# Importance of Social Hierarchy in Morphometry, and Socio-Sexual and Reproductive Behaviors in Dorper Sheep in Northern Mexico

## TL;DR

This study explores how social rank affects the reproductive behavior of Dorper sheep in Northern Mexico, finding that certain social rank combinations influence embryo and corpus luteum numbers.

## Contribution

The study reveals new insights into how social rank combinations affect reproductive outcomes in Dorper sheep.

## Key findings

- Low-social-rank rams paired with high-social-rank ewes produced the highest number of embryos.
- High-social-rank rams paired with high-social-rank ewes had a higher corpus luteum number.
- No significant differences were found in morphometric variables based on social rank.

## Abstract

Improving the productive and reproductive performance of sheep flocks presents a significant challenge. Implementing strategies (e.g., the male effect × social rank) can contribute to this challenge. The objective of this study was to evaluate how social rank influences morphometric and socio-sexual variables in Dorper sheep in Northern Mexico. Through behavioral tests, 33 rams and 59 ewes were divided into two groups, taking into account their social rank (i.e., high social rank and low social rank). The results showed no significant differences (p > 0.05) for the morphometric variables considered. Meanwhile, regarding the reproductive variables, the combination of low-social-rank rams × high-social-rank ewes resulted in the highest number of embryos (p < 0.05), while the corpus luteum number was higher for the combination of high-social-rank rams × high-social-rank ewes (p < 0.05). However, no significant differences were observed for the remaining variables (p > 0.05). These results contribute to the ongoing effort to improve reproductive performance in sheep, enhancing the sustainability of the activity, with the potential to increase the income of families who depend on sheep production.

One of the most important aspects of animal production is the reproductive behavior, where a widely used strategy in small ruminants is the “male effect”. However, the response to this effect can vary depending on several factors, including the social rank (SR) of both sexes. The objective of this study was to evaluate how SR influences morphometric and socio-sexual variables in Dorper sheep in Northern Mexico. Through behavioral tests, 33 rams and 59 ewes were divided into two groups taking into account their SR. Rams included high SR (HSR; n = 14) and low SR (LSR; n = 19), while ewes included HSR (n = 23) and LSR (n = 36). Morphometric response variables included age, live weight, body condition, thoracic circumference, wither height, presence of horns, and testicular circumference, whereas reproductive variables included estrus rate, ovulation rate, corpus luteum, left ovary, right ovary, pregnancy rate, and embryos’ number. The results showed no differences (p > 0.05) for the morphometric variables considered, whilst, regarding the reproductive variables, the LSR rams × HSR ewes group showed the highest number of embryos (p < 0.05), and the corpus luteum number was higher in the HSR rams × HSR ewes group (p < 0.05). However, no significant differences were found for the remaining variables (p > 0.05). Improving productive and reproductive performance can contribute to increased income for sheep farmers.