Abstract |
- This study involved the use of the two-choice preference test,
where the choices were tap water and tap water-chemical solutions,
to determine the responses of sheep to ascending concentrations of
20 chemicals (taste stimulants). The chemicals tested were: the
sugars, sucrose, maltose, lactose, glucose, fructose and galactose;
the sodium salts of chloride, acetate (NaAc), propionate (NaPr) and
butyrate (NaBu); the acids, hydrochloric, acetic (HAc), propionic
(HPr), butyric (HBu) and lactic (HLa); and, quinine hydrochloride
(QHC1), urea, sodium saccharin, sodium hydroxide and ethanol.
Each sheep was individually penned and fed to appetite. Responses
were expressed on the basis of percent intake (that is, the
percent that the amount of test fluid consumed was of total fluid intake
for a given time period). Three groups of ten sheep. each
were used successively, the groups being divided into two units of
five animals and these units then being placed on alternate concentrations
of a test chemical. The mean responses of the units of five sheep were plotted
graphically and analyzed by the linear regression technique when
definite rejection trends were apparent. The chemical concentrations
at the acceptance and rejection thresholds (that is, where the
test chemical comprised 40% and 20% of total fluid intake, respectively)
were estimated from the regression line. When rejection
trends did not occur the responses were assessed on the basis of
their position relative to the non-discrimination zone. The nondiscrimination
zone was described as that zone where the test fluid
comprised not less than 40% nor more than 60% of total fluid intake.
It was derived by determining the normal variation, with tap water
in both containers, around a theoretical mean intake of 50% from
each container.
The responses to the sugars were, generally, of an indifferent
nature. One unit of animals displayed a. moderately strong preference
(79. 2% of intake) for sucrose at the . 1461 M concentration while
another unit was indifferent to the sugar at that concentration. A
weak preference (69.0% of intake) occurred for glucose at the . 2775 M
concentration. These were the only positive preferences observed
for any of the test chemicals. Moderate degrees of rejection were
manifested for sucrose concentrations above . 4382.M and for maltose
concentrations above. 0028 M. The pattern of the responses to sodium
saccharin was similar to that of the sugars: indifference at lower
and intermediate concentrations and moderate degrees of rejection
at higher concentrations.
The acceptance and rejection thresholds for NaC1 were at concentrations
of . 0429 M and . 3764 M, respectively. The thresholds
for NaAc were similar to those for NaC1. NaPr and NaBu had lower
threshold concentrations than NaCl and NaAc-.-possibly because of
smell.
The threshold concentrations and pH's obtained for HAc were:
acceptance, . 0024 M, pH of 4. 2; rejection, . 0276 M, pH of 3. 4. The
thresholds for HC1 were at lower concentrations and lower pH's than
for HAc. HPr and HBu were discriminated against at lower concentrations
and higher pH's than was HAc--possibly due 'to smell. The
concentrations at the acceptance and rejection thresholds of NaOH
were, respectively, .0036 M ('pH 11. 5) and .0132 M (pH 12. 0). A
comparison of these values with those for HC1 indicates that sheep
are more tolerant of highly alkaline pH's than of highly acid pH's.
QHC1 elicited acceptance and rejection threshold concentrations
of. 00048 M and . 0037 M, respectively. The responses to
urea were highly variable, but appreciable intake was observed at
concentrations of .4163 and 8325 M,
The thresholds for ethyl alcohol were at higher concentrations
than for any other of the test chemicals, sucrose and glucose being the
exceptions. The acceptance threshold for ethanol was at a
concentration of. 2621 M and the rejection threshold was at 1. 422 M.
With respect to glucose, NaC1, HAc and QHC1, the sensitivity
series for the four primary taste groups, in order of increasing
sensitivity, was: sweet, salty, sour and bitter. However, after
comparing the threshold values derived in this study for the sheep
to values reported for the goat and calf, the conclusions can be made
that the sheep is relatively indifferent to sweet tasting substances
and relatively tolerant to bitter tasting substances.
Considerable individual variation existed in the taste responses
exhibited by the sheep used in this study.
|