Variation of sexual behavior of photo-stimulated bucks during the transition from winter to spring in the semi-arid climate of Mexico

Sheep and goat production takes place under unsuitable climate conditions, where 28 animals are more susceptible to high temperatures. The objectives of this study were to 29 determine, i) whether sexual behavior of photo-stimulated bucks varies through 24 h/day 30 in March and April and, ii) whether the environmental temperature and the relative 31 humidity affect their expression. Six bucks were submitted to artificial long days (16 h 32 light and 8 h darkness per day/2.5 months). Bucks were exposed to ovariectomized 33 females once a week during the non-breeding period and sexual behavior was recorded 34 for 15 min at 2 h intervals along 24 h/day. The environmental temperature, relative 35 humidity, temperature-humidity index (THI), and body temperature were recorded in 36 each behavior test. Plasma testosterone, sexual behavior, environmental temperature, 37 relative humidity, and body temperature were analyzed using Generalized Estimation 38 Equations. Plasma testosterone showed a significant difference over the experimental 39 period ( P < 0.001). The highest frequency of nudging and anogenital sniffing was at 08:00 40 h ( P < 0.001); flehmen and penis unsheathed were variable ( P < 0.001). The highest 41 environmental temperature and the lowest relative humidity were registered from 14:00 42 to 18:00 h ( P < 0.001). The highest body temperature was at 18:00 h and the lowest was 43 at 06:00 h ( P < 0.001). The highest THI >77 was recorded at 16:00 h. In conclusion, 44 photo-stimulated bucks showed a variation of sexual behavior through 24 h/day exposed 45 to ovariectomized females, and these sexual activities were affected by the high 46 environmental temperature and the low relative humidity throughout the study. Our results show that photo-stimulated bucks increased plasma testosterone 295 concentration during March and April as was previously reported by Delgadillo et al 296 (2002), in contrast to untreated bucks which do not present high testosterone secretion 297 during the natural sexual rest (Delgadillo et al 2002). Furthermore, photo-stimulated 298 bucks during the same breeding season increased the level of plasma testosterone even 299 without exposing them to females (Ponce et al 2014). The present results show that our 300 photo-stimulated bucks, sexual behaviors such as nudging and anogenital sniffing were 301 negatively affected by the high environmental temperature. These sexual behaviors 302 stimulate female sexual behavior (Fernández et al 2018). In the current study in March 303 and April from 10:00 to 18:00, a THI between 71-77 units was recorded. In fact, in animal 304 production, the thermal-neutral zone is considered with a THI <70, in these conditions 305 the animal feels more comfortable and is more efficient, whereas a THI of 71-78 units 306 indicates that the animals are in a state of alert, and a THI 79-83 indicates a danger 307 category (Du Preez 2000). Likewise, heat stress occurs when these animals are exposed 308 to higher environmental temperatures compared to those recorded in the thermal-neutral 309 zone, this high temperature is the result of an increase in heat production due to increased 310 body temperature (Du Preez 2000). Heat stress is described as the result of continuous 311 environmental forces that act on the animal causing alteration of homeostasis (Al- 312 Dawood 2017). Then, animals exposed to high ambient temperatures activate various 313 physiological mechanisms to compensate for the adverse effects caused by heat stress 314 (Berihulay et al 2019).