Energy values in pig nutrition:I. The relationship between digestible energy, metabolizable energy and total digestible nutrient values of a range of feedstuffs

SUMMARY Nineteen feedstuffs were evaluated for total digestible nutrients (TDN), digestible energy (DE) and metabolizable energy (ME) using growing pigs. DE values, on a drymatter basis, ranged from 1570 kcal/kg D.M. (grassmeal) to 4890 kcal/kg D.M. (BP Grangemouth protein). ME averaged 97·4% of DE for cereal feeds and 81·9% of DE for protein feeds, the ratio of DE to ME being significantly affected by the crudeprotein content of the feedstuff: ME/DE × 100 = 99·7–0·18 × crude protein (%): r = –0·94; P < 0·01. TDN was more closely related to ME than DE: DE (kcal/kg D.M.) = 45 TDN + 156: r = 0·92; P < 0·01, ME (kcal/kg D.M.) = 43 TDN + 71: r = 0·98; P < 0·01. ME values were corrected to both 30% and 0% nitrogen retention. Correction to 30% retention caused a maximum change of 3% in ME value while correction to 0% retention had a variable effect related to protein content of the feedstuff: (ME( N 0 )/ME) × 100 = 98·3–0·113 × crude protein (%): r = –0·80; P < 0·01.