Hogeveen, H.

Inchaisri, C.

Jorritsma, R.

Vos, P.L.A.M.

Weijden, G.C., van der

English

Name not available

Determining the optimal voluntary waiting period in dairy cows

Wageningen Yield 

Nantes, 14-15 January 2010: Farm Animal Health Economics 
 
DETERMINING THE OPTIMAL VOLUNTARY WAITING PERIOD IN 
DAIRY COWS 
 
 
C.Inchaisria,c, R.Jorritsmaa, P.L.A.M.Vosa, G.C. van der Weijdena, H.Hogeveena,b 
a Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht 
University, The Netherlands 
b Business Economics Group, Wageningen University, Wageningen, The Netherlands 
   c Department of Veterianry Medicine, Faculty of Veterinary Science, Chulalongkorn 
University, Thailand 
E-mail address of main author: C.inchaisri@uu.nl 
A Monte-Carlo stochastic simulation model was created to calculate the economic 
effects of non-optimal fertility in dairy cattle. The model is dynamic and uses time steps of 
one week. The model simulates the reproductive cycle, the occurrence of postpartum 
disorders and milk production. Elements of the cow performance having an economic effect, 
such as milk production per year, number of calves per year, number of inseminations and 
number of culled cows, were summarized. An important managerial aspect of fertility is the 
voluntary waiting period (VWP), defined as the moment (in weeks post partum) when 
insemination of a cows starts, when seen in oestrus. Although there used to be general 
agreement that a calving interval of 365 days, and thus a VWP of 60-80 days was optimal, 
there are currently questions with regard to the optimal VWP. For instance, the shape of the 
lactation curve and the economic of effects of a lower milk production per cow per day have 
changed over the time. The simulation model allows for calculation of the economic effect of 
postponing the VWP. Because cow factors and economic values can differ between and 
within farms, the economic effect of extending the VWP can be estimated. Using varying cow 
factors and economic values for the Dutch situation, based on literature and expertise of the 
authors, data on the economic effect of different VWP were generated. The variables of 
interest were randomly varied, based upon relevant distributions. Cow factors of interest 
were: parity (varying from 1-5), time of the first ovulation (varying from 8-16wks pp), 
ovulation rate (fixed at 0.95), estrous detection rate (varying from 0.3-0.7), conception rate 
(varying from 0.3-0.7), gestation period (varying from 38-42 wks), milk production level 
(varying from 5200-10700 kg/305 days), milk persistency represented by factor C in Wood’s 
curve (varying from 0.012-0.0562), time to peak milk production (varying from 4-8 wks pp), 
milk production loss due to gestation (varying from 0.26-4.32 kg/week depending on 
gestation period), incidence rate of postpartum disorders  reducing ovulation rate (varying 
from 0.03-0.11) and time of disorder occurrence (varying from 6-14 wks pp), incidence rate 
of postpartum disorder reducing conception rate (between 0.20-0.33) and late embryonic 
death rate (between 0.05-0.09). The economic values in the analysis were the costs of a 
decreased milk production (varying from €0.07-0.20 per kg), calf price (varying from €50-
200 per calf), insemination cost (varying from €7-24 per insemination), calving cost (varying 
from €137-167 per calving, and including costs for diseases associated with calving) and 
culling costs, expressed as the retention pay-off (varying from €-1479-261). The culling costs 
depend on parity and the level of milk production of that cow.  
78
Nantes, 14-15 January 2010: Farm Animal Health Economics 
 
FIG. 1. Frequency distribution of optimal voluntary waiting period (VWP) for different cow 
factors and economic values (bar graph, left axis) and average of annual net economic losses 
(€/cow) for different VWP relative to a VWP of 6 weeks (line graph, right axis) 
 
Each simulation is made up of 10,000 iterations. For each iteration, the economic effect 
VWP’s varying from 7 to 15 weeks pp was calculated, using a VWP of 6 weeks as basis. Per 
iteration, the VWP with the minimum of economic loss or the maximum profit was 
determined. The optimal VWP of most cows (95%) was earlier than 10 weeks (FIG. 1.). For 
only 5% of the iterations, a VWP extended beyond 10 weeks pp was optimal. The average 
economic losses, when comparing the extended VWP with a VWP of 6 weeks, was also 
calculated and given in FIG. 1. Every VWP larger than 6 weeks gives, on average, economic 
losses. For instance, the average annual net economic losses of a VWP of 7 weeks are €2.20 
per cow, while for 27 % of the cows, a VWP of 7 weeks is optimal. A VWP of 15 weeks is 
never optimal and is associated with, on average, €65.12 net annual economic losses. As a 
next step in this research, it is interesting to further explore the specific circumstances that 
determine when an extension of the VWP 
 
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