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Bull management involves ensuring the right number of healthy bulls for your herd, minimising stress and reducing injury risks. A correct ratio depends on your herd's size and percentage of pregnant cows. Generally, one yearling bull per 20 heifers is advisable. Select bulls considering their health, age, size, and temperament. Keep bulls in good condition before and during mating periods, ensuring their diet and body score are appropriate. Regular checks and quarantine are essential to maintain a healthy herd. Lastly, monitor their mating performance by comparing expected and actual in-calf rates.
Good bull management means running adequate numbers of bulls with the herd, reducing their stress, and handling bulls to minimise the risk of injury to people and animals.
Having enough bulls when cows are likely to be on heat is important in ensuring good reproductive performance. The number of bulls required will depend on the number of cows or yearling heifers likely to come on heat while the bulls are with the group.
A minimum of 2 bulls should be with a mob at all times. The table below shows the minimum number of bulls required to run with the herd/mob at any one time. For a full bull rotation during mating, the total number of bulls required is double the numbers in the table.
|Likely % of herd pregnant at start of bull mating|
|No. cows in the herd or mob||30%||40%||50%||60%||70%||80%|
Run one yearling bull per 20 yearling heifers at all times to cover the poorer performance of yearling bulls. Ensure there are always at least two sexually active bulls running with each mob throughout the mating period. Bulls are typically run with yearling heifers on an all-in basis. You may want a few extra bulls around in case any need to be replaced. The ratio should be about one bull to 15-20 heifers.
If you are using heat synchrony, and returns will occur when bulls are running, you need to estimate the minimum number of bulls running with cattle during this period (using one bull per 10 non-pregnant cows). Alternatively, recommence heat detection and AB for 3 or 4 days, starting 19 days after the previously synchronised inseminations.
To make sure bulls are sexually mature and able to serve, bulls need to be well grown. By the time a bull reaches 14–15 months, they should have achieved 50% of their mature weight. This should increase to 85% by two years of age.
To maintain the health of bulls and all other animals, ensure that bulls receive the same vaccination programme as the heifers and cows. Develop a drenching programme with your vet as well.
Bulls need to be kept in good body condition, particularly in the 3 months prior to their mating start date. Several weeks before the bulls will be used, make any required diet changes to ensure bulls are not too fat or too thin. They should be in body condition score 4.5 to 5.5 prior to mating. Body condition score bulls well before mating to give you time to make diet changes.
Consider veterinary examination of bulls at least a month before the bulls start work. Examinations range from a simple physical exam, to a serving ability test, or a full assessment of semen quality.
Good bull management will ensure bulls are well adjusted to their environment before mating and have been through a biosecurity quarantine. Bulls should be moved to the farm between two to three months and ten days before they are required for work. Split the bulls into teams for rotating (half resting, half working) to reduce fighting.
When bulls are running with the herd, you can take several steps to increase bull activity and reduce health risks.
In many herds, the period following the first 6 weeks of mating reflects the bull mating period. Herd reproductive performance during this time is an indicator of bull performance. By assessing performance at this time, you may be alerted that changes to bull management may be required.
Below is the expected not-in-calf rate based on a given 6-week in-calf rate and length of mating.
|6-week in-calf rate||Total weeks of mating (AB period plus bull mating period)|