Controlling leptin levels in the blood of pigs may let you modify their biological signals to breed, eat and turn energy into lean or fat.

Researchers at Purina Mills, St. Louis, Mo., are looking at leptin’s role as a messenger in the pig’s body that signals, among other things, fat metabolism.

It may also be the link between body condition and the brain’s control of the reproductive cycle. Levels of leptin appear to send a signal to the brain that ultimately tells the sow to release luteinizing hormone, which causes her to come into heat. Higher leptin levels indicate the sow’s body condition is not too thin to rebreed. Lower levels suggest a thin sow isn’t ready to cycle.

Richard Chapple, Purina swine research manager, warns that you can’t just keep sows overly fat to promote high leptin levels. You’ll compromise lactation and subsequent reproductive performance with extra body fat. Still, there seems to be a threshold for leptin, below which sows may not cycle.

Leptin also can affect appetite, notes Michael Spurlock, another Purina swine research manager. Animals that produce low leptin levels may show an increased desire to eat. Purina scientists are studying whether leptin might be the link between feed-intake control centers in the brain and the rate and composition of body growth.

Finally, leptin appears to play another role on the cellular level. Produced by fat cells, leptin may be a messenger to muscle cells that helps regulate how much energy each tissue type has available for growth. More leptin may partition more energy into lean muscle and less into fat.

If these premises hold up, someday you may be measuring leptin levels to gain information about your pigs’ metabolism. You may use such data to formulate diets to “match” your pigs’ lean growth potential. Or you may be able to control leptin in the pig. That could happen in one of four ways.

Information about the leptin gene eventually may be used in genetic selection programs. 

Leptin may be used as a guide to evaluate the pig’s immune system. The jury’s out on how this may be done. Many basic questions are still unanswered.

You might be able to monitor leptin in conjunction with feeding programs to better control body condition for rebreeding after weaning.

You may have a vehicle to provide leptin directly to the pig. This could be an injection or some other manner of getting more leptin into the pig.

Again, several questions still need answers, but leptin appears to offer some potential to alter the pig’s reproductive abilities, its appetite and how much energy goes to lean muscle as opposed to fat deposition.