Voluntary Waiting Periods – the interval postpartum when producers refrain from breeding cows – are typically 42 days on most UK dairy farms.
But anecdotal data from 16 high-production herds has shown that it could be too short.
Dr Scott Abbott from Dairy Vet Management, who is also director of technical services at breeding company World Wide Sires, studied more than 4,500 first lactation animals in their first 305 days of milking. He found:
- If high production animals (>8,500litres) got pregnant at 71-90 days in milk (DIM) in their first lactation they produced 300 litres more milk compared with those served earlier than 70 days and hit higher peak milk yields (1.2 litres more on average).
- The animals served later in first lactation also had higher milk yields in second lactation (+300 litres when served at 71-90 DIM and +500 litres when they conceived at 91-120 DIM).
- Although there was no benefit to first lactation milk yield if lower producing animals (<8,500 litres) conceived earlier, they did produce more milk in second lactation (300 litres on average).
- This effect was not seen in mature cows bred early.
“There’s not a lot of good reasons in good producing herds to start breeding before 50 days,” Dr Abbott told delegates at Dairy-Tech on 6 February, adding that most farms he worked with used a VWP of 50 days on cows and 70 days on heifers.
“Each herd is different so I’m not telling you which days to breed but I think you should be looking at it within your herd.”
He said breeders should assess if they should wait longer to serve animals on an individual herd basis by reviewing the following data:
1. Heat detection
What really drives conception rate is heat detection. If you have poor heat detection then you are going to miss too many opportunities to breed cows.
A good heat detection is key if you are going to extend your voluntary waiting period otherwise you shouldn’t bother.
Target: >60% heat detection rate
Is your herd producing over 8,500 litres? These are the herds that benefits the most from extending their voluntary waiting period, research shows.
Target: >8,500 litres
3. Conception rate
Look at the animals that were bred under 50-days and compare them to the number of animals that got in-calf after 50-90 days.
Is the conception rate in the latter group higher? If so, consider moving the goalposts.
4. Look at your failure rate
Don’t get hung up on averages because they don’t always reveal the full picture.
“You also have to look at failure rates,” Dr Abbott said. “That’s the missing link because they can hide if you don’t look at your failure rate.”
He said farmers should assess their percentage of cows open at 150 DIM. This figure should also include “do not breed” cows.
Target: 12-15%. More than 15% suggests a problem.
What if moving my VWP to 70 days extends my days in milk?
There is a bigger concern with long-lactation cows because their milking persistency isn’t as good and the risk of having delayed conception on first lactation animals is low.
Heifers out-perform cows at the tail end, and that is because they’re persistent. Heifers tend to lose about 50-55ml/day and peak at 80 days, whereas mature cows lose about 75ml/day and peak at 55 days.