EFFECT OF MOLASSES, ANISEED AND OTHER ADDITIVES ON THE ACCEPTABILITY OF SALT LICKS TO SHEEP
R.L. ROCKS*, J.L. WHEELER* and D.A. HEDGES*
SUMMARY
The acceptability to grazing sheep of mixtures of salt with bentonite, dried and liquid molasses, powdered aniseed, and the methyl ester of methionine hydroxy analogue (MeMHA) was determined by two-choice preference tests. Bentonite and MeMHA reduced (P c-02) the acceptability of the mixture to wethers but commercial dried molasses had no effect. Acceptance of liquid molasses/salt mixtures was increased with addition of 4or8% molasses but not with lor2%. Aniseed mixtures were initially unacceptable but were not so after four weeks.
INTRODUCTION
Salt licks are often used commercially as a means of administering minerals and other supplements to grazing animals. Licks are convenient and relatively inexpensive but as a means of administering a supplement they have the disadvant- age that frequently a proportion of animals in a flock or herd make little or no use of a salt lick and hence intake of the supplement varies greatly between animals. Certain substances may be added to the licks by manufacturers to in- crease acceptability but there are no published data on their effect on intake.
Moreover, some compounds that could be included in loose or compacted salt licks may reduce their acceptance by stock. We report a series of tests of the effect of five possible additives on the acceptance of salt licks by Merino wethers.
The relative acceptability of the salt mixtures was determined by a modification of the two-choice preference test for liquids described by Goatcher and Church
(1970).
MATERIALS AND METHODS
Merino wethers aged two years and with prior experience of salt licks were allocated at random to form eight groups of eight sheep with an initial mean weight of 37 kg. Each group grazed an 0.8 ha pasture, consisting primarily of perennial ryegrass with some white clover, at the CSIRO, Pastoral Research Lab- oratory, Armidale,N.S.W. Four shelters, eachcalxlx3m, were erected to pro- tect the salt mixtures from rain. They were open on one side and were located across the common fence of pairs of plots.
Each group was offered salt in two plastic tubs placed 15 cm apart on a stand 20 cm above ground. One, the control, contained initially 2.0 kg of loose salt dried at 100°C, the other, 2.0 kg loose salt mixed with a known proportion of additive. After seven days the salt in both containers was removed, dried and weighed. The relative acceptability of the test mixture was expressed as the percentage of the total intake that had been drawn from the test mixture i.e.
consumption of test mixture/(consumption of test mixture + consumption of control) x 100. A value of 50% indicates no discrimination but 20% or less in a test of this type was taken by Bell (1959) to indicate rejection. During the week the positions of the two containers were exchanged to overcome any possibility of bias due to position within the shelter.
A test of each additive was conducted in separate experiments as a latin -
* -CSIRO, Division of Animal Production, Armidale, N.S.W. 2350.
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Animal Production in Australia
square using four flocks (columns) and four levels of additive (treatments) over four 7-day periods (rows) with two replications. The following compounds were tested in succession at levels shown in parentheses <w/w>:
1. sodium bentonite, a montmorillonite clay, containing 9% water (0.5, 1.0, 2.0 and 4%);
2. commercial dried molasses ("Molasso powder") containing Pollard, ground charcoal, limestone.and approximately 40% liquid molasses;
3. powdered aniseed (PimpineZZa aniswn) containing 17% water (0.012, 0.025, 0.05 and 0.1%);
4. liquid molasses, commercial feeding grade, containing approximately 20%
water (1.0, 2.0, 4.0 and 8.0%); and
5. methyl ester of methionine hydroxy analogue (MeMHA; Wheeler et al. 1979) (0, 1.0, 10.0 and 15.0%).
Bentonite has been used by some manufacturers to increase the hardness of compressed salt blocks, and dried molasses and aniseed are frequently included in proprietary mineral mixtures in the expectation that they will increase the vol- untary intake. MeMHA is a form of S-amino acid supplement that in some circum- stances increases wool growth when administered orally (Wheeler et al. 1979).
Before these additives were tested, each flock was offered plain salt in both containers to determine whether there was any preference shown by sheep for the right or left hand container in the shelters. This uniformity test and the tests of the five additives were conducted over six successive months from 28 June 1979 to 11 December 1979.
RESULTS
Rainfall throughout the experimental period averaged 62 mm per month and was below average. The quantity of pasture available was ample and when analysed in June 1979 contained 0.33 + 0.02% sodium (dry matter basis).-
In the initial (uniformity) period with plain salt there was no consistent preference by sheep for the left or right container of a pair. The proportion of total intake taken in this period from the container allocated for the test mix- ture in subsequent months was 51% and the standard error of this mean was 1.5%.
The mean intake of salt from the reference tubs containing plain salt, and from the tubs with varying levels of additives, declined over the period in which these experiments were conducted (Table 1).
Separate analyses of variance of the relative acceptability were made for each latin square. There were no significant effects between weeks, groups of . sheep or level of additive inthe case of bentonite, molasses powder or MeMHA.
Mean values are given in Table 2. Addition of 1 or 2% liquid molasses slightly depressed the acceptance of the salt mixture but 4 or 8% enhanced it (P < 0.01).
TABLE 1 Intake of ,salt offered alone or with various additives (g/sheep/d)?
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Animal production in Australia
Acceptance of the salt/aniseed mixture increased with time but the level of ani- seed had no significant effect (Table 3).
TABLE 2 Effect of additives on acceptability of salt mixtures?
In the absence of any effect of level with bentonite, molasses powder and MeMHA the significance of differences in acceptability between the observed mean values and the value of 50% expected if the additive had no effect was assessed by a t-test for each compound; overall, bentonite reduced acceptance (PC 0.01) as did MeMHA (P< 0.02).
TABLE 3 Effect of time and proportion of aniseed powder on acceptability of salt mixturet
DISCUSSION
Mean monthly intakes of salt declined from 16.6 to 6.9 g/sheep/day during the six months of experimentation. In the control containers holding plain 'salt, intakes declined from 8.2 to 4.1g/d (Table 1). Intakes of this order are normal for Merino sheep in this environment. We have observed in other unpub- lished studies that even on actively growing pasture voluntary intakes of salt decline, sometimes to zero, in summer. On the only occasion when the forage was analysed for sodium, the content was high (0.33%). Data reviewed by Aitken
(1976) suggest that the sheep's requirement for sodium would have been exceeded tenfold on a diet of this forage.
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Animal production in Australia
The addition of bentonite tended to reduce acceptance of the salt.
Although differences between levels of this additive were not significant, the data (Table 2) suggest that the reduction would be unimportant at a level of 0.2%, the rate that we understand to be used in commercial practice.
The difference in the results obtained with dry and liquid molasses could be due to the presence of other components in the commercial preparation of dried molasses we used. However, the difference was small and is probably attributable to the lower content of actual molasses (dry matter basis) in the mixture when derived from the commercial source than from liquid molasses. It is worth noting
(Table 2) that low levels of liquid molasses (1 or 2%) appeared to reduce accept- ability whereas addition of 4 or 8% enhanced it. Goatcher and Church (1970), in a study of reactions to sugars in drinking water, found that on average, sheep were only weakly responsive to sweet tasting substances; sucrose was not only a fairly ineffective stimulant at low concentrations but at higher concentrations
(20 g/l00 ml) tended to depress intake.
Aniseed would appear to be an acquired taste as the mean acceptance rose from near rejection (26%) in the first week to 54 % in the fourth week of expos- ure. This may have masked any effect due to level of the additive but with the design we used it was not possible to estimate the timebytreatment interaction.
Methyl-MHA has, to human sense, an unpleasant odour arising from its decomposit- ion products such as methyl mercaptan and intake of its admixture with salt was markedly reduced. In a grazing experiment we found that pregnant ewes consumed 10 g/d of a salt plus 13% molasses mix but only 5.4 g/d when the mixture included 10% MeMHA (unpublished data). Unless the effects of such substan- ces can be masked, intakes of the desired supplement are likely to be too low to be effective. The effect of generally unacceptable additives on the distribution of intakes within a flock or herd (Wheeler et al. 1980) has not been determined.
ACKNOWLEDGEMENTS
We acknowledge, with appreciation the statistical advice and assistance of Dr. H.I. Davies, Mathematics Department, University of New England and the comp- etent technical assistance of Mr. C. Mulcahy and Mr. P.A. Hunt.
REFERENCES AITKEN, F.C. (1976). ”'Sodium and Potassium in
No. 2 6 , comm . Bur. Nutr. Aberdeen.
Nutrition of Mammals".
BELL, F.R. (1959). J. Agric. Sci. (Camb). 52: 125.
GOATCHER, W.D. and CHURCH, D.C. (1970). J.xim. Sci.
HINKS, N.T. (1979).
WHEELER, J.L., FERGUSON, K.A. and 711.
Tech. comm
30: 777.
Aust. J. Agric. Res. z e30:
WHEELER, J.L., ROCKS, R.L. and HEDGES, D.A. (1980). Proc. Aust. Soc. Anim. Prod.
13: 297.
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