Nutritional Consequences of Formulating pig Diets with Low Energy Values Using Fibrous Rich Byproducts

Albert van Dijk, Francesc Molist

The objective of this study is to provide insight in how to formulate pig diets in the most economical way in times of high feedstuff prices. Regarding this, energy level and the way of calculating energy in swine feeds will be taking into consideration, as well as the nutrients to energy ratios. Moreover, the effects of diet concentration on feed intake and growth performance of pigs will be evaluated. The lowest cost per energy value in swine feeds can be assessed by iterative simulations in least cost calculations using linear programming. In this case, a fixed nutrient to energy ratio has to be maintained for each cost per energy value that is calculated. Since feedstuff prices are subject to changes, these calculations have to be made on a regular basis. A dataset of 6 growth performance experiments in growing finishing (GF) pigs varying in energy values performed at Schothorst Feed Research (SFR) was analyzed. While decreasing the net energy value of the feed (at fixed nutrient to energy ratios), feed intake and energy conversion increased, while energy intake, daily gain and feed conversion ratio decreased. In general, pigs fed diets with reduced energy concentration are prone to maintain constant daily energy intake by eating more feed until feed intake is limited by other factors, such as physical gut capacity or certain dietary components (Li and Patience, 2017). In the same SFR analysis, the effect of the lysine (and other essential AA) to NE ratio was investigated. While decreasing this ratio, feed intake and energy intake were unaffected, while daily gain decreased, and the feed conversion ratio and energy conversion ratio increased. Another analysis of several GF experiments conducted at SFR was done to assess the optimal amino ccid (SID EAA) content of grower/finisher pig feeds in relation to technical performance, carcass characteristics and profitability. It was concluded that decreasing the SID AA/NE ratio to a certain extend will decrease technical performance (ADG and lean meat %) but increase economical results. However, it must be taken into account that optimal economic performance depends on market situation (feedstuff prices) and production goals (optimal ADG, carcass quality or costs/kg pork). In the current situation with high feedstuff prices, the inclusion of fibrous rich byproducts in the Dutch market may be more economical than corn and soybean meal. For an optimal estimation of the proportion of energy of those fibrous byproducts that will be attributed to the growth and maintenance energy requirements of the pigs, the net energy system is more appropriate than the metabolizable energy (ME) system, because the ME system overestimates the proportion of energy that will be used for growth and maintenance.