Dr Eric van Heugten Swine Nutrition Specialist North Carolina State University

Introduction

Plasma magnesium values usually range from 17 to 25 parts per million (ppm), and muscle concentrations are approximately 950 ppm (Apple et al., 2001). Two-thirds of a pig's body magnesium is located in bone. The remaining third is disbursed in soft tissue and extracelluar fluid. Plasma magnesium values usually range from 17 to 25 parts per million (ppm), and muscle concentrations are approximately 950 ppm (Apple et al., 2001). Only 1 to 3 percent of the total intracellular magnesium concentration (5 to 20 mmol) is free ionized magnesium. Therefore, a majority of the intracellular magnesium is bound to organic compounds, including ATP, DNA, RNA, and proteins.

Much information is available about magnesium in ruminants because of the occurrence of grass tetany associated with magnesium deficiency, especially when animals are fed on lush green pasture. Less research has focused on magnesium metabolism in nonruminants. Magnesium is present in adequate concentrations (0.14 to 0.18 percent) in typical corn-soybean meal diets consumed by pigs (Svajgr et al., 1969; Krider et al., 1975). Deficiency signs include hyperirritability, muscle twitching, reluctance to stand, loss of equilibrium, tetany, and eventually death (Mayo et al., 1959; Miller et al., 1965). Although toxicity is rare, the estimated tolerable concentration is 0.3 percent (National Research Council, 1980).

Pork Quality

Using dietary magnesium supplementation has been found to improve pork quality, specifically, color and fluid loss (D'Souza et al., 1998, 1999, and 2000). Furthermore, magnesium supplementation has been reported to reduce oxidation of meat during storage (Apple et al., 2001). However, the presence or consistency of the positive effect has been questioned (Apple et al., 2000; Hamilton et al., 2002), even when plasma magnesium was increased 10 percent (van Laack, 2000). The following section will summarize the most relevant research.

The literature pertaining to magnesium supplementation can be divided into two main sections, depending on:

1. the physiological status of pigs at harvest and
2. the manner in which the pigs are harvested.

Pigs harvested in Australia are boars or gilts of 70 to 90 kg bodyweight, and they are stunned by administration of carbon dioxide (D'Souza et al., 1998). However, in the United States and Canada, boars are not harvested, the pigs are usually heavier (110 to 125 kg BW), and they are harvested primarily by electrical stunning. The presence and consistency of a magnesium response to improve pork quality have been different across conditions.

The first three experiments presented in Table 1 summarize the research conducted by D'Souza in Australia. These studies have shown the most consistent, positive effect of magnesium on pork quality, including reduced drip loss (D'Souza et al., 1998, 1999, and 2000) and reduced paleness (L*) (D'Souza et al., 1998 and 2000). Although a consistent effect on pork quality was present, the effect of magnesium on glycogen, lactate, and pH post-mortem was not consistent. Nevertheless, these three experiments demonstrate that magnesium provides a positive effect on drip loss and, to a lesser extent, on paleness, regardless of amount (1.6 or 3.2 g/d), source (aspartate, sulfate, or chloride), or duration (2 or 5 d prior to harvest) of supplementation.

The data collected in North America (presented at the bottom of Table 1) have been less consistent within and across experiments than those collected in Australia. Drip loss was reduced in one experiment conducted in the United States (Hamilton et al., 2002). But the reduction of drip loss within the experiment was not present across all durations: it was affirmative for 2 d and 5 d, but not for 3 d of supplementation. The effect of magnesium on color was more consistent than the effect on drip loss, indicating that magnesium may increase redness (Apple et al., 2000 and 2001) and reduce paleness (Hamilton et al., 2002).

Thus, in North America the effects of magnesium supplementation in heavier pigs stunned electrically have not been as consistent and positive as those in experiments conducted in Australia with lighter weight pigs stunned with carbon dioxide.

Summary

Magnesium supplementation has been shown to improve pork quality. However, practical application of magnesium through feed for brief periods before harvest may be difficult, especially when multiple marketing occurs within a pen of pigs. Magnesium supplementation through drinking water before harvest could represent a novel and practical way to improve pork quality. Research on this approach is not present in the literature, so we decided to address it. Results of three investigations can be found at the following NCSU Swine Extension Husbandry Web sites:

http://mark.asci.ncsu.edu/SwineReports/2002/frederick.htm
http://mark.asci.ncsu.edu/SwineReports/2003/frederick1.htm
http://mark.asci.ncsu.edu/SwineReports/2003/frederick2.htm

Reproduced Courtesy