Setting the voluntary waiting period: one number that should not be one number

The voluntary waiting period is the interval after calving before a cow is deliberately made eligible for service. Most herds run a single figure — commonly 50 to 60 days — applied to every cow. The biology does not support that uniformity, and a growing body of controlled work suggests that differentiating the number by parity and production is one of the cheapest reproductive gains available.

The biological floor

Uterine involution is substantially complete by around 30 days in an uncomplicated calving and considerably later where there was dystocia, retained membranes or metritis. Serving before involution is complete depresses conception regardless of whether oestrus is expressed, which is why almost no well-run herd sets a VWP below about 40 days and why cows with a recorded calving complication should carry an individually extended one.

Parity is the practical dividing line

• First-lactation cows are still growing, peak lower and flatter, and generally return to positive energy balance sooner — they tolerate earlier service well.
• High-producing multiparous cows are in deeper and longer negative energy balance, and their conception at early service is measurably poorer.
• Splitting the herd into two VWPs — for example earlier for primiparous, later for high-yielding multiparous — is simple to operate and usually gives an immediate conception-rate gain at first service.

The extended-VWP question

Recent Scandinavian and Dutch trials have tested substantially extended waiting periods, sometimes beyond 100 days, as part of a longer-lactation strategy. Burgers et al. (2021) and subsequent work report improved conception at first service and fewer services per conception, alongside changes in lactation persistency and body condition. The honest summary for a herd manager in 2026 is that extended VWP is credible and interesting, works best for healthy high-persistency cows, and should be tested on a defined group in your own herd rather than imposed herd-wide on the strength of trial results.

The audit

Pull the distribution of days in milk at first service for the last twelve months and split it by parity. If the distribution has a long right tail, the problem is detection or eligibility management, not the VWP. If conception at first service is markedly poorer in the earliest-served multiparous cows, the VWP is too short for that group and the correction is essentially free.