Taste responses in sheep Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/70795b65z

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  • 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.
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