Lifetime productivity of sows is below a potential of 80-90 pigs weaned per lifetime in many countries due to culling of sows during the early parities (Smits et al, 2005). Main reasons are inferior reproductive performance that can result from losses of maternal body tissue in the lactation period. Loss of protein mass in lactation and having suboptimal body reserves of lipid after weaning the first litter are primary causes. Gilts have lower lactation feed intakes than sows and this can be aggravated by high ambient temperatures in summer. Prolific gilts can have similar litter sizes to sows, but if daily nutrient intake is suboptimal, then mobilisation of body tissue can occur to meet the milk yield demands of the suckling piglets.
Effect of digestible energy
PORK CRC in Australia has reported two trials to investigate the effect of digestible energy (DE) and available lysine levels in gilt lactation diets on subsequent performance.
In the DE study, diets were based on 0.9g available lysine per MJ DE and fed for a 27-day lactation period. Increasing DE levels from 13.0 to 15.3MJ/kg, when gilts only consumed 4.7kg/day in hot summer months, had no effect on piglet growth or subsequent litter size. Gilt body weight loss was reduced with increasing DE level. When the DE was over 14.2MJ/kg, P2 back fat loss was reduced and more gilts were rebred within seven days of weaning and more were retained in the herd. There was no effect on subsequent litter size.
In the lysine study, gilts with 12 or seven suckling pigs were fed diets with either 0.58g available lysine per MJ DE or 0. 90g available lysine per MJ DE for a 21-day lactation. Feed intake was about 5.6kg/day. Gilts with fewer pigs suckled or fed higher lysine levels had higher total born in the second parity. Piglets weaned from a litter size of seven had 850g heavier weaning weights.
Higher daily intakes
These trials clearly indicate that gilts respond to higher daily intakes of energy and lysine.
As genotypes become leaner and of higher prolificacy, the daily intake of energy and lysine will need to increase to prevent excessive mobilisation of body tissue that adversely affects subsequent performance and can result in early culling from the herd.
The goal should be to achieve a high weaning weight at 28 days with minimal loss of body tissue. Given a lactating gilt body weight of 150kg, suckling 10 piglets and targeting a litter weaning weight of 85kg (8.5kg/pig) will need 10kg milk production per day. This needs a daily nutrient intake of 90 MJ and available lysine of 64g per day to minimise loss of body tissue (British Society of Animal Science, 2003).
Know your gilt daily lactation feed intake and design the diet according to the target litter weaning weight to minimise the loss of gilt body condition. Sows need to have more than three litters to recover the cost of the replacement gilt and feeding up to third litter.