Common Terms Used in Animal Feeding and Nutrition
Palatability: the appeal and acceptability of feedstuffs to the animal. Palatability is affected by the odor, texture, moisture, physical form and temperature of the feed. For a forage to be considered “high-quality,” it generally must be highly palatable because quality includes intake in the definition and palatability is required for high levels of intake (see dry matter intake).
Palatability is a plant trait that can be measured when the animal has the opportunity to selectively feed. However, when not given the opportunity to selectively feed the animal may perform just as well on the less palatable forage.
Particle Size: the diameter of granular feed materials (e.g., grains, pellets, mineral particles) and/or the length and sometimes width of roughage or forage fragments. Particle size can affect mixing of feed ingredients and digestion rate.
Parts Per Million (ppm): a unit of measurement used to state the concentration of specific nutrients, compounds, or elements present in small quantities in a feedstuff. (e.g., 1 ppm = milligrams per kilogram (mg/kg), 1 lb per million pounds, 1 milligram per liter (mg/L), or 1 microliter per litre (µL/L). Some more practical equivalence of 1 ppm are:
- 1 inch in 16 miles
- 1 second in 11 days and 16 hours
- 1 cent in $10,000
- 1 pinch of salt in 10 kg of potato chips
- 1 bad apple in 2000 barrels
pH: a measure of acidity or alkalinity. Values range from 0 (most acidic) to 14 (most alkaline or basic). A pH value of 7.0 is neutral (neither acidic nor alkaline). The values give the negative log of the hydrogen ion concentration.
Pectin: an intercellular (occurs in between cells) polysaccharide (carbohydrate) that functions as a cellular glue. Like the nonstructural carbohydrates, it is easily degraded in the rumen. Unlike the NSCs, though, it does not lower rumen pH (i.e., acidic condition in the rumen).
Protein: an essential nutrient in animal nutrition. Proteins are composed of long chains of amino acids (various kinds). Animals meet protein needs by breaking down plant and microbial protein (formed in the rumen) and reassembling them as animal proteins.
Proximate Analysis: a chemical method of quantitative analysis that separates, identifies, and quantifies the major categories of compounds in a mixture. In feed and food analysis, it serves as a tool of assessing and expressing the broad nutritional value of a feed sample. The proximate system for routine analysis of animal feedstuffs was devised in the mid-nineteenth century at the Weende Experiment Station in Germany (Henneberg and Stohmann, 1860, 1864) and is referred to as the Weende System of proximate analysis (or simply, the Weende analysis). It is important to remember that proximate analysis is not a nutrient analysis. It is a partitioning of both nutrients and non-nutrients into categories based on common chemical properties. The technique was developed to provide a top level, very broad, classification of food components. The system consists of the consecutive steps of analytical separations and determinations of six categories of components and expressing the percentage of each that is present in a feed sample (Figure 2):
- Water/moisture (or dry matter)
- Total or crude protein (total nitrogen×6.25)
- Total or crude Fat (or ether extract)
- Crude fiber (incompletely digested carbohydrates)
- Nitrogen-free extract (readily digestible carbohydrate)
Figure 2. A schematic that describes various components of feedstuffs usually partitioned in proximate analysis
This system was developed at a time when the chemistry of most feed and food constituents was only partially understood, and the growth of nutritional sciences was at its earliest stages. Some of the methods used historically in the proximate system of analysis are not recommended for feed analysis anymore (e.g., crude fiber). Nevertheless, the concepts formed the basis of modern feed analyses. Further, proximate analysis, including the original methodology, is still commonly used for food and feed regulations in many countries.