Advances in swine productivity through genetic selection, management, health and nutritional strategies have resulted in reproductive performance once unimaginable.
Feed efficiencies during the growing and finishing phase of production have improved in the range of 25 percent over the past 15 years. Sow reproductive efficiency has shown equal improvement and the biological potential of today's hyperprolific modern genotypes is truly staggering. However, currently defined nutrient requirements are largely outdated as they are based on research conducted decades ago.
Indeed the question has been raised, if a technology exists to improve reproductive performance, while maintaining or lowering cost of production and at the same time reducing the impact on the environment, are nutritionists not obligated to consider it? This is a very timely question and one that should be seriously considered during diet formulations.
Traditionally, dietary formulation has relied on the research-based requirements set forth by scientific collaborations such as the NRC (1998) and ARC (1981). Also, detailed models have been developed to accurately estimate the amino acid and energy requirements of sows (Nobles et al., 1990; Pettigrew et al.,1992a,b; and NRC, 1998).
While these applications are accurate for the energy and amino acid component of sow nutrient requirements, very little research has focused on the trace mineral requirements of hyperprolific sows. The trace mineral recommendations can also vary considerably between industry and reference recommendations and many of these recommendations are based on research that is decades old.
For example, in 2005 Mateos et al looked at the recommended trace mineral levels for lactating sows and found a large difference between levels of zinc for NRC requirements, 50 mg/kg of complete feed, to studies completed by the University of Nebraska and South Dakota State University with levels of zinc at 80 to 150 mg/kg of complete feed.
So the question could then be asked, has trace mineral nutrition kept up with genetic progress, and if not, what are the consequences?
The role of trace minerals in sow and boar production is extremely important. In 1995, Mahan and Newton clearly demonstrated that the draining effects of enhanced reproduction result in the depletion of sow body mineral reserves after three parities. In working boars, although the impact of trace mineral supplementation and research is very limited, current research findings are proving to be interesting and indicate that enhanced supplementation to working boars with organic trace minerals improves semen concentration and increases the number of doses of extended semen per ejaculate.
Unfortunately, dealing with today's breeding stock of higher genetic potential does not simply allow nutritionists to continually supplement diets with higher levels of minerals due to the known interactions between the elements. In addition, environmental pressures exist to reduce heavy metals in effluent, yet higher recommended levels may contribute unnecessarily to pollution. Therefore, a more detailed approach to diet formulations must be undertaken to ensure the nutritional needs of the modern sow and boar are met, allowing them to express their genetic potential while improving longevity and lifelong performance.
The ultimate goal of nutritionists and producers alike is to maximize the number of healthy, top quality piglets from the sow that can then be reared to maximize meat production per sow per year at minimal cost. (Close and Turnley, 2004). With this goal in mind, developing feeding strategies for the hyperprolific sow allows nutritionists to maintain a focused approach tending away from least cost formulation to formulations focusing on optimal costs and return over feed cost. During program development, the following objectives should be front and center:
1) To maintain or improve reproductive performance;
2) To maintain cost or reduce the cost of production; and
3) To reduce nutrient emissions in effluent to protect the environment.
Keeping these objectives in mind, the swine industry needs to look at the current recommendations for minerals and the source of the minerals. Studies by Fehse and Close (2000) were among the first to show the impact of organic trace mineral supplementation on reproductive performance (Figure 1). This data, coupled with the report by Mahan and Newton, indicated a depletion of trace elements as sows age. Supplementation with organic trace minerals appeared to offer a solution due to their higher retention.
Several studies have supplemented additional trace minerals on top' of the existing diet to elicit the reproductive response. However this approach could potentially conflict with several of the objectives listed. The first diets to contain organic trace minerals (in the form of Bioplex and Sel-Plex) were lactation rations. Large nutrient drains occur during the late gestation and lactation periods of the reproductive cycle. Before the increased feed intake seen during lactation, the final two weeks of gestation may potentially pose the largest drain on the sow, with over 50 percent of the mineral content of the fetal tissue being deposited during this time.
Drain of lactation
Therefore, supplementing the lactation ration with organic trace minerals and feeding these diets pre-farrowing may be an excellent management technique to ensure maximum mineralization of the fetus while minimizing the drain on the sow. Recent research findings (Peters, 2006) demonstrated that the level and source of trace mineral supplementation affect sow reproductive performance. Over a six parity period, utilizing 375 litters, Peters found that increasing the dietary trace mineral level improved performance when organic trace mineral forms were fed, whereas increasing the levels using sulphate minerals reduced performance.
The supplementation of organic trace minerals in this trial resulted in one extra pig per litter when trace minerals were fed at typical industry levels compared with the NRC recommended levels. Likewise, sow and piglet body mineral data were evaluated and it was found that while there were effectively no differences between the treatments, with the exception of selenium, the mineral drain on the sows was greater as indicated by the larger litter size and higher sow productivity. The author concluded that feeding inorganic trace minerals in excess of NRC recommendations may be detrimental to sow reproductive performance; however, when these same levels of trace minerals are fed in the organic form, sow reproductive performance is not adversely affected (Peters, 2006) (Figure 2).
Nutrition and the genome
Enhancing reproductive performance in terms of pigs/sow/year is only one measure that should be investigated. Longevity in sow herds is a major focal point as culling rates (mortality and culls) in many situations are approaching 60 percent (Henman, 2006). Genetics can play a major role in longevity as indicated by Close and in a thorough review of the literature heritability estimates were found to be very low and variable (Serenius and Stalder, 2006).
However, Serenius and Stalder (2006) also indicated that although selection for sow longevity may be possible, the application of such technologies would be difficult as selection decisions for sow longevity must be carried out by pedigrees. Enhancing lifetime sow reproductive performance should be an industry goal. Close indicated genetic differences in populations of sows enable certain lines to have an increased herd life of up to one extra parity. Supplementation of sow diets with organic trace minerals under commercial conditions, was found to increase the number of sows remaining in the herd after parity four. In addition, reducing the removal rate in a herd spreads the cost of replacements over more animals. Special attention must be given to reducing the number of animals culled after a single parity as this is extremely expensive.
The future of research in livestock production will undoubtedly utilize molecular tools to measure and evaluate the impact of new technologies on economically viable production parameters. The term 'nutrigenomics' is descriptive of the interaction between nutrition and the genome, thereby combining nutritional research with functional genomics. The information generated from these studies should improve the understanding of nutrition-related diseases and production-related issues. Dawson (2006) reviewed the impact of nutrients on the genome and how this translates into the formation of functional proteins that drive biological processes, including reproduction. In the not-too-distant future, the utilization of these techniques should allow researchers, and possibly nutritionists, to provide specific nutritional recommendations to combat fertility problems at the commercial level.