Hollard and Davison (1971) and Miller (1976) have found that ... groups of animals as the major dependent ... All cows were kept as a group on a .5-ha pasture.
1979, 32, 245-254
JOURNAL OF THE EXPERIMENTAL ANALYSIS OF BEHAVIOR
NUMBER
2
(SEPTEMBER)
CONCURRENT SCHEDULE ASSESSMENT OF FOOD PREFERENCE IN COWS L. R. MATTHEWS AND W. TEMPLE UNIVERSITY OF WAIKATO
Six dairy cows (Bos taurus) were trained on several pairs of concurrent variable-interval schedules with different types of food available on each alternative. The required response was a plate press made by the animal's muzzle. Performance generally replicated that found with other species. The generalized matching law accounted for the preference data, showing that food preference could be quantitatively analyzed as a special case of response bias. The preference functions showed that the response- and time-allocation ratios were not as extreme as obtained reinforcement rate ratios (undermatching). Key words: different reinforcers, concurrent schedules, matching law, nose-plate press, cows
Preference under concurrent variable interval (VI) schedules has been shown to be a function of parameters such as the rates, amounts, immediacies, and qualities of the reinforcers (Baum, 1974). The data are described by the generalized matching law:
P_
=k (rk)a
then its behavior might be expected to conform to the equation: p, = bc (r' )
(2)
when b is a measure of position bias (Baum, 1974), c is a measure of bias due to the differing qualities of reinforcer, and rl, r2 and a are as defined in Equation 1. An estimate of b may be made from the data from a single condition with the same food at equal programmed reinforcement rates by use of Equation 2 with c = 1. Solving for b gives:
(1)
where P1 and P2 are measures of behavior (numbers of responses or times spent responding), r, and r2 are the two obtained rates of reinforcer delivery, a is a measure of the sensitivity of the organism's behavior to differences in reinforcement rates, and k is a measure of invariant biases caused by other constant factors in the experimental situation (Baum, 1974). Killeen (1972) has proposed that k may be a composite of several functions which combine multiplicatively to relate preference to other parameters such as position bias, quality of reinforcer, amount of reinforcer, and
b-=(PI)r2)
(3)
When equal nonindependent reinforcement rates are programmed, then r, and r2 will be approximately equal (and therefore r1/r2 is approximately unity); and since a has usually been found to be in the range .7 to 1.0 (Davison & Hunter, 1976) then a reasonable approximation to b is given by the following equation:
so on. If an organism is choosing between two different reinforcers available at different rates,
b
Based on a Masters thesis by L. R. Matthews under the supervision of W. Temple. This research was supported by Ruakura Agricultural Research Centre and the University Grants Committee. The authors gratefully acknowledge the assistance of T. M. Foster in the preparation of this nianuscript. Reprints may be obtained from either author at the University of Waikato, Private Bag, Hamilton, New Zealand.
,
(_)
r2)
(4)
Hollard and Davison (1971) and Miller (1976) have found that regarding c as a ratio qllq2 (where q1 and q2 are measures of the "qualities" of the two reinforcers delivered) provides a means of assessing preference between two different reinforcers. 245
L. R. MATTHEWS and W. TEMPLE
246
Equation 2 then becomes:
P2
\q2) r2)
(5)
When b (position bias due to factors other than the differing reinforcers) is assumed constant, then division of both sides of Equation 2 by this constant will leave data which will (if the form of the equation is correct) be straight lines on a log-log plot and in which the only bias (Baum, 1974) will be a measure of preference between the two foods. Traditional measures of food preference in cows have generally used the relative amounts of voluntary intake of differing foods by groups of animals as the major dependent variables (Marten, 1970). These measures may be confounded by many factors, such as postingestional consequences and physiological state (Baile, 1975) and eating experience or social history of the animal (Arnold, 1970). Although such factors may be important determinants of intake, their effects on preference would be minimized if food were delivered in small quantities and the measures of preference were from individual animals and independent of the food intake. The present experiment attempted to ascertain whether a general form of the matching law (Equation 5) would hold when dairy cows choose between two qualitatively different types of food. This would extend the generality of the matching law by further supporting the inclusion of ql/q2 as a multiplicative factor and by extending its applicability to the behavior of the dairy cow. METHOD Subjects Five Jersey cows (961, 963, 964, 965, and 967) and one Friesian cow (968), all approximately 18 mo old, nonpregnant, nonlactating, and experimentally naive were used. All cows were kept as a group on a .5-ha pasture. After each experimental session, supplementary feed at the rate of about 3.0 kg of pasture hay per animal was provided. Other and equivalent fields were used during the experiment, but each usually contained low pasture growth of 2 cm to 3 cm average length. Despite this low level of forage avail-
ability, the animals increased in weight, on the average, from 223 kg to 348 kg during the study.
Apparatus The sound attenuating experimental chamber measured 2.45 m wide, 2.85 m long, and 2.30 m high. A ventilation fan in the ceiling masked extraneous sounds. An observation window was set high on one wall. Illumination was provided by two 40-W 1.20-m fluorescent tubes on the ceiling. Two square nose-plates, .10 m by .10 m, were mounted .67 m apart on a dual feeddelivery unit (Cate, Mullord, Temple, & Matthews, 1978). The unit was .45 m wide by .90 m long by .80 m high. The side, front, and top panels were solid. Food presentation occurred when either of the two food hoppers situated in the unit was raised to the appropriate access hole cut in the top panel. The hoppers, each of volume 18 1 and .54 m apart at the midpoints, were raised by pneumatically operated rams. When the hoppers were lowered, food was inaccessible. The noseplates were placed behind the access holes at an angle of 30 degrees to the horizontal. A panel was fitted flush with the plates and ran the width of the feeder unit. This attachment prevented fouling of control equipment behind the unit and restricted access to the response plates. The plates were operated by presses exceeding .4 N. Feedback for plate presses was provided by a 35-msec illumination of a 5-W bulb situated midway between the plates and by a click from a relay placed behind the feeder unit. Figure 1 shows a cow (965) pressing the left nose-plate. The reinforcer consisted of a nominal 5-sec presentation of a food hopper containing either chopped hay or dairy meal,' a concentrated feed. The hay was of average quality and had been harvested from rye-dominant pasture about four months before the beginning of the experiment. It was chopped into average lengths of 2 to 3 cm in order to limit spillage when eaten from the hopper. Reinforcer delivery was accompanied by an audible hiss from the pneumatic feeder-drive. Food was accessible 1.5 sec after hopper activation. 'Registered trademark, Tomoana Dairy Ration, manufactured by W. & T. Fletcher (N.Z.) Ltd., Auckland and Wellington, New Zealand.
FOOD PREFERENCE IN COWS
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