A712
Reproduction Management -
Management, EPDs, & Breeding Soundness

Because the reproductive ability varies greatly between different breeds of cattle and even between animals of the same breed, a producer must be aware of certain breed trends and the heritability of certain traits. For example, when compared to a Simmental, a Jersey dam on average will routinely produce a smaller calf, but have an easier time delivering. Performance sheets with EPDs and accuracy levels can be very valuable in helping to predict these genetic differences. The EPD records are kept by most of the beef breed associations and can be accessed by the internet or by contacting each breed association directly. Many performance records contain EPDs for birth weights (lbs), calving ease (ratio), weaning weights (lbs), yearling weights (lbs), scrotal circumference (cm), along with growth and milk characteristics.

Once a performance record has been obtained, the challenge comes in understanding and applying the data. The term Expected Progeny Difference (EPD), is a measure of the expected difference in traits the offspring from one sire or dam will have when compared to others in the same breed. For example, a bull with a +50 lbs. yearling weight EPD will produce yearling calves weighing 50 lbs. more than a bull with a yearling weight EPD of 0.0 lb. The other item to consider when evaluating EPDs is the accuracy or reliability of the EPD values. The accuracy is reported as a low of 0.0 to a high of 1.00. The higher the number, the more reliable the sire or dam will produce the indicated EPD in the traits of their offspring.

The table below lists various traits that can be influenced by genetics. The numbers expressed next to each trait estimate how easily or probable the particular trait will be passed on genetically. These numbers are actually the heritability of each trait and can range anywhere from 0.0 to 1.00. The higher the number, the greater the chance of passing on the trait.

Because many animals are not purebred and may not have EPD values calculated, on-farm records are essential in determining which animals to keep or cull. The on-farm records must be complete and accurate. The information and table below are a sample of one of these records. Specific instructions on how to calculate each desired number are also provided. Actual information for a specific cow can be recorded on page K125 of the appendix.

1. To calculate the adjusted 205-day weaning weight, use the following equation:
   
   [(Weaning wt - birth wt*) / (age in days) X 205 ]+ birth wt + adjustment for age of the dam**
   
   For example, the first female calf’s adjusted 205-day weaning weight in table 2 is calculated as follows:
   
   [(420 - 89) / (205) X 205] + 89 + 54** = 474 lbs
   
   * If birth weights are not available, use 75-85 lbs in the equation.
   ** This number is taken from table 3.
   
   
2. To calculate the weaning ratio, take the calf’s adjusted 205-day weaning weight and divide it by the average 205-day weaning weight of the other animals of the same sex in the herd. (In this example the average 205-day weaning weight ratio for the female calves in this herd is 475 lbs, and for the male calves it is 555 lbs.)
   
   For example, the first female calf’s weaning weight ratio in table 2 is calculated as follows:
   
   474 / 475 = 99.8%
   
   
3. The adjusted yearling weight is calculated using the following equation:
   
   [160 X (Actual yearling wt - actual weaning wt) / number of days between weights] + adjusted 205-day wt
   
   For example, the first female animal’s adjusted yearling weight in table 2 is calculated as follows:
   
   [160 X (765 - 420) / (365 - 205)] + 474 = 819
   
   
4. Yearling weight ratios are calculated by taking the yearling’s adjusted yearling weight and dividing it by the average yearling weight of the other animals of the same sex in the herd. (In this example the average yearling weight ratio for the female animals in this herd is 810 lbs, and for the male animals it is 1,112 lbs.)

* Calves should be weighed as close to the 205-day mark (165-245 days acceptable range) as possible. If they are weighed when they are outside of this range, the weights cannot be accurately compared to other animals.

From the information collected in table 2, the following conclusions can be made about this cow and her offspring:

1. This cow produces female calves that have an average weaning weight that is just slightly lower than the herd average. This is calculated by finding the average weaning weight ratio of her two female calves (99.8 + 97.2 = 197 / 2 =98.5). An average weaning rate ratio of 98.5 means that when compared with the rest of the herd, this cow produces female offspring that weigh 1.5% less than the herd average at weaning time.
2. The male calf born in 1999 is above the herd average in both weaning weight and yearling weight. This conclusion is made from the weaning and yearling weight ratios. This calf has a weaning weight ratio of 105.6% and a yearling weight ratio of 106%. This means that this calf weighs 5.6% more than the other male calves in the herd at weaning time and 6% more at a year.
3. One final conclusion that can be made based on this cow’s average yearling weight ratios for both male and female animals is that she normally produces calves that have yearling weights that are close to or above average. This is determined by calculating the average yearling weight ratio for all four calves (100 + 110 + 95.6 + 106 = 412 / 4 = 103%). This means that her calves on average weigh 3% more when compared to other yearlings.

* Ratios can only be used to compare animals that have similar genetics, nutrition, and environmental conditions.

A breeding soundness evaluation (BSE) should be performed on every animal that is brought into a herd or is kept to be a replacement. This exam is essential for all bulls and should include the following:

1. Physical Examination: This is the first step in the BSE protocol. Detailed information on performing a physical exam can be found on page A632.
   
   
2. Testicles, Prepuce, and Penis: These areas should be felt (palpated) for abnormalities, adhesions, lesions, tone, consistency, and shape.
   
   
3. Semen Evaluation: Bulls that are sterile or low in semen quality often have no external visual marks of identity. Female animals that fail to get pregnant are often sold immediately, yet the bull that may be responsible for the problem stays home from market to continue causing the same problem–a low calf crop. Evaluation of semen prior to the breeding season identifies males not capable of settling females.
   
   The semen evaluation is based upon the examination of sperm and grading of samples taken from each male. A machine using fluctuations of low voltage current (or battery powered for portables) stimulates ejaculation and is commonly used to obtain semen samples from bulls. This method uses a tool to accomplish this ejaculation called an "electroejaculator." Because the voltage is very low, no harm is done to the male. After collection, each semen sample is examined and graded for the following:
   • Color
   • Motility - Movement of sperm cells.
   • Concentration of sperm cells (population density).
   • Morphology - Anatomy, shape, or form of the sperm.
   • Percent live sperm cells.
   
   The "ideal" semen should be free of white blood cells (WBCs) and have greater than 50% progressively motile sperm. The semen should also have a minimum of 70% structurally (morphologically) normal spermatozoa. If these values drop, so does the reproductive capacity of the potential bull.

Sperm Cells: Poor semen quality (left) and good semen quality (right).

This table identifies the reproductive characteristics used to identify bulls that have the potential to be good breeders:

* Studies show that scrotal circumference size relates directly to quality of semen that is produced.

Use of Scrotal Circumference Tape: The testicles are pulled firmly into the lower part of the scrotum by encircling the top of the scrotum with one hand and pulling down gently on the testicles. The scrotal tape is formed into a loop and slipped over the scrotum and its contents. The tape is pulled up snugly around the greatest diameter of the scrotal contents. When weather is cold, males retract their testicles making it difficult to take proper measurements. Special care should be taken to pull the testicles into the bottom of the scrotum and eliminate any wrinkles. The thumb and fingers should be placed on the side of the scrotum, rather than between the testicles. This helps to prevent separation of the testicles and an inaccurate measurement. The circumference is measured in centimeters (cm) and is read at the point where the tape crosses the small steel crossbar on the tape thumb piece.

Other characteristics that should be considered when evaluating a bull for breeding soundness include body condition, size in relation to cows, conformation (feet and legs), testes/scrotum, penis/prepuce, and disposition. A rectal exam should be performed to evaluate the ampullae and prostate. A trichomoniasis test should also be part of any reproductive exam.

When evaluating a female cow for reproductive soundness, a thorough physical exam should be performed. This includes a rectal palpation to evaluate the cervix, uterus, uterine horns, ovaries, and pelvic diameter. Animals that have narrow pelvic diameters may have difficulty calving. Animals that are "freemartins" may not have normal reproductive organs and yet may have relatively normal looking external genitalia (vulva). Freemartins are infertile females that are born twin to a male. Replacement heifers and cows should also be examined and determined to be free of any infectious disease, not only in the reproductive tract, but elsewhere. Diseases of concern include brucellosis, vibriosis, trichomoniasis, leptospirosis, IBR, BVD, and neosporosis. An evaluation of the cow’s body condition, size in relation to bull, conformation (feet and legs), udder, and external genitalia should also be done.

Crossbreeding is the process of mating animals from two different breeds. This mating can result in offspring that experience increased growth, better fertility, better mothering ability, and changes in other production traits. Hybrid vigor is the term used to describe this advantage to crossbreeding. Breeds that are more genetically different (like a Hereford and a Brahman) are more likely to produce hybrid vigor in their offspring when crossbred. Hybrid vigor can make those traits that have a low heritability (like fertility - see table 1 on A712) and give them a greater possibility of occurring in the crossbred offspring. Crossbreeding can be an effective tool for the producer if used in the right situations.

Summary: The decisions on what animal to buy, cull, or keep should be based on facts and if possible, past production. Economics and environmental conditions also influence these decisions. In general, one genetic trait that needs improvement in the herd should be chosen. All purchasing, culling, and replacement decisions should be made based on making this improvement. Once the trait is improved, another trait should be chosen and management decisions based on improving it should follow.

Because a bull can distribute his genetics to multiple offspring, he has a greater impact on the genetics of a herd than any individual heifer or cow. Therefore, selection of a breeding bull is one of the most important decisions a producer can make.