Dairy Sheep Symposium - the Department of Animal Sciences ...

that of the average milking time. Milk was sold for $1.32/kg. Additional labor and expenses,
relative to the S system and one milking technician, included $9.00/hr for labor and $0.37/ewe
per milking for ewe purchase price, management, and feed costs (Berger, 1998).
Statistical Analyses. Pre-experimental, experimental, and total lactation data for lactation
traits (Table 1) and machine milking and stripping traits (Table 2) were analyzed separately.
Reports on parlor throughput, economic returns, and frequency of overmilking were not analyzed
statistically and are only provided to give the reader a reasonable estimation from a hypothetical
simulation. Least squares means analysis of variance was conducted with the general linear
models procedure of SAS (1999). The experimental design was a split plot on time for the
measurements taken every 20 d during the morning milking. The model included the main plot
effects of: block (pre-experimental stripping percentage: ≤ 15% or > 15%), treatment (NS or S),
block × treatment, and ewe within block × treatment, and the sub-plot effects of: time (d-100,
120, 140, and 160), two-way interactions with time, and residual error. Least squares means for
treatment, block, and block × treatment were tested against ewe within block × treatment as the
error term; time and all interactions with time were tested against residual error. All lactation
trait data (Table 1) and the pre-experimental machine milking and stripping data were analyzed
with the following model: block (pre-experimental stripping percentage: ≤ 15% or > 15%),
treatment (S or NS), and the two-way interaction. Pre-experimental SCC and percentage of milk
fat were used as a continuous covariable in the analyses of SCC and percentage of milk fat,
respectively, during the experimental period and for the entire lactation.
Results
Milk Production. Lactation trait data are summarized in Table 1 and Figure 1. Milk yield
for NS ewes during the experimental period was 14% less (-17.1 kg, P < 0.01) compared to S
ewes, however, overall lactation yields were not statistically different (Table 1). Average daily
milk yield (Figure 1) for S ewes was consistently higher (P < 0.05), compared to NS ewes,
through d 140 during the experimental period. Both treatment groups lactated for a similar
number of days (182.5 d) and had similar overall milk protein content (4.78 %, Table 1). After
correcting for slight differences in percentage of milk fat and SCC during the pre-experimental
period, milk fat content and SCC were not different between treatment groups for the entire
lactation (5.58 % milk fat and 4.77 log units, respectively, Table 1). Block × treatment interaction
was not significant for any lactation trait.
Machine milk yield (the amount of milk obtained without or prior to stripping) was higher
for NS ewes than for S ewes at all test days during the experimental period (Figure 1), however,
only the difference at 120 d of lactation was statistically significant, and the average superiority
of the NS ewes over the S ewes for machine milk yield (Table 2) during the experimental period
(0.68 vs. 0.63 kg/milking, respectively) was not statistically significant. Total morning milk
yield was lower (P < 0.01) for NS ewes compared to S ewes (0.68 vs. 0.80 kg, respectively), of
which machine stripped milk accounted for 23.6 % of the total milk volume for the latter (Table
2). Machine milking time (the time to obtain machine milk) was not different between treatment
groups, however, total machine-on time tended to be longer (P < 0.10) for S ewes compared to
NS ewes (89.1 vs. 78.7 s, respectively, Table 2). Block × treatment interaction was not significant
for any machine milk or stripping trait. Machine milk emission kinetics (milk flow latency,
maximum milk flow rate, average milk flow rate) were not different between treatment groups at