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Heird, J. C., Lennon, A. M., & Bell, R. W. (1981). Effects of early experience on the learning ability of yearling horses. J. Anim Sci., 53(5), 1204–1209.
Abstract: Twenty-four yearling Quarter Horse fillies were divided into three groups (I) very limited handling, (II) intermediate handling and (III) extensive handling. At about 14 months of age, each horse was preconditioned for 2 weeks and then run in a simple place-learning T-maze test in which it had to locate its feed. Thirty trials were run daily for 20 days, with the location of the feed changed each day. To retire from the maze, a horse had to meet the criterion: 11 correct responses in 12 tries, with the last eight being consecutive. Horses in Group II required the fewest trials to reach criterion. These horses also learned more and had the highest percentage of correct responses (P less than .05). Mean trainability tended to predict learning ability; however, trainability and trials to criterion were not significantly correlated. Mean emotionality scores indicated a tendency for horses in the intermediately handled group to be less emotional than those in Group I or III. Results indicated that horses with an intermediate amount of handling scored higher on an intermediate test of learning. All handled horses scored higher on learning tests than those not handled.
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Heird, J. C., Whitaker, D. D., Bell, R. W., Ramsey, C. B., & Lokey, C. E. (1986). The effects of handling at different ages on the subsequent learning ability of 2-year-old horses. Appl. Anim. Behav. Sci., 15(1), 15–25.
Abstract: Forty weanling Quarter Horses, from the Pitchfork Ranch, Dickens, Texas, were randomly assigned to one of five groups based on the amount of handling they would receive. The five groups were: (1) limited handling; (2) 1 week of handling; (3) 2 weeks of handling; (4) 3 weeks of handling; (5) continuous handling for 18 months. As 2-year-olds, the horses were tested in a simple place-learning T-maze after being preconditioned. A maximum of 30 daily trials were conducted for 20 consecutive days, with feed location alternating between sides on successive days. If a horse met the criterion of 11 out of 12 correct responses with 8 correct responses being consecutive, it was retired without completing the 30 trials. Group 1 made fewer correct responses during the 20 days than any other group except Group 3. All groups achieved learning by Day 10, but the most-handled group reached a consistently higher percentage of correct responses earlier than the less-handled groups. Group 5, the group receiving the most handling, was the least emotional, as determined by the animals' reactivity to a novel stimulus, and received the highest scores for trainability after being ridden. Preconditioning trainability scores, or estimates of the horses' ability to learn prior to conditioning and testing, tended to predict maze-learning ability. These scores were also significantly correlated with post-maze training scores.
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McCann, J. S., Heird, J. C., Bell, R. W., & Lutherer, L. O. (1988). Normal and more highly reactive horses. II. The effect of handling and reserpine on the cardiac response to stimuli. Appl. Anim. Behav. Sci., 19(3-4), 215–226.
Abstract: A split-plot experiment evaluated the effect of handling and reserpine on the autonomic heart-rate response of yearling horses to various stimuli. The emotionality levels of 32 Quarter-Horse yearlings were rated by 4 experienced horsemen on a scale from 1 to 4 (1 = most nervous and erratic disposition; 4=quiet disposition). The yearlings were subsequently classified and penned based on their emotionality level; normal or nervous. Within each emotionality group, one-half the yearlings were handled daily for 14 days and the other one-half remained free in the pens. Following the handling treatment, every yearling was individually exposed to a series of stimuli, while the heart rate was monitored via a radio-telemetry system. A second treatment, reserpine, was subsequently given intramuscularly (0.005 mg/kg body weight) to one-half the yearlings of each treatment combination of emotionality and handling. The heart rate of the yearlings to the same series of stimuli previously employed was determined at 24 and 120 h and 16 days following the reserpine injection. Summarizing the results, the handled yearlings tended to exhibit lower heart rates with the handling stimulus, but the heart rate with a more novel stimulus was not affected by the previous handling treatment. Reserpine tended to suppress the heart rate of the unhandled group during the presence of a handler, but the permanency of this effect was not evident 16 days after the drug was administered. The reserpine-treated groups tended to exhibit the lowest heart-rate response to stimuli during the 120-h test-day following the administration of the drug. Heart-rate responses to the stimuli were not different between the normal and nervous yearlings.
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McCann, J. S., Heird, J. C., Bell, R. W., & Lutherer, L. O. (1988). Normal and more highly reactive horses. I. Heart rate, respiration rate and behavioral observations. Appl. Anim. Behav. Sci., 19(3-4), 201–214.
Abstract: Thirty-two Quarter horse yearlings were utilized in a split-plot experiment to establish behavioral tendencies for two levels of emotionality; normal and a more highly reactive level of emotionality termed nervous. Four observers who were experienced with horses scored the yearlings on an emotionality scale from 1 to 4, with 1 representing the highly nervous yearlings and 4 representing the quiet yearlings. Emotionality evaluations were based upon the response of the yearlings to a standard regimen of standing in a chute, being identified and being released from the chute. The inter-rater reliability coefficients were 0.90 for the normal yearlings and 0.65 for the nervous yearlings, indicating that the raters agreed less when evaluating the nervous yearlings. Yearling heart rates in the chute were correlated (r = -0.54, P<0.002) with the average emotionality score. Observational data on behavior collected 2 days following the emotionality scoring procedure indicated that the normal yearlings maintained a greater (P<0.001) individual distance than the nervous yearlings. From an activity summary, the normal yearlings spent 10.9% of the time lying down (LD), 79.1% standing (S), 9.6% walking or trotting (WT) and 0.4% of the time cantering or galloping (CG). The nervous yearlings spent 5.7% of the observational periods LD, 79.2% S, 11.7% WT and 3.4% CG. The nervous yearlings tended to have a higher overall activity index level than did the normal yearlings. Results indicate horses of different emotionality levels exhibited different behavioral patterns.
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