The digestion, voluntary intake, and utilisation of energy by romney hoggets fed five winter forage crops

Abstract

Abstract The comparative nutritive value of five winter forage crops was studied over a 42-day period using Romney hoggets. The apparent digestibility coefficients for energy were swedes 90.8%, turnips 90.1%, chou moellier 83.0%, mangolds 86.4%, and fodder beet 87.7%. Digestible energy per unit of organic matter intake was less (P < 0.01) for chou moellier and fodder beet (4.15 – 4.20 Mcal/kg OM) than for the other crops (4.34 – 4.45 Mcal/kg OM). The digestibility coefficients and the molar proportions of volatile fatty acids (VFAs) in rumen fluid for all crops were similar to those normally found with high-energy concentrate rations. Chou moellier had the lowest digestibility and the highest molar proportions of ruminal acetate. Animals grazing swedes and turnips had higher voluntary intakes of digestible energy (DE) and live-weight gains than animals grazing chou moellier, mangolds, and fodder beet (P < 0.01). Differences in DE intake between crops were not related to teeth lost or to digestibility of energy, but were related to crop dry-matter content, which was less than 10% for swedes and turnips and greater than 12% for chou moellier, mangolds, and fodder beet. The utilisation of DE did not appear to be related to rumen VFA patterns, and it was concluded that there were unlikely to be differences between crops in the efficiency with which DE was used for maintenance or for live-weight gain above maintenance. Analyses of pooled data from all crops showed that 0.242 Meal DE/kg W0.73 was required for maintenance and 12.01 Meal DE for each kg of gain above maintenance. These figures are compared with published estimates of the energy requirements of sheep grazing other types of forage.