problem involve the injection and subsequent 
dilution of water-soluble markers (Black et al. 
1964; Budtz-Olsen et al. 1961; Hydén 1961; 
Macfarlane et al. 1966; Till and Downes 1962; 
Ulyatt 1964a; and others). We also need to 
consider physical and electrical phenomena 
such as beta particle attenuation and electrical 
capacitance for detecting body water contents. 
DRINKING-WATER TRACERS 
Suitable drinking-water tracers can supple- 
ment or replace dry-matter tracers for the esti- 
mation of fecal output, forage intake, and di- 
gestibility. Beyond these functional applica- 
tions, water tracers can be used to obtain more 
fundamental information concerning water 
turnover and partitioning by animals in graz- 
ing environments. Three water tracers are 
needed to determine water turnover and parti- 
tioning by nonlactating animals. One tracer 
should move throughout the animal system and 
should be excreted in all water vapor and liq- 
uid phases. The other two tracers should equi- 
librate and be excreted separately in urine and 
feces to permit the calculation of the individ- 
ual water components. When the respective 
volumes of water are known, then dry matter, 
nutrient, and mineral concentrations therein 
can be expanded to total quantities. 
Deuterium oxide, lithium chloride, and ery- 
throsine have been tested at the Central Plains 
Experimental Range as potentially valuable 
drinking-water tracers equivalent to markers 
A, B, and C of figure 1, respectively (Hyder et 
al. 1968b). Since the results of this research 
are included in a manuscript that is in review 
for publication, they cannot be given here. 
However, it is appropriate to say that we expe- 
rienced more problems than success. The ery- 
throsine disappeared completely, and the deter- 
minations for deuterium led to some ridiculous 
estimates. Lithium, on the other hand, was re- 
covered almost entirely in the urine (95 to 99 
percent) (see also Ulyatt 1964b). Since the 
amount of water drunk was metered to the 
steers, the change in lithium concentration 
from drinking water to urine provided an esti- 
mate of the amount of water excreted in urine. 
Other appropriate water tracers should be 
investigated. Analytical and sampling prob- 
lems should be solved, because drinking-water 
tracers surely can provide new methods of de- 
termining animal-forage relations on a herd or 
lot basis without imposing severe restrictions 
on land, animals, or grazing practices. 
SCHEME OF WATER TURNOVER AND PARTITIONING WITH 
THEORETICAL PATHWAYS FOR WATER TRACERS A, B, AND C 
DRINKING 
WATER 
+A+B+C 
WATER IN 
FORAGE 
METABOLIC 
WATER 
RESPIRATORY 
AND 
CUTANEOUS 
WATER 
+A 
| URINARY WATER | 
+A+B 
FECAL WATER 
+A+C 
Figure 1. 
125 
