Metabolizable Energy (ME) Requirement For Growing Goats

To estimate the dietary ME concentration, often feed tags list the Total Digestible Nutrient (TDN) concentration. Likewise, most commercial feed laboratories estimate the TDN concentration based on various analyses, such as for crude protein and fiber fractions.

Our example would require a total of 9.26 MJ (5.80 MJ for maintenance plus 3.46 MJ for gain). The total ME requirement for a 30-kg dairy goat wether gaining 150 g/day is slightly greater (10.34 MJ = 6.88 MJ for maintenance plus 3.46 MJ for gain). The total ME requirement for a 30-kg indigenous or local wether goat gaining 150 g/day is slightly less (8.77 MJ = 5.80 MJ for maintenance and 2.97 MJ for gain).

In the study to determine the ME requirements of growing goats (Luo et al., 2004), from weaning up to 1.5 years of age, biotype of the goat had significant effects. The biotype categories used were meat (50% or more Boer), dairy (selected for milk production, such as Alpine and Saanen), and indigenous or local. The ME requirement for maintenance was 489 kJ/kg body weight^0.75 for meat and indigenous goats and 580 kJ/kg body weight^0.75 for dairy goats. The ME requirement for gain was 23.1 kJ/g average daily gain for meat goats and dairy goats and 19.8 kJ/g average daily gain for indigenous goats. Angora requirements are addressed separately in another calculator. Because of the manner in which data were reported in the studies used, it was not possible to directly assess possible differences among genders. Hence, based on NRC (2000), it was assumed that the maintenance ME requirement for females and male castrates was 92.5% of the estimated value, and that for intact males was 107.5%. Dry matter intakes, unadjusted and adjusted for influences of dietary ME concentration on efficiencies of ME utilization, necessary to meet the ME requirement are calculated. 

The determined maintenance ME requirements include an activity energy cost typical of confinement rearing systems for growing goats.  However, by use of the Grazing Factor Calculator, the maintenance ME requirement can be adjusted for a predicted grazing activity energy cost. A default of 1 is included for housing in a pen or stall setting. In addition, there are similar adjustments for previous nutritional plane and acclimatization. These are optional adjustment factors, with default values of 1 or 0  that result in no adjustment.

As is performed in the boxes above, to calculate the amount of dietary dry matter (DM) to provide these amounts of ME, the total ME requirement is first divided by the dietary ME concentration. As an example, for the 30-kg meat goat wether gaining 150 g/day and a dietary ME concentration of 10.0 MJ/kg DM (2.39 Mcal/kg DM), this is 9.26 MJ / 10.0 MJ/kg = 0.926 kg DM. A second step is to account for differences among diets in efficiencies with which ruminants utilize dietary ME. This is handled by estimating a correction factor, for which knowledge of the dietary ME concentration and ME requirements are needed.

For a diet with 10.0 MJ/kg of ME, no adjustment for dietary ME concentration is necessary. This is because 10.0 MJ/kg DM was the average ME concentration for the database used to derive the requirements. But with diets having a lower ME concentration, the amount of DM needed to be consumed to meet the maintenance need and to support the particular rate of gain, the amount of dietary DM would need to be adjusted upwards. A downward adjustment is needed for diets with ME concentrations greater than 10.0 MJ/kg DM. Also, the size of the correction factor is affected by the level of intake relative to the maintenance energy requirement. For our 30-kg meat goat wether, the ratio of the total ME requirement relative to the maintenance need is 1.60 (9.26 MJ total ME requirement / 5.80 MJ for maintenance). For a diet with 9 MJ/kg of ME, the intake correction factor is 1.0441, and for a diet with a ME concentration of 11 MJ/kg the correction factor is 0.9489. Therefore, adjusted DM intake requirements are 1.074 kg for the 9.0 MJ/kg diet (9.26 MJ of ME required / 9 MJ/kg × 1.0441) and 0.800 kg for the 11.0 MJ/kg diet (9.26 MJ of ME required / 11 MJ/kg × 0.9489).

This calculator is also fitted to estimate the ME requirement with body weight loss, assuming tissue energy concentration of MJ/kg = 4.972 + (0.3274 x body weight, kg) and efficiency of tissue energy use for maintenance of 0.503 + (0.019 x dietary ME, MJ/kg DM)(AFRC, 1998). However, most observations in the database used to determine the ME requirements entailed positive body weight change. Therefore, caution should be exercised when using this calculator to determine requirements with body weight loss.

To determine if consumption of a calculated amount of a specific diet necessary to meet the ME requirement is possible, the Feed Intake Calculator can be used. Caution should also be exercised when using a Feed Intake Calculator when body weight change is negative.