The objective of this study was to evaluate the effects of dietary betaine and yeast supplementation for multiparous sows without adiabatic cooling on performance, physiological parameters, milk composition, and litter performance. A total of 192 sows (Topigs Norsvin) were distributed in a 4 × 4 completely randomized factorial design, with 4 experimental diets (control diet; diet with 0.2% betaine;2.0 × 10 CFU of Saccharomyces cerevisiae /kg of diet; and diet with 0.2% betaine and 2.0 × 10 CFU of Saccharomyces cerevisiae /kg of diet) and 4 parity order (PO) groups (1st, 2nd, 3rd-4th, and above 5th), considering each sow and their litter as experimental unit. The dietary supply of betaine for sows provided a lower neck temperature in relation to the sows supplemented with yeast (P < 0.05). Sows above 5th PO supplemented with betaine or yeast had a higher milk yield than sows of the control group (P < 0.05). Sows that fed betaine and yeast had a higher body loss of protein in relation to the control group (P < 0.05). Betaine associated or not to yeast provided a higher litter size at weaning compared to the control group for sows above the 5th PO (P < 0.05). Betaine supply for sows above the 5th PO provided a higher litter weight at weaning in relation to the control group (P < 0.05). Sows above 5th PO, supplemented with betaine and/or yeast weaned litters with higher average daily gain (P < 0.05). Primiparous sows that fed the yeast diet had higher concentration of C16:1 in milk (P < 0.05). Yeast supplementation for sows of 2nd PO provided higher levels of C20:3n6 and C20:4n6 in milk (P < 0.05). The dietary supply of betaine and yeast to primiparous sows promoted a higher content of C20:4n6 in milk. Sows above the 5th PO that fed the control diet had a higher concentration of C16:1, C20:3n6 and C20:4n6 in relation to sows from other PO (P < 0.05). Dietary supply of betaine and yeast for lactating sows above 5th parity order under heat stress improves milk production and litter performance. Supplementation of these additives beneficially modulates the fatty acid profile of the milk.