Bulls have a major influence on the future performance of the herd. A superior bull can increase performance and decrease risk; while a poor performance bull can adversely affect future production and increase your risk as a manager. In pastoral areas which are extensive or which have numerous watering places, bull selection costs are exacerbated by the need for higher bull percentages. The process of bull selection requires much thought and considerations of relevant objective information.
There are some issues of concern when it comes to bull selection
- How many cows per bull: This may vary according to average bull age, the fertility of bulls as well as the number and diversity of watering points, etc. Lower percentages may be acceptable if sub fertile or infertile bulls are not present in the herd.
- How much to pay for replacement bulls: Is the extra cost recovered from the extra value of subsequent sales? Does paying more get you a better bull anyway? How much emphasis should be placed on objective information?
- How long to keep them, or how many to replace each year?
- Whether to breed some, most or all of your own bulls?
What are the effects of buying bulls that are better?
By purchasing better bulls we hope to achieve some of the following:
- produce more calves per bull
- produce off-springs that grow faster
- produce progeny that have desirable carcass traits
- produce future breeders which will produce more valuable offspring
- Produce animals that repeatedly meet market specifications
- for the years that they are in the herd, these bulls will sire superior male and female off-springs
- Improvements using genetics are permanent and will continue to accumulate as high performing sires are selected.
Traits that are looked at when selecting a bull/ Genetic improvement
Traits or characteristics can be controlled from the smallest point of development being the cell. Genetics best describes the transfer of traits from generation to generation. Different farmers want different characteristics in their stock hence it is very important for them to have a bull that will satisfy their interest. As mentioned trait transfer to offspring start at cell level where the cell will carry genetic characteristics. Genetic improvements involves increasing production in the next generations and one must take advantage of the normal biological variability and follow the steps:
- measure as accurately as possible the production characteristics (traits) you want to improve in the parent herd
- select the best animals with the traits of highest economic importance and use them to breed the next generation
- select for traits of reasonable heritability
- cull the poorest performers
- Select animals using the fewest number of ‘selection criteria’ as possible for the most rapid gains.
These steps must be carried out with each successive generation in order to obtain continual production and profit improvement from genetic means.
Selection can be for many reasons but this article will shed light on a few traits for selection
- Selection for fertility: it is not easy to assess the bull`s fertility until it reaches maturity. To determine the fertility of the bull one should assess the following: examination of the testicles (physical examination of scrotal contents and measurement of scrotal circumference/size), examination of the penis, prepuce and sheath, collection and evaluation of semen, physical examination of internal sex organs, assessing the bull’s desire (libido) and ability to serve females (serving ability), structural soundness of the bull’s legs, feet, eyes and general structure.
- Selection for growth: this can be based on weight, average daily gain and weight ratios as well asBreeding plan estimates of genetic merit. Selection of animals using an animal’s actual measure of weight and daily gain do not allow for differences in management, age etc between animals. Weight ratios only allow accurate ranking of animals within a group where all animals are treated the same and are similar in age. The best method of selecting is that based on an EBV which is calculated in Breeding Plan.
- Selection for carcass:Most beef producers want ‘feedback’ but fail to see that they are sending the wrong feedback to studs themselves. Unfortunately there are still some cattle buyers who have difficulty in visualizing ‘what is fat’ and ‘what is muscle’ in the live animal. Over-fat bulls do not work as well as bulls in working order. Obese bulls tend to have lower libido or desire to serve cows, arthritic conditions and deteriorating semen quality. The sad fact of life is that many commercial producers complain that the studs over-feed their bulls and that they have to be ‘let down’ before they will work. Yet they still pay high prices for the fat bull. The farmer needs to know where fat is deposited in large amounts, which part of the bull are mostly muscle and what is the retail beef yield.
- Selecting for tenderness: Tenderness of beef is one of the traits frequently identified by consumers as a desirable trait for eating quality. The Cattle and Beef Quality has clearly identified that beef tenderness can be modified genetically. Tenderness can be improved by selecting bulls that are more docile. However producers are reminded that this selection decision should be relative to the market requirements for their beef. An EBV for tenderness will ultimately be of greater value in bull selection.
- Selecting for marbling: The amount of intra-muscular fat is scored in carcasses as a Marble Score (MS). In the live animal the ultrasound measurement at the 12/13th rib provides a percentage of intramuscular fat in the eye muscle. This measurement is then converted to a genetic difference of an EBV for IMF%.
Abnormalities that can be detected in bulls
- Premature spiral deviation of penis
Spiral deviation of the penis is a genetic problem in a percentage of bulls. It variesin incidence between horned and polled bulls and between herds and breeds. Spiral deviation is a condition where the erect, free end of the penis of an affected bull prematurely spirals to the right hand side in an anticlockwise direction. The effective width of the penis doubles, thus preventing service. A characteristic of the early stages of spiral deviation is that it occurs intermittently. It appears to be more common in beef than in dairy bulls and in polled rather than horned bulls and gets progressively worse as the bull reaches 5 to 6 years of age. Young bulls (12 to 24 month old) with the early stages of the condition will achieve conception rates of 60-65% in 2 months of mating. This will drop to 20-30% conception rates as the bull reaches 4 to 5 years of age. Corkscrew or premature spiral deviation of the penis has been reported in a range of breeds. Other abnormalities identified include: In some bulls the penis upon erection may deviate down or to one side as a result of a previous physical injury. Following injury an adhesion may develop between the penis prepuce and sheath. As the penis becomes erect the adhesion restricts the free extension and causes the penis to bend to one side or down (‘broken’ penis).
Injury to the penis can cause the blood vessels to rupture causing blood to permeate surrounding tissues causing a massive ‘blood blister’ or haematoma. This inhibits effective erection causing pain to the bull and lowered fertility.
This is a ‘tag’ of tissue on the free end of the penis that normally releases during maturity. The end of the glans penis may be deviated back, reducing effective mating if the tissue is not severed. This is apparently a heritable condition as it is seen more frequently in some herds.
Warts on the penis are reasonably common, but unless excessively large, will not affect the bull’s sensitivity and ability to effectively serve cows. These may disappear with time.
Granular infection of the prepuce is a common venereal disease, particularly in young bulls which reduces the bull’s desire to serve because of the pain. It can be treated with antibiotics and older animals may develop immunity.