In a December 2016 Dairy Star article, we discussed economics of changing the voluntary waiting period comparing a 60-day voluntary waiting period to an 88-day VWP for first lactation and for second and more lactation cows. Extending the VWP is often recommended to improve reproductive performance on first breeding, improve pregnancy rates and to increase profitability by extending lactations.
    Cows with extended lactations would be expected to have higher milk production per day of productive life (including dry periods) because of relatively lower days spent dry compared to lactating. Two papers in the Journal of Dairy Science by Stangaferro in 2018 looked at effects of 60- versus 88-day VWPs for double ovsynch protocols in three commercial New York herds during 2014-16. Results of the comparison showed improvement in first service conception rates for first lactation cows with the longer VWP, but no change in conception rates for older cows with a longer VWP.
    The main message from those studies was that extending the VWP from 60 to 88 days using a double ovsynch protocol resulted in a net gain of $68 per cow for lactation one and a net loss of $85 per cow for lactation two or more over 18 months. The main reason for the loss in older cows was increased culling and replacement of an older cow with a heifer. The take home message is that a longer VWP may make sense for first lactation animals but does not make sense for older cows.
    More recently, the same group looked at three options: double ovsynch with a 60-day VWP (DOVS60), double ovsynch with an 88-day VWP (DOVS88), and presynch ovsynch with cherry picking cows in heat and a 50-day VWP (PSOv50).
    Once again they compared first lactation cows to older cows. The study was based on one herd and a modeling program. The herd was using BST during the trial. Cows became pregnant sooner after calving with the DOVS60 and PSOv50 than with DOVS88 for both younger and older cows. At 350 DIM, the proportion of nonpregnant cows was no different for each of the three protocols for lactation one animals, but for older cows more animals were open at 350 DIM for DOVS88 than the other two protocols.
    For culling, all protocols had similar outcomes for lactation one animals, but culling was significantly increased for older cows in the DOVS88 protocol. Regarding milk income, first lactation animals showed more income for the total lactation with the DOVS88 compared to DOVS60 and PSOv50, but there was no difference between protocols for older cows.
    Cash flow per available milking slot was modeled for the 18-month period after calving with various pricing scenarios. On average, cash flow for first lactation cows was $16.70 greater per available milking slot with the DOVS88 versus the DOVS60. Over the entire range of variables, the return was negative $38 per slot to positive $75 per slot. The average difference for DOVS88 versus PSOv50 in first lactation animals was only $1.20, in favor of DOVS88. The difference for DOVS60 versus PSOv50 was negative $15.50 for DOVS60 for first lactation cows.
    For second lactation and older animals, the mean return of the DOVS60 versus DOVS88 was negative $87 per slot. Over the range of input costs, the return was negative over 99% of the time for the DOVS88 versus DOVS60. For DOVS88 versus PSOv50, the average return was negative $83 per slot. The average difference between DOVS88 and PSOv50 was about $4 per slot over 18 months.
    The bottom line from these studies is that the most likely of the three different VWPs and protocols that are likely to be most profitable for first lactation cows are DOVS88 and PSOv50. However, the economic gain versus the DOVS60 is fairly small. For older cows, DOV60 and PSOv50 would be better than DOVS88, and the difference between the low VWP protocols and the 88-day VWP is significantly greater than the difference for younger cows. Thus, a blanket recommendation to increase the VWP beyond 60 days in all lactation groups is not likely to be profitable. Increasing the VWP in lactation one may be slightly profitable. The main reason longer VWPs were not more profitable in older cows was increased culling.
    There are three other points to consider. First, these studies were all done on cows injected with BST. It is likely that not using BST might result in better profitability with shorter VWPs, because the rate of decline in milk production in later lactation is greater in animals not supplemented. Second, the performance of a PSOv protocol is, to some degree, dependent on heat detection for first insemination, and this may vary significantly between herds. Third, in today’s world of high pregnancy rates and farms needing fewer replacements, cows get fewer breedings, and thus chances to get pregnant before being coded do not breed. Extending the VWP lowers the number of available days for a cow to get pregnant. As a result these studies may actually underestimate the negative effects of increasing VWPs in older cows today.
    Thus, ask questions when someone tells you to increase your herd’s voluntary waiting period. Talk to your veterinarian and ask him or her to help evaluate any potential changes.
    Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minnesota. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.