A712
Reproduction Management - 
Management, PTAs, & Breeding Soundness

breeding stock selection | linear data systems | predicted transmitting abilities | breeding soundness evaluation | scrotal circumference tape

Breeding Stock Selection: The decision on what semen to use, or what animals to use or keep for breeding is a critical one. The animal’s reproductive history and reproductive potential should be major considerations when making a buy, cull, or keep decision. Because this decision is such a critical one, it should be based on sound statistical information. This information can come from linear type data and predicted transmitting abilities (PTAs). It can also come from records kept by the farm and from a reproductive evaluation/breeding soundness exam (BSE) performed by a veterinarian or other professional. Evaluating reproductive ability is best done by utilizing a combination of linear data, PTAs, farm records, and BSEs. The following will discuss these methods of evaluating reproductive ability and give suggestions on how to apply the results.

  1. Linear Data Systems are used to identify the ability a bull has to pass on particular traits. Each trait is given a value between a -3 and a 3. Traits for an average bull will cluster around the zero (0) value. In general, the traits that are greater than 0 mean that the bull will have a positive influence on that trait in his offspring. For example, a bull that has a rear udder width value of 1.04 will produce daughters that have wider udders. The following is a sample of linear trait values for a particular bull:

    Trait    -3  -2  -1   0   1   2   3 

    Values
    Stature                                 X -0.04    Short
    Strength                        X -1.26    Frail
    Body Depth                               X -0.31    Shallow
    Dairy Form   

    X

    		 3.43    Open
    Rump Angle                   X -1.81    High Pins
    Thurl Width   

                 X

    		 0.63    Wide
    Rear Legs-Side Set   

                                 X

    		 -0.15    Straight
    Rear Legs-Rear View   

           X

    		 0.21    Straight
    Foot Angle   

    X                   

    		 0.89    Steep
    Foot & Legs Score   

    X                 

    		 1.14    High
    Fore Udder Attachment   

    X             

    		 1.56    Strong
    Rear Udder Height   

    X                 

    		 1.17    High
    Rear Udder Width   

    X                  

    		 1.04    Wide
    Udder Cleft   

    X          

    		 1.82    Strong
    Udder Depth   

    X             

    		 1.56    Shallow
    Front Teat Placement   

    X  

    		 3.02    Close
    Teat Length                          X -0.95    Short
    Udder Composite                     X 1.69         -
    Foot & Leg Composite   

    X                   

    		 0.83        -

    Understanding the Linear Data Results: Based on the information found in this report, this bull will produce daughters that on average are shorter and potentially frail. However, this bull will also sire daughters that have good udders.

  2. Predicted Transmitting Abilities (PTAs): Because the reproductive ability varies greatly between different animals, a producer must be aware of certain breed trends and the heritability of certain traits. For example, when compared to a Holstein, a Jersey cow on average will routinely produce less milk. Particularly in bulls, PTAs and linear data can be very valuable in helping to predict these genetic differences. The PTAs and linear data can be obtained from many of the breed and/or breeding associations and also on the internet at Select Sires and American Breeders Service (ABS).

    The term Predicted Transmitting Abilities (PTAs) is used to describe the extra performance the daughters from a bull or cow may experience when compared to other daughters of a zero (0) PTA bull or cow. For example, a bull with a PTA of +1206 for milk, will on average sire daughters that will produce 1,206 lbs. more milk during a lactation than other daughters sired by a bull with a 0 PTA for milk production. The other item to consider when evaluating PTAs is the accuracy or reliability (REL) of the PTA values. The reliability is reported to be between 0 and 100%. The higher the number, the more reliable the sire or dam will produce the indicated PTA in the traits of their offspring. Reliability should not be used to select a bull, but should be used to access the risk that future PTAs will vary from the current PTA. PTAs are often given for milk production, protein, fat, somatic cell score, calving ease, and productive life. Some PTAs, like fat and protein, are given a PTA$. This PTA$ estimates the extra income a daughter from this bull would produce in a given lactation. The following is a sample PTA for a bull that is used for semen collection and breeding:

    USDA PTA, 08/2001, Dtrs 256, Herds 123, TPI+1433
            %   lbs   Reliability
    Milk   +1070M   - - -
    Protein   $   0.00   +38   96%
    Fat   $   -0.02   +39   93%
    Net Merit   +$349    -   -   - 
    Calving Ease: 10% Difficult, 93% Reliability, 503 Compared
    Somatic Cell Score: +3.08 82% Rel
    Productive Life: +1.11 78% Rel

    * Information for these reports was taken from American Breeders Service.

    Understanding the PTA Results:     Based on the information found in this report, this bull will produce daughters that on average produce 1,070 lbs. more milk and gain the producer about $349 extra dollars in a given lactation when compared to the average bull with a zero (0) PTA. Currently, average milk PTAs for most bulls range from less than 100 to +2700. The 10% calving ease means that 10% of the heifers bred to this bull may have calving difficulties. A bull with < 8-10% difficulty for calving ease is desirable. Somatic cell scores range from about 1 to 5, with an average of 3.1. Scores that are below 3.1 are considered desirable and reflect a lower somatic cell count in their offspring. With productive life, the higher the number the better. Productive life scores range from about -2.5 to 4.0. TPI stands for Total Performance Index and is a calculation that is made from a combination of many different traits. Higher TPIs indicate superior animals. Currently, TPIs for most bulls range from +1000 to +1700.

  3. Heritability: The following table 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.

    Trait   Heritability
    Milk production   .25
    Fat production   .25
    Protein production   .25
    Percent fat and protein   .50
    Stature   .35
    Strength   .25
    Teat placement   .21
    Birth weight   .45
    Fertility   <.05

     

Breeding Soundness Evaluation (BSE):

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. Evaluation of semen prior to using the bull for breeding 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 bull. 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.

    4. 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).

   

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.

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

Characteristic   

Very Good   

Good   

Fair   

Poor

Scrotal Circumference by age:
<15 months
<18 months
<21 months
<24 months
>24 months   

>34 cm
>35 cm
>36 cm
>37 cm
>38 cm   

>30 cm
>31 cm
>32 cm
>33 cm
>34 cm   

<30 cm
<30 cm
<31 cm
<32 cm
<34 cm   

<30 cm
<30 cm
<31 cm
<32 cm
<34 cm

Semen Activity    

Rapidly swirling
(>70%)   

Slower swirling
(50-69%)   

Some movement or oscillation
(30-49%)   

Very slow or sporadic oscillation
(<30%)

Semen Quality   

>90% normal sperm with no abnormalities   

>70% normal sperm with no abnormalities   

>40% normal sperm with no abnormalities   

<40% normal sperm with no abnormalities

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

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. See page F842 for additional information on trichomoniasis.

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.

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 or semen is one of the most important decisions a producer can make.