The use of chromium oxide and faecal nitrogen concentration to estimate the pasture intake of Merino wethers

Abstract

Statistical analysis of the results of digestion trials on a wide range of fresh pasture herbages shows that their digestibility might be estimated as the intake factor or feed faeces ratio (Y) from the equation: YO.M. = (2.04 – 0.24XN ± 0.186X2N) ± 0.53 where YO.M. is the intake factor for organic matter, and XN is the percentage of nitrogen in faecal organic matter. The results were subdivided arbitrarily into "summer" (September–April) and "winter" (May–August) periods, and these proved to yield significantly different linear equations. The summer regression yielded higher intake factors (corresponding to 2–3% higher digestibility) for a given value of faecal nitrogen percentage. This subdivision reduced the standard deviation from regression only slightly, to about 0.50, which amounts to ± 17% for pasture of 75% digestibility. These equations give considerably lower values of digestibility for a given nitrogen concentration than regressions hitherto published. The present pooled equation, based on short leafy herbage, probably gives sounder estimates for grazing sheep than do the existing equations derived from trials with more mature herbages. When sheep with a wide range in body weight were all fed a maintenance ration, it was found that feed digestibility was not detectably reduced at high levels of feeding. The undoubtedly higher feed intake of grazing than of pen-fed animals, due in large measure to their higher maintenance requirements, therefore may not cause the reduction in digestive efficiency, and thus the bias in estimates of feed intake, that has been supposed. On the basis of the pooled regression, which is felt to be preferable to a subjectively selected "seasonal" equation, estimates of the intake of digestible organic matter (D.O.M.) by sheep in metabolism pens fed on fresh pasture herbage averaged 97 ± 22% of the true figures, or ± 80 g D.O.M.

Climatic adaptation in recently shorn merino sheep

“…Lambourne and Reardon's (1963) technique of feed intake estimation which was used by the last two research groups could not show up any initial depression of intake as faecal samples were bulked over 5 days. The only data from sheep at pasture suggest that during the first week after shearing there is either no increase in intake (Wheeler, Readon and Lambourne, 1963) or an increase of up to 30% (Hutchinson and McRae, 1969).…”

Does body mass convey a digestive advantage for large herbivores?

“…However, measuring digestibility directly (which is traditionally carried out in digestion studies that require some manipulation or even confinement of animals to quantify food intake and faecal elimination) cannot be considered a viable option in free-ranging conditions; therefore, any such evaluation basically depends on the availability of an appropriate proxy that can quantify, or at least rank, digestibility under free-range conditions. The most common method in this respect is (total) faecal nitrogen (TFN), which was established first by Lancaster 1949, but has been used routinely since, mostly in ruminants (Lambourne & Reardon 1963;Wallace & Van Dyne 1970;Hofmann & Musangi 1973;Boval et al 2003;Lukas et al 2005;Wang et al 2009), but also in equids (M esochina et al 1998). Although regularly misinterpreted as a measure for the protein content or protein digestibility of the diet, it should be basically regarded as a proxy for organic matter (OM) digestibility.…”

The indirect estimation of the digestibility in cattle of herbage from Belgian permanent pasture

“…= 2-09), so in agreement with many other authors, it is considered to be better to use local than general regressions. We have no information on the influence of leaf to stem ratio on the relationships, but Greenhaigh et al (1966) showed that there was no consistent difference between regressions derived from the upper and lower fractions of the herbage, although this disagrees with the findings of Lambourne and Reardon (1963).…”