters. Higher levels of milk production require greater feed resources to retain a high reproductive rate. Consequently, selecting and using a bull with a milk EPD well below the average of the breed could reduce the weaning weight of his daughters' calves. Most breed EPD averages for all traits are not zero. It is important to obtain an up-to-date breed sire evaluation report to determine different breeds' average EPDs for different traits. These sire evaluation reports can be obtained by writing to the particular breed association or finding it on the Web.

What If I Do Not Save My Own Replacement Heifers?

If heifers are not saved from within the herd, milk EPD does not have to be considered in the selection process. Emphasis should be given to other traits of importance.

Do I Need to Increase Weaning Weights?

If weaning weights need increasing, then a bull to consider should have an EPD for weaning weight higher than the breed average. If your previous bull was of the same breed as the bull you are considering, his weaning weight EPD needs to be greater than the previous bull's EPD. If you are considering changing breeds, then you at least need a bull that exceeds the breed average EPD for weaning weight. EPDs are useful only for comparing prospective bulls of the same breed, not between breeds. There is a positive relationship between increased weaning weight and increased birth weight. As weaning weights and growth increase, birth weights also tend to increase. Be sure that as you find individuals with high weaning-weight EPDs, they do not have excessively high birthweight EPDs.

Will I Use This Bull on Mature Cows and Replacement Heifers?

If you use the same bull for mature cows and first and second-calf heifers, then you need to consider the bull's birthweight EPD. Dystocia (calving problems) is highly related to birth weight. Larger calves experience more difficulty in the birthing process. The largest amount of calving difficulty occurs in first- and second-calf females. It is important to select a bull used for all females in the herd to have a birthweight EPD that is below the breed average. If replacement females are to be synchronized and artificially inseminated to a low birthweight EPD bull, then the bull selected for the mature cows can have more latitude in birthweight EPD.

Do I Want to Increase the Frame Size of My Calves?

If calves are discounted at the market due to frame size, then the frame size of the bull should be considered in the selection procedure. Frame size is one of the highest heritable traits (about 45 percent) in beef cattle, so changes in frame size can be realized fairly rapidly. Small-framed bulls sire small-framed calves. If frame size needs to be increased in your calf crop, a bull with a larger frame size than the present one being used should be selected. Selecting a large-framed bull that is extremely different in frame size than the mature cow herd may present calving problems. There is a positive relationship with with mature size and birth weight. Strict-attention must be given to the birth weight EPD of extreme-framed bulls that are in consideration for selection. Also, as selection is made for increased frame size, there tends to be a "frame creep" in the replacement heifers retained. You will eventually increase the mature size of the cow herd, and if feed resources are not available to support larger-framed females, reproduction may suffer.

Does My Percent Calf Crop Weaned Need Improvement?

The single most economically important trait in beef cattle production is reproduction. Many factors have an effect on reproduction; using them as indicator traits may improve the percent of the calf crop weaned. Birth weights certainly have a bearing on reproduction, as the frequency of calving difficulties is increased. Females experiencing calving difficulty usually require a greater length of time to return to estrus, and if eventually rebred, calve later in the calving season the following year. Also, females with difficult births produce calves that are more susceptible to sickness and death, which can drastically affect the percent of the calf crop weaned. Consider birthweight EPDs as a means of protecting against dystocia (calving difficulty).

High milk production levels of a cow herd with limited feed resources also may have an detrimental effect on reproduction. Take care when attempting to maximize milk production levels in replacement females that are expected to be productive on poor forage quality and/or quantity. Using milk EPDs and being aware of the breed averages can guard against this problem in the sire selection process.

The prospective herd sire should have passed a Breeding Soundness Examination (BSE) within the last 30 to 45 days prior to selection. Scrotal circumference is measured in the exam. For example, a 12-month-old bull should have a minimum scrotal circumference of 31 centimeters. Some breed association sire evaluation programs have scrotal circumference EPDs. Research has indicated that bulls with larger scrotal circumferences sire daughters that reach puberty at earlier ages than those sired by bulls with smaller scrotal circumferences. Selecting prospective herd sires with larger scrotal circumferences and positive scrotal circumference EPDs are indirect selection procedures for improved reproductive efficiency.

Is Temperament of the Bull Important?

Temperament is inherited. Cows that are ill-tempered usually produce calves that are similar. Pay attention to the attitude of the prospective herd sire to reduce temperament problems within your herd.

Should I Be Concerned about Carcass Traits?

Most cow-calf producers are not concerned about carcass qualities of their calves, since they feel like they only sell weaning weight. However, with the emphasis in the industry on carcass value, carcass predictability will continue to play a more important part in merchandising feeders. This would be important if cooperative marketing of feeder cattle was the method of merchandising your feeders. Many breed association sire evaluation reports provide carcass EPDs on individuals that can be used in designing feeder cattle with carcass predictability.

Where Can I Find a Bull That Will Fit My Needs?

There are many sources of bulls with documented and predicted performance. Purebred breeders who maintain performance records on their beef cattle operations will have both adjusted performance records and EPDs for traits of economic importance. These records should help in deciding what kind of bull will best fit your needs. If breeders do not have these records and information, then neither you nor the seller will have any idea how that particular bull can contribute. He may or may not provide a means of making improvements. Just being a purebred and registered bull does not necessarily mean a bull will improve a herd.

Other sources are performance﷓tested bull and central test station sales. Many breed associations sponsor sales that have animals consigned with performance records and EPDs.


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