The nutritive ratio/crude-protein relationships in ruminant and non-ruminant digestion

Abstract

The nutritive ratio provides a direct link between the digestible protein and digestible non-protein components of a feed, and this relationship may be used to study various aspects of food digestibility, not only in ruminants but also in non-ruminants. It may be written as Nr= %Tdn-%dig.P % dig. PWhere Nr is the nutritive ratio and % Tdn and % dig. P are the respective percentages on a drymatter basis of total digestible nutrients and digestible crude protein.Since a ratio is invariant with respect to multiplication or division by a common factor it does not matter whether the values of dig. P and Tdn are expressed as percentages of dry matter, as in common usage, or if dig. P is expressed as a percentage of Tdn (i.e. dig. Pj). The latter form is perhaps simpler to use when considering the relationship between Nr and dig. P and the above expression (1) reduces to * , = _ ™ _ -l .(2)Thus, the nutritive ratio is a function of the digestible protein only, irrespective of the form in which the latter is expressed; it is entirely independent of the nature of the animal, whether ruminant or non-ruminant, and the relationship between Nr and dig. P will always be a curve of the above form.The nutritive ratio must also be related to the crude-protein content (c.p.) of a feed if the digestible protein is found to be related to the crude protein.Conversely, there must also be a relationship between the digestible and crude-protein contents if nutritive ratio is found to be related to crude-protein content. This paper deals with the form of these relationships as derived from the results of digestibility trials with pigs and horses as well as with cattle, sheep and goats. 15 RUMINANTS (CATTLE, SHEEP AND GOATS)It has earlier been shown for these ruminants, that there is a simple general relationship between the total crude protein of a single or compound feedingstuff and its apparent digestibility coefficient (Glover, Duthie & French, 1957). This also means that there is a relationship between the crude-protein content of a feed and the amount of digestible protein. Thus, if the original general relationship is real there should be an intimate relationship between the crudeprotein content of a feed and its nutritive ratio. This was tested by plotting the values for crude protein and nutritive ratio from the data published by Schneider (1947). Only those from direct digestibility trials were used and those determined 'by difference' were excluded. Further, the 392 records for cattle (Fig. 1 a) were plotted separately from the 902 records for sheep and goats (Fig. 16) in case there were marked differences between them. For convenience of reproduction the few records of nutritive ratio which exceeded 50:1 are excluded from the figures; thirteen were not included in Fig. l a and fifteen in Fig. 16. These records were, however, included in the calculation of the relevant curves.Both figures confirm that the relationship is substantially of the form of log Nr = a + b log c.p., and the relevant regressions are Cattle log Nr= 2-61 -...

The apparent digestibility of the non-nitrogenous components of ruminant feeds

“…= 2-049-M631ogc.p. (4) between 2 and 30% c.p., and, from earlier work (Glover & Duthie, 1958), log N.B. = 2-632-l-6451ogc.p.…”

“…(5) Equation (5) has earlier been given as 2-63-1-65 log c.p. for simplicity (Glover & Duthie, 1958); but here the nearest third place of decimals had been used for convenience. By eliminating log c.p.…”

Diet selection and plant nutritional quality in Attwater's pocket gopher (Geomys attwateri)

“…While the current study only analyzed nutrients in food plants, Rezsutek and Cameron (in press) computed a nutrient budget for G. attwateri that verified a low protein content in their diet (e.g., 3.5% in the winter breeding season and 1.3% in the summer non-breeding season). Because fiber decreases digestibility, decreases extraction of nutrients from food, and decreases assimilation of protein (Glover and Duthie 1958;Shah et al 1982;Hume et al 1993;Bozinovic 1995), it is likely that a low protein:fiber ratio in the diet limited reproduction during winter and contributed to the lack of reproduction during summer (Williams and Cameron 1990).…”

The apparent digestibility of the non-nitrogenous fraction of pig feeds

“…and the c.p. content of their pig feeds has already been calculated (Glover & Duthie, 1958). It is log N.B.…”

“…have been derived from the earlier published equations relating these to the C.P. level of the feed (Glover & Duthie, 1958;Glover & Dougall, 1961).…”