Livestock Feed Calculator

Dry matter intake (DMI) is the amount of feed consumed per day on a moisture-free basis, expressed in kg. It is the most important measure in livestock nutrition because it determines the total quantity of nutrients an animal can ingest. This calculator estimates DMI as a percentage of body weight: cattle 2.5%, sheep 3.0%, goats 3.5%, horses 2.0%. These base rates are then multiplied by an activity factor (1.0 for maintenance up to 1.4 for lactating animals).

Goats have higher relative DMI (3.5% BW) compared to cattle (2.5% BW) because smaller animals have a higher metabolic rate per unit of body weight. This is the metabolic scaling effect: metabolic rate scales approximately as BW^0.75, not linearly with weight. Goats also tend to be more selective browsers and have faster feed passage rates than cattle, which supports higher relative intake. Sheep fall between at 3.0% BW.

Total digestible nutrients (TDN) is a traditional measure of the energy value of a feed, representing the sum of digestible protein, fiber, carbohydrates, and fat (fat × 2.25). TDN in percent indicates what fraction of the dry matter is energetically available to the animal. This calculator estimates TDN requirement per day by multiplying DMI by species-specific TDN percentage (55–60%) adjusted by an energy activity multiplier. For precise ration balancing, metabolizable energy (ME) or net energy (NE) systems are more accurate.

Water requirement is estimated as a multiple of daily dry matter intake. Horses have the highest water need at 5.0× DMI due to sweating during work and their relatively inefficient kidney function. Cattle need about 4.0× DMI, goats 3.5× DMI, and sheep 3.0× DMI. Actual water consumption increases significantly in hot weather, during lactation, and when feeding dry forages. These estimates represent baseline requirements under moderate conditions.

Net energy for maintenance (NEm) is the amount of energy required to keep an animal at its current body weight with no production or work — it covers basic metabolic functions such as respiration, body temperature regulation, and organ function. This calculator uses the standard formula NEm = 0.077 × BW^0.75 Mcal/day, where BW is body weight in kg and the exponent 0.75 represents the metabolic body size scaling factor. For a 500 kg cow, NEm ≈ 0.077 × 500^0.75 ≈ 8.6 Mcal/day.

This calculator computes requirements for one group of animals at a single representative body weight. For a mixed herd with different animal sizes or ages, calculate separately for each weight class and sum the results. For example, if you have 10 mature cows at 550 kg and 5 yearlings at 300 kg, run the calculator once for each weight class and add the herd totals together for a complete feed budget.

The lactating activity level applies the highest multipliers: DMI ×1.4, protein ×1.5, and energy ×1.6. This reflects the very high nutritional demands of milk production. A lactating dairy cow or nursing ewe must consume significantly more energy and protein than a dry animal of the same weight to support both her own maintenance and milk synthesis. Energy and protein deficits during early lactation lead to body condition loss and reduced reproductive performance.

This calculator provides estimates for planning and budgeting purposes, not for precise ration formulation. Actual requirements vary with breed genetics, specific stage of production, ambient temperature (cold weather increases energy needs), forage quality and digestibility, and individual animal variation. For precise ration balancing, use NRC (National Research Council) nutrient requirement tables specific to the species and production stage, and work with a certified animal nutritionist.