Summary

During the last 14 days of pregnancy approximately 50% of the total minerals (macro and micro) minerals are retained in the body of developing fetal pigs. During lactation the mineral retention by the nursing litter is higher than late gestation and greater as litter size increases. The critical stage of minerals for the sow appears to be during late gestation and lactation.

Sow milk mineral composition is largely under genetic control but is influenced by stage of lactation, and litter size. Feeding organic trace minerals over a 6 parity period showed improved reproductive performance and may enhance litter size by 1 to 2 pigs per year.

High producing sows have a lower body mineral content than low producing or non reproducing sows with the amount of mineral depletion exacerbated by greater sow productivities.

Introduction

With the introduction of new maternal sow lines capable of producing litters of larger size and heavier
birth weights, and sows with greater milk productions resulting in more pigs weaned at heavier weaning
weights, the nutritional demand on these animals is exceedingly high. The large turnover rate in many
sow herds conservatively approaches 30 to 45%, and it would be expected that sows of greater productivities would be more nutritionally challenged and thus among the first animals culled.

Although the reasons for culling sows are many, they can be generally categorized in the areas of anestrus, poor conception rate, low litter size, and poor feet and legs. The anestrus and poor conception rates have largely been associated with poor sow condition and low lactation feed intakes, thus attributed to being energy and protein deficient, whereas the skeletal problems have been associated largely with Ca and P inadequacy.

Calcium and P as well as the trace minerals are involved in skeletal formation as well as being associated in other biological functions influencing anestrus, conception rate, litter size, and feet and leg problems.

The NRC (1998) swine mineral recommendations, has not materially changed, except for Se, for the past 25 years (1973 to 1998), even though sow productivity has increased tremendously during this time frame. Any effect of mineral inadequacy or supplemental trace minerals on sow turnover rate is unknown.

Clearly the sow cannot meet her biological need for nutrients, particularly the minerals, using recommendations of the previous decades. A recent report has demonstrated that sow mineral reserves are depleted over a 3 parity period, and that sows of a higher productivity had a greater loss of both macro and micro minerals than sows of lower productivities (Mahan and Newton, 1995).

To counter the anticipated greater biological need for minerals by high producing sow lines, the feed industry and university specialists have routinely recommended higher dietary fortification levels of both macro and micro minerals, as well as other nutrients, in gestation and lactation sow diets. Although this practice is perhaps logical and may be exactly what these sows need for higher productivities, it is enerally not based on research but field observations and educated guess work”.

This brief review will investigate when the mineral requirements of sows are greatest, what is the effects of fortifying additional minerals, evaluating the role of organic and inorganic trace minerals, and examining sow mineral status in high producing sows over a long reproductive life.

Calcium and Phosphorus

Calcium and P are the two major minerals largely associated with leg structure and integrity. The eesearch of Nimmo et al. (1981) demonstrated that a higher percentage of gilts were unable to stand through the first parity when fed NRC (1978) dietary levels of Ca and P during developmental and reproductive periods. Other work has shown that sows of greater productivities have greater amounts of bone demineralization taking place during their reproductive life (Maxson and Mahan, 1986).

These combined results suggest that during the developmental growth period and the reproductive period there is a high Ca and P demand for these two minerals. These minerals can thus be removed from bone tissue when milk production demands are great. Other research by Mahan and Fetter (1982) demonstrated that the trabecular bone (i.e., spongy bone) was the main reservoir where these minerals were initially removed, but later bone demineralization takes place in the cortical bone shaft. Posterior paralysis or “downer sow syndrome” has been common in many sows and is generally observed during late pregnancy and early lactation.

This suggests that when fetal demands are high or when sow milk production is great, the mineral needs for these physiological functions are not easily met by the diet fed to the sow, particularly when fortified with existing recommendation levels. An experiment to evaluate fetal deposition of minerals, from 45 days post coitum to late pregnancy was conducted.

The data suggested that the total body mineral content of the developing litter approximately doubled every 15 to 20 days of pregnancy, but more than 50% of the total mineral content in the developing litter occurred during the last 2 weeks of gestation.

Although this graph reflects the total mineral content of the litter, when the individual minerals were plotted for the same period, both Ca and P approximately doubled during the last 2 weeks of pregnancy. Thus it is understandable why the sow undergo bone demineralization during this critical stage of gestation, and that the responses would be exacerbated in sows having larger litter size or milk production capabilities.

Upon farrowing sow colostrum is low in its Ca concentration but rises as lactation progresses. The low Ca level at parturition can be explained by the diminishing Ca status of the gestating sow because she has been transferring tremendous amounts of Ca to her developing fetus. This has resulted in minimal body stores for later transfer to the mammary tissue. Consequently, the amount being secreted into colostrum is lowered.

During the postpartum or lactation period when feed intake increases, the demands for fetal development have been eliminated, milk secretion now has the primary demand for Ca, the amount of Ca in the mature milk thus is increased. There appears, however, to be an effect of litter size or amount on the resulting Ca composition in the milk possibly increasing bone demineralization. When sows nursed 8 versus 11 pigs per litter the amount of Ca in the milk of sows nursing the larger litter size was lower (P < 0.05). The same trend was true for milk P where sows nursing larger litters and thus producing more milk had low milk P contents.

As a result of the above findings the total deposition of Ca and P in litters of pigs at weaning (11 or 21 days) was greater in larger litter sizes (Figures 5 and 6). When expressed on an individual pig basis, there was no difference in the Ca and P content of these individual pigs suggesting that the progeny had
approximately the same mineral contents. Consequently, the trace mineral content in individual pigs in at least somewhat under genetic control, and that the sow supplied additional Ca and P not only from
the diet but also from her body tissue (i.e., bone) for the nursing litter.

Micro-minerals

The data presented in Figures 1 to 3 implies that the largest response to the increased mineral retention in the developing litter was attributable to Ca and P. The data demonstrated that all essential trace minerals followed the same general pattern of retention as Ca and P, but they also showed some differences. This difference is attributed to the different biological functions of each element as to when it is needed by the fetus at a specific stage of development or later in gestation, where the fetus retains minerals for its subsequent postnatal life. For example, the greater Zn content in the fetus is in largely in the epidermal tissue and its increase would be expected to be in proportion to body surface area, whereas the greatest need for Fe would be during late gestation when the need for blood hemoglobin synthesis is high in the neonate.

Two of the critical trace elements (Fe, and Zn) will be presented in Figure 7. Although the amount
of Zn did not double during the last 2 weeks of fetal development, as did Ca and P, the quantity of Fe
increased greatly during this latter gestation period.Although total Fe content is shown to increase
greatly during late gestation, it is still below that necessary for the neonate postnatally. Consequently,
an exogenous supply is needed to prevent anemia in the young pig. The amount of Fe secreted into the
mammary tissue is considered to be inadequate in meeting the high Fe demands of the rapidly growing
pig. Sow colostrum and milk Fe composition is presented in Figure 8. The Fe content in colostrum
and later in the mature milk declined as lactation progressed, and that its content during late lactation
appeared to be also influenced by the number of pigs nursing the sow. Pigs of a larger litter size received milk of a lower Fe contents than pigs nursing sows of a lower litter size.

The total Fe content in litter sizes of 8 or 11 pigs when weaned at 11 or 21 days of age showed that
larger litters had greater total Fe contents (Figure 9). Consequently, sows nursing larger litters would be
expected to have a lower body Fe status or the sow had to consume more feed during lactation to maintain her body Fe status. Fields reports are indicating increasing evidence of anemia in adult sows.
The Zn content of the developing litter during gestation presented in Figure 7 demonstrates that the Zn content in the litter increased greatly over the gestation period with the greatest increase occurring
during the last 2 weeks of pregnancy. Colostrum had the highest concentration of Zn compared to later
milks. Zinc concentration declined in the later milk.

There appeared to be little effect of litter size on milk Zn concentration during lactation. The total Zn content in the litter increased as the pig reached weaning age, and sows having larger litters had litters with the greater total Zn contents. Organic vs. Inorganic mineral sources Trace minerals perform several roles in the body and are essential for several reproductive functions. Not only are they involved in enzyme control of various metabolic and hormonal processes, but they re also important in growth processes, health and immune control.

When provided in slight excess they are retained in the liver but they have also been shown to be pro oxidants, and thus can be a detriment to body functions. Consequently, the form of the element provided to the animal may become more important in the future as dietary needs increase. For example, inorganic or organic Se when provided to meet the pig’s requirement will enhance the immune system and antioxidant control systems. However, when either form in provided in some excess, much of the organic Se is retained in tissue whereas excess inorganic Se has been shown to cause oxidative damage to the tissue and thus is detrimental to animal performance. Therefore the role of different forms of trace minerals may now become more important, particularly when higher dietary levels are fed.

With increasing mineral needs of sows, there is concurrently an interest in increasing dietary trace mineral levels in sows during gestation and lactation. Research investigations have been lacking in this
area, and most of the dietary adjustments by specialists (University, Feed industry, and Veterinarians) have simply increased each of the trace minerals in proportion to estimated needs. We have recently
completed a long term (6 parity) sow study evaluating various dietary trace mineral levels when fed as
either as inorganic (sulfate or oxide form) or organic trace minerals (Bio Plex). The experiment included
NRC (1998) levels or higher trace mineral levels typical of what is provided by the industry. Two additional treatments were initiated at breeding where the gilts had been fed the industry level of the trace minerals during their developmental period, but at breeding additional Ca and P were provided along with the higher trace mineral level.

The experiment involved a total of 375 litters and the overall results are presented in Figure 12 (Peters, 2006). Although not presented here the total number of pigs born was approximately 1 additional pig per litter when the organic trace minerals were fed. As evident in Figure 12 there was no difference in the number of live pigs born when NRC (1998) was provided. However when pigs were fed the industry level of both trace mineral sources along with the groups fed additional Ca and P, litter size was lower when inorganic minerals were fed. Although this experiment needs to be confirmed with another set of animals, the results suggest that organic minerals may be superior to inorganic minerals, and that extra fortification of minerals in the organic form may be beneficial to sow reproductive performance.

Both Ca and P had more of the greater loss having approximately 15 to 20% less total contents of these two minerals. Of the remaining minerals Mg, Cu, Se and Zn also had lower contents in the reproducing sow. It is of interest to note that sows of higher productivities had a greater loss of minerals than the sows of lower productivities.

Future

Although mineral requirements are poorly defined for reproducing animals (Hostetler et al., 2003), continued research is needed to determine these requirements. Clearly high producing sows have a greater need for minerals than sows of lower productivities. The results presented in these series of studies imply that there is perhaps an “ideal ratio” and perhaps “critical window of need” for the trace minerals for reproduction. This “ideal ratio of minerals” and their biological need at specific time periods during gestation might also differ by stage of reproduction.

Higher productivities have higher dietary requirements for these minerals thus depleting body
reserves. Although we are accustomed to increasing dietary minerals in proportion to estimated needs,
this practice may be in error because of the differing “windows of need” and the potential detrimental
effects of excess levels. Mineral needs are perhaps regulated both genetically and by litter size, whereas
lactation mammary secretions may not only reflect genetic input into milk secretion patterns, but may
also reflect an avenue where excess minerals may be excreted by the body. The requirement for the trace minerals may be influenced by the form of mineral provided.

It is also possible that higher dietary minerals may be desirable at some stages of reproduction
and detrimental at other stages. The role of organic minerals in this area is as yet unknown, but our
results indicate that they may have a positive influence on sow reproductive performance when elevated
in the diet, whereas when inorganic minerals are provided at the “normal” higher levels they may be
detrimental, particularly if provided continually. Determining the mineral needs of the reproducing sow
is indeed in its infancy compared to other nutrients. More extensive research needs to be conducted and
their requirement appears to be exacerbated as the genetic capability of the animal changes.

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September 2006