Role of male novelty and familiarity in male-induced LH secretion in female sheep

Abstract

Ewes supposedly need to be separated from rams before male stimuli can increase gonadotrophin secretion and induce ovulation. In the present study, we investigated the LH response of ewes to 'novel' and 'familiar' rams after varying periods of separation. In Experiment 1, ewes (n = 8 per treatment) were separated from familiar rams for 15 min or 1 month and then exposed to either familiar rams, novel rams or novel wethers. After 15 min or 1 month of separation, exposure to novel rams increased pulsatile LH secretion (P < 0.05) and induced an LH surge in all ewes whereas exposure to familiar rams or novel wethers had no effect on LH secretion (P > 0.1). After 1 month of separation, re-exposure to the same familiar rams increased pulsatile LH secretion (P < 0.05) in six of eight ewes, but only induced an LH surge in two of eight ewes. In Experiment 2, familiar rams were removed and returned after 15 min, 1 day or 17 days (n = 5 per treatment). None of these treatments affected LH secretion. We conclude that separation of ewes from rams is a prerequisite for familiar rams to increase LH secretion, but is not necessary if the rams are novel.

Sexually active males prevent the display of seasonal anestrus in female goats

“…On the other hand, it must be underlined that in various breeds of sheep, rams tend to maintain some sexual activity even during the natural period of seasonal rest, contrary to goat bucks which show a more complete inhibition of their sexual behavior at the time females are in seasonal anoestrus. Therefore, it cannot be excluded that in sheep, social novelty of the stimulus male plays a more important role than in goats, at least in those breeds whose males maintain some sexual activity all year round (Hawken and Beard, 2009;Jorre de St Jorre et al, 2012). Here again, further studies are needed to investigate to what extent the present results can apply to sheep, but also to other seasonal ruminants or any species in which seasonal reproduction is controlled by photoperiod.…”

“…In fact, in sheep the lack of familiarity of the stimulus male has long been considered to be an important factor for a good response in the females (Hawken and Beard, 2009;Jorre de St Jorre et al, 2012), even though several studies in goats have now shown that the level of sexual activity of the male plays a critical role (Delgadillo et al, 2006;Martínez-Alfaro et al, 2014;Vielma et al, 2009). The results of experiment 3 confirm without any ambiguity, at least in the goat, that it is the sexual activity of the male and not its novelty that induces the ovarian response of the females.…”

“…We also took into account a possible effect of male "novelty" that would be due to the contact with an unknown male when we changed the males every 2 months (Hawken and Beard, 2009;Jorre de St Jorre et al, 2012). To prevent this possibility, we placed the males waiting to be used in pens adjacent to those of the females about one month before introducing them; the males were only separated from females by an openwork wood barrier that allowed visual, olfactory and nose-to-nose contact between sexes.…”

Progesterone (P4), luteinizing hormone (LH) levels and ovarian activity in postpartum Santa Inês ewes subject to a male effect

“…Blood plasma LH analysis was determined by duplicate double-antibody radioimmunoassay, following De St Jorre et al (2012), and the limit of detection was 0.27 η g mL −1 ; the intra-assay and inter-assay coefficients of variation were 3.5 and 8.74 %, respectively. Variations in LH levels were considered significant when they increased by 20 η g mL −1 or more for two consecutive measurements, as suggested by Martin et al (1983).…”

Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect

“…There were large follicles (O3.5 mm diameter) present in most ewes (Table 3). The increased concentration of E 2 following the 'ram effect' is undoubtedly the result of increased pulsatile secretion of LH that in itself is a response to the sociosexual stimulation that always follows exposure to an unfamiliar sexual partner (Hawken et al 2007, Jorre de St Jorre et al 2012. Sheep have particularly low concentrations of blood E 2 , especially during anoestrus, and present considerable technical difficulties when attempting to assay the circulating concentrations of E 2 .…”