Effect of Dorper Rams’ Social-Sexual Hierarchy on Their Sexual Behavior and Capacity to Induce Estrus in Ewes

Andrea González-Tavizón,Gerardo Arellano-Rodríguez,Miguel Mellado,Oscar Ángel-García,Francisco G Véliz-Deras,César A Meza-Herrera,Viridiana Contreras-Villarreal,José R Arévalo

doi:10.3390/agriculture12030391

Andrea González-Tavizón, Gerardo Arellano-Rodríguez + Show 6 more

Open Access

https://doi.org/10.3390/agriculture12030391

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Abstract

This study aimed to assess the influence of the social rank of rams and quality of stimuli to ewes between dominant and subordinate Dorper rams joined to anestrus ewes. Social rank was evaluated for two days (ESR; n = 36); rams were exposed to estrogenized ewes in a competitive test. According to the reproductive response, anovulatory ewes (n = 76) were divided into two groups: LHRe (n = 38; ewes exposed to four low hierarchy rams (LHR)) and HHRe (n = 38; ewes exposed to four high hierarchy rams (HHR)). Regarding aggressive behaviors, HHR showed a higher (p < 0.05) proportion of rams showing threatening, knocking, and blocking behaviors than LHR. Appetitive behavior was higher (p < 0.05) in HHR than LHR rams (3576 ± 0.7 vs. 3054 ± 0.7 number of events). Consummatory sexual behavior was higher (p < 0.05) in HHR than LHR (499 ± 0.3 vs. 205 ± 0.1 number of events). Indicators of sexual inactivity (SRI) were similar between HHR and LHR (499 ± 0.3 vs. 433 ± 0.1; p > 0.05). The estrus response (>80%; p > 0.05) and ovarian response (70%, p > 0.05) were similar for both groups of ewes. It was concluded that LHR are equally effective as HHR in inducing sexual activity in ewes showing postpartum anestrus.

Highlights

The ram effect induces estrus in non-cycling ewes [1] and increases luteinizing hormone (LH) secretion advancing the LH surge in cycling ewes [2]
Social status refers to the relative position of an individual animal within a dominant hierarchy established in a group [8,9]
During the success index test, more AG and MO behaviors were observed in hierarchy rams (HHR) than low hierarchy rams (LHR)

Summary

Introduction

The ram effect induces estrus in non-cycling ewes [1] and increases luteinizing hormone (LH) secretion advancing the LH surge in cycling ewes [2]. The response may differ due to other factors related to ewes, such as body energy reserves and hierarchy [5,6]. Social status refers to the relative position of an individual animal within a dominant hierarchy established in a group [8,9]. In addition to having a larger body weight or body energy reserves, have a greater interaction time (i.e., stimulus) which seems to make them more sensitive to socio-sexual cues emitted by rams. Such physiological and behavioral scenarios favor sexual bio-stimulation, which triggers an early reproductive activity [13,14]

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