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email:fortpflanzungsklinik@vetmed.fu-berlin.de
Objective was to assess the effect of each unit increment of culling
(CULL; from 25 to 43%) on profitability of dairy herds achieving 20%
pregnancy rate (PR) using a cow-based model. Same reproductive
program was used, Presynch-Ovsynch with estrus detection (ED) and
timed-artificial insemination (TAI) with a voluntary waiting period of
60 d in milk (DIM). Probability of involuntary CULL was set at 0.1%
per d for the first 60 DIM, and 0.03% per d for the remaining of the
lactation and dry period. Probability of death was set at 0.05% per d for
the first 60 DIM, and 0.0076% per d for the remaining of the lactation
and dry period. Herd size was set to 1,000 cows and each unit of CULL
was modeled using the same TAI-ED to achieve 20% PR. Four factors
affecting the economic benefits of dairy herds remain unchanged for the
simulation: (1) milk price ($0.37 per kg), (2) feed prices for lactating
($0.25 per kg of dry matter [DM]) and dry cows ($0.15 per kg of DM),
(3) cull cow price ($1.00/kg of live weight), and (4) replacement price
($1,600 per heifer). Conception to first service was set at 32% and then
decreased by 2.6% for every subsequent service. Abortion was set at
9.3% for the first 90 DIM and at 1.7% for the remaining of gestation.
Cows were not bred after 366 DIM and open cows were culled after
450 DIM. Simulation was performed until steady state was reached
(3,000 d), and then average daily values for the subsequent 2,000 d were
used to calculate profit/cow per yr. Net daily value was calculated by
subtracting the costs (replacement, feeding, breeding, and other costs)
from the daily income (milk sales, cow sales, and calf sales). Higher
CULL reduced (P < 0.05) the proportion of cows with lactations ≥
3, increased replacement costs, and reduced profit by $186 per cow/
yr. For each unit increment of CULL, the proportion of first lactation
cows increased by 0.66 percentage points and the proportion of net
profit decreased by 1.09 percentage points. On average, it took 53 mo
to reach the breakeven point considering the heifer replacement cost
to first calving and the subsequent milk revenues over 3 consecutive
lactations. Excessive CULL increased the proportion of first lactation
cows and replacement costs; thus, reducing profitability.