D
aily w
eight gain (g/day)
Male Female
Lineair (Male)Linear Lineair (Female)Linear
Figure 3.3 For male and female groups, the average daily weight gain (g/day)
plotted against the tail damage duration, including a linear trend line.
For male piglets, the DWG reduced as tail damage duration increased (see solid trend line in Figure 3.3). In contrast, DWG for female piglets increased as tail damage duration increased (see dashed trend line). A similar significant interaction on DWG was found between gender and tail wound duration (P<0.001).
No differences in feed intake were found between the three sex-ratio groups (25.2, 27.1 and 26.0 kg for all-male, all-female and mixed-sex pens). However, a significant interaction between sex-ratio and tail damage duration (P<0.001) was found. In Figure 3.4, the feed intake in relation to the tail damage duration is shown for the three different sex-ratios.
0 5 10 15 20 25 30 35 40 45 0 5 10 15 20 25 30
Number of days with tail damage
Feed intake (kg)
All-male All-female Mixed-sex
Lineair (All-male)Linear Lineair (All-female)Linear Lineair (Mixed-sex)Linear
Figure 3.4 For the different sex-ratios (all-male, all-female and mixed-sex pens),
the average feed intake (kg) over the observation period is plotted against the tail damage duration, including a linear trend line.
In all-male pens feed intake decreased as tail damage duration increased (see solid trend line in Figure 3.4). In contrast, feed intake in all-female pens increased as tail damage duration increased (see short dashed trend line in Figure 3.4). Feed intake in mixed-pens remained relatively constant as tail damage duration increased and was not significantly different from all-male or all-female pens (see dashed trend line in Figure 3.4). A similar significant interaction on feed intake was found between gender and tail wound duration (P<0.001).
3.4 Discussion
After tail biting started, all-female groups had a lower 40% tail damage incident point compared with all-male, mixed-male and mixed-female. Similar, all-female groups had a higher tail damage duration score compared with the other three treatment categories. These results are in agreement with Schrøder-Petersen et al. (2004), who found that among pigs between 40 and 50 kg tail-in-mouth (TIM) behaviour was higher in all-female groups compared with all-male groups. This indicates that female piglets are more prone to tail bite compared with male piglets, or that female piglets are more likely to become victims of tail biting. We found an interaction between gender and mixing for both the 40% tail damage incident point and the tail damage duration score. Male piglets in mixed-sex groups developed tail damage more rapidly compared with female piglets in mixed-sex groups. These findings are in agreement with Kritas and Morrison (2004), who observed in mixed-sex groups twice as much tail damage of castrated males (21%) compared with females (9.8%). Also, Hunter et al. (1999) found that males in mixed-sex groups had 1.4 times more chance of being bitten than female pigs. With this interaction for tail damage development, our results indicate that female piglets are more likely to tail bite than male piglets.
The reason why female piglets are more likely to tail bite is not clear. Sambraus (1985), Simonsen (1995) and Schrøder-Petersen and Simonsen (2001) speculated that as female pigs start to become sexually mature, they become more active and also more interested in ano-genital investigation. Furthermore, pigs have been observed to perform more ano-genital manipulation before and after TIM behaviour than any other behaviour (Schrøder-Petersen, 2005). The higher motivation of female pigs to direct their ano-genital behaviour to (if present) the opposite sex (Schrøder-Petersen and Simonsen, 2001), can explain the higher tail damage among male piglets compared with the females in our mixed-sex groups. Furthermore, Breuer et al. (2003) investigated the manipulation motivation of 300 weaned piglets in a ‘Tail Chew Test’ and found that females had a tendency to manipulate a rope more often than the non-castrated males (2.0 versus 1.0, P=0.07). This higher motivation to perform manipulating behaviour and/or higher motivation to perform ano-genital
behaviour among female piglets could explain the higher tail damage development in the all-female groups.
Beside the role of the biter within a group, there might also be a role of the victims. Presumed lower levels of activity can make males more attractive targets for tail biting by penmates (EFSA, 2007). For more evidence to support these hypotheses, further study on characteristics of biters and victims is necessary.
Differences in tail damage averages per pen at the end of the observation period were small; tail damage had developed to high levels in all groups. At this point our results showed a mixing effect (piglets in single-sex groups had more tail damage than in mixed-sex groups). This is in contrast with our conclusion that all-female groups had the highest tail damage development. Therefore, looking only at the end of the observation period leads to different conclusions about the effect of gender and mixing on tail damage compared with looking at tail damage development. For an effective treatment of tail biting, it must be diagnosed and treated in an early stage in order to minimize the negative consequences of tail damage (Zonderland et al., 2008). This suggests that it is important to test the effect of internal or external factors on the early development of tail biting. Therefore tail damage development is a more appropriate measure to test these effects compared with end point observations. Both 40% tail damage incident point and tail damage duration can be used. In our experiment these two parameters were highly correlated.
We found that female piglets had a higher DWG compared with male piglets. Van der Mheen and Spoolder (2003) found no difference in DWG between male and female piglets (uncastrated weaned piglets housed in mixed-pens) in the same experimental facility, but without tail biting problems. Furthermore, DWG of males decreased as the number of days with tail damage or with a tail wound increased. This is in agreement with several studies that showed a negative effect of tail damage on DWG (e.g. Wallgren and Lindahl, 1996). In contrast, DWG of females increased as the number of days with tail damage or a tail wound increased. In addition, a higher feed intake was found in all-female pens as the number of days with tail damage or a tail wound increased. The reason why females with tail damage had a higher DWG and feed intake is not clear. A possible explanation could be that piglets with a high DWG
and feed intake are probably the heavier and more dominant piglets. These piglets will occupy the feeder during the active periods of the day, when all piglets want to feed. While standing at the feeder, these piglets are an easy target for tail biters. It is most likely that these heavier female piglets also experienced a negative effect from tail damage and might have had even higher DWG when they had no tail damage. However, further research on potential victims and their dominance status is necessary to support this hypothesis.
3.5 Conclusions and implications
When tail biting starts, all-female groups had a higher tail damage development compared with all-male and mixed-sex groups. At the end of the observation period this difference between all-female groups and the other treatment categories was not found. At that point tail damage developed to high levels in all groups. Tail damage development is therefore a better way to analyse effects of external and internal factors resulting in tail biting, compared with methods based on end point analyses.
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