A long, productive life is important to the sow’s well-being and to a swine breeding operation’s profitability. In recent years, undesirably high sow wastage rates (deaths + culls) have caught the attention of pork producers, veterinarians and researchers.

According to the PigChamp database, annual sow wastage rates ranged from 49 percent to 60 percent in U.S. herds from 2002 to 2005. High wastage rates reduce the sow’s productive life and decrease the operation’s overall productivity. As a result, most sow herds do not achieve the desired lifetime production target of 60 pigs born alive and 55 pigs weaned. There are many reasons for and possible solutions to address these high wastage rates. The farm’s program to develop and prepare gilts to enter the breeding herd could play an important role in determining the length and productivity of a sow’s lifespan. 

The gilt’s growth rate has some influence on the sow’s eventual lifetime productivity. Slow growth and extremely rapid growth are both detrimental to a sow’s productive lifetime and its lifetime productivity. 

Gilts should gain at least 1.2 pounds per day from birth to 160 days of age for optimal puberty expression and to optimize length of productive life. However, growth rates that exceed 1.75 pounds per day during this same period should be avoided. In a recent retrospective study of 11,500 gilts raised in a commercial environment, we found that growth rates exceeding 1.75 pounds per day actually reduced lifetime productivity of sows.

Body composition and body weight at first mating also are important. Body fat and body protein both play an important role in successful reproduction. Diet composition and quality can influence the relative contributions of each tissue to reproductive maintenance functions. Under commercial conditions, if adequate body protein mass is achieved in the gilt and maintained throughout the sow’s reproductive life, longevity seems to improve. 

Also to enhance lifetime productivity, a gilt should receive its first mating on its second post-pubertal heat and weigh at least 300 pounds but not exceed 350 pounds. A recent study demonstrated that gilts weighing less than 300 pounds at their first mating farrowed fewer pigs in the first three parities versus heavier females. On the opposite end of the spectrum, very heavy gilts at first mating have decreased lifetime productivity and may become too large to fit comfortably in existing farrowing and gestation stalls, which could create sow well-being problems. 

We are just beginning to learn the details of how a gilt’s skeleton influences sow longevity. The skeleton provides the body’s structural framework and support, so it’s easy to surmise that developing the gilt’s skeleton properly before it enters the breeding herd could impact sow longevity. Bone mineralization is an important factor in determining bone strength, but other factors such as exercise and growth rate also influence skeletal integrity. Exercise helps improve bone mass and strength, so the common practice of housing the gilt pool in group pens should be continued in order to optimize skeleton development. 

Very rapidly growing gilts may develop an adequate collagen network in bone but have insufficient time for that network to fully mineralize before the gilts enter the breeding herd. Therefore, you need to consider joint quality and integrity as part of proper skeletal development. Very rapid growth may increase the osteochondrosis incidence in joints, which leads to more lameness problems. So, it seems prudent to control gilts’ growth rate from birth to selection in order to enhance skeletal development, which will encourage improved sow longevity. More research is needed to improve our understanding of the relationship between skeletal growth in developing gilts and sow longevity. 

Structural correctness describes the position and alignment of bones in the front and rear legs in relation to each other and to the bones in the body skeleton. A structurally correct animal bears its body weight uniformly on the joints and feet of its front and rear legs. We assume that this uniformity reduces the injury risk or joint damage and minimizes lameness. 

Structural correctness is a subjective trait that a trained observer must evaluate. Feet and leg structural defects need to be identified at selection. Gilts displaying structural defects must be culled from the breeding-gilt pool, as structural defects tend to worsen as the female ages and body weight increases. 

It’s wise to consider structural correctness as a fitness trait and impose minimum culling standards to ensure that females entering the breeding herd are properly suited to perform their intended functions.

Unfortunately, the ability to evaluate fitness traits has been lost in many modern production systems. But if the industry intends to improve sow longevity, people with the ability to evaluate such traits must be given a meaningful role in gilt selection decisions. In the end, selecting gilts with structurally correct front and rear legs can improve sow longevity.