A vital component of an adequate bull fertility rate is the high fertility level of each breeding animal in the herd. Since individual bulls provide services to many females, a deficiency in the breeding capacity of one bull has a more significant impact on herd productivity than the fertility problems in a single female. Using a sub-fertile bull may lead to longer calving intervals, fewer calves produced, and increased costs from wintering open females. All these results cause severe financial loss to the cow-calf producers.
Bull fertility is measured by the percentage of cycling females exposed to the bull and impregnated during a specific period (usually 60–90 days). Actual fertility levels result from genetic potential and environmental factors, including nutrition, health, and cow and bull management. Determining actual fertility before a bull is used in the herd is impossible. However, a bull can be evaluated for breeding soundness, and this information can be used to assess its potential fertility. A few bulls may be sterile, but most have fertility levels ranging from very high to very low.
When it comes to bull fertility, the nutritional composition of their feed and forage is not just a factor; it’s a game-changer. While various factors can contribute to reproductive failure, the role of proper nutrition cannot be overstated. Failure to meet the nutritional needs of a bull often leads to sacrificing its reproductive function first. This underscores the importance of carefully considering the diet of bulls to enhance their reproductive capabilities.
Regarding nutritional considerations for bull fertility, energy takes the top spot. Bulls require ample energy to grow and maintain their bodies, and the energy level in their diet has a direct impact on their testicular activities. Dietary energy profoundly affects the bull fertility rate, and striking the right balance is crucial. The energy level should be tailored to the animal’s growing stage and body condition, ensuring it’s neither too high nor too low.
Protein is the second controlling nutrient in most ratios. Insufficient protein in the diet further decreases daily feed consumption, feed passage rates, and overall digestive efficiency—reduced feed intake results in both a protein and energy deficiency.
Along with the building block of skeleton tissue, they are the supporting factor of various enzymes and biochemical reactions involved in metabolism, reproduction, etc. Minerals are divided into two parts of their body: micro-minerals and macro-minerals. Macro minerals include Calcium, Phosphorus, Magnesium, Potassium, Sulphur, Sodium, and chlorine. Micro-minerals include Cobalt, Copper, Iodine, Iron, Manganese, Selenium, Zinc, etc. However, Copper, Selenium, and Zinc have essential roles in reproduction as they are the trace minerals most commonly deficient in the diet.
Bulls fed diets deficient in vitamin A have delayed puberty, reduced libido, and reduced spermatogenesis. Vitamin E deficiency has a deleterious effect on germ cell proliferation. Vitamin E affects intra-testicular factors that directly or indirectly regulate specific steps of germ cell development.
Calves predicted to become bulls with delayed maturity and smaller testicles exhibited reduced levels of LH secretion during the early period of gonadotropin elevation (8-16 weeks of age). Administering GnRH treatments to these calves increased their circulating LH concentrations during this critical phase, leading to an accelerated onset of puberty. Additionally, administering FSH treatments during childhood had a similar effect on the scrotal circumference and sperm production, aiding in the hastening of reproductive development.
The organic eatables that bulls prefer for their betterment in an increase of fertility rate:
Sufficient intake of these food supplements ensures the good health of the Gir cow breed and increases the fertility rates of bulls.
A well-balanced mineral and vitamin intake contributes to robust immune systems, successful reproduction, and optimal calf growth. Achieving the proper mineral balance requires considering the past mineral nutrition of cows and calves, the mineral content of hay or pasture forage, and the mineral concentration in feed or mineral supplements. Diets with mineral imbalances can lead to poor animal performance, reducing profitability.
Optimising fertility in feeding bulls depends not just on protein and energy but also on minerals and vitamins, which are crucial for spermatogenesis and semen quality. Copper, zinc, and phosphorus directly impact fertility, and these minerals are often lacking in forages. It is essential to closely monitor the nutritional status of growing bulls during their initial breeding seasons.
Bulls should be fed according to their specific requirements from a young age, allowing them to reach puberty at the appropriate time, develop larger scrotal circumferences, and experience increased release of gonadotropic hormones, which leads to healthy and fertile sperm.
The fertility of breeding bulls is a critical factor in maintainable cattle production and growth programs. Feeding management is always the key factor in producing a good bull. The essential phases of bull feeding are preweaning nutrition, postweaning nutrition, conditioning before breeding season, and post-breeding season.
The finest feeding programs and the plane of nutrition during these phases are essential not only to maintain bulls in physically sound condition but also to impact the secretion of gonadotropins and, consequently, sexual development in bulls. Thus, an adequate level of energy, protein, minerals, and vitamins during different stages of growth and reproduction is of supreme importance to maximise the fertility potential of a bull.
The bull’s diet must contain balanced amounts of protein and energy required for sperm production and the physical activity associated with breeding. Enough vitamins and minerals are also significant in reproduction.
Cattles are specially formulated feed supplements that provide essential organically bound trace minerals, selenium, and vitamin E to support fertility in cattle udder health and claw integrity.
The mineral zinc is crucial for immune function and testosterone production. Studies have demonstrated that adding zinc to the diet can enhance the amount of semen, sperm concentration, and sperm movement in male cattle.
The energy-dense feedstuffs will be cereal grains or co-products like corn, oats, corn gluten feed, and dried distiller grains. Fibre-based energy-supplying co-products are also acceptable feed choices.
Low libido, sperm defects, or physical factors affecting bull mobility or mating ability can directly cause subfertility. An estimated 20-25% of bulls are believed to experience subfertility.
The vitamins B1, B2, B3, B6, and B12 are linked to a reduced likelihood of experiencing ovulation disorder and ovulatory infertility.
Various elements can influence the effectiveness of appropriate bull-to-cow ratios, including the landscape, season, the bull’s motivation to mate, mating capability, semen quality, the bull’s condition at the start of the breeding season, and the bull’s age.
Hay comes in many types, each with its nutritional benefits and uses. Alfalfa hay has higher phosphorus and calcium levels than grass hay, which is high in proteins.
The bull’s evaluation only involves the proportion of normal sperm, which needs to exceed 70%. To assess sperm function, the integrity of sperm plasma can be determined using a vital stain like eosin.
The range in the Fertility Index is +15 to -15. A bull with an above-average FI will breed cows with improved calving intervals and better non-return levels. Every point increase in the fertility index from -3 to -2 will decrease the calving interval by 0.6 a day and improve non-return rates by 0.25%.
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