Agriculture Reference
In-Depth Information
Energy in feed
Heat
Digestible energy
Heat
Amino acids
Recovered energy
Protein, fat,
glycogen, lactose
Basal
metabolism
Monoscaccharides,
organic acids
Fatty acids,
glycerol
Urinary energy
(urea)
Urinary energy
(urea)
Fecal energy
Figure 6.1. Energy flow from feed to retained energy in proteins, fats, and fetal glycogen in the gestating sow,
or in milk components (lactose, proteins and fats) in the lactating sow. Digestible energy is the difference
between energy intake and fecal energy. Metabolizable energy is calculated as the difference between DE
and energy in urine. Net energy is represented as energy recovered minus heat associated with protein, fat,
glycogen and lactose deposition.
as substrates for protein, fat and lactose (lactating sows) synthesis or to provide energy
in support of a wide range of metabolic processes associated with body maintenance
functions or production. Amino acids that are not utilized for protein synthesis either
for maintenance or accretion are deaminated; the resulting amino-nitrogen is excreted
primarily in the form of urea, hence the energy lost in urine is attributed mainly to urea.
Metabolizable energy is the energy remaining after urinary energy and gaseous energy
are subtracted from DE. Because gaseous energy losses are very small in pig, they are
ignored from the calculation. So, depending on the feed ingredients provided to the sow,
ME may range between 92 and 98% of DE (NRC, 2012). For instance, the ME content
of lipids (fats and oils) is 98% that of DE (NRC, 2012). In contrast, the ME content of a
high-protein ingredient such as soybean meal is 91% of DE (NRC, 2012).
The difference between ME and NE is the heat associated with processes of feed digestion,
nutrient absorption and metabolism of the absorbed nutrients, collectively known as heat
increment of feeding or eating. Therefore, NE represents the recovered energy in protein,
fat, glycogen and lactose in accreted tissues and products during gestation and lactation
(Figure 6.1). The NE values for feed ingredients vary widely because of the variation in
starch, fiber, protein and fat composition. The heat increment associated with digestion
and absorption of fiber or protein is greater than that of starch and fats. Consequently,
