Part 1 – Heifer and semen requirements
Whilst there are often a lot of moving parts when it comes to devising a breeding plan, there are some general rules that can be followed. And while no plan is ever fool proof, it can be made simple and easy to follow if we take the time to think it through carefully at the start and then review periodically to how it is working in practice.
Calculate heifer requirements
The first thing to get a handle on is the number of heifers you need coming through in future, remembering that heifers being conceived now will be calving into the herd in 2 years and 9 months’ time. Don’t forget to factor in:
Cull rate – both voluntary and involuntary culls
Calf mortality <12mths
Heifer mortality or failure to conceive >12mths
Age at first calving (AFC) – If calving heifers in at over 24months you will need more replacements. For every month over 24 months you will need around 4% extra heifers.
Contingency – We need some surplus in case of unforeseen losses or growth requirements
As an example, a herd of 200 milkers, with a 30% cull rate will need 60 heifers as a starting point, however once you factor in 5% calf losses and 5% failure to conceive then they now need an extra 10% or 6 heifers. If the average AFC is 26months then another 5 are needed and then we need a contingency of at least 15%, adding another 9. So in total we are now looking at needing 80 heifers to be hitting the ground each year.
Calculate the number of straws of sexed semen required
Once we have our heifer requirement figure, we now need to work out where those are going to come from and how many straws of semen will be required. I previously would have discussed the merits of sexed semen here, but I’m hoping that anyone reading this has now ditched the use of conventional semen, save when there are real fertility issues going on.
We now need to work backwards from numbers of heifers required to get to number of straws required. We must factor in:
Conception rate (CR) using sexed semen – This is likely different for heifers and cows but we should be aiming for >60% on the heifers and >40% on the cows.
Number of services we are willing to use sexed – I always recommend 2 services toi sexed and then beef thereafter. Essentially if you have decided she is worth putting to sexed then she should be worth 2 attempts. After 2 attempts, the risk of her remaining open for long periods is high so I would use conventional beef AI or put to the beef bull on the 3rd service which should have a higher CR than the dairy sexed.
Early embryonic death, abortion and stillbirths. Usually not a significant factor but if it is an issue then obviously more straws of sexed will be needed to generate our replacement number.
Going back to our example where 80 heifers are required. If we used 2 services of sexed semen on the best 60 maiden heifers with a CR of 60%, we would generate 50 heifers from heifers. This leaves us 30 heifers needed from the cows. With a little fag packet maths, to get to that number with a 40% CR, we would need to breed just under 50 of the eligible herd to 2 services of sexed. I usually factor in that the bottom 15-25% of maiden heifers will be genetically worse than the top 25% of the cows so putting the bottom 20% of heifers straight to beef is a sensible starting point.
It is always tempting to ignore genetic figures and go on looks, milk records and gut feel when choosing cows to go to sexed however it’s important to remember that how an animal performs in the herd is down to both genetics and environment. If the best genetic heifer in a cohort didn’t receive any colostrum at birth and went down with pneumonia as a young calf, she will never appear to be the best animal in the herd. However, her genetics are still the best in the bunch and there’s a good chance her offspring will be too. We just need to make sure they get a better start than she did!
In the second part of this article we will look at bull, heifer and cow selection.
If you would like to find out more about anything discussed here, or for support improving your herd’s genetic selection, please give us a call at the practice on 01453511311.