For the last decade, the majority of the genetic breeding programs have focused on increasing litter size, aiming to create a highly productive sow that would easily wean more than 27-28 piglets per year. This goal has been clearly achieved, but the increased feed costs and the growing health challenges meant that at the end, this model of genetic improvement is by and large economically inefficient since it does not ensure the financial soundness of a pig unit.
As feed costs remain high, pig producers are struggling to ensure that pigs demonstrate excellent linear growth throughout their rearing and finishing phases and that any parameter relevant to the reproductive performance will not fall behind according to the genetic potential of the stock. Given the current highly-charged environment of the global swine industry, genetic progress is vitally important and definitely a critical factor in ensuring pig farmers continue to remain sustainably profitable in the long run.
Dam line and finishers performance
Before going any further on how nutrition, and specifically energy, should be specified for growing-finishing pigs of modern genotypes (always aiming at maximizing final financial outcome), I would like to remind us the obvious: that is the fact that 50 percent of the genes in every fattening pig originate from the sow. This fact is frequently forgotten, as if all genes affecting growth performance and carcass characteristics of a finishing pig originated from the sire line alone. It is therefore very important that pig farmers select genetic suppliers that can provide very efficient dam lines capable of high growth and low FCR. However, this does not imply that genetic improvement traits such as mothering ability, litter size, piglet viability, robustness, etc., should not constitute major factors in the overall required genetic program. In truth, a balanced breeding program that, alongside the temporal genetic traits, considers financial important markers such as FCR is required, especially for those markets that still sell pigs on the hoof.
The total energy content of a complete diet is an overall determinant of pig performance and, consequently, is rightly considered by nutritionists the most important nutrient. Moreover, energy, which is the first limiting nutrient as far as growth is considered, is the most expensive component by its sheer volume alone. Thus, from a purely financial point of view, it is very important to determine with accuracy the energy needs of a growing-finishing pig.
Feed energy is used by the animal first for maintenance, then for protein synthesis, and finally for fat deposition.
For several years, it was common practice to reduce the energy content of the complete feed for finishing pigs in order to reduce backfat thickness and increase the carcass yield. This recommendation was developed from data and field trials collected with genotypes that were not very lean, were less capable eaters and with diets that may have been imbalanced in terms of amino acids to energy ratios. Pigs of modern genotypes, however, do not appear to become overfat with high-energy diets, especially when the amino acids are balanced to the energy level of the diet (percent or g SID Lysine per Mcal ME). In contrast, modern pigs experience a better feed-to-gain ratio with high-energy, well-balanced diets. In such balanced diets, if pigs eat to a fixed level of intake, then growth rate is increased. Alternatively, if pigs eat to a fixed energy level, then feed intake is reduced. In either case the feed efficiency index is improved.
Formulating diets using the net energy system
The most commonly used systems today are those based on digestible energy (DE) or metabolizable energy (ME). Nevertheless, during the last few years, and especially in Europe, the net energy system (NE) is gaining ground. One of the main reasons for this is the fact that now it is very well accepted and verified by both scientific evidence and field trials (the other one is the plethora of various byproducts nowadays available in Europe). And, as modern pig genotypes benefit from low crude protein diets (but balanced in amino acids), such diets are best formulated using crystalline amino acids and the net energy system. This is because modern pigs have the ability to consume large quantities of feed from the very early beginning of their lives.
The DE and ME systems compared to the NE system suffer, firstly because they underestimate the energy value of the starch-rich raw materials (e.g cereals), and secondly because they overestimate the energy content of protein-rich or fiber-rich raw materials (e.g soybean meal, wheat bran etc.). These inaccuracies are easily explained if one takes into account the losses due to the heat increment, which accompanies the metabolism of different raw materials, something that the NE system does with accuracy.
In this direction, and when it comes to practical feed formulation, the question that needs to be answered is: Why waste energy? Formulating diets on an NE basis is a "one way" decision for nutritionists if they are to target correctly the full expression of the genetic potential of the animal while factoring in the best possible financial result for the farmer. In practical terms, formulating diets using the net energy system decreases the reliance on high protein sources (leading to low protein but balanced amino acid diets) and normally reduces diet cost. However, the supply of the essential amino acids in the right quantities and ratios is still imperative, as they influence average daily gain, overall growth rate and therefore FCR.
In summary, one of the main advantages, when formulating on a net energy basis, is that the NE system avoids imbalances in the energy to protein-amino acids ratio when low protein diets are fed, thus ensuring optimum FCR, growth rate, and carcass quality. There are indeed plenty of data from field trials demonstrating that diets formulated (for modern pig genotypes) on an NE basis and the same digestible amino acids levels compared to ME or DE have significantly improved conversion rates, higher carcass weights, better carcass yields and, most importantly, lower costs.