The effect of pre- and post-mating dietary restriction on embryonic survival in gilts
Introduction
Group housing during gestation potentially improves sow welfare by allowing freedom of movement, increased socialisation and increased capacity to express natural behaviours. However, there are a number of negative aspects associated with group housing systems including competition for resources and a resultant variation in feed intake (Kongsted, 2005) with low ranking sows thought to receive less feed than their higher ranking counterparts (Andersen et al., 1999).
Changes in feed intake affect ovarian function directly via the effect of metabolic hormones on ovarian follicle growth, or indirectly via changes in the pattern and concentration of gonadotrophin release (van Wettere and Hughes, 2007). Feed restriction prior to mating decreased embryonic survival in gilts and lactating sows, most likely due to impaired follicular development, oocyte quality and luteal function (Almeida et al., 2000, Zak et al., 1997b). Feed restriction during the late luteal phase (days 8–15) of the oestrous cycle preceeding mating had the greatest negative effect on embryonic survival (Almeida et al., 2000).
Although litter size was similar between sows fed at a moderate or high level post-mating (Quesnel et al., 2010), more severe feed restriction such as below maintenance has been shown to be detrimental to embryonic survival, with a moderate feed restriction of 1.2× maintenance during early pregnancy resulting in significantly greater embryonic survival rates compared with that of the more severe feed restriction of 0.6 times maintenance in gilts (De et al., 2009). It is, therefore, suggested that sows experiencing a restricted feed intake post mating may experience impaired reproductive performance. This effect may be seen in low ranking sows, such as first parity sows, in a group housing system where competition for feed exists (Kongsted, 2005). An association between reduced feed intake during early gestation in group housed sows and impaired reproduction has been proposed, with the likelihood of pregnancy loss or low litter sizes increased with decreased backfat gain between weaning and day 21 post-mating (Kongsted, 2006).
The interaction between feed intake pre-mating and post-mating on embryo survival and litter size has received little attention. Ashworth et al. (1999) observed decreased embryonic survival rates in gilts receiving a maintenance feed intake before and after mating compared with those fed at three times maintenance. However, these authors only looked at embryonic survival to day 12 and it is known that the majority of embryonic mortality occurs during the implantation period (days 12–18; Geisert and Schmitt, 2002). Therefore, it is not known whether the effect on embryonic survival of a restricted feed intake post mating experienced by a group housed low ranking parity one sow is likely to be greater in those sows that were previously metabolically challenged from lactation.
Using an established gilt model for a lactating sow (Almeida et al., 2000, Chen et al., 2012) we hypothesise that there will be an interaction between the pre-mating and post-mating feed intake on embryonic survival.
Section snippets
Materials and methods
This experiment was conducted at the University of Adelaide's piggery, South Australia, with approval from the Animal Ethics Committee of the University of Adelaide. The experimental design was a 2 × 2 factorial randomised block design with main effects being feeding level from day 1 to day 14 of the second oestrous cycle (0.8× maintenance; low, n = 23 vs. 1× maintenance; high, n = 23) and feeding level from mating until slaughter (1× maintenance; LOW, n = 23) vs. 1.5× maintenance; HIGH, n = 23).
Growth characteristics
Gilt liveweight was not different at detection of second oestrus among treatment groups (Table 2). During the pre-mating treatment period, gilts in the low group lost more weight than those in the high group (6.7 ± 0.8 versus 3.7 ± 0.7 kg; P < 0.05). Liveweight changes from day 14 of the second oestrous cycle to insemination were similar among treatment groups, with all treatments gaining weight. During this period there was a significant interaction, with low×LOW gilt gaining more backfat than
Discussion
The current investigation demonstrated that there was no interaction between the pre-mating and post-mating feed intake on embryonic survival, and that the post-mating feed intake had a greater effect on embryonic survival than the pre-mating feed intake. Ashworth et al. (1999) reported no interaction between the pre-mating and post-mating feed intake on embryonic survival to day 12 of gestation, agreeing with the present findings. However, in contrast to the present data, Ashworth et al. (1999)
Conclusions
This study has identified that there was no significant interaction between pre-mating and post-mating feed intake on embryonic survival. Within the limit of this study, the pre-mating feed intake had little effect on embryonic survival. However, feeding less post-mating decreased embryonic survival when compared with greater post-mating feeding levels, demonstrating the importance of ensuring sows receive adequate post-mating nutrition.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgements
The scholarship for this project was provided by the Pork Cooperative Research Centre. We acknowledge Paul Herde, Kate Plush, Alice Weaver and Robyn Terry for their technical and statistical assistance throughout the study.
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