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The effect of pre- and post-mating dietary restriction on embryonic survival in gilts
Animal Reproduction Science 148 (2014) 130–136
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The effect of pre- and post-mating dietary restriction on embryonic survival in gilts P.C. Condous ∗ , R.N. Kirkwood, W.H.E.J. van Wettere School of Animal and Veterinary Science, University of Adelaide, Roseworthy, SA 5371, Australia
a r t i c l e
i n f o
Article history: Received 28 February 2014 Received in revised form 30 May 2014 Accepted 9 June 2014 Available online 17 June 2014 Keywords: Gilt Pig Embryo Nutrition
a b s t r a c t The aims of this study were to determine if pre- and post-mating feeding levels interact to affect embryonic survival, and to determine whether feeding to the maintenance requirement would impair embryo survival. Gilts were allocated to a pre-mating treatment of 1 or 0.8× energy maintenance from day 1 to 14 of their oestrous cycle prior to mating. From day 15 to mating all gilts were group housed and fed ad lib. Gilts were artificially inseminated at their third oestrus. The day after mating, gilts were group housed and allocated to post-mating treatments of 1.5 or 1× maintenance. Gilts were slaughtered day 25.5 ± 0.2 post-insemination and reproductive tracts collected. Gilts fed the restricted pre-mating diet lost significantly more weight than gilts fed the increased pre-mating diet (6.7 ± 0.8 versus 3.7 ± 0.7 kg). From mating to slaughter, gilts fed the restricted post-mating diet lost 0.5 ± 1.02 kg liveweight, while gilts fed the increased post-mating diet gained 5.7 ± 0.90 kg liveweight (P < 0.05). The pre-mating dietary treatment had no effect on any reproductive measure. Embryonic survival was greater (P < 0.05) in gilts fed the high post-mating diet compared with gilts fed the low post-mating diet (88.4 ± 2.5 versus 77.8 ± 4.0%), resulting in more (P < 0.05) conceptuses present (14.0 ± 0.6 versus 11.7 ± 0.7). There was no interaction between pre-mating and post-mating feed intake on any reproductive measure. These data demonstrated that reducing post-mating feed intakes to maintenance levels impaired embryo survival. © 2014 Elsevier B.V. All rights reserved.
1. 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).
∗ Corresponding author. Tel.: +61 08 83132233. E-mail address: [email protected] (P.C. Condous). http://dx.doi.org/10.1016/j.anireprosci.2014.06.003 0378-4320/© 2014 Elsevier B.V. All rights reserved.
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,
P.C. Condous et al. / Animal Reproduction Science 148 (2014) 130–136
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 postmating (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.
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400 IU equine chorionic gonadotrophin plus 200 IU human chorionic gonadotrophin (PG600® , Intervet, Australia) and 15 min of daily, physical contact with a mature boar. Oestrus was defined as the exhibition of a standing reflex, either in response to pressure to the gilts back (the back pressure test), or mounting by the boar. From day 12 after detection of the first oestrus until second oestrus, gilts received 15 min/day fenceline contact with a mature boar in order to maintain oestrous cyclicity and fascilitate oestrus detection. Following the completion of one oestrous cycle of normal duration (20.8 ± 0.14 days), gilts were stratified according to liveweight and allocated sequentially to the low or high feed intake pre-mating treatment groups. From day 1 to day 14 of the second oestrous cycle (day 0 corresponds to the first day of behavioural oestrus), gilts were fed a barley based gilt developer diet formulated to provide 13.2 MJ DE/kg, 15.13% protein and 0.69% lysine. The maintenance energy levels of the pre-mating feed intake treatment groups were designed to replicate the energy deficit often experienced by parity one sows over lactation to that of maintenance energy levels, represented by the high feeding level, and a more severe energy deficit, represented by the low feeding level. From day 15 of the second oestrous cycle until exhibition of their third oestrus, gilts were fed the gilt developer diet ad libitum. From 12 days after detection of the second oestrus until third oestrus, gilts received 15 min of daily fenceline contact with a mature boar in order to maintain oestrous cyclicity and enable oestrus detection. Gilts were artificially inseminated at detection of their third oestrus, stratified according to weight within the pre-insemination treatments and allocated sequentially to either the LOW or HIGH feed intake post-mating treatment groups. From day 1 post insemination until slaughter at 25 ± 0.22 days of gestation, gilts were fed a barley based gestation diet formulated to provide 13 MJ DE/kg, 13.82% protein and 0.55% lysine. The maintenance energy levels of the post-mating feed intake treatment groups were designed to replicate a decreased feed intake experienced by a low ranking first parity sow and a greater feed intake experienced by a greater ranking first parity sow in a group housing system, represented by the reduced and increased feeding levels respectively. Details of the feed intake, digestible energy and protein and lysine content of the pre- and post-mating diets are shown in Table 1. Gilts were weighed weekly during the pre- and postmating nutritional treatment periods and the daily feed intake required was adjusted for each gilt. Maintenance energy intake was calculated using the following formula (0.444 × LW0.75 ; Feeding Standards for Australian Livestock Pigs).
2. 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). 2.1. Experimental design Forty-nine Large White × Landrace gilts were used in this study. At 171 days of age, puberty was stimulated using the combination of a single intramuscular injection of
Table 1 Feed intake, digestible energy, protein and lysine content of the diet fed to gilts at 1 times maintenance (h) or 0.8 times maintenance (l) before mating and 1.5 times maintenance (H) or 1 times maintenance (L) after mating. high Average feed intake (kg) Digestible energy (MJ/day) Protein (g) Lysine (g)
1.32 17.2 198.5 9.25
low ± ± ± ±
0.1 0.27 3.07 0.13
1.05 13.8 158.5 7.3
HIGH ± ± ± ±
0.07 0.18 2.08 0.10
2.06 26.8 309.4 14.4
LOW ± ± ± ±
0.14 0.36 4.17 0.19
1.37 17.8 205.1 9.6
± ± ± ±
0.09 0.25 2.98 0.13
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2.2. Housing and management
2.6. Statistical analyses
From selection until their second oestrus, gilts were group housed in grower sheds. From the start of their pre-insemination dietary treatment gilts were housed individually in stalls. From day 15 of the second oestrous cycle through to slaughter on day 25 post-insemination, gilts were housed in groups of six in a grower shed, with a space allowance of 1.25 m2 per pig. From insemination at their third oestrus until slaughter, gilts were moved daily to individual stalls where they received post-insemination feed intake, and then were returned to the grower shed.
All analyses were performed using SPSS, version 19 (IBM) and data expressed as means ± standard error of the mean (SEM). A general linear model, with slaughter weight and weight and backfat changes as co-variates, and block as a fixed effect, was used to study the effects of the pre- and post-mating diet and their interaction on ovulation rate, embryo number and embryo survival. Embryo weights were analysed using a general linear model, with slaughter weight and day of gestation at slaughter as co-variates, and block and treatment as fixed effects. Statistical significance between treatments was determined using least significant difference. Results were considered significant at P < 0.05.
2.3. Artificial insemination All gilts were artificially inseminated at detection of their third oestrus, and again 24 h later if still displaying oestrus, with 3 × 109 sperm in 80 mL extender (SABOR, Clare, South Australia). 2.4. Liveweight and backfat measurements Gilts were weighed at onset of their second oestrus, day 7 and 14 of the second oestrous cycle, insemination, days 7, 14 and 21 post insemination, and day of slaughter. Backfat depth measurements (P2; 65 mm off the midline at the last rib) were recorded at detection of second oestrus, insemination and day of slaughter using a 3.5 MHz linear-array transducer (Ausonics Impact, Kimberly, WI, USA). 2.5. Reproductive tracts Gilts were slaughtered on day 25.5 ± 0.2 after insemination and their reproductive tracts recovered for determination of numbers of corpora lutea (ovulation rate) and numbers and weights of conceptuses. Within gilt any conceptuses more than two standard deviations below the average conceptus weight were deemed non-viable (Jindal et al., 1996).
3. Results 3.1. 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 high*LOW gilt (2.6 ± 1.1 versus 1.7 ± 0.7 mm). During the post-mating treatment period, HIGH gilts gained significantly more weight than those in the LOW group (5.7 ± 0.9 versus −0.5 ± 1.0 kg). During this period, there was a significant interaction with low*HIGH gilts gaining more backfat than low*LOW gilts. At slaughter, gilts receiving the HIGH treatment were significantly heavier (142.6 ± 2.82 kg) compared with those in the low treatment (137.8 ± 2.90 kg). 3.2. Reproductive characteristics Pre-mating feed intake did not affect ovarian or conceptus weight, nor ovulation rate (Table 3). Pregnancy rates
Table 2 Liveweight, liveweight change and backfat change of gilts fed 1 times maintenance (high) or 0.8 times maintenance (low) before mating and 1.5 times maintenance (HIGH) or 1 times maintenance (LOW) after mating. high×HIGH (n = 11)
Live weight (kg) Prior to pre-mating diet End of pre-mating diet (day 14) AI Slaughter Live weight change (kg) During pre-mating diet Day 14–AI During post-mating diet Backfat change (mm) During pre-mating diet Day 14–AI During post-mating diet
131.8 128.1 139.2 145.0
± ± ± ±
3.71 4.13 3.81 4.48
high×LOW (n = 12)
134.0 130.3 138.0 137.6
± ± ± ±
3.74 4.39 3.91 4.71
low×HIGH (n = 12)
131.6 123.9 134.9 140.5
± ± ± ±
3.07 3.59 2.94 3.60
low×LOW (n = 11)
134.9 129.2 138.7 138.1
± ± ± ±
2.94 3.24 3.46 3.46
Significance
PreM
PostM
PreMPostM
ns ns ns ns
ns ns ns P = 0.014
ns ns ns ns
−3.7 ± 1.13 11.0 ± 1.28 5.8 ± 1.61
−3.7 ± 0.92 7.7 ± 1.58 −0.5 ± 1.66
−7.6 ± 1.04 10.9 ± 1.13 5.6 ± 0.98
−5.7 ± 1.32 9.5 ± 1.21 −0.5 ± 1.22
P = 0.0004 ns ns
ns ns P = 0.0001
P = 0.002 ns ns
−1.1 ± 1.42 2.0 ± 0.97 −0.7 ± 1.65
−2.6 ± 1.68 1.7 ± 0.65 1.2 ± 0.96
−2.4 ± 1.26 1.9 ± 0.83 4.02 ± 1.65
−2.7 ± 1.90 2.6 ± 1.13 −1.3 ± 1.18
ns ns ns
ns ns ns
ns P = 0.021 P = 0.004
Values are means ± SEM; ns: not significant at P > 0.05; PreM, pre-mating diet; PostM, post-mating diet; PreMPostM, interaction between the PreM and PostM dietary treatments.
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Table 3 Reproductive characteristics on day 25.5 ± .22 of pregnancy in gilts fed 1 times maintenance (high) or 0.8 times maintenance (low) before mating and 1.5 times maintenance (HIGH) or 1 times maintenance (LOW) after mating.
Pregnancy rate (%) Ovary weight (g) Ovulation rate Uterine weight (g) Placenta weight (g) Pregnancy rate (%) Embryo weight (g) Number of Embryos Embryo survival (%)
high×HIGH (n = 11)
high×LOW (n = 12)
low×HIGH (n = 12)
low×LOW (n = 11)
91.7 15.1 ± 0.49 15.1 ± 0.48 1019.3 ± 32.06 16.5 ± 1.89 91.7 0.90 ± 0.09 13.2 ± 0.72 86.6 ± 4.19
100 15.2 ± 0.71 14.9 ± 0.53 1054.6 ± 45.72 16.8 ± 2.26 100 0.94 ± 0.09 11.7 ± 0.88 78.1 ± 5.64
100 14.0 ± 0.43 16.4 ± 0.99 1019.1 ± 49.49 15.2 ± 2.47 100 0.76 ± 0.08 14.8 ± 0.99 90.0 ± 3.04
91.7 14.8 ± 0.66 15.0 ± 0.63 958.6 ± 35.46 15.9 ± 2.66 91.7 0.81 ± 0.10 11.8 ± 1.09 77.6 ± 5.87
Significance
PreM
PostM
PreMPostM
ns ns ns ns ns
ns ns ns P = 0.095 ns
ns ns ns ns ns
ns ns ns
ns P = 0.006 P = 0.026
ns ns ns
Values are means ± SEM; ns: not significant at P > 0.05; PreM, pre-mating diet; PostM, post-mating diet; PreMPostM, interaction between the PreM and PostM dietary treatments.
were not affected by treatment (Table 3). There were no effects of post-mating feed intake on numbers of corpora lutea or conceptus weight. Embryonic survival (77.8 ± 4.0 versus 88.4 ± 2.5) and conceptus number (11.7 ± 0.7 versus 14.0 ± 0.6) were less (P < 0.05) for the gilts in the LOW compared with the HIGH group.
was positively correlated with weight at day 0 (r = 0.402, P = 0.006), 14 (r = 0.396, P = 0.006) and mating (r = 0.379, P = 0.009), as well as backfat thickness at day 14 (r = 0.349, P = 0.017) and mating (r = 0.346, P = 0.019). Liveweight at day 0 was positively (P < 0.01) correlated with liveweight at day 14 (r = 0.956) and mating (r = 0.913).
3.3. Correlation between reproductive and growth measurements
3.4. Correlations between reproductive traits
Embryonic survival was positively correlated with backfat thickness at day of slaughter (Table 4). Conceptus number was positively correlated with liveweight at day 0 (r = 0.337, P = 0.022), 14 (r = 0.305, P = 0.039), mating (r = 0.347, P = 0.018), slaughter (r = 0.434, P = 0.003) and with backfat thickness at day of slaughter (r = 0.486, P = 0.001). Conceptus number was also positively correlated with weight change over the post-mating treatment (r = 0.343, P = 0.020) and backfat thickness change over the pre-mating treatment (r = 0.391, P = 0.007). Ovulation rate
There was a positive correlation (P < 0.01) between conceptus number and both ovulation rate (r = 0.624) and embryonic survival (r = 0.781). Embryonic survival was not significantly correlated to conceptus weight (r = −0.122, P > 0.05). Conceptus number was negatively correlated with placenta weight (r = −0.343, P = 0.019). 4. Discussion The current investigation demonstrated that there was no interaction between the pre-mating and post-mating
Table 4 Relationship between reproductive and growth characteristics (Pearson correlation coefficients (r) and P-value). Embryo survival (%)
Embryo number
Embryo weight (g)
Ovulation rate
r
r
P-value
r
P-value
r
0.337 0.305 0.347 0.434
0.022 0.039 0.018 0.003
0.009 0.098 −0.029 0.107
ns ns ns ns
−0.303 0.287 0.289 0.486
0.040 ns ns 0.001
0.251 0.296 0.260 0.113
P-value
Live weight (kg) Prior to pre-mating diet End of pre-mating diet AI Slaughter
0.106 0.077 0.148 0.204
Backfat (mm) Prior to pre-mating diet End of pre-mating diet AI Slaughter
−0.286 0.135 0.103 0.369
ns ns ns 0.012
Live weight change (kg) During pre-mating diet Day 14–AI During post-mating diet
−0.047 0.161 0.194
ns ns ns
0.045 0.027 0.343
ns ns 0.020
Backfat change (mm) During pre-mating diet Day 14–AI During post-mating diet
0.280 0.012 0.191
ns ns ns
0.391 0.133 0.106
0.007 ns ns
ns: not significant at P > 0.01.
ns ns ns ns
P-value 0.402 0.396 0.379 0.465
0.006 0.006 0.009 0.001
ns 0.046 ns ns
−0.154 0.349 0.346 0.308
ns 0.017 0.019 0.037
0.295 −0.355 0.328
0.046 0.015 0.026
0.158 −0.150 0.353
ns ns 0.016
0.024 0.083 −0.161
ns ns ns
0.330 0.160 −0.090
0.025 ns ns
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feed intake on embryonic survival, and that the postmating 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) demonstrated that pre-mating feed intake exerted a greater effect on embryonic survival than post-mating feed intake. In support of recent findings (De et al., 2009), the current data demonstrated that reducing post-mating feed intake to below maintenance levels decreased embryonic survival, emphasising the importance of optimising post-mating feed intake to achieve maximum reproductive performance in pigs. While the larger effect of the post-mating diet compared with the pre-mating diet in the current study conflicts with the findings of Ashworth et al. (1999), this could be due to differences between experimental designs. Firstly, Ashworth et al. (1999) looked at embryonic survival only to day 12 of gestation, before placental attachment. The current study measured embryonic survival at day 25 of gestation, after placental attachment was complete. It is established that most embryonic mortality occurs during the placental attachment period (Geisert and Schmitt, 2002) and, therefore, a measure of embryonic survival after this period may better reflect the effect of feed intake postmating on embryonic survival. The pre-mating treatment used by Ashworth et al. (1999) was imposed for the whole of the oestrous cycle prior to mating, while the gilts in the current study received the pre-mating diet for the first two weeks of the cycle only. The greater duration of the pre-mating treatment and that it was imposed until mating may have had a greater influence on ovulation rate and embryonic survival compared with the current study. Finally, Ashworth et al. (1999) used feeding levels of 1 or 3× maintenance, and it was earlier shown that increased and decreased feeding levels post-mating impaired embryonic survival compared with that of a moderate feed intake (1.5× maintenance) (De et al., 2009). Therefore, it is possible that the high and low feeding levels post-mating would both have impaired embryonic survival and masked any effect of post mating feed intake. Although the beneficial effects of moderate feed restriction post-mating (1.2–1.5 times maintenance) on embryonic survival have previously been demonstrated (De et al., 2009; Jindal et al., 1997), the effect of a severe feed restriction (maintenance level or below) on embryonic survival has received little attention. The present study found that feeding gilts at maintenance levels post-mating decreased embryonic survival. De et al. (2009) found a similar effect, with a feeding level of 0.6× maintenance significantly decreasing embryonic survival compared with a moderate post-mating feed level of 1.2× maintenance. The positive effects of reducing post-mating feed intake from 2 to 1.5 times maintenance on embryonic survival have been related to increased circulating progesterone levels (Jindal et al., 1997). In contrast, severe feed restriction post-mating decreased plasma progesterone, which resulted in a decreased embryo cleavage rate and a decrease in the transport rate of ova along the oviduct,
affecting the development of the embryo and its synchrony with the oviductal environment (Mburu et al., 1998; Mwanza et al., 2000). Furthermore, it has been shown that asynchrony, in which the uterine environment is further advanced than the embryo, resulted in lighter embryos and placentas (Wilson et al., 2001). Therefore, the embryos of the low feed intake group should have been less developed due to asynchrony between the uterine environment and embryo. However, the current data demonstrated that there was no significant difference between conceptus weights from gilts fed a low post-mating feed intake compared with a high post-mating feed intake. Furthermore, conceptus weight was not significantly correlated with embryonic survival. This is in contrast with previous studies which found a positive relationship between embryonic weigh and survival (De et al., 2009) and crown rump length and survival (Jindal et al., 1997). However, similar to the current study, Almeida et al. (2000) observed no reduction in embryonic weights in gilts with decreased embryonic survival rates. The level of feed restriction imposed post-mating in the current study is likely to be similar to the intake achieved in low ranking sows in a group housing system. Low ranking sows receive increased aggression over competition for feed, resulting in less feed intake (Andersen et al., 1999). While it has been found that unintentional variation of feed intake in a group housing situation decreases the chance of pregnancy (Kongsted, 2006), it has not yet been investigated if the unintentional variation of feed intake in group housing has an effect on embryonic survival. Furthermore, it is currently unknown how individual feed intake in a group housing system varies between sows. However, if low ranking sows receive a feed intake of maintenance or below, both the current data and that of De et al. (2009) indicates that impaired reproductive performance due to reduced embryonic survival is a likely consequence. These data indicate the need to modify feeding strategies for group housed sows so that maximum reproductive performance is achieved. The effect of feed intake prior to mating on reproductive performance has been widely studied in pigs, with high feed intake increasing ovulation rate and embryonic survival (Almeida et al., 2000; Zak et al., 1997a). However, during lactation sows, particularly parity one sows, generally suffer a negative energy balance due to increased energy demands from milk production and decreased appetite resulting in weight and backfat loss (Quesnel et al., 1998). Excessive body condition loss negatively affects subsequent reproductive performance, with ovulation rate and embryonic survival decreased in sows that were restrictively fed during lactation (Zak et al., 1997a) and cycling gilts (Almeida et al., 2000). While there was no effect of restricted feed intake prior to mating in the present study on ovulation rate or embryonic survival, this could be due to the timing of pre-mating feed restriction used in the current study. The period of pre-mating feed restriction ended one week before mating in the current study, which caused increased growth rates in all of the gilts in the week prior to mating. This would have permitted an increased follicle development and subsequently improved embryonic survival. Hazeleger et al. (2005) found similar results,
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demonstrating that a period of increased feeding during the follicular phase prior to mating counteracted the negative effects of previous feed restriction. Conversely, other studies (Chen et al., 2012; Almeida et al., 2000) indicated that increased feeding during the follicular phase prior to mating, following a period of restrictive feeding, resulted in reduced ovulation rates, embryonic survival and embryo number. However, the increase in feed intake and growth rate throughout the week prior to mating were much greater in the current study compared with the gilts in the Almeida et al. (2000) study. This could suggest that a period of increased feeding during the follicular phase prior to mating may counteract the negative effects of previous feed restriction, but this effect may only be shown when the increase in feed intake and growth is large enough. The length of the ad-lib feeding period may also have had an influence in counteracting the negative effects of previous feed restriction. Previous studies have reported an increase in the weaning to oestrus interval when sows were subjected to feed restriction during lactation. Zak et al. (1997a) found that restricted-fed sows during lactation had a marginally greater weaning to oestrus interval, suggesting this could have had an effect on the ovulation rate. It has been suggested that a period of 5 days or more of refeeding after feed restriction allows recovery at the ovarian level through increased follicular growth and oestradiol synthesis and subsequent improved embryonic survival (Baidoo et al., 1992). Therefore, a period of almost seven days of ad-lib feeding in this study may have allowed the gilts to recover from the previous feed restriction. While there was no treatment effect on ovulation rate in the current study, ovulation rate was positively correlated with liveweight prior to the experimental treatment period. Furthermore, liveweight at day 0 was positively correlated with liveweight at day 14 and at mating. Therefore, the heavier gilts at the start of the trial stayed heavier throughout the pre-mating period, which could explain the lack of an effect of the imposed dietary treatments. As growth rate and liveweight have been shown to influence ovarian development (Prunier et al., 1987) and follicle development (van Wettere et al., 2011), it is possible that the heavier gilts may have been more sexually mature prior to the pre-mating treatment, potentially causing an increased ovulation rate.
5. 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 postmating feeding levels, demonstrating the importance of ensuring sows receive adequate post-mating nutrition.
Conflict of interest The authors declare no conflict of interest.
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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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Animal Reproduction Science journal homepage: www.elsevier.com/locate/anireprosci
The effect of pre- and post-mating dietary restriction on embryonic survival in gilts P.C. Condous ∗ , R.N. Kirkwood, W.H.E.J. van Wettere School of Animal and Veterinary Science, University of Adelaide, Roseworthy, SA 5371, Australia
a r t i c l e
i n f o
Article history: Received 28 February 2014 Received in revised form 30 May 2014 Accepted 9 June 2014 Available online 17 June 2014 Keywords: Gilt Pig Embryo Nutrition
a b s t r a c t The aims of this study were to determine if pre- and post-mating feeding levels interact to affect embryonic survival, and to determine whether feeding to the maintenance requirement would impair embryo survival. Gilts were allocated to a pre-mating treatment of 1 or 0.8× energy maintenance from day 1 to 14 of their oestrous cycle prior to mating. From day 15 to mating all gilts were group housed and fed ad lib. Gilts were artificially inseminated at their third oestrus. The day after mating, gilts were group housed and allocated to post-mating treatments of 1.5 or 1× maintenance. Gilts were slaughtered day 25.5 ± 0.2 post-insemination and reproductive tracts collected. Gilts fed the restricted pre-mating diet lost significantly more weight than gilts fed the increased pre-mating diet (6.7 ± 0.8 versus 3.7 ± 0.7 kg). From mating to slaughter, gilts fed the restricted post-mating diet lost 0.5 ± 1.02 kg liveweight, while gilts fed the increased post-mating diet gained 5.7 ± 0.90 kg liveweight (P < 0.05). The pre-mating dietary treatment had no effect on any reproductive measure. Embryonic survival was greater (P < 0.05) in gilts fed the high post-mating diet compared with gilts fed the low post-mating diet (88.4 ± 2.5 versus 77.8 ± 4.0%), resulting in more (P < 0.05) conceptuses present (14.0 ± 0.6 versus 11.7 ± 0.7). There was no interaction between pre-mating and post-mating feed intake on any reproductive measure. These data demonstrated that reducing post-mating feed intakes to maintenance levels impaired embryo survival. © 2014 Elsevier B.V. All rights reserved.
1. 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).
∗ Corresponding author. Tel.: +61 08 83132233. E-mail address: [email protected] (P.C. Condous). http://dx.doi.org/10.1016/j.anireprosci.2014.06.003 0378-4320/© 2014 Elsevier B.V. All rights reserved.
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,
P.C. Condous et al. / Animal Reproduction Science 148 (2014) 130–136
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 postmating (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.
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400 IU equine chorionic gonadotrophin plus 200 IU human chorionic gonadotrophin (PG600® , Intervet, Australia) and 15 min of daily, physical contact with a mature boar. Oestrus was defined as the exhibition of a standing reflex, either in response to pressure to the gilts back (the back pressure test), or mounting by the boar. From day 12 after detection of the first oestrus until second oestrus, gilts received 15 min/day fenceline contact with a mature boar in order to maintain oestrous cyclicity and fascilitate oestrus detection. Following the completion of one oestrous cycle of normal duration (20.8 ± 0.14 days), gilts were stratified according to liveweight and allocated sequentially to the low or high feed intake pre-mating treatment groups. From day 1 to day 14 of the second oestrous cycle (day 0 corresponds to the first day of behavioural oestrus), gilts were fed a barley based gilt developer diet formulated to provide 13.2 MJ DE/kg, 15.13% protein and 0.69% lysine. The maintenance energy levels of the pre-mating feed intake treatment groups were designed to replicate the energy deficit often experienced by parity one sows over lactation to that of maintenance energy levels, represented by the high feeding level, and a more severe energy deficit, represented by the low feeding level. From day 15 of the second oestrous cycle until exhibition of their third oestrus, gilts were fed the gilt developer diet ad libitum. From 12 days after detection of the second oestrus until third oestrus, gilts received 15 min of daily fenceline contact with a mature boar in order to maintain oestrous cyclicity and enable oestrus detection. Gilts were artificially inseminated at detection of their third oestrus, stratified according to weight within the pre-insemination treatments and allocated sequentially to either the LOW or HIGH feed intake post-mating treatment groups. From day 1 post insemination until slaughter at 25 ± 0.22 days of gestation, gilts were fed a barley based gestation diet formulated to provide 13 MJ DE/kg, 13.82% protein and 0.55% lysine. The maintenance energy levels of the post-mating feed intake treatment groups were designed to replicate a decreased feed intake experienced by a low ranking first parity sow and a greater feed intake experienced by a greater ranking first parity sow in a group housing system, represented by the reduced and increased feeding levels respectively. Details of the feed intake, digestible energy and protein and lysine content of the pre- and post-mating diets are shown in Table 1. Gilts were weighed weekly during the pre- and postmating nutritional treatment periods and the daily feed intake required was adjusted for each gilt. Maintenance energy intake was calculated using the following formula (0.444 × LW0.75 ; Feeding Standards for Australian Livestock Pigs).
2. 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). 2.1. Experimental design Forty-nine Large White × Landrace gilts were used in this study. At 171 days of age, puberty was stimulated using the combination of a single intramuscular injection of
Table 1 Feed intake, digestible energy, protein and lysine content of the diet fed to gilts at 1 times maintenance (h) or 0.8 times maintenance (l) before mating and 1.5 times maintenance (H) or 1 times maintenance (L) after mating. high Average feed intake (kg) Digestible energy (MJ/day) Protein (g) Lysine (g)
1.32 17.2 198.5 9.25
low ± ± ± ±
0.1 0.27 3.07 0.13
1.05 13.8 158.5 7.3
HIGH ± ± ± ±
0.07 0.18 2.08 0.10
2.06 26.8 309.4 14.4
LOW ± ± ± ±
0.14 0.36 4.17 0.19
1.37 17.8 205.1 9.6
± ± ± ±
0.09 0.25 2.98 0.13
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2.2. Housing and management
2.6. Statistical analyses
From selection until their second oestrus, gilts were group housed in grower sheds. From the start of their pre-insemination dietary treatment gilts were housed individually in stalls. From day 15 of the second oestrous cycle through to slaughter on day 25 post-insemination, gilts were housed in groups of six in a grower shed, with a space allowance of 1.25 m2 per pig. From insemination at their third oestrus until slaughter, gilts were moved daily to individual stalls where they received post-insemination feed intake, and then were returned to the grower shed.
All analyses were performed using SPSS, version 19 (IBM) and data expressed as means ± standard error of the mean (SEM). A general linear model, with slaughter weight and weight and backfat changes as co-variates, and block as a fixed effect, was used to study the effects of the pre- and post-mating diet and their interaction on ovulation rate, embryo number and embryo survival. Embryo weights were analysed using a general linear model, with slaughter weight and day of gestation at slaughter as co-variates, and block and treatment as fixed effects. Statistical significance between treatments was determined using least significant difference. Results were considered significant at P < 0.05.
2.3. Artificial insemination All gilts were artificially inseminated at detection of their third oestrus, and again 24 h later if still displaying oestrus, with 3 × 109 sperm in 80 mL extender (SABOR, Clare, South Australia). 2.4. Liveweight and backfat measurements Gilts were weighed at onset of their second oestrus, day 7 and 14 of the second oestrous cycle, insemination, days 7, 14 and 21 post insemination, and day of slaughter. Backfat depth measurements (P2; 65 mm off the midline at the last rib) were recorded at detection of second oestrus, insemination and day of slaughter using a 3.5 MHz linear-array transducer (Ausonics Impact, Kimberly, WI, USA). 2.5. Reproductive tracts Gilts were slaughtered on day 25.5 ± 0.2 after insemination and their reproductive tracts recovered for determination of numbers of corpora lutea (ovulation rate) and numbers and weights of conceptuses. Within gilt any conceptuses more than two standard deviations below the average conceptus weight were deemed non-viable (Jindal et al., 1996).
3. Results 3.1. 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 high*LOW gilt (2.6 ± 1.1 versus 1.7 ± 0.7 mm). During the post-mating treatment period, HIGH gilts gained significantly more weight than those in the LOW group (5.7 ± 0.9 versus −0.5 ± 1.0 kg). During this period, there was a significant interaction with low*HIGH gilts gaining more backfat than low*LOW gilts. At slaughter, gilts receiving the HIGH treatment were significantly heavier (142.6 ± 2.82 kg) compared with those in the low treatment (137.8 ± 2.90 kg). 3.2. Reproductive characteristics Pre-mating feed intake did not affect ovarian or conceptus weight, nor ovulation rate (Table 3). Pregnancy rates
Table 2 Liveweight, liveweight change and backfat change of gilts fed 1 times maintenance (high) or 0.8 times maintenance (low) before mating and 1.5 times maintenance (HIGH) or 1 times maintenance (LOW) after mating. high×HIGH (n = 11)
Live weight (kg) Prior to pre-mating diet End of pre-mating diet (day 14) AI Slaughter Live weight change (kg) During pre-mating diet Day 14–AI During post-mating diet Backfat change (mm) During pre-mating diet Day 14–AI During post-mating diet
131.8 128.1 139.2 145.0
± ± ± ±
3.71 4.13 3.81 4.48
high×LOW (n = 12)
134.0 130.3 138.0 137.6
± ± ± ±
3.74 4.39 3.91 4.71
low×HIGH (n = 12)
131.6 123.9 134.9 140.5
± ± ± ±
3.07 3.59 2.94 3.60
low×LOW (n = 11)
134.9 129.2 138.7 138.1
± ± ± ±
2.94 3.24 3.46 3.46
Significance
PreM
PostM
PreMPostM
ns ns ns ns
ns ns ns P = 0.014
ns ns ns ns
−3.7 ± 1.13 11.0 ± 1.28 5.8 ± 1.61
−3.7 ± 0.92 7.7 ± 1.58 −0.5 ± 1.66
−7.6 ± 1.04 10.9 ± 1.13 5.6 ± 0.98
−5.7 ± 1.32 9.5 ± 1.21 −0.5 ± 1.22
P = 0.0004 ns ns
ns ns P = 0.0001
P = 0.002 ns ns
−1.1 ± 1.42 2.0 ± 0.97 −0.7 ± 1.65
−2.6 ± 1.68 1.7 ± 0.65 1.2 ± 0.96
−2.4 ± 1.26 1.9 ± 0.83 4.02 ± 1.65
−2.7 ± 1.90 2.6 ± 1.13 −1.3 ± 1.18
ns ns ns
ns ns ns
ns P = 0.021 P = 0.004
Values are means ± SEM; ns: not significant at P > 0.05; PreM, pre-mating diet; PostM, post-mating diet; PreMPostM, interaction between the PreM and PostM dietary treatments.
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Table 3 Reproductive characteristics on day 25.5 ± .22 of pregnancy in gilts fed 1 times maintenance (high) or 0.8 times maintenance (low) before mating and 1.5 times maintenance (HIGH) or 1 times maintenance (LOW) after mating.
Pregnancy rate (%) Ovary weight (g) Ovulation rate Uterine weight (g) Placenta weight (g) Pregnancy rate (%) Embryo weight (g) Number of Embryos Embryo survival (%)
high×HIGH (n = 11)
high×LOW (n = 12)
low×HIGH (n = 12)
low×LOW (n = 11)
91.7 15.1 ± 0.49 15.1 ± 0.48 1019.3 ± 32.06 16.5 ± 1.89 91.7 0.90 ± 0.09 13.2 ± 0.72 86.6 ± 4.19
100 15.2 ± 0.71 14.9 ± 0.53 1054.6 ± 45.72 16.8 ± 2.26 100 0.94 ± 0.09 11.7 ± 0.88 78.1 ± 5.64
100 14.0 ± 0.43 16.4 ± 0.99 1019.1 ± 49.49 15.2 ± 2.47 100 0.76 ± 0.08 14.8 ± 0.99 90.0 ± 3.04
91.7 14.8 ± 0.66 15.0 ± 0.63 958.6 ± 35.46 15.9 ± 2.66 91.7 0.81 ± 0.10 11.8 ± 1.09 77.6 ± 5.87
Significance
PreM
PostM
PreMPostM
ns ns ns ns ns
ns ns ns P = 0.095 ns
ns ns ns ns ns
ns ns ns
ns P = 0.006 P = 0.026
ns ns ns
Values are means ± SEM; ns: not significant at P > 0.05; PreM, pre-mating diet; PostM, post-mating diet; PreMPostM, interaction between the PreM and PostM dietary treatments.
were not affected by treatment (Table 3). There were no effects of post-mating feed intake on numbers of corpora lutea or conceptus weight. Embryonic survival (77.8 ± 4.0 versus 88.4 ± 2.5) and conceptus number (11.7 ± 0.7 versus 14.0 ± 0.6) were less (P < 0.05) for the gilts in the LOW compared with the HIGH group.
was positively correlated with weight at day 0 (r = 0.402, P = 0.006), 14 (r = 0.396, P = 0.006) and mating (r = 0.379, P = 0.009), as well as backfat thickness at day 14 (r = 0.349, P = 0.017) and mating (r = 0.346, P = 0.019). Liveweight at day 0 was positively (P < 0.01) correlated with liveweight at day 14 (r = 0.956) and mating (r = 0.913).
3.3. Correlation between reproductive and growth measurements
3.4. Correlations between reproductive traits
Embryonic survival was positively correlated with backfat thickness at day of slaughter (Table 4). Conceptus number was positively correlated with liveweight at day 0 (r = 0.337, P = 0.022), 14 (r = 0.305, P = 0.039), mating (r = 0.347, P = 0.018), slaughter (r = 0.434, P = 0.003) and with backfat thickness at day of slaughter (r = 0.486, P = 0.001). Conceptus number was also positively correlated with weight change over the post-mating treatment (r = 0.343, P = 0.020) and backfat thickness change over the pre-mating treatment (r = 0.391, P = 0.007). Ovulation rate
There was a positive correlation (P < 0.01) between conceptus number and both ovulation rate (r = 0.624) and embryonic survival (r = 0.781). Embryonic survival was not significantly correlated to conceptus weight (r = −0.122, P > 0.05). Conceptus number was negatively correlated with placenta weight (r = −0.343, P = 0.019). 4. Discussion The current investigation demonstrated that there was no interaction between the pre-mating and post-mating
Table 4 Relationship between reproductive and growth characteristics (Pearson correlation coefficients (r) and P-value). Embryo survival (%)
Embryo number
Embryo weight (g)
Ovulation rate
r
r
P-value
r
P-value
r
0.337 0.305 0.347 0.434
0.022 0.039 0.018 0.003
0.009 0.098 −0.029 0.107
ns ns ns ns
−0.303 0.287 0.289 0.486
0.040 ns ns 0.001
0.251 0.296 0.260 0.113
P-value
Live weight (kg) Prior to pre-mating diet End of pre-mating diet AI Slaughter
0.106 0.077 0.148 0.204
Backfat (mm) Prior to pre-mating diet End of pre-mating diet AI Slaughter
−0.286 0.135 0.103 0.369
ns ns ns 0.012
Live weight change (kg) During pre-mating diet Day 14–AI During post-mating diet
−0.047 0.161 0.194
ns ns ns
0.045 0.027 0.343
ns ns 0.020
Backfat change (mm) During pre-mating diet Day 14–AI During post-mating diet
0.280 0.012 0.191
ns ns ns
0.391 0.133 0.106
0.007 ns ns
ns: not significant at P > 0.01.
ns ns ns ns
P-value 0.402 0.396 0.379 0.465
0.006 0.006 0.009 0.001
ns 0.046 ns ns
−0.154 0.349 0.346 0.308
ns 0.017 0.019 0.037
0.295 −0.355 0.328
0.046 0.015 0.026
0.158 −0.150 0.353
ns ns 0.016
0.024 0.083 −0.161
ns ns ns
0.330 0.160 −0.090
0.025 ns ns
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feed intake on embryonic survival, and that the postmating 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) demonstrated that pre-mating feed intake exerted a greater effect on embryonic survival than post-mating feed intake. In support of recent findings (De et al., 2009), the current data demonstrated that reducing post-mating feed intake to below maintenance levels decreased embryonic survival, emphasising the importance of optimising post-mating feed intake to achieve maximum reproductive performance in pigs. While the larger effect of the post-mating diet compared with the pre-mating diet in the current study conflicts with the findings of Ashworth et al. (1999), this could be due to differences between experimental designs. Firstly, Ashworth et al. (1999) looked at embryonic survival only to day 12 of gestation, before placental attachment. The current study measured embryonic survival at day 25 of gestation, after placental attachment was complete. It is established that most embryonic mortality occurs during the placental attachment period (Geisert and Schmitt, 2002) and, therefore, a measure of embryonic survival after this period may better reflect the effect of feed intake postmating on embryonic survival. The pre-mating treatment used by Ashworth et al. (1999) was imposed for the whole of the oestrous cycle prior to mating, while the gilts in the current study received the pre-mating diet for the first two weeks of the cycle only. The greater duration of the pre-mating treatment and that it was imposed until mating may have had a greater influence on ovulation rate and embryonic survival compared with the current study. Finally, Ashworth et al. (1999) used feeding levels of 1 or 3× maintenance, and it was earlier shown that increased and decreased feeding levels post-mating impaired embryonic survival compared with that of a moderate feed intake (1.5× maintenance) (De et al., 2009). Therefore, it is possible that the high and low feeding levels post-mating would both have impaired embryonic survival and masked any effect of post mating feed intake. Although the beneficial effects of moderate feed restriction post-mating (1.2–1.5 times maintenance) on embryonic survival have previously been demonstrated (De et al., 2009; Jindal et al., 1997), the effect of a severe feed restriction (maintenance level or below) on embryonic survival has received little attention. The present study found that feeding gilts at maintenance levels post-mating decreased embryonic survival. De et al. (2009) found a similar effect, with a feeding level of 0.6× maintenance significantly decreasing embryonic survival compared with a moderate post-mating feed level of 1.2× maintenance. The positive effects of reducing post-mating feed intake from 2 to 1.5 times maintenance on embryonic survival have been related to increased circulating progesterone levels (Jindal et al., 1997). In contrast, severe feed restriction post-mating decreased plasma progesterone, which resulted in a decreased embryo cleavage rate and a decrease in the transport rate of ova along the oviduct,
affecting the development of the embryo and its synchrony with the oviductal environment (Mburu et al., 1998; Mwanza et al., 2000). Furthermore, it has been shown that asynchrony, in which the uterine environment is further advanced than the embryo, resulted in lighter embryos and placentas (Wilson et al., 2001). Therefore, the embryos of the low feed intake group should have been less developed due to asynchrony between the uterine environment and embryo. However, the current data demonstrated that there was no significant difference between conceptus weights from gilts fed a low post-mating feed intake compared with a high post-mating feed intake. Furthermore, conceptus weight was not significantly correlated with embryonic survival. This is in contrast with previous studies which found a positive relationship between embryonic weigh and survival (De et al., 2009) and crown rump length and survival (Jindal et al., 1997). However, similar to the current study, Almeida et al. (2000) observed no reduction in embryonic weights in gilts with decreased embryonic survival rates. The level of feed restriction imposed post-mating in the current study is likely to be similar to the intake achieved in low ranking sows in a group housing system. Low ranking sows receive increased aggression over competition for feed, resulting in less feed intake (Andersen et al., 1999). While it has been found that unintentional variation of feed intake in a group housing situation decreases the chance of pregnancy (Kongsted, 2006), it has not yet been investigated if the unintentional variation of feed intake in group housing has an effect on embryonic survival. Furthermore, it is currently unknown how individual feed intake in a group housing system varies between sows. However, if low ranking sows receive a feed intake of maintenance or below, both the current data and that of De et al. (2009) indicates that impaired reproductive performance due to reduced embryonic survival is a likely consequence. These data indicate the need to modify feeding strategies for group housed sows so that maximum reproductive performance is achieved. The effect of feed intake prior to mating on reproductive performance has been widely studied in pigs, with high feed intake increasing ovulation rate and embryonic survival (Almeida et al., 2000; Zak et al., 1997a). However, during lactation sows, particularly parity one sows, generally suffer a negative energy balance due to increased energy demands from milk production and decreased appetite resulting in weight and backfat loss (Quesnel et al., 1998). Excessive body condition loss negatively affects subsequent reproductive performance, with ovulation rate and embryonic survival decreased in sows that were restrictively fed during lactation (Zak et al., 1997a) and cycling gilts (Almeida et al., 2000). While there was no effect of restricted feed intake prior to mating in the present study on ovulation rate or embryonic survival, this could be due to the timing of pre-mating feed restriction used in the current study. The period of pre-mating feed restriction ended one week before mating in the current study, which caused increased growth rates in all of the gilts in the week prior to mating. This would have permitted an increased follicle development and subsequently improved embryonic survival. Hazeleger et al. (2005) found similar results,
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demonstrating that a period of increased feeding during the follicular phase prior to mating counteracted the negative effects of previous feed restriction. Conversely, other studies (Chen et al., 2012; Almeida et al., 2000) indicated that increased feeding during the follicular phase prior to mating, following a period of restrictive feeding, resulted in reduced ovulation rates, embryonic survival and embryo number. However, the increase in feed intake and growth rate throughout the week prior to mating were much greater in the current study compared with the gilts in the Almeida et al. (2000) study. This could suggest that a period of increased feeding during the follicular phase prior to mating may counteract the negative effects of previous feed restriction, but this effect may only be shown when the increase in feed intake and growth is large enough. The length of the ad-lib feeding period may also have had an influence in counteracting the negative effects of previous feed restriction. Previous studies have reported an increase in the weaning to oestrus interval when sows were subjected to feed restriction during lactation. Zak et al. (1997a) found that restricted-fed sows during lactation had a marginally greater weaning to oestrus interval, suggesting this could have had an effect on the ovulation rate. It has been suggested that a period of 5 days or more of refeeding after feed restriction allows recovery at the ovarian level through increased follicular growth and oestradiol synthesis and subsequent improved embryonic survival (Baidoo et al., 1992). Therefore, a period of almost seven days of ad-lib feeding in this study may have allowed the gilts to recover from the previous feed restriction. While there was no treatment effect on ovulation rate in the current study, ovulation rate was positively correlated with liveweight prior to the experimental treatment period. Furthermore, liveweight at day 0 was positively correlated with liveweight at day 14 and at mating. Therefore, the heavier gilts at the start of the trial stayed heavier throughout the pre-mating period, which could explain the lack of an effect of the imposed dietary treatments. As growth rate and liveweight have been shown to influence ovarian development (Prunier et al., 1987) and follicle development (van Wettere et al., 2011), it is possible that the heavier gilts may have been more sexually mature prior to the pre-mating treatment, potentially causing an increased ovulation rate.
5. 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 postmating feeding levels, demonstrating the importance of ensuring sows receive adequate post-mating nutrition.
Conflict of interest The authors declare no conflict of interest.
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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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