Today, feeding ractopamine to finishing hogs is fairly common. The key is determining how long to feed it to optimize growth. That’s what Kansas State University researchers set out to identify.

Led by Casey Neill, graduate student, and Mike Tokach, swine nutritionist, a team of researchers conducted feeding trials to determine the effects of ractopamine withdrawal and intermittent use to effectively manage its use with lightweight pigs. Even though ractopamine use has proven to increase average daily gain, improve feed-to-gain rates and increase finishing weights, lightweight pigs remain a challenge.

Depending on the production system, some producers move their lightweight pigs to a separate barn to be fed out. Some producers continue to feed ractopamine to the lightweight pigs, while others withdraw it from the diet. In other cases, producers may pull pigs off ractopamine, but put it back in the diet as pigs approach market weight.

Kansas State researchers studied 110 barrows with an initial weight of 154.4 pounds each in a 56-day feeding trial. The pigs were housed at the university’s swine research and teaching unit in an environmentally controlled finishing barn with slatted floors and two pigs per pen. Pigs were fed a sorghum/soybean meal-based diet formulated to have 1 percent lysine with no added fat.

The five separate experimental treatments were to:

1. Feed a control diet for 56 days.

2. Feed 9 grams per ton of ractopamine for 56 days.

3. Feed ractopamine for 21 days, then the control diet for 14 days, followed by 21 days with ractopamine.

4. Feed the control diet for seven days, ractopamine for 21 days, the control diet for seven days and then ractopamine for 21days.

5. Feed a control diet for 35 days, then ractopamine for 21 days.

Researchers weighed each pig weekly to determine average daily gain, average daily feed intake and feed-to-gain ratio. There were 11 pens per treatment.

For the first 21 days, pigs fed ractopamine had an increased average daily gain and improved feed-to-gain ratio compared to pigs fed diets without ractopamine. Pigs fed ractopamine for the entire trial had improved average daily gain and feed-to-gain ratio at the beginning of the trial, but lost some of   ractopamine’s response by the end of the trial.          

When ractopamine was fed for 21 days, then withdrawn for either seven days or 14 days and re-fed for 21 days, the pigs had the same overall average daily gain and feed-to-gain ratio as pigs that received ractopamine for only the last 21 days.

Pigs fed ractopamine for the last 21 days had increased average daily gain compared to the control pigs.

“This research shows that tailend pigs should be taken off of ractopamine for a short period (seven to 14 days), then receive it again for the last three weeks before they are marketed,” says Tokach. “If producers leave lightweight market hogs on a diet with ractopamine for the entire time, they will spend more money and have lower final weights.”

The study suggests that the optimal program is to feed all pigs ractopamine for three to four weeks before market. However, that’s a challenge if tailend pigs are moved to another finishing unit.

Implementing this type of feeding program could give lightweight pigs a much-needed boost.