Lactational Oestrus Research Articles

Selecting the optimal strategies when using nurse sows for supernumerous piglets.

Hyper-prolific sows frequently do not have a sufficient number of functional teats for their piglets to nurse which has led to the use of nurse sows to manage these surplus piglets. This review discusses strategies for using nurse sows and factors that influence preweaning survival and weight gain of their litters, as well as those that affect their subsequent rebreeding performance. Rearing piglets using a nurse sow can be as successful as piglets reared with their biological mother and is thus a powerful management tool to decrease preweaning piglet mortality. Selecting a young sow as nurse sow is beneficial for piglet survival; however, piglets nursing first parity sows often have a lower daily weight gain than piglets nursing multiparous sows. A litter of uniform surplus piglets is preferably handled using the two-step nurse sow strategy. A consequence of nonuniform litters will most likely be an increased mortality and decreased weaning weight among the smallest piglets within a litter. The subsequent fertility of nurse sows is not compromised. There is an increased risk of lactational oestrus when using nurse sows leading to an increased weaning-to-oestrus interval; however, litter size in nurse sows is identical or even moderately higher in the subsequent parity compared with nonnurse sows.

Prevalence of lactational oestrus in cats and consequences for kittens.

Although lactation and suckling suppresses fertility in most mammals, some feline breeders have reported spontaneous oestrus during lactation, causing distress to kittens. This led the Official French Feline Pedigree Registry (Livre Officiel des Origines Félines - LOOF) to send a questionnaire to cat breeders requesting data on their last three litters. The aim of this study was to investigate the prevalence of lactational oestrus, its impact on litters and potential associations with litter size, age, parity, breed and seasonality. Answers from 108 breeders were collected, providing data on 238 litters in 23 different breeds. Data were also collected on successive litters from multiparous queens (n = 20) and were analysed separately from the 195 independent births. Of the 195 independent births with complete data sets, 96 (49%) queens came into oestrus during lactation, 37 (38%) of which were associated with loss of maternal interest (n = 20), milk quality variation (n = 2), clotted milk (n = 3), reduced milk quantity (n = 13), which in kittens led to reduced weight (n = 6), diarrhoea (n = 9), vomiting (n = 4), nausea (n = 2) or death (n = 4), and bottle feeding (n = 2), early weaning (n = 4) or modified litter behaviour (n = 1). A significant association was found between small litter size (one or two kittens) and the onset of lactational oestrus (P = 0.007) and between births occurring in February, March and April and lactational oestrus (P = 0.005); there was no association with age or breed. Breeders perceived a relationship in 38% of cases of lactational oestrus with maternal disinterest, clotted milk, reduced milk yield and in kittens, weight loss, vomiting, diarrhoea or even death. An association between small litter size and lactational oestrus was found, as well as with births occurring between February and April. Breeders presenting with at-risk females should be warned. Conservative and preventive measures such as contraceptive options are discussed as a possible therapy.

Characteristics of Pregnancy Following Mating in Three Types of Estrus in the Captive Harvest Mouse (Micromys minutus)

Mating in harvest mice, Micromys minutus, was observed by introducing males to females that were in cyclic estrus (CE), that had just delivered pup (postpartum estrus, PPE), or that were not pregnant but lactating after PPE (lactational estrus after PPE: LEAP). Copulation leading to pregnancy and weaning of pups occurred at every trial for CE (n = 11) and for PPE (n = 6). In LEAP, estrus with copulation and subsequent pregnancy occurred at each of seven mating trials. At six of these trials, weaning of pups occurred as well. The mean length of gestation (± SE) was 17.55 ± 0.12 days for mating in CE, 17.56 ± 0.17 days for mating in PPE, and 17.75 ± 0.20 days for mating in LEAP. Generalized linear mixed modeling found no significant effect of the type of estrus at mating on gestation length. The number of pups conceived from mating in the three estrus types did not significantly differ. Mating and pregnancy in the lactation period (PPE and LEAP) had no significant effect on the number of pups at weaning that were suckling during mating.

Optimal timing of boar exposure relative to parturition for stimulation of lactation oestrus

This study evaluated the effect of full physical boar exposure at different stages of lactation on the incidence of lactation oestrus in both primiparous and multiparous sows. A total of 38 primiparous (PP) and 80 multiparous (MP) sows (parity 2–6; 3.1±0.18) of Large White×Landrace genetics were individually housed in conventional farrowing crates from 1 week before expected farrowing until weaning on day 27.5±0.08 post-parturition. The experiment was designed as a 2×4 factorial, incorporating the two sow parity groups, and boar exposure commencing on one of four days post-farrowing (days 10, 14 and 18 of lactation and weaning). The eight treatments were as follows: PP sows, boar exposure starting on day 10 (n=10), day 14 (n=9), day 18 (n=9) and weaning (n=10); MP sows boar exposure starting on day 10 (n=20), day 14 (n=20), day 18 (n=20) and weaning (n=20). According to treatment, sows were taken daily to a detection mating area where they received 20min of boar exposure and were artificially inseminated at the first observed oestrus. A significant effect of replicate on the incidence of lactation oestrus was found; specifically, the proportion of sows expressing a lactation oestrus was lower in replicate 4 (autumn) than in the other three replicates (winter/spring; 0.15 versus 0.51; P<0.01). In replicate 1–3, a significantly higher proportion of MP compared to PP sows experienced a lactation oestrus (0.63 versus 0.36; P<0.05). Lactation oestrus expression was lower for MP sows starting boar exposure on day 14 compared to day 18 post-partum (0.38 versus 0.79, respectively; P<0.05), but was similar for days 10 and 18 of lactation (0.69 versus 0.79, respectively; P<0.05). Commencing boar exposure on day 18 as opposed to day 10 post-partum significantly reduced the interval from boar exposure to lactation oestrus expression (4.5±0.8 versus 7.7±0.8 days, respectively; P<0.05). Therefore, full physical boar exposure stimulated a high proportion of lactation oestrus in multiparous sows; however, season impacted this expression, and first parity sows are less likely than multiparous sows to express a lactation oestrus. In conclusion, there appears to be no benefit in commencing boar exposure before day 18 post-partum to stimulate a lactation oestrus.

Aggression and cortisol levels in three different group housing routines for lactating sows.

BackgroundLactating sows in Swedish organic piglet production are commonly group-housed with piglets in a multi-suckling pen within 14 days after farrowing. Nursing behaviour may be disturbed when lactating sows are moved to a new environment and mixed with other sows, as they spend more time fighting with other sows and exploring the new surroundings. This can disrupt the inhibitory effect of suckling on ovarian activity and increase the risk of lactational oestrus, making efficient reproductive management difficult. Therefore this study evaluated aggression and levels of the stress hormone cortisol in lactating sows group-housed together with their piglets at one (W1), two (W2) or three (W3) weeks post farrowing.ResultsThere was no significant difference (P > 0.05) between the three management routines (W1, W2, W3) regarding number of attacks initiated or received in the mixed group. After mixing, W2 sows had a lower number of shoulder scratches (P < 0.05) than W3 sows. Among the W3 sows, there was a lower (P < 0.01) cortisol concentration in saliva when sows were group housed compared to when they were individually housed. The cortisol response, measured as variation in cortisol concentration in saliva, was also lower (P < 0.05) in group-housed W3 sows compared with W1 sows.For all management routines, sows already living in the new environment (resident sows) initiated more attacks (P < 0.001) and received fewer attacks (P < 0.01) than sows entering the new environment (intruder sows). Overall, multiparous sows initiated more attacks and received fewer attacks than primiparous sows (P <0.001).ConclusionsOverall, the results suggest that mixing and group housing sows at three weeks post farrowing is less stressful than mixing and group housing sows at one week post farrowing. The results also indicate that parity and whether a sow is a resident or intruder in the group housing environment may have an effect on aggression levels when sows are group-housed.

An opportunity to revolutionise sow management

Research in any area of animal production can provide the opportunity to change how the system operates and is managed. The reliance on having to wean lactating sows to re-mate them has limited the commercial options for sow management. The desire to limit lactation length to maximise the litters per sow per year concurrently creates major challenges for such-aged piglets weaned abruptly. These issues are discussed in the review. This management system also fails to recognise that sows have the potential to spontaneously ovulate in lactation even when housed in farrowing crates. Inhibition of luteinising hormone release is the basis of lactational anoestrus with the suckling stimulus providing the strongest afferent signal to this inhibitory system. Any management strategy that reduces this inhibition has the potential to trigger lactational oestrus. In this review, group housing of sows, boar exposure and intermittent suckling are identified as strong stimuli that can promote lactational oestrus. Removing the need to wean sows to mate them offers further opportunities to change the way lactating sows are managed. One option is a two-stage lactation system in which the sows are housed in farrowing crates for the first 10–14 days and then moved to group accommodation for the remainder of lactation. This system provides welfare benefits for the litter in the early stage of lactation and then the benefits of less confinement for the sows in later lactation. Group lactation would also lend itself to the implementation of stimuli to assist the mating of sows in lactation, such as piglet separation and/or boar exposure. It also accommodates the mating of sows that spontaneously ovulate in lactation. Removing the need to wean sows to re-mate them provides the opportunity to increase weaning age and implement a gradual weaning, helping to attenuate the post-weaning growth check and potentially limiting antimicrobial use in weaner pigs.

A ‘two-stage’ farrowing and lactation system: assessing the impacts of group lactation on the incidence of lactational oestrus and reproductive performance

A ‘two-stage’ farrowing and lactation system: assessing the impacts of group lactation on the incidence of lactational oestrus and reproductive performance

Nursing Reduction Strategies to Enhance Estrus in Lactating Sows and Effects on Performance of Pigs to Market Weight

A total of 135 sows (PIC 1050), ranging from parity 1 to 5 (2.6 ± 1.4), were used in 5 consecutive farrowing groups (February to August). The objectives were to evaluate different suckling reduction strategies for inducing lactational estrus and the effects on sow fertility and piglet growth. Litter size was equalized within parity (11.5 ± 1.1 piglets) at d 2 after farrowing. At d 18, sows were assigned to 1 of 5 treatments (n = 26 to 28) based on parity, farrowing date, and suckled litter size. Treatments were: 1) control; 2) sows that were paired within parity and placed in adjacent stalls, on d 18 all but 5 of the lightest piglets were weaned, and the remaining piglets were combined and alternated between sows at 12 h intervals until d 25 (ALT); 3) piglets separated from sows for 12 h/d from d 18 to 25 (SEP); 4) all but the 5 lightest piglets weaned on d 18, splitweaning (SW); and 5) piglets separated from sows for 24 h on d 18 (24HR). Controls were weaned at d 21 with other treatments weaned at d 25. All sows were provided nose-to-nose contact with a mature boar for 5 min/d from d 18 until weaning without removing them from farrowing crates. Creep feed and water were provided from d 14 to weaning. Offspring ADG was recorded to market for 2 farrowing groups. Sow backfat and BW losses during lactation were similar across treatments. Of the 106 sows subjected to reduced suckling, 80 (76%) expressed estrus during lactation. The SEP and 24HR sows were in estrus earlier (P 0.05) on final BW or carcass composition were observed for the reduced suckling treatments. Altered suckling treatments differed in their ability to induce lactational estrus and their impact on gain immediately post-weaning. However, no benefits were observed for pig growth to market weight.

Effects of lactation length and boar contact in early lactation on expression of oestrus in multiparous sows

The ability to stimulate a fertile oestrus during early lactation provides an opportunity to increase piglet weaning age whilst maintaining 2.4litters per sow per year. This study evaluated the effects of boar contact beginning on day 7 of lactation and lactation length on lactation oestrus induction and subsequent reproductive output in multiparous sows (parity 2.9±0.16; mean±SEM; range 2–6). Large White×Landrace multiparous sows were allocated to one of four treatment groups; weaning at 26 days post-partum and no boar contact (control); weaning at 26 days and boar contact (BC); weaning at 7 days and boar contact (BC+short lactation (SL)); and weaning at 7 days and no boar contact (SL). Control and SL sows were taken for a short walk daily during which a backpressure test was performed in the absence of a boar. Oestrus expression within 26 days of farrowing was significantly higher in BC (67%) and BC+SL (93%) sows than control (11%) and SL (13%) sows (P<0.05). Of sows mated within 26 days of farrowing, there was no difference in the number of piglets born alive or stillborn. Therefore, boar contact is an effective method to stimulate oestrus within 26 days of farrowing in both lactating and weaned sows.

A 25years experience of group-housed sows-reproduction in animal welfare-friendly systems.

Since January 1 2013, group housing of sows has been compulsory within the European Union (EU) in all pig holdings with more than ten sows. Sows and gilts need to be kept in groups from 4 weeks after service to 1 week before the expected time of farrowing (Article 3(4) of Directive 2008/120/EC on the protection of pigs). The legislation regarding group housing was adopted already in 2001 and a long transitional period was allowed to give member states and producers enough time for adaptation. Even so, group housing of sows still seems to be uncommon in the EU, and is also uncommon in commercial pig farming systems in the rest of the world. In this review we share our experience of the Swedish 25 years of animal welfare legislation stipulating that sows must be loose-housed which de facto means group housed. The two most important concerns related to reproductive function among group-housed sows are the occurrence of lactational oestrus when sows are group-housed during lactation, and the stress that is associated with group housing during mating and gestation. Field and clinical observations in non-lactating, group-housed sows in Sweden suggest that by making basic facts known about the pig reproductive physiology related to mating, we might achieve application of efficient batch-wise breeding without pharmacological interventions. Group housing of lactating sows has some production disadvantages and somewhat lower productivity would likely have to be expected. Recordings of behavioural indicators in different housing systems suggest a lower welfare level in stalled animals compared with group-housed ones. However, there are no consistent effects on the reproductive performance associated with different housing systems. Experimental studies suggest that the most sensitive period, regarding disturbance of reproductive functions by external stressors, is the time around oestrus. We conclude that by keeping sows according to the pig welfare-friendly Directive 2008/120/EC, it is possible to combine group-housing of sows with good reproductive performance and productivity. However, substantially increased research and development is needed to optimize these systems.

Split weaning increases the incidence of lactation oestrus in boar-exposed sows

This study evaluated the effect of split weaning and fence-line boar exposure during lactation on the incidence of lactation oestrus. Large White and Large White×Landrace sows (parity 2.9±0.17; mean±SEM) were housed in conventional farrowing crates from day −4 to 30 post-parturition. Four treatments (n=18) were used: control (SPW0): continuous lactation of 10 piglets with all piglets weaned on day 30 of lactation; and three split wean (SPW) treatments with 3 (SPW3), 5 (SPW5) or 7 (SPW7) of the heaviest piglets removed from the sow on day 18 lactation. From day 18 lactation all sows received 15min daily, fence-line boar exposure in a detection mating area. Fewer sows in the SPW0 treatment (56% (10/18)) expressed a lactation oestrus compared to the SPW3, SPW5, and SPW7 treatments (83%; 89%; 94%, respectively). SPW0 sows had a lower subsequent total born compared to SPW5 or SPW7 sows (8.9±1.1 vs. 12.5±1.0 and 13.1±1.1, respectively). Between day 18 and 30 of lactation, sows in SPW5 and SPW7 gained weight (4.5±1.4 and 1.9±1.4kg, respectively) whereas SPW0 and SPW3 sows lost weight (4.9±1.4 and 2.9±1.4kg, respectively) (P<0.05). Split weaned piglets were heavier at day 17 of age by 1.0kg however by day 40 of age no weight differences were observed between piglets weaned on day 18 compared to day 30 (P<0.05). In conclusion, split weaning coupled with fence-line boar exposure in late lactation induced lactation oestrus in a higher proportion of sows compared to those suckling a normal litter size.

Boar contact is an effective stimulant of ovulation during early lactation

The efficacy of 400IU equine chorionic gonadotrophin (eCG) and 200IU human chorionic gonadotrophin (hCG) (PG600; Intervet, Australia) and boar exposure as stimuli of oestrus and ovulation have been established in pre-pubertal gilts and weaned sows, but there is little published data on their use to overcome lactation anoestrus. Designed as a 2×2 factorial, the current study used 40 Large White/Landrace sows (parity 1.9±0.14), to determine the effects of boar exposure (BE) versus NoBE and PG600 versus NoPG600 on the incidence of lactation oestrus and ovulation. On day 1 of lactation, PG600 was administered and BE commenced. Throughout lactation all sows were housed individually in farrowing crates (0.6×2.4m2). BE consisted of 15min of daily, full physical boar exposure in a detection mating area. For all sows, litter size suckled was standardized to 10 piglets on day 1 of lactation, and maintained at this level until weaning on day 26 post-partum. Oestrus detection was performed daily, with oestrus defined as the exhibition of a standing reflex, and ovulation confirmed when progesterone concentrations exceeded 1.0ng/ml on day 3 and 4.0ng/ml on day 10 post-oestrus detection. There was no effect of PG600 on any reproductive measures, and no interactions with the BE treatment. A higher proportion of BE compared to non-BE sows exhibited a behavioural oestrus without ovulation within 5 days of parturition (0.83 versus 0.09; P<0.05). The interval from parturition to lactation ovulation was unaffected by treatment (15.4±1.21 days). However, BE increased the proportion of sows ovulating during lactation (0.61 versus 0.09; P<0.05), and resulted in an earlier ovulation relative to parturition (20.6±1.30 versus 30.1±1.35 days) compared to non-BE sows. In conclusion, this is the first study to demonstrate that taking lactating sows to a detection mating area for 15min of daily, physical boar contact resulted in a high incidence of lactation ovulation within 22 days of parturition.

Stimulation of estrus and ovulation in lactating sows (2013)

A total of 53 sows were used to determine the effects of a lactational estrus stimulation strategy on reproductive and litter growth performance. Treatment differences within parity group, multiparous and primiparous, were also considered. Litter size was equalized to 11.6 ± 1.2 pigs at d 2 postfarrowing. At d 18 of lactation, sows were allotted to the control or an altered suckling method (ALT). The ALT sows were placed in adjacent pairs within parity so pigs could be moved between litters by temporarily lifting the divider between the two litters. On d 18, all but the 5 lightest weight pigs from each ALT litter were weaned. The 5 lightweight pigs for each pair of litters formed a combined litter that nursed each sow of the pair 12 h/d from d 18 to 25. Therefore, pigs had nursing access 24 h/d, but each ALT sow was suckled only 12 h/d. Boar exposure was provided to ALT sows for 15 min/d by removing sows to a pen outside the farrowing room. Control and ALT sows were weaned at d 21 and d 25, respectively. Sow weights and litter growth performance during lactation was similar between treatments, although ALT sows had 16% greater total feed intake (P < 0.01) due to the extended lactation length. Primiparous sows lost a greater percentage (7.4 vs. 3.4%) of BW and consumed less feed (P < 0.01) than multiparous sows. A total of 26 ALT sows (93%) were detected in estrus and mated in lactation. Although duration from initiating ALT to estrus was greater (P < 0.001) than the wean-to-estrus interval for controls, ALT sows were in estrus earlier (23.0 vs. 24.6 d; P < 0.001) than controls postfarrowing, with primiparous sows responding more slowly (5.4 vs. 3.8 d; P < 0.01) than multiparous sows for both treatments. Pregnancy rate and subsequent reproductive performance were similar between treatments. In conclusion, ALT sows expressed lactational estrus and performed reproductively similar to sows with conventionally weaned litters.

Reproductive Issues in Welfare‐Friendly Housing Systems in Pig Husbandry: A Review

In Europe, housing conditions of sows are currently changing, related with a larger emphasis on pig welfare. As a result, sows are and will be less kept in crates, but more so in loose housing systems (farrowing, lactation) and group housing systems (pregnancy, lactation, weaning-to-oestrus interval). These changes in housing conditions may affect reproductive functioning of the sows. Group housing of sows may decrease farrowing rate and litter size when stress levels rise or when feed intake in early pregnancy is not fully secured. Loose housing during farrowing results in an improved farrowing process, but may increase piglet mortality by crushing during early lactation. Further, group housing during lactation may increase the risk of lactational oestrus. Thus, new - welfare friendly - housing systems require increased attention to management to ensure optimal reproductive performance.

Should Weaning be the Start of the Reproductive Cycle in Hyper‐prolific Sows? A Physiological View

Normally, sows are in anoestrus during lactation and start their new cycle at the day of weaning. Modern hybrid primiparous sows that suckle large numbers of piglets may lose substantial amounts of body reserves during lactation. This compromises follicle development during lactation. As modern sows have short weaning-to-oestrus intervals, these compromised follicles are recruited for ovulation directly after weaning, resulting in lower ovulation rates and lower embryo survival. Postponing or skipping first oestrus after weaning in primiparous sows may help to limit the negative consequences of lactation on subsequent reproduction. Multiparous sows may have very high litter sizes, especially after long lactations as applied in organic sows. These high litter sizes compromise piglet birthweight and survival and subsequent performance. Inducing lactation oestrus in multiparous sows may help to limit litter size and improve piglet survival and performance. This study discusses physiological and reproductive effects of extending the start of a new pregnancy after lactation in primiparous sows and induction of lactation oestrus in multiparous sows. We thereby challenge the view that weaning is an ideal start for the reproductive cycle in modern sows.

Timing of lactational oestrus in intermittent suckling regimes: Consequences for sow fertility

Three intermittent suckling (IS) regimes were evaluated for their effects on lactational oestrus and subsequent fertility. Control sows were weaned (CW; n=38) at d 26±2 of lactation. In IS19-7D (n=40) and IS19-14D (n=42) sows, IS started at d 19±1 of lactation and sows were weaned 7 or 14d later. In IS26-7D (n=41), IS started at d 26±1 of lactation and sows were weaned 7d later. During IS, sows were separated from their piglets for 10h/day. Oestrus detection was performed twice daily without a boar and ovulation was confirmed by ultrasound once a week. In IS19-7D, IS19-14D and IS26-7D, respectively, 50%, 64% and 61% of the sows showed oestrus and ovulation during IS (P>0.05), and, of the remaining sows, 100%, 93%, and 69% showed oestrus in the first week after weaning. In CW sows, 95% showed oestrus in the first week after weaning. Parity 1 sows were considerably less likely than older parities (23% vs. 68%) to show oestrus in lactation. Pregnancy rate of the first post partum oestrus (during lactation or after weaning) was 89% (CW), 92% (IS19-7D), 80% (IS19-14D) and 77% (IS26-7D) (P>0.05) and subsequent litter size was 14.5±0.5, 14.5±0.6, 15.3±0.5 and 15.2±0.8, respectively (P>0.05). Sows mated during lactation had similar pregnancy rate and litter size to those mated after weaning. Hence, ongoing lactation for the first 2–9d of pregnancy did not negatively affect fertility. A total of 50–64% of IS sows showed lactational oestrus, regardless of the stage of lactation. Pregnancy rates and litter size were similar to control sows, and were not affected by stage of lactation at mating.

Reproductive Features and Faecal Progesterone Metabolite Profile in Female Ferrets

Elevated post-partum progesterone metabolite (P(4) -met) levels have been recently postulated to occur in lactating lynxes. The aims of this study were to monitor reproductive features in female ferrets, changes in the faecal P(4) -met concentrations throughout the breeding season and ovarian activity in post-partum lactating and non-lactating (NL) female ferrets. Our results indicate that coinciding with the results described in the lynx, elevated faecal P4-met concentrations occur in lactating ferrets, furthermore, that the duration of elevated secretion of P(4) seems to be dependent on the duration of lactation (P4-met at delivery, n=47: <500 ng/g; 5-7 days after delivery, during lactation, n=47: ≥ 500-800 ng/g; in females weaned at delivery, n=4: baseline levels). Three days after ovariohysterectomy of lactating females, P(4) -met concentrations decreased to baseline levels. In lactating females, the ovarian stroma is more active than that in NL ones implicating that the ovary is at least in part responsible for the elevated P4-met concentrations. Ovaries of lactating females contained many luteinized cells either as luteinized granulose cells in the wall of late pre-antral/early antral follicles or as corpus luteum (CL)-like structures. Early resumption of the entire ovarian activity (developed follicles and oestrus) occurs in NL post-partum females, while final follicular development is blocked (follicles stalls at antral stage) in the lactating ones (however, occasionally lactational oestrus may occur). We suppose that the elevated faecal P4-met during lactation together with suckling and other hormonal effects may contribute to prevention of early returning to oestrus in nursing female ferrets.

Induction of lactational estrus in organic piglet production

The longer lactation period required in organic piglet producing herds reduces the potential number of produced litters per sow per year compared with that of conventional production. Induction and use of lactational estrus may be a way to increase the productivity in organic production. However, if lactational estrus is to be beneficial under practical husbandry conditions, it is crucial that the majority of sows are successfully mated within a few days to make batch farrowing procedures possible. The objective of this study was to investigate the occurrence and timing of lactational estrus in an organic outdoor system based on ad libitum feeding, individual housing until Day 35 in lactation, followed by grouping and introduction of a boar and weaning of piglets after 8 wk. Five groups with four sows ((Danish Yorkshire × Danish Landrace) × Danish Duroc) in each were observed, and rank was determined by a food competition test. All sows showed lactational estrus, and 84% of these sows showed estrus within 1 wk, on average 43.5 d and 7.3 d after farrowing and boar introduction, respectively. The number of days from boar introduction to estrus increased significantly with increasing feed competition rank (the lowest number being the top rank position). Eighty-four percent of all sows were diagnosed pregnant 5 wk after estrus. Behavioral observations revealed that the average total number of copulations per estrus sow was 2.3 with a range of 0 to 5 copulations. The findings of the current study indicate that it is possible to combine lactational estrus and batch farrowing procedures to increase the number of weaned piglets per year per sow in organic piglet production based on 8 wk of lactation or more.

The Intermittent Suckling Regimen in Pigs: Consequences for Reproductive Performance of Sows

Intermittent suckling (IS), a system in which the sow and the piglets are separated for a number of hours per day during lactation, is put forward as a system that can increase piglet welfare around weaning and also induce lactational oestrus. To be of practical use, IS regimes need to result in a predictable oestrus and good reproductive performance. This review describes the effects of IS on sow reproductive performance. During IS, the LH pulsatility pattern switches to a high frequency, low amplitude release during separation, as is normally observed at weaning. In sows that ovulate during IS, LH pulsatility remains higher than in anovulatory sows. Around 90% of the IS sows show follicle growth up to pre-ovulatory size in a similar time period as sows post-weaning. Depending on the stage of lactation that IS commenced, 13% (day 21) to 21% (day 14) of the sows with pre-ovulatory follicles did not ovulate, but follicles either regressed or developed into cystic follicles. In the ovulatory IS sows oestradiol production is comparable but the LH surge is lower with an early start of IS (day 14) when compared with the weaned sows. Continuation of IS post-ovulation has negative effects on pregnancy rate, embryo development and progesterone levels. Factors related to lactation (e.g. a high metabolic clearance rate), may play a role in this. In conclusion, IS can result in a fertile oestrus when the timing of start of IS and duration of IS are taken into account, but for practical use IS regimes result in a too variable reproductive performance.

Early Embryo Survival and Development in Sows with Lactational Ovulation

During lactation, daily separation of sow and piglets, intermittent suckling (IS), can induce lactational oestrus and ovulation. This study examined effects of IS on subsequent early embryo survival and development. Multiparous Topigs40 sows were separated from their piglets for either 12 consecutive hours per day (IS12, n = 13) or two times for 6 h per day (IS6, n = 10) from day 14 of lactation onwards until 23 days after ovulation. Control sows (C, n = 17) were weaned at day 21 of lactation. Oestrus was shown in all treatments within 5 days after the start of treatment. Sows were inseminated each day of oestrus and slaughtered at D23 after ovulation. Intermittent suckling did not significantly affect pregnancy rates of sows (75% IS12 vs 78% IS6 vs 94% C; p > 0.10). Embryo survival was not significantly affected by IS (IS12: 57%; IS6: 51%; p > 0.10) although it seemed to be lower than in C sows (70%). Some parameters of embryo, placental and uterine development were affected by IS, especially in the IS6 group. IS6 embryos had shorter placentas (17.5 +/- 1.2 cm; p < 0.05) than C (20.3 +/- 1.4 cm) and IS12 sows (20.9 +/- 0.7 cm) were smaller and less developed than C sows (p < 0.05). In conclusion, embryo survival does not seem significantly affected by IS, although numerical differences were great. Embryo development, however, was negatively affected in IS6 sows possibly due to a combination of high milk production, stress and lactational effects on uterine development.