Lactation in Swine Lactation Lochia are normally present for the first week and rapid uterine involution is completed by 21 to 28 days after farrowing.
Lactational anestrus occurs in most sows and lasts until weaning.
With proper genetic selection and management, sows can be weaned at 21 days and bred by 28 days after farrowing, with good pregnancy rates. Synchronization of estrus can be accomplished by group weaning sows with introduction of the boars to close contact pens. Sows weaned in summer may have a longer time to first estrus and in more severe situations reduced fertility when the animals do breed. Reduced feed intake during lactation in the summer months is thought to contribute to this seasonal delay in return to estrus. Nutritional inadequacies during lactation of high producing 1st litter or primiparous gilts has led to pronounced decreases in fecundity during their next litter.