BVSc & Veearts
Age is one of the most important factors among them; bull fertility typically increases with age, peaking between the ages of 3 and 4 years of age. While older bulls may see a loss in their ability to procreate, younger bulls may show diminished fertility due to a higher percentage of morphological abnormal sperm and/ or lower semen concentration.
Since healthy and viable sperm are necessary for successful reproduction and are more likely to be produced by bulls with advantageous genetic features. It is critical to maintain optimal nutrition together with good genetics to create a balanced diet that is rich in minerals and vitamins to assist the development of healthy sperm. At our bull station we feed bulls a fertility pellet ration from one of the leading animal feed companies. A body condition score of around 3,5 (out of 5) is ideal due to the fact that bulls which are too fat have lower semen quality.
The bull’s clinical health is crucial, and it should be free of illnesses and infections that could harm its reproductive system or general well-being. Fertility can be negatively impacted by infections such as brucellosis, leptospirosis, infectious bovine rhinotracheitis (IBR), and bovine viral diarrhoea (BVD). Any disease (or even vaccination with live strains) can lead to a loss in fertility of up to 8 weeks.
It is very important to only buy bulls and produce semen from bulls that have been fertility tested, including all disease that can be transmitted via the semen – for example Trich + Vibrio sheath washes should be done 3x, with weekly intervals and all should be negative before a bull can be used for mating and/ or semen production.
If a bull is to be registered as an AI bull, then it is imperative that the bull be approved by the relevant breed society and be collected in a registered quarantine facility, registered with Department Animal Improvement. There are further stringent conditions applicable to AI bulls. The main reason for all these health tests is to ensure that no disease transmission can occur via the semen straws that are sold to other breeders. Bulls that have been collected and frozen from farm collections have an increased risk of disease transmission, depending on whether all relevant health tests have been performed.
Testicle quality and scrotal circumference are two markers of fertility; higher scrotal circumferences are typically linked to greater reproductive potential. It is important to note the scientific evidence which points to the fact that bulls with large scrotal volume will breed early maturing heifers – i.e. a younger age to first calving. Successful fertilization depends on sperm motility, morphology, and concentration, among other aspects of semen quality. Bull fertility can be impacted by environmental stress, especially heat stress, which is why hot regions call for cooling and proper protection. Remember that all bull camps must have some form of shade for the bulls during hot months. Seasonal differences, such as harsh weather, can also have an impact on fertility. In extremes summers or harsh winters, some bulls may show lower reproductive capacities and decreased libido.
Bull fertility is positively impacted by proper handling and management techniques, such as reducing stress while handling, keeping an environment clean, and doing routine health checks. It is essential to have a veterinarian perform a Breeding Soundness Examination (BSE), which assesses physical condition, scrotal measures, and semen quality. Bulls’ chances of mating are influenced by social dynamics within their herd; dominant bulls are more likely to mate than inferior bulls. DNA testing of calves born is a good way of determining which bulls have a higher libido + fertility.
Hormonal balance is important because imbalances can cause problems with conception, and physical harm to the reproductive organs can have a deleterious effect on fertility. It is imperative for cattle producers to closely monitor and effectively manage these elements. They should seek advice from veterinarians or livestock specialists to optimize bull fertility to ensure successful reproduction and the general health of the herd. Never inject a reproductively active bull with any hormones unless you have consulted with a veterinarian, as hormone treatments can negatively impact the semen parameters of a breeding animal.
SEMEN QUALITY
An essential component of artificial insemination programs for cattle reproduction is the quality of bull semen. Bull semen quality is determined by several factors, some of which may vary slightly between laboratories and organizations. These factors include volume, concentration, motility, morphology, viability, concentration of sperm abnormalities, pH level, colour and consistency, concentration of nonsperm cells, and cryopreservation tolerance.
The amount of semen that the bull produces is indicated by the millilitres of ejaculate volume. For artificial insemination, concentration—the number of sperm cells per millilitre—is essential, with a higher concentration of sperm generally being preferred. Sperm motility, which is measured as the fraction of progressively motile and non-progressively motile sperm, evaluates the ability of sperm cells to proliferate. Sperm morphology is important because irregular morphology can affect fertility. It measures the size, form, and composition of individual cells.
A high percentage of viable sperm cells in the sample is a sign of high-quality semen. Viability counts the number of living sperm cells in the sample. The percentage of cells with defects is determined by the concentration of abnormalities in the sperm. Sperm motility and viability are influenced by semen pH, which is normally slightly alkaline. Semen, which is often pale to transparent with a gel-like texture, is also assessed for colour and consistency. Furthermore, the amount of non-sperm cells in the sample indicates the presence of other cells and detritus; excessive concentrations may be an indication of contamination or infection.
Sperm cryopreservation tolerance, which gauges the sperm’s ability to withstand freezing and thawing, is essential for transporting and storing semen in preparation for artificial insemination. Together, these factors help determine if bull semen is suitable for artificial insemination programs and what level of overall quality it possesses. These factors may have different requirements in different breeding programs, and values between breeds and individual bulls may differ. Working with an experienced veterinarian or reproductive specialist is essential when assessing and interpreting these characteristics considering breeding objectives.
When buying semen straws insist on an evaluation report that includes among other: ID of the straws, motility, morphology and a 2-hour post thaw stress test. If you are uncertain of the quality of semen straws or if you have experienced poor conception with AI, please ask your local AI station to evaluate the various batches of semen in your liquid nitrogen tank. It is also advisable to store semen straws at a local AI centre as these will ensure that adequate liquid nitrogen levels are maintained – remember that every time a semen straw is raised above the frost line there is loss of sperm / semen quality. Never handle semen straws outside of liquid nitrogen.
SPERM MORPHOLOGY
The size, shape, and structural properties of the sperm cells in a sample of semen are referred to as sperm morphological parameters in bulls. This evaluation is important for semen analysis since it provides important information about the bull’s reproductive capacity. During the examination, a few important parameters are usually assessed.
A well-defined acrosome covering the front portion of a typical sperm head and an oval or elliptical shape are characteristics of normal sperm heads that are crucial for fertilization. Fertility can be affected by excessively tiny or large heads; thus, head size is examined to make sure it falls within the normal range. The midpiece, which joins the head and tail, should be straight and free of defects since it houses the mitochondria that supply energy for movement. It is expected that the flagellum, or tail, will be long, straight, and evenly thick, free of kinks or other imperfections that could make swimming more difficult.
A large proportion of sperm containing leftover cytoplasmic droplets can lower fertility since they may be an indication of inadequate maturation. A well-defined and intact acrosomal cap, which covers the front portion of the sperm head, is necessary for the effective entry of the egg during fertilization. The capacity of the sperm to fertilize an egg might be affected by several abnormalities, such as double heads, double tails, bent tails, and other structural flaws, which are evaluated.
Examiners can see and evaluate individual sperm cell structures under a microscope by utilizing a stained semen sample to evaluate sperm morphology. One of the most important factors in determining a sample’s reproductive potential is the proportion of normal sperm. Bulls that possess a greater proportion of sperm that is morphologically normal are more likely to be viable, whereas those that possess a higher proportion of aberrant sperm may have lower fertility.
It’s crucial to remember that different laboratories and organizations may have slightly varying standards for evaluating sperm morphology. To offer a thorough assessment of a bull’s fertility, the interpretation of sperm morphology should also be considered in conjunction with other semen metrics such sperm concentration, motility, and overall semen quality.
For any bull to freeze successfully – be that conventional or sexed semen the following parameters will apply:
