Kansas State University (KSU) researchers report feeding pigs supplemental L-carnitine or Paylean in the late finisher improves average daily gain and feed efficiency.

Researchers analyzed data from four experiments to reach conclusions about how Paylean and L-carnitine can contribute to faster pig growth using less feed, while improving meat quality traits.

Paylean, Elanco Animal Health's trade name for ractopamine hydrochloride, improves growth performance and carcass leanness by causing a pig's metabolism to shift nutrients away from fat deposition towards lean deposition. Protein deposition occurs very rapidly during the first two weeks when Paylean is fed. This may be a time when pigs are in an energy-dependent phase of growth and are not consuming enough feed to maximize protein deposition. To support this increased lean deposition, pigs fed Paylean need a higher dietary lysine level.

Combined average daily gain (ADG) data from four experiments suggests feeding pigs L-carnitine for 21 days will produce an extra 2.3 lb. of pork compared to control pigs. Pigs fed Paylean would produce 5.7 lb. more pork. And, pigs fed both L-carnitine and Paylean would produce 6.3 lb. more pork as compared to controls, the researchers say.

Improvements in meat quality and less drip loss are additional benefits.

Experiment No. 1

The first experiment studied the interactive effects between Paylean and dietary L-carnitine on finishing pig growth performance and carcass characteristics.

KSU researchers speculated that adding carnitine to the diet could increase the amount of energy available for protein deposition and increase the response to Paylean. They used 126 gilts to evaluate the effects of Paylean dosage and dietary carnitine on growth performance and carcass parameters, plus loin quality characteristics such as color, marbling and firmness.

The pigs, housed in an environmentally controlled, slotted floor building, were fed a corn-soybean meal diet with L-carnitine added at 0, 25 or 50 ppm from 74 lb. until slaughter at approximately 240 lb. The basal diet was formulated to contain 1.1% lysine from 74 to 164 lb., and 1.0% lysine from 164 lb. to the end of the 6-7-week experiment. Dietary Paylean treatments (0, 4.5 or 9 g./ton) were fed for the last four weeks of the experiment. Carcass information was collected at 24 hours postmortem.

Diets supplemented with L-carnitine did not affect growth performance between 74 and 164 lb. Nor were interactions between Paylean and carnitine observed for ADG, average daily feed intake (ADFI) or feed/gain (F/G) during the last four weeks of the experiment. Increasing Paylean increased ADG and improved F/G.

Table 1. Interactive Effects of L-Carnitine and Paylean on Finishing Pig Growth Performance in Four Trials Combined
Paylean, g./ton
0 9
Carnitine, ppm Probability (P <)
0 50 0 50 SEM Carnitine x
Item Paylean Paylean Carnitine
ADG, lb. 1.99 2.10 2.26 2.29 0.04 0.27 0.07 0.01
ADFI, lb. 5.85 5.85 5.87 5.77 0.10 0.60 0.61 0.73
Feed/gain 2.97 2.82 2.62 2.54 0.04 0.40 0.01 0.01
aValues are means of 33 replications from four different experiments with 2, 2, 22 to 26, and 18 to 19 pigs per pen in experiments 1, 2, 3 and 4, respectively.
aTreatment diets were fed for 28 days in experiments 1, 2 and 3 and for 21 days in experiment 4.

ADG decreased in pigs fed 0 or 4.5 g./ton Paylean, but increased and was highest for pigs fed 9 g./ton. Feed efficiency improved when Paylean was fed and was best at the 9 g./ton level.

There were no interactions between Paylean and carnitine for carcass characteristics. Feeding Paylean or dietary L-carnitine did not affect shrink loss, average backfat, 10th rib fat depth, carcass length, longissimus muscle area and percentage lean. Dressing percentage was greater for Paylean-fed pigs compared to control pigs.

Researchers did observe a Paylean x carnitine interaction for color scores. Carnitine did not improve visual color scores in control pigs. However, pigs fed increasing levels of carnitine had darker colored longissimus muscle measured at the 10th rib when fed 4.5 or 9 g./ton of Paylean. The longissimus muscle measured less yellow color with increasing carnitine. The saturation index showing intensity of color in the longissimus muscle tended to decrease with increasing levels of carnitine.

Both drip loss (measured 48 hours postmortem) and temperature at 45-minute postmortem, decreased with increasing carnitine. Twenty-four-hour pH increased and then decreased with increasing Paylean, and was highest for pigs fed 4.5 g./ton. Ultimate (24-hour) pH also increased with increasing dietary L-carnitine.

Researchers speculate the improvements in meat quality of pigs fed L-carnitine in combination with Paylean may be the result of carnitine's impact on the pigs' metabolism, either before slaughter or postmortem.

The results of this experiment suggest L-carnitine improves meat quality in pigs fed Paylean. Further research needs to be conducted to understand the metabolic action of carnitine on lactate levels before slaughter and during postmortem glycolysis.

Experiment No. 2

In a second experiment, researchers studied L-carnitine and Paylean effects on growth performance, carcass characteristics and postmortem pH decline of 120 PIC gilts.

Beginning at an initial weight of 192 lb., gilts were housed two/pen in an environmentally controlled, slotted floor building with ad-libitum access to feed and water. There were 10 replicates/treatment.

A 1.0% lysine, 16.9% crude protein, corn-soybean meal basal diet was fed. Paylean was fed at either 0 or 9 g./ton and L-carnitine was added at 0, 25 or 50-ppm levels during this four-week experiment.

One pig per pen was randomly selected and slaughtered at the KSU Meats Laboratory at approximately 240 lb.

Researchers found no interactions between Paylean and carnitine when measuring ADG, ADFI or F/G. Paylean improved ADG and F/G while L-carnitine had no effect on ADG, but did improve F/G, which was best when fed at 25 ppm.

A Paylean x carnitine interaction was observed for dressing percentage, which was higher for pigs fed 25 ppm carnitine and no Paylean, and lower for pigs fed 25 ppm carnitine and 9 g./ton Paylean.

Neither Paylean nor L-carnitine affected shrink loss, carcass length and longissimus muscle. Paylean did not affect 10th rib and average backfat depth, but did increase lean percentage. Pigs fed increasing levels of carnitine tended to have lower 10th rib and average backfat.

This experiment suggests L-carnitine improves meat quality in pigs fed Paylean, although postmortem pH was not affected as much as expected. Transmission values pointed toward more soluble protein, which indicates higher muscle quality and less drip loss.

The duration of carnitine supplementation was shorter in this experiment and may contribute to some of the variation from results of other experiments.

Researchers speculate the affect of carnitine may be different at a commercial finishing facility where pigs have lower feed intake and different metabolic stressors compared to pigs reared at a university research facility.

Experiment No. 3

A third experiment studied growth and carcass characteristics of 1,104 barrows fed combinations of L-carnitine, Paylean and added fat in the later stages of finishing in a commercial environment.

Dietary treatments of L-carnitine at 0 to 50 ppm levels, and fat at 0 or 6% were initiated at approximately 97 lb. Paylean was fed at 0 or 9 g./ton levels for the last four weeks prior to slaughter at approximately 260 lb.

Housed 23/pen, pigs were fed a corn-soybean meal diet with or without the added L-carnitine and with or without added fat. The basal diet was formulated on a total lysine-to-calorie ratio basis, with ratios of 3.16 g./Mcal. from 97 to 135 lb., 2.70 g./Mcal. from 135 to 203 lb., and 3.0 g./Mcal. from 203 lb. to 260 lb. Corresponding lysine levels in the 0 and 6% added fat diets were 1.05% and 1.14%, 0.90% and 0.97%, and 1.0% and 1.08% for the three phases, respectively.

Pigs were fed a higher lysine level than would typically be fed in the late finishing period to ensure adequate lysine for pigs receiving Paylean. Paylean-fed pigs need a higher level of lysine to meet their protein deposition needs. Researchers theorized that higher lysine levels may also be needed for protein deposition to demonstrate a growth response to feeding supplemental L-carnitine.

Both L-carnitine and Paylean improved growth performance, but the responses were not additive. Pigs fed added fat had improved feed efficiency during the Paylean supplementation period.

An interaction between carnitine and Paylean was observed for backfat thickness and percentage lean. Fat thickness decreased and lean percentage increased in pigs fed carnitine or Paylean, but the responses were not additive. Pigs fed added fat had more backfat and lower percentage lean than pigs not fed added fat.

In general, adding carnitine, Paylean or fat to the diet increased longissimus muscle area, but again, results were not fully additive. Pigs fed carnitine and 6% added fat had heavier carcasses.

Adding Paylean to the diet increased ultimate longissimus pH and reduced drip loss as measured by a filter paper method. Similar to other experiments, adding carnitine to the diet tended to decrease drip loss as measured by the suspension method.

This experiment shows pigs fed L-carnitine had improved meat quality and improved growth performance during the last four weeks of the experiment. Researchers speculated the results may be related to feed intake, environment or larger sample population compared with previous experiments.

Experiment No. 4

A fourth experiment, seeking to confirm the results of the previous experiment, studied the impact of feeding L-carnitine and Paylean on growth performance in a commercial finishing facility.

Researchers measured growth performance and carcass traits on 796 barrows fed L-carnitine and/or Paylean for three weeks.

Pigs were housed 18-19/pen, fed a corn-soybean meal diet with or without L-carnitine, at 0-50 ppm, or Paylean at 0 and 9 g./ton. The basal diet was formulated to contain 1.0% lysine with a total lysine:calorie ratio of 3.0 g./Mcal.

Pigs fed Paylean had improved ADG and F/G. Growth performance of pigs fed carnitine also improved and was additive to the response of Paylean. There were no interactions between carnitine and Paylean for growth performance during any week of the experiment, or for the overall experiment.

Feeding carnitine did not affect any of the carcass criteria in this experiment. Pigs fed Paylean had greater carcass weight, fat-free lean index, loin depth, percentage lean, and yield compared to pigs not fed Paylean.

Experiments Summarized

The KSU researchers combined the growth performance data from common treatments of L-carnitine at 0 or 50 ppm, and Paylean at 0 or 9 g./ton, from the four research experiments in Table 1.

There were no carnitine x Paylean interactions. Paylean improved ADG and F/G. Pigs fed carnitine had better ADG than controls. Pigs fed carnitine in the last 3-4 weeks in the finisher also had improved F/G compared to pigs not fed carnitine.

These results suggest that L-carnitine and Paylean improve growth performance of finishing pigs. Further research is needed to determine the optimal lysine level to be fed in combination with L-carnitine. Research is also needed to figure out how long L-carnitine should be supplemented for best results.

Researchers: Brad W. James, Mike D. Tokach, Robert D. Goodband, Jim L. Nelssen, Steve S. Dritz, Kansas State University. Contact James at (785) 532-1277.