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Dominance and Mating Behavior in Ram Lambs¹

Oregon State University, Corvallis 97331

Abstract

A linear dominance order was determined for five Suffolk ram lambs by tabulating the aggressive acts between rams using estrous ewes as a stimulus. Each day for 20 consecutive days a randomly chosen two or three ram combination was allowed access to a confined flock of 38 normally estrous cycling ewe lambs for 90 min. morning and afternoon test periods. Dominance rank was not related to weight or linear measurements at the start of the trial or to rams' earlier weights. Agonistic behavior within ram pairs was greater in two ram combinations than in three ram combinations (P< .01). In three ram combinations the dominant individual was more aggressive to the higher ranking subordinate and agonistic interactions between the two subordinates were suppressed (P< .05). The number of aggressive acts increased as the number of ewes in estrus increased (P< .05). Individual effects due to both the dominant and subordinate ram were also found (P< .01). The interaction constants for the number of rams x dominant individual (n.s.) and number of rams x subordinate individual (P< .01) indicated that individual differences were intensified in two compared to three ram combinations.

The proportion of estrous ewes mounted by a ram was influenced only by individual ram differences. Average mounts per estrous ewe was affected by the number of ewes in estrus, the mating activity of other rams and by individual ram differences. Total mounts of estrous ewes per test period was influenced by the number of estrous ewes and by individual effects. Position effect, or whether a ram was dominant or subordinate in two or three ram combinations, did not affect any of the measures of mating behavior. Rams tended to rank similarly for all components of mating behavior. Individual differences in the amount of mating behavior were not closely related to dominance order. Possible explanations for the relationships between dominance and mating behavior are discussed.

¹ Technical paper No. 3718, Oregon Agricultural Experiment Station.

² Department of Animal Science.