Methodologies for energy evaluation of pig and poultry feeds: A review

Abstract

The cost of feed represents an important part of the total cost in swine and poultry production (>60%) with energy accounting for at least 70% of feed cost. The energy value of ingredients or compound feeds can be estimated as digestible (DE), metabolisable (ME) and net energy (NE) in pigs and ME and NE in poultry. The current paper reviews the different methods for evaluating DE, ME and NE of feeds for monogastric animals and their difficulties and limits, with a focus on NE. In pigs and poultry, energy digestibility depends on the chemical characteristics of the feed, but also on technology (pelleting, for instance) and animal factors such as their health and body weight. The ME value includes the energy losses in urine that are directly dependent on the proportion of dietary N excreted in urine resulting in the concept of ME adjusted for a zero N balance (MEn) in poultry. For poultry, the concept of true ME (TME, TMEn), which excludes the endogenous fecal and urinary energy losses from the excreta energy, was also developed. The measurement of dietary NE is more complex, and NE values of a given feed depend on the animal and environmental factors and also measurement and calculation methods. The combination of NE values of diets obtained under standardised conditions allows calculating NE prediction equations that are applicable to both ingredients and compound feeds. The abundance of energy concepts, especially for poultry, and the numerous feed and animal factors of variation related to energy digestibility or ME utilisation for NE suggest that attention must be paid to the experimental conditions for evaluating DE, ME or NE content. This also suggests the necessity of standardisations, one of them being, as implemented in pigs, an adjustment of ME values in poultry for an N retention representative of modern production conditions (MEs). In conclusion, this review illustrates that, in addition to numerous technical difficulties for evaluating energy in pigs and poultry, the absolute energy values depend on feed and animal factors, the environment, and the methods and concepts. Finally, as implemented in pigs, the use of NE values should be the objective of a more reliable energy system for poultry feeds.

Keywords: Energy value; Feed; Methodology; Pig; Poultry.

Fig. 1

Components of heat production in a growing pig (60 kg) offered 2.4 MJ ME/kg BW^0.60 per day in 4 meals at 09:00, 13:00, 17:00, and 21:00. TEF = thermic effect of feeding; from Noblet and van Milgen (2013).

Fig. 2

Relationship between measured NE of 26 pig diets (Institute for Livestock Feeding and Nutrition Research, personal communication; FHP = 750 kJ/kg BW^0.60) and their NE value calculated according to Eqs. (Eq. 2), (Eq. 4)) (mean of both) of Noblet et al. (1994a); trial 1 (n = 10 diets) and trial 2 (n = 16 diets) correspond to values of 2 successive series of measurements; the measured and calculated values are almost identical for trial 1 (10.20 and 10.14 MJ/kg DM) but markedly different (9.93 and 10.76 MJ/kg DM) for trial 2; trial 3 data correspond to values of trial 2 when HP is equal to 0.905 measured HP (see text for explanations). NE = net energy; FHP = fasting heat production; HP = heat production.

Fig. 3

Schematic representation of the effect of feeding level (FLi) on heat production and fasting heat production (FHP) in nonruminant animals. Each FHPi corresponds to the FHP measured on animals receiving the FLi during the immediately preceding period. The FHPr (r for regression) is obtained from the regression between hear production (HP) and metabolisable energy (ME). The slope is the “regression” heat increment (HIr), and the slope between each FHPi and HPi corresponds to the measured heat increment (HIi) (from Noblet and van Milgen, 2013).

Fig. 4

Relationship between measured NE of 29 broilers diets (Carré et al., 2014; mean = 10.79 MJ/kg DM; FHP = 500 kJ/kg BW^0.60) and NE values calculated according to Wu et al. (2019) (mean = 10.66 MJ/kg DM; FHP = 450 kJ/kg BW^0.70); the correlation coefficient between the 2 sets of values is 0.95. NE = net energy; FHP = fasting heat production.

Fig. 5

Relationship between measured NE of 41 pig diets at INRA facilities (de Lange et al., 2006a; Le Bellego et al., 2001; Le Goff et al., 2002; Noblet et al., 2001; van Milgen et al., 2001; unpublished data; mean = 11.95 MJ/kg DM; FHP = 750 kJ/kg BW^0.60) and their NE values calculated according to Eqs. (Eq. 2), (Eq. 4)) (mean of both) of Noblet et al. (1994a); the correlation coefficient between both sets of values is 0.96. NE = net energy; FHP = fasting heat production.

Fig. 6

Relationship between measured NE of 46 diets at China Agricultural University in Beijing (mean: 11.75 MJ/kg DM; Li et al., 2018a) and NE as calculated from NE Eqs. (Eq. 2), (Eq. 4)) (mean of both) of Noblet et al. (1994a) (mean: 11.61 MJ/kg DM); the measured NE were adjusted for a common value of FHP equal to 750 kJ/kg BW^0.60 as in the data of Noblet et al. (1994a). The correlation coefficient between both sets of values is 0.91. NE = net energy.