The objective of this experiment was to evaluate the effects of betaine supplementation during lactation in hot summer months on piglet growth and sow subsequent reproductive performance. The betaine feeding portion of the experiment was conducted between December 2014 and March 2015 with subsequent litter data completed by July 2015 in Rancagua, Chile. Dietary treatments were allotted randomly to concurrent farrowing rooms of sows. Sows were fed diets supplemented with either 0% (n = 193) or 0.3% (n = 175 sows) of betaine-HCl (70.7% betaine) from 2 d before their farrowing due date until weaning (average lactation length = 21.0 d). Betaine supplemented sows had 3.90% greater ADFI during lactation than control sows (P = 0.005). Treatments by parity interactions were significant for ADFI and sow BW loss (P = 0.008 and P = 0.005, respectively). Parity 2 sows that received betaine supplementation had greater ADFI (6.89 versus 6.17 kg/d) and 6.70 kg less BW loss than parity 2 control sows (P < 0.001 and P = 0.022, respectively). Wean-to-estrus intervals were 0.31 d shorter for betaine supplemented sows than control sows (P = 0.004). There were shifts in the distribution of wean-to-estrus intervals between sows fed control and betaine supplemented diets (P = 0.029). No treatment differences were found for subsequent total born, born alive, conception, and farrowing rate (P = 0.64, P = 0.29, P = 0.83, and P = 0.68, respectively). Betaine supplementation increased daily feed intake and reduced wean-to-estrus intervals during summer months in sows.