Written by Rachel Frost and Jeff Mosley, Montana State University
The nutrient requirements of domestic livestock have been provided in detail by various National Research Council (NRC) publications. However, these NRC requirements have been developed on pen-fed livestock where maintenance requirements are easily calculated and tend to vary only slightly within a given weight, sex, age, and physiological state.
- Physiological stage
- The greatest influence on nutritional requirements of livestock is their life stage in production. The key physiological stages in the life of grazing animals are growth (i.e., young animals), late pregnancy, lactation, and maintenance, generally during non-lactating periods. In general, the highest nutritional requirements are for lactation, followed by late gestation, growth, and finally maintenance. Managing livestock production schedules to match nutritional demands with forage quality and availability can greatly improve the efficiency of a production system.
- Topography and Climate
- The nutrient requirements of grazing animals are also dependent on environmental and climatic variables. Grazing and voluntary travel also require substantial increases in energy expenditure. Range animals walk long distances, climb gradients, and ingest herbage often of low dry matter content, thus spending more time eating and foraging for food. Research estimates that cows grazing rangeland use 30% more energy than confined cows because of longer grazing time and longer travel distance.
- Climate, particularly temperature, also affects the amount of feed an animal needs to maintain its body functions. As ambient temperature drops, an animal’s metabolic rate increases, and more energy is needed to maintain internal heat. This effect can be exacerbated by wind or wet hide/hair on the animals.