Metabolisable energy utilisation

Wilkinson (1984) presents information showing that the amount of metabolisable energy utilised on dairy farms can vary by more than a factor of four. He suggests that high levels of efficiency can be achieved by ... 

Fig. 11.5 Efficiency of metabolisable energy utilisation (an example based on metabolisable energy utilisation by a growing ruminant).

Table 11.6 Typical values for the efficiency of metabolisable energy utilisation for growth in pigs...

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

BOX 11.6 Efficiency factors (k) used to describe the efficiency of metabolisable energy (ME) utilisation... 

Table 11.7 Efficiency of utilisation of metabolisable energy from various nutrients and foods for growth and fattening in ruminants...

Other factors affecting the utilisation of metabolisable energy... 

The effects of the relative proportions of nutrients in a diet have been partly covered above. However, a fattening animal will tend to use metabolisable energy more efficiently if it is provided as carbohydrate rather than protein. Similarly, if a growing animal is provided with insufficient protein, or with insufficient amoimts of a particular amino acid, then protein synthesis will be reduced and it wUl tend to store energy as fat rather than protein. In this situation, the efficiency of ME utilisation will probably be altered. 

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 ... 

The efficiency of utilisation of metabolisable energy is influenced by the level of protein in the diet. When protein content is inadequate, body tissues are catabolised to make good the deficiency, a process that is wasteful of energy. AVhen protein content is too high, excess amino acids are used as a source of energy. Since protein is used relatively inefficiently for this purpose, the overall efficiency of utilisation of metabolisable energy is reduced. 

There is some evidence (Fig. 16.4) that the efficiency of utilisation of metabolisable energy for milk production is influenced by the proportion of acetate in the fatty acids produced during rumen fermentation. 

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

In calculating the energy requirements of the dairy cow, cognisance must be taken of the decline in the efficiency of utilisation of metabolisable energy with increasing level of energy intake. In order to do this, the calculated requirement has to be increased accordingly. The procedure, which involves the use of a correction factor, is best illustrated by an example, as shown in Box 16.2. 

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. 

The energy yield from grass and forage - the Utilised Metabolisable Energy (UME) calculation... 

Cohen, D.C., C.R. Stockdale and RT. Doyle, 2006. Feeding an energy supplement with white elover silage improves rumen fermentation, metabolisable protein utilisation, and milk production in dairy cows. AusL J. Agric. Sci. 57, 367-375. 

Other metabolic effects. In addition to enabling glucose to pass across cell membranes, the transit of amino acids and potassium into the cell is enhanced. Insulin regulates carbohydrate utilisation and energy production. It enhances protein synthesis. It inhibits breakdown of fats (lipolysis). An insulin-deficient diabehc (Type 1) becomes dehydrated due to osmotic diuresis, and is ketotic because fats break down faster than the ketoacid metabolites can be metabolised. 

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