Supporting the hyper prolific sow and her litter through the perinatal period by dietary nitrate supplementation

In the Netherlands, approximately 8% of piglets is stillborn and on average 12.2% is lost due to pre-weaning mortality. Farrowing is a crucial and challenging event for both the sow and her piglets. Exhaustion of the sow is likely to occur and can impair uterine contractions, thereby increasing the duration of farrowing. For piglets, farrowing is also stressful and the odds of dying are highest during parturition and the first days of life.Maternal nutrition is one of the factors that can reduce piglet losses. Sports nutrition in humans is a good source of inspiration for potential nutritional solutions that could support the sows through the process of farrowing. A new method to enhance competitive performance in athletes is red beetroot juice. One of the main active compounds in beetroot juice is nitrate (NO3-). Nitrate itself is not known for specific physiological functions, but in vivo, nitrate is non-enzymatically reduced via nitrite (NO2-) to nitric oxide (NO), a multivarious messenger molecule with important vascular functions, which particularly occur in environments of hypoxia and acidosis during high physical activity. In addition, in athletes nitrate supplementation increased exercise efficiency and increased time until exhaustion. Maternal dietary nitrate supplementation is hypothesized to support the sow and her litter in the perinatal period due to 1) the vasodilative effect NO has by being a major endothelium-derived relaxing factor. By ensuring a larger blood, and therefore oxygen, flow in the placenta and the umbilical cord during farrowing, the risk for asphyxiation can be reduced. 2) By reducing the duration of farrowing by improving sow stamina, which would in its turn decrease the incidence of stillbirth and decrease the levels of asphyxiation in new born piglets. The main aim of this thesis was to investigate whether or not supplementation of nitrate to the sow  during the perinatal period is an applicable solution to decrease incidence of stillbirth and pre-weaning mortality.To test if maternal nitrate supplementation can indeed decrease the incidence of stillbirth and pre-weaning mortality, two studies were conducted. In Study I, initial testing was done on a commercial farm in Denmark. 120 Hyper prolific sows (Landrace x Yorkshire; Danbred) were allocated based on parity and received either a control diet without nitrate or a diet containing 0.06% of nitrate (0.1% of calcium nitrate; 5Ca(NO3)2·NH4NO3.10H2O; containing 63.1% of nitrate) from approximately 5 days before the onset of farrowing until day 4 of lactation. No effect of nitrate supplementation was found on piglet weights, piglet growth, placental redness score, and total pre-weaning mortality. Maternal dietary nitrate supplementation decreased stillbirth percentage with 2.5%.Since Study I was the first time maternal dietary nitrate supplementation in the perinatal period was evaluated, the optimal dosage of nitrate supplementation for both sow and piglets performance was unknown. Therefore in Study II, different dosages of nitrate supplementation from day 108 of gestation until day 5 of lactation were evaluated. In eight consecutive batches, 305 crossbred (Yorkshire × Dutch Landrace; Topigs 20) sows were allocated to one of six diets containing 0.00% (control), 0.03%, 0.06%, 0.09%, 0.12%, or 0.15% of nitrate. Maternal nitrate supplementation tended to show a lower incidence of pre-weaning mortality when dosed at 0.09-0.12% (-3.9% and -4.3% compared to the control, respectively). In addition, a linear effect of dosage of maternal nitrate supplementation was found on piglet birth weight, which might be caused by a linear increase in placental width. Litter uniformity (SD) at birth was not affected by maternal nitrate supplementation level, but SD tended to be higher at 72 h of age in the control treatment than in all nitrate-supplemented treatments, and SD decreased linearly (increased uniformity) at weaning with increasing dosages of nitrate. Piglet weight at weaning and average daily gain of piglets during lactation were not affected by maternal nitrate supplementation. Vitality score of piglets linear increased (more vital) with an increasing dosage of nitrate, and partial oxygen pressure (pO2) in umbilical cord blood measured immediately after birth tended to be positively related to nitrate dosage. No effect of dosage of nitrate supplementation was found on duration of farrowing and placenta redness score. It was concluded that obtained effects of maternal dietary nitrate supplementation appears to have a larger effect on vasodilation (indicated by the effects found on piglet vitality and partial oxygen pressure in umbilical cord blood) than on stamina (since no effect on farrowing duration was found). Additional analyses on data of Study I and II showed that hyper prolific sows (≥16 piglets) did not benefit more from maternal nitrate supplementation compared to non-hyper prolific sows.Data of in total 159 crossbred gilts and sows of Study II was leveraged to evaluate the interactions between farrowing duration and litter size on the level of asphyxia, vitality, percentage of stillbirth and pre-weaning mortality of piglets aiming to disentangle effects of litter size at birth and farrowing duration. Litter size (small: 12-15 piglets, medium: 16-18 piglet and large: 19-21 piglets) as well as farrowing duration (short: 250 min) were categorized to evaluate the interaction between the two. In small litters, a prolonged farrowing duration tended to increase pre-weaning mortality compared to a short and medium farrowing duration, while for large litters a medium to long farrowing duration tended to decrease pre-weaning mortality. No other interactions were found. Each additional piglet born to a litter linearly decreased average piglet birth weight with 17.6 grams, increased farrowing duration with 11 min and increased stillbirth with 0.5%. A medium farrowing duration resulted in a lower stillborn percentage compared to a short or prolonged farrowing duration, suggesting that farrowing duration might have an optimum. When analysed linearly, stillborn percentage increased with 1.85% per every 100 min of farrowing duration. It was concluded that both litter size and farrowing duration affect stillborn percentage, but independent from each other. However, these two factors tended to interact for pre-weaning mortality, suggesting that setting a certain threshold for maximal farrowing duration should be taken with care, because this appears to depend on litter size