Young pigs in the early nutritional phase after weaning could benefit from receiving supplemental carnitine in their diet. That was the conclusion offered at a swine science seminar held this year in the UK. It's been discovered that a reduced store of the compound has been found in piglets after suckling ends. With the removal of animal-based ingredients from livestock feeds in many parts of the world, the argument for supplementing may even have increased in recent years.

Derived from an amino acid

Carnitine is derived from an amino acid and is the generic term for a number of compounds that include L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine. It plays a critical role in energy production, transporting long-chain fatty acids into the mitochondria so they can be oxidized to produce energy. It also transports the toxic compounds generated out of this cellular organelle to prevent their accumulation.

The idea of providing extra carnitine has been raised before, because of the compound's involvement in the carnitine palmitoyltransferase or CPT enzyme that regulates fatty acid oxidation and therefore the energy supply reaching the mitochondrial power generators of the animal's cells. Adult mammals can synthesize their own carnitine from the amino acids lysine and methionine, but a dietary source is recommended for immature pigs which appear to lack the ability to do so adequately.

Supplementing the sow diet

One approach is to add L-carnitine to the sow's diet in gestation and lactation so that more is available to be passed to the piglets through her milk. Jack Odle, Department of Animal Science, North Carolina State University, referred to a 2007 publication in a refereed nutrition journal that has examined the carnitine status of the pig. Specifically, Odle reported, the work compared free carnitine concentrations in the liver throughout the growth period of the pig from newborn to adult. The results showed concentrations reaching their maximum in piglets at the time of suckling, reflecting the contribution from their mother's milk.

However, this peak was followed by a precipitous drop with the removal of the sow's milk at weaning, leaving the pig exposed in terms of capacity for lipid metabolism unless a carnitine supplement in the nursery feed compensated for the change. The opportunity to obtain extra supplies from standard feed raw materials may be limited, Odle pointed out. Carnitine is found naturally at significant levels in meat and other animal products, but is unlikely to be supplied adequately by a diet based on vegetable ingredients alone.

Results from studies of a few years ago done jointly by the Department of Animal Science, Oklahoma State University; Department of Animal Sciences and Industry, Kansas State University; and Lonza, Inc., Fair Lawn, N.J. suggested that the addition of L-carnitine to nutrient-dense diets enhances gain-to-feed ratios of weanling pigs by 10 to 15 percent approximately 2 to 4 weeks after weaning, resulting in an overall improvement in the efficiency of gain.

Dietary fat

Although not conclusive, those results suggested that the response to added L-carnitine may depend on dietary fat inclusion level. The results suggested that relatively low concentrations (50 to 100 ppm) of L-carnitine elicit an improvement in gain-to-feed ratios of weanling pigs consuming nutrient-dense diets containing soybean oil. However, because the response to L-carnitine supplementation seemed to occur approximately 2 to 4 weeks after weaning, the results indicate a greater need for L-carnitine during that period compared with the preceding and subsequent phases of the nursery period.

Supplementation of carnitine, averaged across experiments, resulted in a 4 to 5 percent improvement in gain-to-feed ratios for the overall period. However, the greatest response occurred during Phase 2, where a 10 to 15 percent improvement in gain-to-feed ratio was observed. During Phase 2 and overall, 50 ppm of added carnitine resulted in an improvement in gain-to-feed ratio similar to that found with 100 ppm.

That particular study acknowledges that earlier research had found no effect of carnitine supplementation on the performance of weanling pigs regardless of whether the diet contained added fat, but suggested that such conflicting results may be due to many factors, such as energy status of the pig, age, health, environment, lean growth potential, diet composition, and nutrient concentration, which were controlled in that study.

So while the idea of supplementation of carnitine is not new, nutritionists have underscored it is worth a second look, particularly in light of the work done to clarify the mechanisms of fat metabolism in the young pig. More evidence is mounting that having more carnitine for CPT could possibly win an increase in net energy from existing ingredients in the feed, even without adding an energy-rich source such as fat.