Voluntary waiting period (VWP)

Definition

The voluntary waiting period (VWP) is the number of days after calving during which a cow will not be bred by management choice, even if she shows heat. It is a herd policy, not a biological fact. After the VWP ends, the cow becomes eligible to be bred.

The VWP exists because fertility is poor in the first weeks after calving: the uterus is still involuting and many cows are in negative energy balance. Herds weigh that against days open: every 21 days added to the VWP adds roughly a cycle to days open for cows that would have conceived at the first chance.

The VWP matters well beyond breeding policy, because it defines eligibility for most reproduction metrics:

21-day pregnancy rate and heat detection rate count a cow as eligible only once she is past the VWP.
Days to first service has the VWP as its floor; the useful measure is how soon after the VWP cows are bred.
Cumulative pregnancy by DIM curves start at the VWP.
Open-cow reports need it to tell “fresh, not yet eligible” from “fresh, eligible but not bred” (see RC codes).

In timed-AI herds the effective VWP is set by the synchronization program: the first timed AI lands at a fixed DIM (e.g. at the end of a presynch-Ovsynch or Double-Ovsynch sequence), and that DIM is often later than the nominal VWP.

Heifer VWP

Heifers have no calving to count from, so their “VWP” is an age (or size) at which they become eligible to breed, commonly around 12–15 months of age or about 55% of mature body weight (Penn State Extension targets 55% of mature weight by 13–15 months). When the setting isn’t known, one practical estimate is the age at which about 10% of a heifer cohort has had a first service. See heifer reproduction.

How to pull it in DC305

The VWP is a herd setting in DC305. BREDSUM uses it to decide when cows enter the eligible pool for the 21-day table. It can be overridden for a single run:

BREDSUM\EV                 21-day table; prompts for the VWP ending day
BREDSUM\EV70               21-day table with a 70-day VWP
BREDSUM\YERV390            heifers, VWP as 390 days of age (Select Sires 2013 example)

A Select Sires guide (2013) says BREDSUM assumes a 50-DIM VWP when none is set (“use V(#) if VWP is not 50 DIM”).

Check the setting against what the herd actually does:

LIST ID LACT FDAT DIM TBRD FOR LACT>0 TBRD=0 DIM>60      past a 60-day VWP, not bred
COUNT ID FOR LACT>0 RC=2                                 fresh (RC 2), not yet bred (all DIM)
EGRAPH BRED \SN1                                         first services by DIM
SUM DIMFB FOR LACT>0                                     average DIM at first breeding

Replace 60 with the herd’s VWP. Then look at the distribution of DIM at first service (EGRAPH BRED \SN1, or a list of first breedings; BREDSUM has no by-DIM-at-breeding table). The earliest common DIM at first service is the herd’s actual VWP. If many first services come earlier than the setting, the setting is wrong or the policy isn’t being followed. DIMFB is not in every setup; see days to first service.

Typical range

Herd context: US Holsteins, lactating cows, freestall or dry-lot, mostly timed AI with some detected heats.

Group	Common VWP
Lactating cows (all)	50–60 DIM
First-lactation cows (where set separately)	60–75 DIM
High producers or herds extending lactation	70–90+ DIM
Range seen in practice	40–90 DIM

Timed-AI first service in many programs falls around 70–80 DIM even with a 50–60 day nominal VWP. In the published trials, first timed AI fell at about 69 DIM (Presynch-Ovsynch; Fricke et al. 2003), about 73 DIM (Presynch-Ovsynch, Ovsynch started at 63 DIM; Moreira et al. 2001) and about 78 DIM (Double-Ovsynch, breeding Ovsynch started at 68 DIM; Souza et al. 2008). See synchronization protocols.
Longer VWPs tend to raise first-service conception rate but add days open; whether that pays depends on persistency and milk price. With Double-Ovsynch, moving the VWP from 60 to 88 days raised first-service P/AI from 41% to 47% (46% to 55% in first-lactation cows, no significant change in older cows), but delayed pregnancy, raised herd exits in multiparous cows, and lengthened lactation by 13 days without raising milk per day (Stangaferro et al. 2018).

Common mistakes

A DC305 setting that doesn’t match practice. If the herd breeds from 50 DIM but DC305 is set to 60, early breedings fall outside the eligible pool, and pregnancy rate and heat detection rate are distorted.
Changing the VWP and comparing history. Changing the setting changes eligibility for past periods, so historical PR shifts too. Note the date of any change.
Comparing herds with different VWPs. A longer VWP removes early, less fertile days from the denominator and flatters PR.
Calling cows inside the VWP “open”. A fresh cow at 35 DIM is not an open-cow problem.
Using one VWP for cows and heifers. Heifer eligibility is by age.
Assuming a VWP when it isn’t known. Report fresh-not-bred cows by DIM band instead of folding them into “open”.