in which y is lean meat percentage or carcass grading and ‘weight’ is birth weight, weight at weaning or weight at the start of the fattening period.
2.4.4. General Ž
. For all models, the Shapiro–Wilk statistics W was calculated as a statistical test for
normality and the skewness and kurtosis of the rest value of the models were deter- Ž
mined. All calculations were performed using the statistical package, SAS SAS
. Institute, 1989 .
P-values - 0.05 were considered to be significant.
3. Results
3.1. General The rest values of all models had a normal distribution, so no transformation of
y-values was necessary. Skewness and kurtosis were between y2 and 2 and the Shapiro–Wilk statistics was not significant.
3.2. Backtest In the first study, a backtest was performed on day 10 for 832 piglets and on day 17
Ž .
for 825 piglets. The average number of escape attempts on day 10 was 1.89 range 0–7 , Ž
. on day 17, it was 2.01 range 0–8 . In the second study, the backtest was done three
Ž .
times with 566 piglets. The average number of escape attempts was 3.20 range 0–12 Ž
. Ž
. on day 3, 2.57 range 0–8 on day 10 and 2.60 range 0–10 on day 17. The number of
Ž .
escape attempts for each test had a unimodal distribution Fig. 1a, b . Ž
In the first study, the correlation between the successive backtest results day 10–day .
Ž .
Ž 17 was 0.42. In the second study, the correlations were 0.41 day 3–day 10 , 0.39 day
. Ž
. 3–day 17 and 0.47 day 10–day 17 . All P-values were 0.0001.
A day-effect was found in the second study for backtest scores between the test on Ž
. day 3 and the test on day 10 or 17 P - 0.0005 . This was caused by the high test scores
in the first test, compared to the other two tests. The mean level of escape attempts was higher on day 3 than on day 10 or 17. In both studies, no day-effect was found between
Ž . Ž
. the tests on day 10 and 17 P s 0.49
Figs. 2 and 3 . 3.3. Parameters related to the backtest scores
In both studies, female piglets showed a higher number of escape attempts than Ž
. Ž
. castrated males Figs. 2 and 3 . No interactions between variables such as daygender
were found. Ž
. In the first study, relations were found between backtest scores and litter P - 0.001 ,
Ž .
Ž . Ž
. gender P - 0.0005 and AI P - 0.05 Fig. 2 . Piglets born from natural serving boars
had higher backtest scores than piglets born from AI. No relations were found with weight, boar number or pen number.
Ž . Ž
. Fig. 1. a Percentage of animals for each backtest score first study .
Ž . Ž
. Fig. 1. b Percentage of animals for each backtest score second study .
Ž .
In the second study, the backtest score per piglet was related to litter P - 0.01 , sow Ž
. Ž
. backtest type P - 0.01 and gender P - 0.01 . Sows with lower backtest scores when
they were piglets had offspring with lower backtest scores. A trend was found between Ž
. Ž .
backtest score of the piglet and sow reaction P - 0.10 Fig. 3 . No relation was found with illness of the piglets.
When the data were analyzed per test day, a small gender effect was observed at 3 days of age, which was not significant. At 10 days, the difference was larger but was
still not significant, while at 17 days, the difference was significant.
Ž .
Fig. 2. Backtest scores and related parameters first study : effect of test day, AI and gender.
Ž .
Fig. 3. Backtest scores and related parameters second study : effect of test day, gender, sow backtest type and sow reaction.
3.4. Performance Due to selling of fattening pigs at 10 weeks of age or missing data, performance data
were collected from 747 of the 823 animals in the first study. The results are shown in Table 1. The correlation between lean meat percentage and carcass grading was high
Ž .
r s 0.91; P - 0.01 .
Table 1 Ž
. Production performance of pigs in the first study ns 747 and estimates of backtest score on performance
parameters Mean
SEM N
Estimate P-value
of backtest Ž
. Weight kg
At birth 1.474
0.312 747
y0.19 0.25
At weaning 8.6
1.76 747
y0.06 0.05
At 9 weeks 24.3
4.442 746
y0.02 0.08
At slaughter 113.1
6.565 747
0.008 0.27
Ž .
Daily weight gain kgrday Suckling period
0.265 0.056
747 y0.002
0.14 Weaning period
0.442 0.098
746 y0.002
0.47 Fattening period
0.804 0.088
746 0.001
0.63 Lean meat percentage
54.03 3.42
740 0.33
- 0.01
3.5. Relations between backtest scores and production parameters In the first study, performance data were gathered. Since no day-effect was found in
both studies between the backtests on 10 and 17 days, in the following calculations, the mean backtest score for these two ages per piglet was used.
Fig. 4. Relation between backtest score and carcass grading.
Fig. 5. Relation between backtest score and lean meat percentage.
No relations were found between daily weight gain in the suckling, weaning or Ž
. fattening period and backtest scores, or between backtest scores and weight Table 1 .
Backtest score and lean meat percentage at the slaughterhouse were related positively Ž
. Ž
. P - 0.01 just as backtest scores and carcass grading at the slaughterhouse P - 0.05 ,
corrected for gender, sow identity, AI and weight. Piglets with higher backtest scores Ž
had a higher carcass grading and a higher lean meat percentage at slaughter Figs. 4 and .
5 .
4. Discussion
