Introduction

Feeding pigs is the single most expensive aspect of pork production accounting for as much as 70 per cent of the variable costs. Surprisingly, at least 50 per cent of these feed costs can be attributed to providing energy to the animal, thus making energy the most important nutrient financially. As such, an investigation of the energy systems used to best meet the energy needs of the animal seems logical.

Similar advancements for other nutrients, including protein, have previously been explored and are now largely accepted in North America. For example, many nutritionists have accepted and are formulating diets on the basis of standardized ileal digestible amino acids (SID AA) and the ideal protein concept, as opposed to total or apparent ileal digestible amino acids which were used in the past. Similarly, total phosphorus content has been gradually replaced with available phosphorus.

However, for energy, many North American nutritionists continue to formulate diets using digestible or metabolizable energy systems (DE or ME) as opposed to more advanced systems, such as net energy (NE). Potential reasons for this change to a more advanced energy system include:

1. Energy is a much more complex nutrient than others as it is derived from numerous dietary sources;
2. There is a lack of data about the energy contents of specific feed ingredients used in North America;
3. There is a lack of research data to support the use of advanced energy systems, or
4. Simply having comfort in using DE or ME systems (Patience et al. 2004; Patience and Beaulieu (2005).

Therefore, the purpose of this paper is to identify the benefits of using an NE system, and then to provide an outline for implementing NE into commercial swine production.

Benefits of Using NE

The NE system was developed to provide more accurate estimates of the'true' energy in an ingredient (and subsequent diet) that is going to be available for a pig to use for maintenance and product formation, i.e. growth, gestation, lactation, etc.

The main difference between the NE system and the DE and ME systems is that the NE system accounts for the amount of heat lost during digestion and subsequent deposition of nutrients in protein and adipose tissue. To illustrate this point, the DE, ME and NE of several commonly used ingredients are reported in Table 1 as an index relative to a reference diet. When corn is compared with soybean meal, for example, their DE and ME index values are similar, suggesting that they are relatively equal energy sources. However, when their respective NE index values are compared, it becomes apparent that there is a significant difference between the abilities of cereal grains and protein sources meal to provide retainable energy to the pig.

The advantages of the NE system and the amount of new research required to adopt the NE system have sometimes been overstated. The advantages of the NE versus the DE/ME system are not related to improvements in growth performance or feed efficiency (Frantz et al., 2004). Instead, advantages of the NE system are related to:

1. Ensuring consistent growth performance and likely carcass quality while making alterations in the macro-nutrient composition and thus NE content of feeds (Cadogan et al., 2005);
2. Managing the risk of inclusion of alternative feedstuffs and co-products into swine diets (Smits and Sijtsma, 2007), and
3. Reductions in feed costs per kg of feed or lean gain (Payne and Zijlstra, 2007).

Energy is the main component of feed costs for swine, i.e. the greatest cost-pressure in swine feed is against energy content, and an accurate system to evaluate energy quality will thus play a role in managing feed costs (Zijlstra et al., 2001; Noblet, 2006).

A simple yet practical example of what this means for diet formulation using wheat-based diet is shown in Table 2. Diets formulated using NE are typically lower in crude protein (CP) than those using DE or ME, because the heat lost during catabolism and excretion of excess nitrogen is considered in the NE system. Additionally, diet costs are often decreased on a per ton and a per pig basis when formulated using a NE system (Patience, 2005; Payne, 2006). By formulating the diets using the ideal protein concept and SID AA, the levels of the essential amino acids (lysine, threonine, tryptophan, methionine and isoleucine) are easily maintained. Hence, negative effects on animal performance would be not expected if dietary CP is reduced when diets are formulated for energy with the NE system, as has been reported by several research groups (Canh et al., 1998; Dourmad et al., 1993; Le Bellego et al., 2000, 2001; Kerr et al.. 2003; Patience et al., 2003).

The actual change in diet formulation will depend on:

1. The main cereal grain and protein feedstuffs that are included in the original feed formulation
2. The prices of the feedstuffs, and in particular the price ratios between the cereal grain and fat sources and between the protein feedstuffs and supplemental amino acid sources
3. The entire matrix of feedstuffs used during least-cost diet formulation, and
4. The specific energy and amino acid levels used in the diet formulation.

For example, the wider the range in the ingredient matrix, especially for protein and fiber, for example via the inclusion of additional by-products, the more important it becomes to formulate diets using NE, SID AA and available P to ensure that predictable growth performance is achieved.

An indirect benefit to the reduction in CP often reported in diets formulated on an NE basis is that nitrogen excretion also is decreased. According to Canh et al. (1998), each percentage point reduction in CP results in a 10 per cent reduction in nitrogen excretion from the pigs. The decrease in nitrogen excretion results in decreased ammonia emissions and odor in the barns, which leads to improved animal performance. Canh et al. (1988) also indicated that water intake of pigs is reduced as dietary CP is reduced, which leads to less slurry volume.

Implementing NE into Commercial Production

Once a decision is made to look into using NE, the next question is how to proceed? A serious downfall of any energy system, including NE, is that most nutritionists have been and still are using the same energy values for their ingredients as they have been using for years. These energy values may have been developed within each company over the years or they could simply be average values from reference tables, such as those in the NRC (1998) or Sauvant et al. (2004). Of course, this practice may work for NE as well, but it is certainly not the best management practice, because with every change in the crude nutrient (protein, fiber, fat, etc.) profile, there also is a change in the energy available from that ingredient. The implementation of any new process can be daunting, but a detailed guideline of how an implementation of a NE system could proceed is provided below in Table 3.

As with any nutrient system, the ideal first step is to develop some sort of database that will help nutritionists better understand the ingredients and their roles in animal diets. Practically speaking, a good place to start is by identifying the energy containing feed ingredients that would typically be used in the grow-finish diets.

There are several reasons for starting with the grow-finish diets including:

• the diets in these phases typically contain the least amount of ingredients and
• these diets make up the bulk of the feed that a pig will consume over its lifetime.

Furthermore, while the concepts of NE certainly apply to all phases of growth, it is conceivable that each phase of growth would require a different set of mathematical equations as the animal's ability to extract nutrients þ including energy – change as the animal grows. This concept is evident with the work of Noblet et al. (1994) as they suggest one set of NE equations for growing pigs and a different set of equations for breeding sows. The idea that the animal's ability to utilise nutrients differently as it grows applies to not only energy, but all nutrients. As with other nutritional advancements, such as digestible amino acids, the understanding of energy and NE is ever-evolving (De Lange and Birkett, 2005) but that should not be a reason to rule out using NE in today's commercial production scenarios.

Once the energy-containing feed ingredients have been identified, the next step towards creating a NE database would be to collect each ingredient over a defined period of time. Ideally, this collection would be in conjunction with an on-going quality control sampling protocol, such that it is as seamless as possible. As each ingredient is collected, it should be analysed for its macronutrient composition, including (but not limited to) crude protein, fat, and fibre, moisture, ash, acid and neutral detergent fiber, sugar and starch. The reason for this is that the two most-widely used NE systems, which were developed by the French (Noblet et al., 1994; Sauvant et al., 2004) and the Dutch (CVB, 2003) are both solidly based on the macronutrient composition of the feed ingredients.

After analysing the ingredients, the next step would be to incorporate the crude nutrient values into the NE equations so that a prediction of the NE content can be made. Concurrently, it would be beneficial to also calculate the DE and ME contents for each ingredient. The calculated DE and ME content of each feed ingredient would then be used as a means of verifying the calculated NE values and, perhaps more importantly, to verify the DE and ME levels that have are currently being used for each ingredient in the formulation software.

Next, the newly-calculated NE values should be incorporated into the formulation software, and if not already present, add NE into each grow-finish diet matrix. Rather than jumping directly into NE at this point, it seems logical to continue for a period of time formulating diets on a DE or ME basis with NE in the matrix, so that the resulting NE diet values can be monitored. The intention of this step is simply to give a nutritionist time to get comfortable seeing these new NE energy levels in diets before formulating to NE.

Finally, once the nutritionist has become comfortable with the NE levels, then he/she should make the switch. Undoubtedly the NE levels of each diet will be smaller than what they were on a DE or ME basis but remember that one of the greatest advantages of NE is that it accounts for all of the energy lost due to metabolic processes, thus the energy provided via NE is as close to exactly what the animal will have for maintenance and growth. With that in mind, the suggestion is to formulate each diet to meet the NE level that each diet contained when it was formulated to meet either DE or ME levels. This will allow for a smoother transition over to using NE, and it should give the nutritionist confidence about the energy levels that they are supplying to the pig. Although energy requirement data for growing pigs is sparse – regardless of type of energy system used – formulating the diet as indicated above should provide adequate levels of NE for pigs. Even when formulating diets on a DE or ME basis, the intention was ultimately to provide enough retainable energy for the pig to perform optimally. Therefore, assuming that the preceding DE or ME diets were adequately achieving this goal, there is no doubt that the new diets using NE would continue to do so.

Take Home Message

The implementation of a NE system is a major step forward from the use of the DE and ME systems. Combined with formulating diets using SID AA and the ideal protein concept, a NE system will allow the nutritionist to formulate diets that provide the animal with the energy and amino acids that it needs for efficient and predictable growth and carcass performance. Additionally, by improving nutrient utilization and efficiency with the use of these systems, these systems promote better environmental stewardship for more sustainable pig production.

While NE may not be the final advancement to be made in energy evaluation systems (De Lange and Birkett, 2005), it is definitely a start in the right direction.

Literature Cited

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Further Reading

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