What is the Correct Sow Replacement Rate?

Sow herd replacement rates have increased over the last several years, from 30-40% to 60-70% or higher. As sows are pushed for higher production, having over 2.5 litters/sow/year, they have less time to recover after farrowing. In addition to the obvious genetic improvement advantage with a higher gilt replacement rate, there is also a productivity advantage.

Productivity records show that the sow herd peaks at 3-4 parities. Older sows actually have lower live born, fewer pigs weaned, and smaller more variable pig weights. In fact, in one South Dakota 2200 sow herd, gilts are the most productive parity with 943 pigs weaned per 100 gilts bred. When keeping a younger sow herd, often gilts are used to over-breed 10-20% to maximize throughput, then older, less productive sows are culled at farrowing. Historically, the high cost of replacement gilts was the prohibiting factor for considering a higher replacement rate. When using an internal multiplication system, replacement gilts are readily available, and replacement cost is not an issue – sows can be sold and replaced with gilts, without paying high premiums. Even if excess replacement gilts are produced, they will still be saleable as market hogs. Midwest packers such as IBP pay top premiums for lean well-muscled hogs weighing in excess of 300 pounds.

Although a young new herd at start-up may have less immunity than an older herd, if replacement gilts are raised on or close to the sow site where they are exposed to cull sows and/or vaccinated for endemic diseases at 50 pounds, gilts will be well acclimated. These replacement gilts may even have better immunity than older sows. As sows age, immunity (titers) will actually decline unless sows are re-exposed or vaccinated. Re-exposure is risky because the herd may actually “break” with the disease. PRRS, for example, does not produce lifelong immunity like parvo and some other diseases. Older sows may actually break with PRRS because they have lost their natural immunity. Ideally, replacement gilts should be exposed to endemic pathogens at a young age so they are stable (not shedding) when they reach the sow herd. If gilts are brought in from another herd or site, they will not be immune to the endemic diseases on the farm.

The bottom line is that a good gilt supply with high immunity is critical in achieving maximum productivity. Focus your efforts on acclimating and developing gilts and reaching breeding targets. Then, let your replacement rate be wherever it needs to be. Your gilts will be as good as the rest of the herd health-wise, and better genetically.