New understanding of an old phenomenon: uncontrolled factors and misconceptions that cast a shadow over studies of the male efect' on reproduction in small ruminants

Abstract

In female sheep and goats, exposure to males can be used to induce ovulation and thus control and synchronise fertility. This male efect ofers simple, cost-efective, and hormone-free management of reproduction in focks and herds but, despite decades ofresearch, signifcant gaps in our knowledge impede commercial application. Many of these gaps can be traced back to misconceptions inthe early documentation of the male efect, and others are the result of uncontrolled factors in experimental design. Consequently, it isofen difcult to draw conclusions from past research, to further our understanding of the phenomenon, and to make recommendationsfor industry application. Here, we describe 2 aspects of the male stimulus used to elicit the male efect that are ofen uncontrolledthenovelty of the stimulus males and factors that contribute to variability in the potency of the male stimulus. We discuss the physiologythat underpins novelty, including the individual specifcity of the sociosexual signals emitted by the male, and the concomitant abilityof females to distinguish among individual males and remember them. Importantly, an understanding of the issue of novelty can makeit easier to use the male efect in commercial practice. We also discuss difculties in interpretation caused by variation in endpoints ofthe male efect (from neuroendocrine reaction to birth). We conclude that more rigour is needed in the control and reporting of malenovelty, in preexperimentation separation of the sexes, and in extrapolation from detection of early responses to the male stimulus toreproductive outcomes.