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Results of previous studies in our laboratory have shown that testosterone (T) inhibits parental response in adult male Mongolian gerbils. Here, we examined developmental changes in parental responses of male gerbils before, during, and after a naturally occurring surge in T that peaks on Day 75 postpartum. On the hypothesis that T inhibits parental response in male gerbils, we predicted that (a) 75-day-old male gerbils would be less responsive to neonates than would either younger or older male gerbils, and (b) young male gerbils whose T titers were rising as the litters that they were helping to rear matured would show a decrease over days in parental effort relative to older male gerbils whose T titers were falling as the litters that they were helping to rear matured. Both predictions were confirmed, providing evidence consistent with the view that naturally occurring, developmental changes in circulating concentrations of T play a role in age-related changes in the level of parental response of male Mongolian gerbils.

Adult. --- Developmental-changes. --- Gerbil. --- Gerbils. --- Laboratory. --- Level. --- Male mongolian gerbils. --- Male. --- Mongolian gerbil. --- Mongolian gerbils. --- Mongolian-gerbil. --- Neonates. --- Parental behavior. --- Parental responses. --- Play. --- Prediction. --- Response. --- Responses. --- Testosterone. --- Young.

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Recent interest has focused on the advantage of intensively handling young foals as a means of producing more tractable horses, accustomed to humans and receptive to training. To date, the effect of this intensive handling, dubbed "imprint training" in the popular literature, has not been tested. The present study compares seven foals handled intensively as neonates with eight untreated controls. The handling protocol started from 2–8 h after birth and continued daily for a total of 5 days. The protocol consisted of a series of stimuli and experiences that were each repeated until the foal no longer resisted or reacted negatively. Subsequently, foals were tested before weaning, at 4 months of age. Results indicated that handled foals (HF) ranked higher than control foals (CF) in subjective ratings of calmness (*P<0.0117) and friendliness (***P<0.0001) and in several specific handling tasks (venipuncture *P<0.0220; placing in stock *P<0.0128). Although, in approach tests all foals but one allowed approach of a person to 4 m, significantly more HF approached the person than CF (**P<0.0080). In stimulus tests, foals were presented specific stimuli to which they had been tested as neonates. Two of eight CF were too unruly and dangerous to test. Of foals that could be tested, CF required significantly more time to hook-up a heart rate monitor (**P<0.0055). Split-plot analysis indicated that HF had lower heart rates to initial left-sided stimuli, presented first, than CF (*P<0.0421). In response to right-sided stimuli, heart rate scores of CF were not significantly different from HF (P<0.2259), suggesting reduced reactivity over time due to a learning effect. Behavioral responses to specific stimuli did not differ between CF and HF, suggesting that neonatal handling has a general rather than specific effect on subsequent behavior. Cortisol concentrations were measured before and after testing and the difference calculated. All foals had higher post-testing levels tha

Age. --- Analysis. --- Behavior. --- Behavioral-responses. --- Birth. --- Control. --- Cortisol. --- Dangerous. --- Experience. --- Foal. --- Foals. --- Handling. --- Heart rate. --- Heart-rate. --- Horse. --- Horses. --- Human. --- Humans. --- Investigation. --- Learning. --- Level. --- Mechanisms. --- Neonatal foal handling. --- Neonatal handling. --- Neonatal. --- Neonates. --- Ratings. --- Reactivity. --- Response. --- Responses. --- Stimuli. --- Stimulus. --- Task. --- Tasks. --- Test. --- Tests. --- Time. --- Training. --- Weaning. --- Young.

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Perinatology --- Fetus --- Newborn infants --- Pregnancy --- Périnatalogie --- Foetus --- Nouveau-nés --- Grossesse --- Fetal Diseases --- Infant, Newborn --- Infant, Newborn, Diseases --- Periodicals --- Diseases --- Complications --- Périodiques --- Maladies --- periodicals --- Fetal Diseases. --- Fetus. --- Infant, Newborn. --- Infant, Newborn, Diseases. --- Newborns --- Neonate --- Infants, Newborn --- Neonates --- Newborn --- Newborn Infant --- Newborn Infants --- Neonatology --- Fetal Tissue --- Fetuses --- Mummified Fetus --- Retained Fetus --- Fetal Structures --- Fetal Structure --- Fetal Tissues --- Fetus, Mummified --- Fetus, Retained --- Structure, Fetal --- Structures, Fetal --- Tissue, Fetal --- Tissues, Fetal --- Embryo, Mammalian --- Fetal Research --- Embryopathies --- Disease, Fetal --- Diseases, Fetal --- Embryopathy --- Fetal Disease --- Obstetrics --- Perinatology. --- Newborn infants. --- Obstetrics. --- Diseases. --- Health Sciences --- Diagnostics --- Obstetrics and Gynecology --- Pediatrics --- Therapeutics --- Neonatal Diseases --- Disease, Neonatal --- Diseases, Neonatal --- Neonatal Disease --- Périnatalogie --- Nouveau-nés --- Périodiques --- MDPEDIAT --- periodicals.