Pig producers should be careful about pushing for increased litter size without understanding the management implications.
“The key message is to optimise rather than maximise litter sizes. Maximising will just result in additional management issues.”
Speaking at the Royal Agricultural College, Cirencester, Dr Baxter said Denmark may be pushing for 30 pigs a sow a year, but the sows were not necessarily rearing them all.
“Some piglets are often raised on nurse sows or rescue decks, which require extra management. It’s important to work on the economics. An animal that is born more robust goes to market quicker, leading to increased production and potentially two tonnes of pigmeat a sow a year.”
Average UK herd figures show 8% of piglets are born dead every year – in total this means 900,000 piglets are stillborn a year, representing a potential £38m loss to the industry.
Most of these stillbirths are caused by asphyxiation at birth, which could occur in the uterus when farrowing starts or immediately after birth.
Such losses are influenced by four main areas, which are all impacted by increased litter size:
1. Prolonged farrowing
2. Poor placenta
3. Oxygen deprivation
4. Maternal effects
“Increased litter size increases the farrowing duration, with 70-80% of piglets stillborn being those at the end of farrowing.” A greater than 45 minute interval between sibling births also increases the risk of asphyxia.
Big litters also effects placenta efficiency. When placenta quality is poor, there is increased risk of poor oxygen supply and a greater chance of piglets being growth retarded.
In the short term, stillbirths can be reduced by improving the gestation environment for the piglets. “Maintaining high feed intakes during lactation influences immediate litter growth and survival and subsequent litters,” said Dr Baxter.
“In the long term, litter size needs to be controlled – at the moment I don’t think this is happening.”
Increasing the physiological maturity of piglets at birth, selecting for optimum weight and reduced in-litter variability can also reduce the likelihood piglets will be stillborn.
“Very small piglets are more likely to be born dead, as are giant ones. Plus large piglets can cause a backlog in the birthing process.” Producers should be selecting for an optimum weight of 1.6kg a piglet.
“You can also reduce maternal effects on piglet losses immediately through management. Consider culling sows after their sixth parity – older sows may have bigger litters, but they will also have more stillbirths.”
Maintaining a farrowing temperature of 20C can also reduce stress and minimise fatigue. And although oxytocin can reduce farrowing time, it can also be counterproductive in increasing the risk of stillbirths by early rupture of the umbilical cord, she said.
“Trial work has shown 76% of ruptured umbilical cords were from sows that had been injected with oxytocin. Using the hormone will increase uterine contractions, compressing the umbilical cord and decreasing foetal heart rate and increasing distress.
“This can happen when oxytocin is used regularly, so think about controlled use and only using when you have to.”
Piglets affected by foetal stress can breathe in faeces and fluid in the uterus and are more likely to have respiratory difficulties and heart problems.