parity

Parity counts the number of complete farrowing cycles a breeding sow has completed in her lifetime. A first-time mother is parity 1 (or P1); after her second litter she becomes parity 2 (P2), and so on. This simple metric matters because it directly affects herd productivity, breeding value, and culling decisions.

Sows typically remain productive through parity 5 or 6, though some operations keep high-performing animals to parity 7 or 8. Gilts (young females before their first farrowing) enter the breeding herd around 130 to 150 kg body weight and are not assigned a parity number until they farrow. Once farrowing begins, parity becomes a permanent part of that animal's record and a key sorting variable in herd management software.

Why parity matters in production

Litter size and piglet survival improve from parity 1 to parity 2 or 3, then plateau or decline slightly as sows age. A P1 sow typically produces 2 to 4 fewer piglets per litter than a P2 or P3 sow. Feed conversion and body condition also shift with parity; older sows lose body reserves faster and require different nutritional management. Health problems such as mastitis, lameness, and reproductive failure accumulate with parity, making older animals more costly to maintain.

Parity influences farrowing interval and lactation performance too. Younger sows may have longer intervals between weaning and the next estrus, while high-parity animals face higher culling pressure if they fail to conceive. Records of parity distribution across the herd help managers assess genetic replacement needs and predict cash flow from piglet sales.

The term originated in reproductive biology as a measure of reproductive history. In swine operations, parity data feeds directly into breeding decisions, feed budgeting, and herd turnover calculations. Most producers aim to maintain a parity structure with the majority of the breeding herd in parities 2 through 5, balancing the productivity of mature animals against the cost of retaining low-performing older sows.