Better Pork - December 2006

Nutrition

Getting a handle on the changing mineral needs of the modern sow

Research suggests that high-producing sows have greater mineral requirements than sows of lower productivities. But care is needed because of the changing windows of need that sows move through

by JANICE MURPHY

Proper nutrition of the breeding herd plays a key role in maximizing herd productivity. Traditional feeding strategies for the reproductive female have used body reserves as a buffer against short-term deficiencies in nutrient intake, resulting in minimal damage to fetal or nursing piglets. However, modern sows, with a lean genotype and higher reproductive performance, must be managed differently, since they start their reproductive life with fewer reserves and have less to lose.

It is well established that the way sows are fed in one stage of the reproductive cycle will affect productivity during subsequent stages. As a result, an integrated feeding strategy is needed, designed to maintain high productivity and prolong the reproductive life of the sow.

Nutrition is the key component that ensures the modern sow achieves her genetic potential for reproduction. In practical terms, the actual level of sow performance in modern herds is well below the animal's capability. Many farms average 20-22 piglets per sow/year compared with the potential of 30 per sow/year. In order to achieve better results, we need to go back to the basics of sow feeding and develop a strategy that makes sense throughout the reproductive cycle.

When it comes to nutrition, the recipe for success includes everything that sows need -- energy, protein (specifically essential amino acids), essential fatty acids, vitamins and minerals. Without all of these basic building blocks, sows cannot support their requirements for maintenance and growth (body, mammary and uterine tissue), let alone the requirements for fetal growth and lactation.

The potential consequences can include a decrease in conception rates, smaller litters and/or reduction in birth weight, lower milk production, an increase in weaning-to-service interval or a shortened reproductive life.

Focus on minerals

Dr. Don Mahan, a swine nutrition researcher at Ohio State University, recently made a presentation to the Midwest Swine Nutrition Conference reviewing the importance of minerals in sow nutrition and reproduction. He focused on when the mineral requirements of sows are at their greatest, the effects of additional minerals, the role of organic and inorganic trace minerals, and of mineral status in high-producing sows over a long reproductive life.

As new sow lines test the limits, farrowing larger litters and heavier birth weights, and sows with greater milk production produce more pigs weaned at heavier weaning weights, the nutritional demand on these animals becomes enormous. The turnover rate in many sow herds conservatively approaches 30 to 45 per cent and, with that rate, we would expect that sows of greater productivities to be more nutritionally strapped and, as a result, among the first to be culled.

The reasons for culling sows vary, but the usual suspects include anestrus, poor conception rate, low litter size and poor feet and legs. Although anestrus and poor conception rates are traditionally associated with poor body condition and low lactation feed intakes, something attributed to energy and protein deficiencies, skeletal problems have been more closely associated with mineral inadequacy. Calcium (Ca) and phosphorus (P) as well as the trace minerals are intimately involved in skeletal formation, as well as other biological functions influencing anestrus, conception rate, litter size, and feet and leg problems.

The National Research Council (NRC) Nutrient Requirements of Swine recommendations for minerals have not changed significantly, except for selenium, in over 30 years, even though sow productivity has increased tremendously during that time. It is obvious that the modern sow cannot meet her nutrient requirements, particularly for minerals, using recommendations that are three decades old.

Assuming that high-producing sows require greater levels of minerals, feed industry and university researchers have routinely recommended higher dietary inclusion rates of both macro- and micro-minerals, as well as other nutrients, in dry and nursing sow diets. Although this seems logical and may be exactly what these sows need to maintain higher levels of productivity, it is generally not based on proven research results but rather on simple field observations and educated guesses.

The vital role of calcium and phosphorus

Calcium and P are the two major minerals associated with leg structure and integrity. During growth and reproduction, there is a high demand for Ca and P. As a result, these minerals tend to get removed from bone tissue when milk production demands are so great that the ration cannot meet the mineral needs.
Data from a recent experiment suggests that the total body mineral content of the developing litter approximately doubled every 15 to 20 days of pregnancy, but more than 50 per cent of the total mineral content in the developing litter occurred over the last two weeks of gestation (see Figure 1). So it is not hard to imagine that sows experience bone demineralization during this critical stage of gestation, and that the level of demineralization would be higher in sows with larger litters.

Figure 1. Total mineral content of developing pig litters from 45 days gestation to birth.

At farrowing, sow colostrum is low in Ca, but the level increases as lactation progresses. As feed intake increases postpartum, the demands for fetal development have been met and a shift occurs whereby milk secretion represents the primary demand for Ca.

However, litter size does appear to have an effect on the resulting Ca composition of the milk, possibly increasing bone demineralization. One experiment showed that when sows nursed eight versus 11 pigs per litter, the concentration of Ca in the milk of sows nursing the larger litter was lower. The same trend was true for milk P levels.

When expressed on an individual basis, there was no difference in the Ca and P content of these pigs, suggesting that the progeny had approximately the same mineral content. Consequently, the trace mineral content in individual pigs is at least partially under genetic control and the sow supplied additional Ca and P from her body tissues, as required according to the size of the nursing litter.

Mineral sources -- organic versus inorganic

Trace minerals perform several roles in the body and are essential for many reproductive functions and growth processes, and in maintaining health and immunity. When provided in slight excess, they are retained in the liver, but they have also been shown to be pro-oxidants, and as such can be detrimental to body functions. Consequently, the form of the element provided to the animal may become more important in the future, as dietary needs increase.

With increasing mineral needs of sows, there is an interest in greater dietary trace mineral levels in sows during gestation and lactation. Mahan’s research team has recently completed a long-term (six parity) sow study evaluating various dietary trace mineral levels when fed as either inorganic or organic trace minerals.
The experiment included NRC (1998) levels or higher trace mineral levels typical of what is provided by industry. Two additional treatments were initiated at breeding in gilts fed the industry level of 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 2. Although not shown in the figure, the total number of pigs born was approximately one additional pig per litter when the organic trace minerals were fed. There was no difference in the number of live pigs born when NRC (1998) was provided.

However, when pigs were fed the standard 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. These results suggest that organic minerals may be superior to inorganic minerals, and that fortification with organic minerals may be beneficial to sow reproductive performance.

Figure 2. Effect of organic and inorganic trace mineral sources at two dietary levels over six parities.

During their reproductive life, sows not only have greater trace mineral requirements, but they also eat more feed and consume more minerals. However, because of the demands of gestation and lactation, the net effect is that they also have a greater loss of body minerals.

As sow productivity increases, the nutritional demand on the sow would be expected to increase, and their body mineral reserves would concurrently diminish. An experiment that compared the mineral content of sows completing three parities to a set of non-reproducing gilts of the same age showed that most of the minerals were lower in sows that had reproduced. Both Ca and P showed the greatest losses and, of the remaining minerals, magnesium, copper, selenium and zinc also had lower levels in the reproducing sow. As suspected, more productive sows had a greater loss of minerals than the less productive sows.

The future of sow mineral nutrition

Research has demonstrated that high-producing sows have a greater need for minerals than sows of lower productivities. The results of several experiments suggest that there may be an ideal ratio and maybe even a critical window of need for trace minerals for reproduction. Although nutritionists have become used to increasing dietary minerals in proportion to estimated requirements, this practice could be counterproductive because of the changing windows of need that sows move through and the potential detrimental effects of mineral excesses.

More extensive research is necessary in order to ensure the proper mineral nutrition of the modern sow. BP

Source: Mahan, D. 2006. “The Changing Mineral Status of High Producing Sows -- What are their needs and when are the Critical Periods?” Midwest Swine Nutrition Conference. Indianapolis, Indiana. Sept. 7, 2006.

Janice Murphy is the former Swine Nutritionist with the Ontario Ministry of Agriculture, Food and Rural Affairs. BP