Goats provide food and fiber to many people of the world, as well as imparting other social and economic benefits. Nonetheless, there is much less known about nutrient requirements of goats than of cattle and sheep. Hence, there is need for more research of the nutrient needs of goats, along with increased employment of most appropriate sophisticated, state-of-the-art techniques of study. But, because goat research at many locations around the globe has been conducted in recent years, it is also desirable to compile these existing findings for use in developing accurate nutrient requirement expressions. To do so, a competitive grant (USDA Project Number 98-38814-6241) entitled "Nutrient Requirements of Goats: An Update and Reevaluation" was received in 1998 by the E (Kika) de la Garza American Institute for Goat Research from the United States Department of Agriculture 1890 Institution Capacity Building Grant Program. Results of this project are described in a Special Issue of the journal Small Ruminant Research (2004, Volume 53, Number 3) published by Elsevier Science. These calculation methods are based on this project and publication. In addition, these energy and protein requirement expressions are those recommended for goats by NRC (2007; Nutrient Requirements of Small Ruminants. National Academy Press. Washington, DC), as well as are the Ca and P requirement calculations.
There are different means of determining expressions of nutrient requirements of livestock. Ones described in the reports of this project and used in these calculators were thought logical given the information available. There was an intent to develop expressions that would be useful in the field. However, goats like other ruminants are not simple animals and, likewise, in some cases most accurate descriptions of requirements may be more complex than desired. It should also be mentioned that, when thought beneficial, there was an attempt to put forward frameworks for expressing some requirements based on limited data or with extrapolation from data with other ruminant species, in order to facilitate future enhancements for greater accuracy.
Approaches taken in the studies were empirical, with energy and protein requirements determined by regressing intake of metabolizable energy or protein, or a partitioned fraction, against production, such as body weight change, milk yield, and(or) clean fiber growth. Hence, particular requirement expressions may not necessarily have direct relevance to the physiology of maintenance or production (e.g., milk, meat,and fiber). Rather, the expressions, taken in the context of the assumptions employed, were found capable of describing responses to changes in nutrient or energy supply.
Body weight expressions are on an unshrunk or fed basis, because an appropriate method of adjusting to an empty body weight basis with the various experimental conditions was not available. As noted in some reports and based on conditions for most observations in the database, the nutrient requirement expressions are pertinent to animals on constant planes of nutrition near maintenance or above, in a thermoneutral and confinement (e.g., pen or stall) environment and without a significant parasite burden. However, a means of accounting for the activity energy costs of grazing was also proposed by Sahlu et al. (2004) and NRC (2007), and a calculation option for this method is available below.
Other factors not considered directly in this project that may influence nutrient requirements and feed intake include acclimatization, heat and cold stress, and previous nutritional plane. Sahlu et al. (2004) presented possible means of addressing impacts of such factors until further research is conducted. These methods for acclimatization and previous nutritional plane are available below. As described in the calculator site, previous nutritional plane is addressed based on body condition score and time after change from a low to high nutritional plane. Energy requirement calculators include these optional adjustment factors.
There are two calculators available to aid in diet formulation. One allows the determination of the appropriate amount of supplemental concentrate needed to meet metabolizable energy and protein requirements for a given basal forage, as well as identifying the concentration of ME in the supplement needed to exactly meet the requirements when MP was most limiting, and vice versa. Assumptions for concentrate substitution for forage or stimulation of forage intake are described in the calculator. The other is a fairly simple spreadsheet-like application for total mixed rations. Both are fitted with links to other sites to derive estimates of requirements and feed intake.
Although much editing and checking of these calculators has occurred, due to the large number of calculators and their interrelatedness, as well as to the considerable challenges in programming to develop a user-friendly format, there may still be undetected errors or other potential means of improvement.