BULL POWER PLANNING - how many bulls do your cows really need?
The bull to cow ratio is the most important metric to consider when aiming for a successful bull mating. The recommended ratio according to InCalf is one bull for every 30 non-pregnant cows. It is important to remember that this recommendation is specifically for bulls with the cows at any point in time and assumes that cows are not synchronised.
If synchronisation has been used, then a minimum of one bull for every 15 non-pregnant cows is required (especially during the period of peak returns).
When deciding on the number of bulls to purchase we need to allow for resting of bulls and for retiring any which suffer lameness or other animal health issues (their fertility will likely be reduced for the remainder of the season). If your plan is to run two separate bull teams to allow for 50% rest time, you will need to purchase double the number of bulls required to be with the herd at any point in time.
Below is a graph which you can use as a quick reference for the number of bulls required to be with the herd (non-synchronised) at any point in time. It pays to be conservative with the estimation of AB in-calf rates, as a poor bull mating after a disappointing AB period would only add salt to the wound – so ensure that bull power will not be limiting even in the face of low AB in-calf rates!
Example: You have a herd of 580 cows and the in-calf rate to AB has ranged from 65% to 69% over the past few seasons. If we use the 600 cow bar from the graph above and 60% estimated AB in-calf rate, to be conservative, we should have 8 bulls with the herd at any point in time after AB is finished. That would mean 16 bulls if running two teams and resting 50% of the time.
Keep an eye on the non-return rate during the AB period to get an early gauge of AB success. If during mating you believe bull power may become an issue and you don’t have the ability to source safe, quality bulls in time, you could consider some extra strategies to get you through:
· AB for longer
· Consolidate bull teams and use periods of AB to allow for resting the bulls
· Rest bulls and AB during periods of peak returns from synchronisation programs
· Use a bull rotation to allow two days work to one day rest (33% rest time)
· Utilise early scanning to make up a herd of non-pregnant cows you wish to continue to AB and use bulls exclusively for the pregnant/non-AB herd
These strategies may also be used if there is a desire to keep bull numbers to a minimum due to cost and Health and Safety.
The graph below illustrates the impact of poor bull mating on profitability. You can find the difference between expected and actual empty rate on your Fertility Focus Report, which is really comparing the performance of the first six weeks of mating to the remainder of mating. Put simply, for every 1% increase in empty rate, total operating profit is reduced by approximately $10 per cow (InCalf).
Successful bull mating also relies on careful bull selection and management. Give The Dairy Vet Team a call to discuss the specifics of your mating plan and talk about what to look for when purchasing bulls, what questions/records to ask of the vendor, how to assess and reduce risk of introducing infectious diseases (to both the cows and their AB foetuses), and how best to manage the bulls once they are on farm.
Written by Reon McMurtrie