Betaine is a methyl donor and osmotic regulator that accumulates naturally in organisms adapted to salt or drought conditions. It maintains cell volume and integrity under challenging conditions, including heat stress.  Dietary supplementation of betaine in gestation and lactation sows is beneficial to reproductive performance of sows, but no studies have been carried out to supplement betaine after weaning and at mating stage.  This study was designed to evaluate the effects of betaine feeding during lactation and after weaning on sows exposed to heat stress.  

To evaluate the effects of natural betaine on reproductive performance of sows in summer (Experiment 1) and non-summer months (experiment 2).  Treatment was designed to be a 2 × 2 factor arrangement consisting of dietary betaine (0 or 0.2%) and a supplement period (lactation or post-weaning to 35 days after insemination).  In experiment 1, 322 and 327 sows were used, and in experiment 2, 300 and 327 sows were used, representing young (1st and 2nd parities) and mature (3rd to 6th parities) sows, respectively.  

In Experiment 1, betaine supplementation during lactation increased body weight loss of sows, reduced feed intake, and tended to reduce the proportion of worthless pigs.  Feeding betaine after weaning can shorten the period from weaning to estrus and reduce the rate of parities, regardless of parity.  Sows with more than 4 parities fed betaine during lactation and sows with 1 parities fed betaine after weaning increased litter size in subsequent cycles.  In Experiment 2, feeding betaine during lactation tended to reduce the interval from weaning to estrus and the rate of calving, regardless of parity.  Feeding betaine after weaning can reduce the number of piglets born and piglets born alive, and has nothing to do with parity.  

Use of 0.2% betaine in non-summer months did not benefit sows' performance.  However, betaine supplementation during lactation increased subsequent litter size in sows with more than 4 parities during the summer.  Feeding betaine after weaning can shorten the period from weaning to estrus and calving rate, increase the total litter size of 1st parities sows and decrease the total litter size of sows above 4th parities.