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Genetic selection for lean growth and B vitamin requirements of pigs

It is now well recognized that optimum vitamin fortification levels of swine will depend on factors ranging from genetics to ration ingredients, health status, environment—and biological function. Researchers at Iowa State University (Lutz and Stahly, 1998) underscored this when they reported that riboflavin requirements of pigs are significantly greater for growth than maintenance, and for protein than for fat accretion. Indeed, riboflavin requirements were six times greater to support protein accretion than fat accretion.

This study suggests that any factor which increases a pig's capacity for lean gain also increases the animal's riboflavin requirements for optimum performance, says Dr. Tim Stahly, one of the researchers. Beyond that, he says, the results are also further evidence that the National Research Council (NRC) minimum vitamin requirements for swine are insufficient for optimizing performance. The current (1998) NRC requirements for swine still rely largely on work conducted from the 1940s through the 1960s, using fatter pigs with poorer-performing genetics, he notes.

The 1998 study is a follow-up to work by Stahly et al. (1995) into the requirements for five B vitamins — riboflavin, pantothenic acid, vitamin B12, folic acid and niacin —that are crucial for protein, carbohydrate and fat metabolism. The 1995 work found that young pigs from current genetic lines required as much as five times the NRC requirements to achieve optimum gains and feed efficiency.

Like the earlier study, the 1998 work used pigs from strains with either high or moderate lean-growth potential to assess vitamin requirements. Pigs were fed from an average starting weight of 22 lbs (10 kg) to an ending weight of 57.2 lbs (26 kg). Treatments were 0, 1.7 or 3.4 mg of supplemental dietary riboflavin per pound of feed (0, 3.7 or 7.4 mg/kg). Because the basal diets differed for the two genotypes, total bioavailable riboflavin allowances ranged from 47 to 297 percent of the NRC requirement for the high lean-growth pigs, and from 140 to 377 percent of the NRC requirement for the moderate lean-growth pigs.

 
Table 1

Feed efficiency, average daily gain (ADG) and protein accretion all improved linearly as the riboflavin content of the diet increased (Table 1). This was true for both genotypes. With the moderate lean-growth pigs, for example, those receiving 377 percent of the NRC riboflavin requirement used 0.14 lb less feed (P < 0.01) to produce 1 lb of gain than the pigs receiving 140 percent.

Similarly, with the high lean-growth genotype, pigs receiving 297 percent of the NRC requirement had 7.8 percent greater ADG (P < 0.05) and produced 18 percent more lean gain per day (P < 0.05) than the pigs receiving the control ration. They produced 2.7 percent more total weight and 5.3 percent more lean weight than the pigs receiving the intermediate treatment of 170 percent of the NRC requirement. Body fat did not differ significantly among any of the treatments.

Feed efficiency data in the high lean-growth pigs showed that those receiving 297 percent of the NRC requirement used 0.02 lb less feed (P < 0.04) than the intermediate group to put on 1 lb of gain, and 0.09 lb less feed than the control group.

These results are in keeping with performance data from the earlier study by Stahly et al. (1995). In that work, feed efficiency and ADG of pigs with high lean-growth potential continued to improve (P < 0.01) with the highest fortification level, which provided 470 percent of the NRC requirements for five B vitamins. Pigs receiving the highest level of fortification required 0.17 lb less feed to produce 1 lb of gain than the control pigs at 70  percent of the NRC requirement.

In pigs with moderate lean-growth potential, ADG continued to increase (P < 0.01) through 370 percent of NRC requirements, and feed efficiency through 270 percent of them.

In the 1998 study, Lutz and Stahly were able to further estimate riboflavin requirements for different biological processes because of the fat and protein accretion data. Requirements were expressed as milligrams of riboflavin required for the expenditure of 1 Mcal of energy to support each biological function per kilogram of metabolic weight (Table 2).

 
Table 2

For example, 1 Mcal of energy expended on maintenance required only 0.825 mg of bioavailable riboflavin. However, for fat accretion 1 Mcal of energy expended required 2.54 mg of riboflavin, and for protein accretion each Mcal of energy expended required 15.51 mg of riboflavin, or six times as much.

Stahly says that, on average, pigs' dietary requirement for bioavailable riboflavin appears to be at least three to 3.8 times greater than 1998 NRC estimates for 10- to 20-kg pigs. More specifically, this work suggests that riboflavin fortification levels for healthy young pigs with high lean-growth genetics may need to be as much as five times the current NRC requirements to maximize growth potential and feed efficiency.

Beyond the immediate application to riboflavin requirements, the 1998 work furnishes a prototype for a factorial approach to optimizing vitamin fortification levels for pigs of varying genetics managed in different environments, Stahly says. The goal is to establish models similar to those for energy and amino acid needs by determining vitamin allowances required for maintenance, and for protein and fat accretion.

The 1998 work allowed Lutz and Stahly to develop a preliminary equation for calculating riboflavin requirements based on various parameters. For an example of how those requirements would vary, the researchers considered two 77-lb (35-kg) pigs with different lean-growth potential.

The first pig had a lean gain rate of 0.81 lb (0.370 kg) per day, whole-body protein accretion of 0.31 lb (0.14 kg) per day, whole-body fat accretion rate of 0.55 lb (0.25 kg) per day and a protein mass of 12.94 lbs (5.88 kg). The researchers estimated this pig's requirement at 5.2 mg per day of bioavailable riboflavin. The second pig had a lean gain rate of 1.04 lb (0.473 kg) per day, whole-body protein accretion rate of 0.40 lb (0.18 kg) per day, whole-body fat accretion rate of 0.48 lb (0.22 kg) per day, and a protein mass of 12.94 lbs (5.88 kg). For this pig, the estimated bioavailable riboflavin requirement would be 10.8 mg per day.

Lutz and Stahly focused on riboflavin in their 1998 study because of its importance in fat, protein and carbohydrate metabolism, but the 1995 study with five B vitamins emphasized the importance of all of them in protein accretion.

Indeed, that work suggested that faster growth and improved feed efficiency with optimum B vitamin fortification returned $23 for every dollar invested in vitamin supplementation.

 

References:

  • Lutz, T.R., and T.S. Stahly. 1998. Dietary riboflavin needs for body maintenance and body protein and fat accretion in pigs. Iowa State University Research Report, ASL-R1564.
  • National Research Council. 1998. Nutrient Requirements of Swine. National Academy of Sciences, Washington, D.C.
  • Stahly, T.S., et al. 1995. Dietary B vitamin needs of high and moderate lean growth pigs fed from 20 to 62 pounds body weight. Iowa State University Research Report, ASL-R1263.

 
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