BACKGROUND
This paper is a narrative review examining how sow nutrition around parturition may affect uterine contractions, placental and umbilical blood flow, and short-term piglet survival. The authors frame the issue around the modern hyper-prolific sow, in which larger litters are associated with longer farrowing duration, reduced placental blood flow per piglet, smaller placental area per piglet, and lower average piglet birth weight. The parturition process is divided into 3 stages: cervical dilation with increasing myometrial activity lasting approximately 6–12 h, expulsion of piglets lasting approximately 5–8 h, and placental expulsion lasting approximately 4 h. The total parturition process can take up to 24 h in the hyper-prolific sow. During the expulsion phase, uterine contractions on average last for 1–2 min and occur at a frequency of 18 per hour, and it is estimated that 4 to 5 uterine contractions, with an average duration of 11.5 s and an intensity of 9.4 mm Hg, are needed to expel 1 fetus. The review emphasizes that oxygen delivery through the placenta and umbilical cord is central to piglet survival and may be compromised by repeated strong uterine contractions, prolonged birth intervals, placental limitation, and umbilical cord damage.
METHODS
This is a qualitative review rather than a clinical trial or systematic review. The authors synthesize older physiologic studies of uterine contractility and placental function with more recent nutritional and production studies in sows. They summarize evidence regarding endocrine control of labor, contraction patterns, fetal responses to hypoxia, litter-size effects, placental structure, umbilical cord functionality, and peri-partum nutritional interventions. No formal search strategy, pooled meta-analysis, or predefined eligibility criteria are reported in the provided text. Instead, the review narratively integrates findings from multiple cited studies and uses selected numerical examples to highlight potentially relevant physiologic and nutritional relationships.
KEY RESULTS
The review presents several findings linking prolonged farrowing and impaired oxygen delivery to piglet loss. The birth interval after which a stillborn piglet is born is approximately twice as long as that of a liveborn piglet, 28 vs. 15 min. As markers of perinatal compromise, piglets that died pre-weaning had higher blood lactate concentrations at birth than survivors, 383 vs. 303 μg lactate/mL blood; p < 0.01. In another cited study, pre-weaning mortality was 8.5% and 10.9% for umbilical cord blood lactate concentrations of 4.45–6.40 mmol/L and >6.40 mmol/L, respectively. Combining data from 15 studies, the authors report an estimated increase of 27 min in stage 2 farrowing duration per extra piglet. Exogenous oxytocin can increase contraction frequency 13-fold and intensity 2-fold compared with spontaneous contractions, which may shorten farrowing but may also impair physiology and reduce piglet vitality or increase stillbirth.
For placental and umbilical factors, the review notes that blood vessels occupy about 3–4% of the chorio-allantoic membrane by mid-gestation, although variation is large. Placental surface and placental weight were lower in piglets that died before weaning by −20.4% and −14.8%, respectively. Umbilical cord length averaged 35 cm, ranging between 17 to 50 cm, and elasticity may reach up to 37.5% of its length. The tension required to break the cord ranges from 545 to 2000 g. The percentage of piglets born with a broken umbilical cord lies between 21 to 71%, and broken cords occurred 2.3 times more often in the second and last third of piglets born than in the first third. A recent review estimated the association between stillbirth and a broken umbilical cord before expulsion to be 50% or more.
The nutrition section focuses first on energy. Some European feeding practices reduce feed allowance to 2.0–3.0 kg/sow/day beginning 2–3 days before expected farrowing. The authors question whether this is adequate because farrowing is highly energy demanding. One cited study found sow plasma lactate was approximately 1.4 mmol/L on day 1 post-partum versus approximately 0.9 mmol/L on day 4, supporting the concept of peri-partum metabolic strain. Another study showed lactate was already increased at 9 and 3 h before expulsion of the first piglet. Feyera et al. estimated the energy requirement for farrowing at 16 MJ ME, approximately 30% of total energy requirements on the day of farrowing. Using 2 studies, the authors calculate that optimal daily energy intake on the day of farrowing may depend on litter size at 2.44 MJ ME/piglet born and/or farrowing duration at 8.66 MJ ME/hour of farrowing duration. They also cite that farrowing duration increased linearly when the last meal was more than 3.13 ± 0.34 h before onset of farrowing.
For minerals, calcium supplementation of 400 mmol Ca as calcium lactate on the day of farrowing was associated with a significant reduction of −34% on sow level in dystocia incidence, defined as birth interval > 60 min, and placenta expulsion was 4–19 min faster. In contrast, magnesium sulfate supplementation at 2.85 kg/mton feed, with sows receiving 2.5 kg of feed/sow/day from 5 days pre-farrowing until 3 days post-farrowing, increased stillbirth incidence by +0.3 stillborn piglets/litter, p = 0.01. Regarding vasoactive nutrients, long-term arginine supplementation did not affect placental weight in one study using 1% L-arginine from day 22 until day 114 of gestation, and did not affect piglet birth weight or stillbirth rate in another study using 25.5 g/d from day 77 until term. In contrast, dietary nitrate started 7 days before farrowing showed a linear dosage effect on piglet vitality and piglet birth weights and a tendency toward lower pre-weaning mortality.
CLINICAL IMPLICATIONS
The central practical implication is that peri-partum hypoxia is a major determinant of piglet survival and may be aggravated in large litters by prolonged labor, repeated contractions, reduced placental supply, and cord compromise. The review suggests that restricted pre-farrow feeding may be mismatched to the energy demands of the modern sow and that strategies ensuring timely glucogenic energy availability may be clinically relevant. Calcium appears promising for improving labor efficiency, while magnesium may be harmful if it suppresses myometrial activity. Nitric oxide precursor strategies, especially nitrate, may improve fetal oxygen delivery through vasodilation and deserve further study. Overall, the paper supports reconsideration of peri-partum feeding strategies, but it also stresses that exact nutrient requirements before, during, and after parturition are still not clearly reported and require more direct investigation in contemporary hyper-prolific sows.