Metabolisable energy maintenance

Table 12.1 Efficiency of metabolisable energy utilisation by ruminants for maintenance, pregnancy, growth and lactation...

In the UK metabolisable energy system for ruminants, animal requirements are expressed in terms of net energy (NE) and food energy values are expressed as metabolisable energy (ME). Animal ME requirements are calculated using efficiency factors (k) for different productive processes (e.g. maintenance, lactation or growth), which depend on the ME concentration of the diet (M/D). 

A hen weighing 2.0 kg has a fasting metabolism of about 0.36 MJ/kg per day, or 0.60 MJ/day, and utUises metabolisable energy for maintenance and production with a combined efficiency of about 0.8. Its requirement for metabolisable energy... 

Erom the calorimetric work of Forbes, Fries and Kellner, an efficiency of utilisation of metabolisable energy for milk production (kj) of about 0.70 is indicated. More recent estimates of k] have varied widely from 0.50 to 0.81, but the majority cluster around 0.60-0.65. There is considerable evidence that much of the variation is due to differences in the energy concentration of the diet. Van Es has suggested that the efficiency of utilisation of metabolisable energy for milk production is related to the metabolisability of the diet, defined as the ME (MJ/kg DM) at the maintenance level as a proportion of the gross energy (MJ/kg DM). His implied relationships for (a) Dutch and (b) American data are ... 

Efficiency of utilisation of dietary metabolisable energy for maintenance (k j) may be calculated as follows ... 

One of the major differences between AFRC (1993) and RM (2004) is the calculation of a combined metabolisable energy requirements for maintenance, lactation, liveweight loss and a proportion of activity (M , MJ/kg fitted using the... 

Values for the efficiency of utilisation of metabolisable energy for maintenance and for milk production are related to the energy concentration of the diet and are very similar. 

In addition to their energy losses in faeces, urine and methane, animals also lose energy as heat. Part of their heat loss arises from the work done by the animal in digesting and metabolising food (heat increment of feeding). The remainder, called the basal or fasting metabolism, arises from the work done by the animal associated with essential body processes (i.e. maintenance). 

When animals are kept at low environmental temperatures, their heat losses, and hence their energy requirements for maintenance, are increased. An animal s thermoneutral range is defined by its lower and higher critical temperatures and is affected by climatic conditions (sun, wind and rain), the insulating properties of the animal and its environment, and food intake. In young animals brown adipose tissue may be metabolised... 

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