2.2. Biogas potential
In order to determine the biogas potential of these various farms, first the biogas production rate, in normal m3 of biogas per animal-day was determined. The values are based on the average size of the animals, which determines the daily manure production per animal, and the accessibility of the manure [27]. The animal sizes used are 636 kg/animal for dairy and 568 kg/animal for beef [27]. For dairy farms, an accessibility of 80% was used. For beef farms, an accessibility of 25% was used as in general beef cattle spend much more time grazing in fields where it is difficult to recover manure [27]. For this analysis, a value of 1.51 Nm3/animalday was used for dairy farms and 0.73 Nm3/animal-day was used
for beef farms. These values agree fairly well with other literature values for dairy cattle, although they may be conservative based on some actual operating data, as shown in Table 1.