Physiology and management of the peri-parturient sow in the context of changing production conditions.

Genetic selection has resulted in a considerable increase in litter size, paralleled by an increase in farrowing duration and perinatal mortality. This paper describes some of the physiological changes around farrowing, and how genetic trends and sow management interact with these. Compromised farrowing can be related to nutritional management, or to housing conditions and handling of periparturient sows. Transition diets, for example, can be formulated to support calcium homeostasis and alleviate constipation. The opportunity to express natural behaviours and minimize stress around farrowing can further optimize farrowing conditions and reduce piglet mortality. Loose farrowing systems are part of the answer to the challenges around farrowing; however, current systems do not perform consistently. In conclusion, increased farrowing duration and increased perinatal mortality may to some extent be inevitably related to trends in pig production; however, they can be improved by nutritional measures, housing conditions and farrowing management.

Follicular fluid steroid profile in sows: relationship to follicle size and oocyte quality†.

Identification of reliable characteristics of follicle quality and developmental competence has been pursued in numerous studies, but with inconsistent outcomes. Here, we aimed to identify these characteristics by analysis of the follicular fluid (FF) steroid profile in relation to cumulus-oocyte complex (COC) morphology and follicle size, followed by molecular substantiation. Multiparous sows at weaning were used to facilitate analysis at the start of the follicular phase of the oestrus cycle. Sows with a higher average follicle size (≥5 mm vs. < 5 mm) had a higher follicular fluid ß-estradiol concentration, but did not differ in other measured steroids. Sows with high compared to low percentage high-quality COCs (<70% vs. ≥70% high-quality) had follicular fluid with a higher concentration of ß-estradiol, 19-norandrostenedione, progesterone, and α-testosterone, while the concentration of cortisol was lower. Transcriptome analysis of granulosa cells of healthy follicles of sows with a high percentage high-quality COCs showed higher abundance of transcripts involved in ovarian steroidogenesis (e.g., CYP19A2 and 3, POR, VEGFA) and growth (IGF1) and differential abundance of transcripts involved in granulosa cell apoptosis (e.g., GADD45A, INHBB). Differences in aromatase transcript abundance (CYP19A1, 2 and 3) were confirmed at the protein level. In addition, sows with a high percentage high-quality COCs lost less weight during lactation and had higher plasma IGF1 concentration at weaning, which may have affected COC quality. To the best of our knowledge, this study is also the first to report the relation between FF steroid profile and COC quality.

Consequences of negative energy balance on follicular development and oocyte quality in primiparous sows†.

Metabolic demands of modern hybrid sows have increased over the years, which increases the chance that sows enter a substantial negative energy balance (NEB) during lactation. This NEB can influence the development of follicles and oocytes that will give rise to the next litter. To study effects of a lactational NEB on follicular development, we used 36 primiparous sows of which 18 were subjected to feed restriction (3.25 kg/day) and 18 were full-fed (6.5 kg/day) during the last 2 weeks of a 24.1 ± 0.3 day lactation. Feed restriction resulted in a 70% larger lactational body weight loss and 76% higher longissimus dorsi depth loss, but similar amounts of backfat loss compared to the full fed sows. These changes were accompanied by lower plasma insulin-like growth factor 1 (IGF1) and higher plasma creatinine levels in the restricted sows from the last week of lactation onward. Ovaries were collected 48 h after weaning. Restricted sows had a lower average size of the 15 largest follicles (-26%) and cumulus-oocyte complexes showed less expansion after 22 h in vitro maturation (-26%). Less zygotes of restricted sows reached the metaphase stage 24 h after in vitro fertilization and showed a higher incidence of polyspermy (+89%). This shows that feed restriction had severe consequences on oocyte developmental competence. Follicular fluid of restricted sows had lower IGF1 (-56%) and steroid levels (e.g., ß-estradiol, progestins, and androgens), which indicated that follicles of restricted sows were less competent to produce steroids and growth factors needed for oocytes to obtain full developmental competence.

In ovaries with high or low variation in follicle size, granulosa cells of antral follicles exhibit distinct size-related processes.

Antral follicle size might be a valuable additive predictive marker for IVF outcome. To better understand consequences of antral follicle size as a marker for reproductive outcome, we aimed to obtain insight in follicle size-related granulosa cell processes, as granulosa cells play an essential role in follicular development via the production of growth factors, steroids and metabolic intermediates. Using the pig as a model, we compared gene expression in granulosa cells of smaller and larger follicles in the healthy antral follicle pool of sows, which had a high variation versus low variation in follicle size. Selected gene expression was confirmed at the protein level. Granulosa cells of smaller antral follicles showed increased cell proliferation, which was accompanied by a metabolic shift towards aerobic glycolysis (i.e. the Warburg effect), similar to other highly proliferating cells. High granulosa cell proliferation rates in smaller follicles might be regulated via increased granulosa cell expression of the androgen receptor and the epidermal growth factor receptor, which are activated in response to locally produced mitogens. While granulosa cells of smaller follicles in the pool are more proliferative, granulosa cells of larger follicles express more maturation markers such as insulin-like growth factor-1 (IGF1) and angiopoietin 1 (ANGPT1) and are therefore more differentiated. As both higher IGF1 and ANGPT1 have been associated with better IVF outcomes, the results of our study imply that including smaller follicles for oocyte aspiration might have negative consequences for IVF outcome.

Post-weaning social and cognitive performance of piglets raised pre-weaning either in a complex multi-suckling group housing system or in a conventional system with a crated sow.

We studied the social and cognitive performance of piglets raised pre-weaning either in a conventional system with a sow in a farrowing crate (FC) or in a multi-suckling (MS) system in which 5 sows and their piglets could interact in a more physically enriched and spacious environment. After weaning at 4 weeks of age, 8 groups of 4 litter-mates per pre-weaning housing treatment were studied under equal and enriched post-weaning housing conditions. From each pen, one pair consisting of a dominant and a submissive pig was selected, based on a feed competition test (FCT) 2 weeks post-weaning. This pair was used in an informed forager test (IFT) which measured aspects of spatial learning and foraging strategies in a competitive context. During individual training, submissive (informed) pigs learned to remember a bait location in a testing arena with 8 buckets (the same bucket was baited in a search visit and a subsequent relocation visit), whereas dominant (non-informed) pigs always found the bait in a random bucket (search visits only). After learning their task, the informed pigs' individual search visit was followed by a pairwise relocation visit in which they were accompanied by the non-informed pig. Effects of pre-weaning housing treatment were not distinctly present regarding the occurrence of aggression in the FCT and the learning performance during individual training in the IFT. During paired visits, informed and non-informed pigs changed their behaviour in response to being tested pairwise instead of individually, but MS and FC pigs showed few distinct behavioural differences.

Temporary undernutrition during early gestation, corpora lutea morphometrics, ovarian progesterone secretion and embryo survival in gilts.

The present study reports effects of severe undernutrition on luteal function and pregnancy in pigs. Gilts were inseminated and either fasted on Day 10 and 11 after conception (n=11) or fully fed throughout (n=10). Fasting did not affect LH or progesterone pulsatile secretion pattern on Day 11 in samples taken from blood vessels draining an ovary. Ultrasonographic measurements of the size of the corpora lutea did not show any effect of fasting either. However, fasted gilts had 10 to 30% lower systemic progesterone from Day 12 through Day 15 after conception (P<0.05). All gilts farrowed, but fasted gilts had fewer born piglets than fully fed gilts (8.8±0.8 vs 10.9±0.5 respectively; P<0.05). In conclusion, fasting during embryo elongation can compromise embryonic survival by affecting ovarian function in the days after fasting, without having an immediate effect on LH secretion and progesterone output by the ovaries.

Effects of birthweight on reproductive system development and onset of puberty in gilts.

The aim of the present study was to investigate the effects of birthweight on bodyweight development, development of the genital tract, onset of puberty and their associations with insulin-like growth factor (IGF) 1 and leptin concentrations. Pairs of littermate gilts from 51 litters were selected: one piglet with the highest birthweight (HW; 1.5±0.2kg) and the other with the lowest birthweight (LW; 1.0±0.2kg). Gilt pairs were killed at either fixed ages (80.8±1.2 days; AG; 16 pairs), fixed bodyweight (35.2±1.4kg; WG; 16 pairs) or after first oestrus (EG; 19 pairs). In the AG group, HW gilts were 5.6kg heavier at the time of death than LW gilts. In the WG group, LW gilts were 5.9 days older at the time of death (P<0.05). There were no significant differences in the number or size of total antral follicles or in the follicle population among birthweight classes. Age at puberty was similar between the HW and LW gilts, but bodyweight at time of death was greater for HW gilts (P<0.05). Birthweight did not affect the development of the genital tract, ovulation rate or hormone plasma concentrations. These results suggest that birthweight does not affect the development of the genital tract before puberty and puberty onset.

Serial transvaginal ultrasound-guided biopsy of the porcine corpus luteum in vivo.

The aims of the present study was to develop and describe a transvaginal ultrasound-guided biopsy method for luteal tissue in the porcine and to evaluate the effects of the method on the reproductive tract, ovarian status and pregnancy status. Biopsies were performed in four multiparous sows on Days 9 and 15 of three consecutive oestrous cycles; the size and histological composition of the samples obtained were evaluated and the reproductive tract of the sows was monitored. Furthermore, biopsies were performed in 26 multiparous sows on Days 10 and 13 after insemination, and the pregnancy rate, gestation length and subsequent litter size were evaluated. RNA was extracted from the samples obtained and the quality and quantity were determined. Altogether, 76 biopsies were performed and 38 samples were obtained. Compared with sows from which no samples were obtained (n=6), sows from which one or more samples were obtained (n=24) were older (parity 5.0±2.8 vs 2.2±0.4, mean±s.d.), heavier (290±26 vs 244±27kg) and had higher back fat (11.4±2.7 vs 6.4±2.5mm; P<0.05 for all). No effect of the biopsies (P>0.05) was observed on the cyclicity and reproductive organs of the sows, or on corpus luteum diameter on Day 13 (8.9±1.0 vs 9.2±1.1mm), pregnancy rate (95% vs 96%), gestation length (115±1 vs 115±1 days) and subsequent litter size (12.7±2.5 vs 13.3±2.8) between sows from which samples were obtained and those from which no samples were obtained. The samples obtained had a diameter of 1mm and contained heterogeneous tissue with various cell types. The RNA quantity was 520±160µg per sample and the RNA integrity number was 8.5±1.0. In conclusion, an ultrasound-guided biopsy method for ovarian tissue, which can be used for gene expression studies, was established in the porcine. No effect on corpus luteum function was found.

Caudal vena cava progesterone and LH release patterns on Day 14 of gestation in primiparous sows.

The aim of the present study was to explore the relationship between systemic and local progesterone secretion and LH pulsatility during implantation in the pig. Differences in progesterone concentrations measured locally in the caudal vena cava and systemically in the jugular vein were studied in eight primiparous sows on Day 14 of pregnancy. LH pulsatility was analysed for its effects on the local progesterone-releasing pattern. Mean (±s.d.) progesterone concentrations in the vena cava (65.5±19.8ngmL-1) were approximately double basal concentrations (33.6±13.1ngmL-1). Basal concentrations of progesterone and LH were calculated as the average of the lowest six values. Basal caudal vena cava and mean jugular (27.6±1.5ngmL-1) progesterone concentrations did not differ significantly. Pre- and postprandial jugular progesterone concentrations were significantly different in the morning and afternoon (P=0.025 and 0.023). Mean LH ranged from 0.24 to 0.43ngmL-1 and was approximately double as high as basal LH in individual sows. In 60.8% of cases, LH pulses were followed by a progesterone pulse within 1h. In conclusion, the present study showed that corpus luteum function appears to respond to LH pulsatility on Day 14 of pregnancy. However, the response varies at the level of individual sows. In addition, systemic postprandial decreases in progesterone were confirmed on Day 14 of pregnancy.

Follicle size and reproductive hormone profiles during a post-weaning altrenogest treatment in primiparous sows.

This study investigated the endocrine background of follicle size changes during post-weaning altrenogest treatment. altrenogest-treated sows received a 20-mg dosage daily at 8.00 a.m. from Day -1 to Day 14 after weaning. On Day -1, only 3/13 altrenogest-treated sows showed LH pulses compared with 8/8 control sows (P=0.001). On Day 0, control sows showed a typical high frequency-low amplitude LH pattern, indicative for recruitment of oestrogenic follicles. In altrenogest-treated animals on Day 0, half of the sows showed high frequency-high amplitude pulses from 4-5h after weaning. In altrenogest-treated sows, average follicle size increased from 3.1±0.5 mm on Day 0 to 4.4±0.6mm on Day 5, then decreased to 3.7±0.5 mm on Day 7 and stabilised thereafter. FSH and oestradiol (E2) concentrations showed a distinct diurnal pattern; high at 7.00 a.m. and low at 3.00 p.m. E2 concentrations (7.00 a.m.) showed a 2.5-fold increase from Day -1 to Day 2, and subsequently a 2-fold decline to reach a plateau at Day 8. FSH concentrations reached maximum levels by Day 5 and slowly declined afterwards. In conclusion, once-daily administration of altrenogest starting one day before weaning delays the weaning-induced increase in LH pulses. Although FSH and follicle size increase until Day 5 after weaning, follicle E2 production already decreased from Day 2 after weaning. Post-weaning altrenogest treatment thus results in a follicular wave of follicles that lose oestrogenic competence at Day 2 after weaning, presumably related to the changed LH dynamics during altrenogest treatment.

Cystic ovaries in intermittently-suckled sows: follicle growth and endocrine profiles.

This paper presents follicle development and hormone profiles for sows with normal ovulation or cystic follicles during an intermittent-suckling (IS) regime that started at Day 14 of lactation. Sows were subjected to separation from their piglets during blocks of 6h or 12h. In total, 8 out of 52 sows developed cystic follicles; either full cystic ovaries (n=6) or partial ovulation (n=2). Increase in follicle size of these sows was similar to that of normal ovulating sows until pre-ovulatory size at Day 5 after the start of separation, but from then on became larger (P<0.05). LH surge was smaller or absent in sows that developed (partially) cystic ovaries (0.4 ± 0.1 vs 3.6 ± 0.3 ngmL(-1); P<0.01). Peak levels of oestradiol (E2) were similar but high E2 levels persisted in sows that developed (partly) cystic ovaries and duration of oestrus tended to be longer. The risk of developing (partly) cystic ovaries was higher when IS occurred in blocks of 6h versus 12h (33 vs 10%). In conclusion, the appearance of cystic ovaries at approximately Day 20 of ongoing lactation was related to an insufficient LH surge, as is also the case in non-lactating sows.

Dietary CP and digestion kinetics influence BW loss, litter weight gain, and reproduction by affecting postprandial amino acid metabolism in lactating sows.

To avoid a high body protein mobilization in modern lean sows during lactation, an adequate dietary amino acid (AA) supply and an efficient AA utilization are crucial. This study evaluated the effects of dietary CP and in vitro protein digestion kinetics on changes in sow body condition, litter weight gain, milk composition, blood metabolites, protein utilization efficiency and subsequent reproductive performance. We hypothesized that a slower digestion of dietary protein would improve AA availability and utilization. In total, 110 multiparous sows were fed one of four lactation diets in a 2 × 2 factorial design, with two CP concentrations: 140 g/kg vs 180 g/kg, and two protein digestion kinetics, expressed as a percentage of slow protein (in vitro degradation between 30 and 240 min): 8 vs 16% of total protein. Feeding sows the high CP diets reduced sow weight loss (Δ = 7.6 kg, P < 0.01), estimated body fat loss (Δ = 2.6 kg, P = 0.02), and estimated body protein loss (Δ = 1.0 kg, P = 0.08), but only at a high percentage of slow protein. A higher percentage of slow protein increased litter weight gain throughout lactation (Δ = 2.6 kg, P = 0.04) regardless of CP concentrations, whereas a higher CP only increased litter weight gain during week 3 of lactation (Δ = 1.2 kg, P = 0.01). On Day 15 postfarrowing, serial blood samples were taken from a subsample of sows fed with the high CP diets. In these sows, a high percentage of slow protein resulted in higher plasma AA concentrations at 150 and 180 min after feeding (Δ = 0.89, P = 0.02, Δ = 0.78, P = 0.03, mmol/L, respectively) and lower increases in urea at 90 and 120 min after feeding (Δ = 0.67, P = 0.04, Δ = 0.70, P = 0.03, mmol/L, respectively). The higher dietary CP concentration increased total nitrogen loss to the environment (Δ = 604 g, P < 0.01) with a reduction of protein efficiency (Δ = 14.8%, P < 0.01). In the next farrowing, a higher percentage of slow protein increased subsequent liveborn litter size (Δ = 0.7, P < 0.05). In conclusion, feeding sows with a high dietary CP concentration alleviated maternal weight loss during lactation when the dietary protein digestion rate was slower, but lowered protein efficiency. A slower protein digestion improved litter weight gain, possibly by reducing AA oxidation and improving plasma AA availability, thus, improving protein efficiency.

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.

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.

Lactation weight loss in primiparous sows: consequences for embryo survival and progesterone and relations with metabolic profiles.

Our objective was to study reproductive consequences of lactation bodyweight loss occurring in primiparous sows with mild feed restriction and to relate these lactation weight losses and its consequences to metabolic profiles during lactation and subsequent early gestation. After weaning, 47 first-litter sows were retrospectively assigned to a high- (HWL, >13.8%, n= 24) or low (LWL, ≤13.8%, n = 23)-weight loss group. Thirty-six animals received an indwelling jugular vein catheter to determine lactational and gestational profiles of insulin-like growth factor-1 (IGF-1), non-esterified fatty acids (NEFA) and urea and gestational profiles of progesterone. At day 35 after insemination, sows were euthanized and their reproductive tract collected. Pregnancy rate was 75% (18/24) for HWL and 96% (22/23) for LWL sows. High-weight loss sows had a lower number of implantation sites (17.2 ± 0.8 vs 19.5 ± 0.7, respectively, p = 0.03) and a lower embryonic survival (65.6 ± 3.4 vs 77.4 ± 2.9%, p = 0.02), resulting in fewer vital embryos (14.9 ± 0.9 vs 16.8 ± 0.7, p = 0.07) than LWL sows. Progesterone peak values were reached later in HWL than in LWL sows (day 13.4 ± 0.5 vs 12.0 ± 0.5, respectively, p = 0.05). Gestational concentrations of IGF-1, NEFA and urea were almost identical for HWL and LWL sows, whilst numerical differences were seen during lactation. The current study shows negative consequences of lactational weight loss in mildly feed-restricted primiparous sows for embryonic survival and shows that these consequences seem only mildly related with metabolic alterations during lactation and not with metabolic alterations during subsequent gestation.

Nutritionally induced relationships between insulin levels during the weaning-to-ovulation interval and reproductive characteristics in multiparous sows: I. Luteinizing hormone, follicle development, oestrus and ovulation.

To get more insight in how insulin secretion patterns and corresponding insulin-like growth factor-1 (IGF-1) levels are related to luteinizing hormone (LH) secretion, follicle development and ovulation, 32 multiparous sows were fed either a dextrose plus lactose-containing diet at 4 h intervals (DL; each 150 g/day) or an isocaloric control diet at 12 h intervals (CTRL; containing soybean oil) during the weaning-to-ovulation interval (WOI). Insulin parameters (basal, peak levels and mean insulin) and IGF-1 levels during the WOI were similar for both treatments, but the insulin secretion pattern differed (related with feeding frequency and meal sizes). Oestrus and ovulation characteristics were not influenced by treatment. The LH surge was higher in CTRL compared with DL sows (3.73 vs 3.00 ng/ml; p = 0.03). Average diameter (6.5 vs 6.1 mm; p = 0.08) and uniformity (CV: 11 vs 15%, p = 0.02) of follicles ≥3 mm at day 4 after weaning was higher in CTRL compared with DL sows. Basal insulin levels were positively related with follicle diameter at ovulation (ß = 0.05 mm/(µU/ml); p = 0.04) and negatively related with LH surge level (ß = -0.07 (ng/ml)/(µU/ml); p = 0.01). Insulin area under the curve (AUC) (ß = 0.037 (ng/ml)/1000 µU; p = 0.02) and IGF-1 levels (ß = 0.002 (ng/ml)/(ng/ml); p < 0.01) were positively related to basal LH level around the LH surge. From these data, we conclude that insulin and IGF-1 levels during the WOI are related to LH secretion and follicle development. Not only the absolute level of insulin seems important, but also the pattern within a day in which insulin is secreted seems to affect LH secretion and development of pre-ovulatory follicles.

Nutritionally induced relationships between insulin levels during the weaning-to-ovulation interval and reproductive characteristics in multiparous sows: II. Luteal development, progesterone and conceptus development and uniformity.

Insulin-stimulating sow diets before mating improve piglet uniformity. We studied effects of nutritionally induced differences in insulin levels during the weaning-to-ovulation interval (WOI) on luteal development, progesterone secretion and pre-implantation conceptus development and uniformity (d10). To create insulin contrasts, 32 multiparous sows were fed either a dextrose plus lactose containing diet (each 150 g/day) at 4 h intervals (DL treatment) or an isocalorically control diet (containing soybean oil) at 12 h intervals (CTRL treatment) during the WOI. After ovulation, all sows received a standard gestation diet at 12 h intervals. Ovulation rate, plasma progesterone levels, pregnancy rate and embryo survival did not differ between treatments. CTRL sows had a higher total luteal weight (11.2 vs 9.7 g; p = 0.03) than DL sows. Conceptus diameter at d10 of pregnancy tended to be larger in CTRL sows (diameter: 7.1 vs 6.4 mm; p = 0.07). Conceptus uniformity was not influenced by treatment. Insulin area under the curve (AUC) and mean insulin during the WOI were positively related with mean progesterone (ß values were 0.78 (ng/ml)/1000 µU and 0.14 (ng/ml)/(µU/ml) for AUC and mean, respectively; p < 0.05) and maximal progesterone (ß values were 1.46 (ng/ml)/1000 µU and 0.27 (ng/ml)/(µU/ml) for AUC and mean, respectively; p < 0.05) levels during the first 10 days of pregnancy, but not with conceptus development and uniformity. In conclusion, high insulin levels during the WOI seem to be beneficial for progesterone secretion in sows, probably mediated through beneficial effects of insulin on follicle development.

Split-weaning before altrenogest synchronization of multiparous sows alters follicular development and reduces embryo survival.

This study used split-weaning (SW) to induce differences in follicle size at weaning and study its consequences for follicle development during and after post-weaning altrenogest feeding and for reproductive performance. Multiparous sows (n=47) were assigned to SW (n=23; litter size reduced to the six smallest piglets 3 days before weaning) or control (C; n=24; normal weaning). Altrenogest (20 mg/day) was fed to all 47 sows from Day -1 till Day 5 (complete weaning = Day 0). Follicle size on Day 1, 2 and 8 was smaller in C than in SW (p ≤ 0.05). Ovulation rate was similar, but C sows had higher embryo survival rate (ESR) than SW sows (83 ± 19 and 58 ± 31%, respectively; p=0.001). SW sows with low ESR (<63%; n=10) had a greater follicle size on days 3-6 than SW sows with high ESR (>63%; n=10; p ≤ 0.04). A decrease in follicle size between Day 5 and 6 of altrenogest feeding was associated with increased ESR in both treatments (p=0.002). Follicle pool analyses (assessment of all follicles >2 mm) revealed that on Day 3, sows with low ESR had a higher % of follicles >5 mm compared with sows with high ESR (30% vs 10%; p=0.04). Thus, sows in which follicle growth was less suppressed during altrenogest feeding had a lower ESR. These effects on follicle development and ESR were more pronounced in split-weaned sows.

Progestagen supplementation during early pregnancy does not improve embryo survival in pigs.

Progesterone supplementation during early pregnancy may increase embryo survival in pigs. The current study evaluated whether oral supplementation with an analogue of progesterone, altrenogest (ALT), affects embryo survival. A first experiment evaluated the effect of a daily 20-mg dosage of ALT during days 1-4 or 2-4 after onset of oestrus on embryo survival at day 42 of pregnancy. A control group (CTR1) was not treated. The time of ovulation was estimated by transrectal ultrasound at 12-h intervals. Altrenogest treatment significantly reduced pregnancy rate when start of treatment was before or at ovulation: 25% (5/20) compared to later start of treatment [85% (28/33)] and non-treated CTR1 [100% (23/23)]. Altrenogest treatment also reduced (p < 0.05) number of foetuses, from 14.6 ± 2.6 in CTR1 to 12.5 ± 2.5 when ALT started 1-1.5 days from ovulation and 10.7 ± 2.9 when ALT started 0-0.5 days from ovulation. In a second experiment, sows with a weaning-to-oestrous interval (WOI) of 6, 7 or 8-14 days were given ALT [either 20 mg (ALT20; n = 49) or 10 mg (ALT10; n = 48)] at day 4 and day 6 after onset of oestrus or were not treated (CTR2; n = 49), and farrowing rate and litter size were evaluated. Weaning-to-oestrous interval did not affect farrowing rate or litter size. ALT did not affect farrowing rate (86% vs 90% in CTR2), but ALT20 tended to have a lower litter size compared with CTR2 (11.7 ± 4.1 vs 13.3 ± 3.1; p = 0.07) and ALT10 was intermediate (12.3 ± 2.9). In conclusion, altrenogest supplementation too soon after ovulation reduces fertilization rate and embryo survival rate and altrenogest supplementation at 4-6 days of pregnancy reduces litter size. As a consequence, altrenogest supplementation during early pregnancy may reduce both farrowing rate and litter size and cannot be applied at this stage in practice as a remedy against low litter size.

Effects of dietary carbohydrate sources on plasma glucose, insulin and IGF-I levels in multiparous sows.

Effects of different carbohydrate sources on plasma glucose, insulin and insulin-like growth factor-I (IGF-I) levels were compared to subsequently be able to study effects of insulin-stimulating diets on follicle development in sows. The following feed components were tested in 12 sows during six consecutive test periods of 9.5 days: dextrose (DEX), sucrose (SUC), lactose (LAC), dextrose plus lactose (DL), sucrose plus lactose (SL), dextrose plus sugarbeet pulp (DSBP) and control (CON). On day 2, 5 and 9 of each test period, plasma glucose (only at day 9), insulin and IGF-I profiles were determined. Despite similar glucose profiles for all diets, the postprandial insulin response was higher for DL and SL compared with CON and LAC; the other diets were intermediate. Plasma IGF-I levels were higher in CON, LAC and SL compared with DSBP, but differences were only marginal. It was concluded that dextrose and sucrose have the potential to stimulate fast and high insulin peaks, especially when combined with additional lactose. Despite the high dextrose in the DSBP diet, the insulin response was flattened, probably due to the viscosity of sugarbeet pulp. The results show that modulation of plasma insulin levels by dietary carbohydrates seems possible in anabolic sows, but IGF-I levels are less easily modified.