Different factors are known to affect milk production in sows, especially sow parity and litter size (LS). In practice, milk production can be estimated from litter growth rate and LS. This approach is generally used for the determination of nutrient requirements.But information on factors affecting litter performance is scarce. Data from about 3 500 litters from three experimental units were used to quantify the effect of LS and parity on milk production estimated from piglet growth rate. On average, milk production reached 10.7 kg/day which is higher than most published results. Total milk production increased with LS, by about 0.75 kg/day perextra piglet, whereas the amount of milk available per piglet decreased, especially when LS exceeded 12 piglets. Milk production increased from parity 1 to 2, was the highest in parity 2 to 4 and decreased thereafter. These results will contribute to a better estimation of milk production and consequently of the variability of nutrient requirement of lactating sows.