Environmental and management factors associated to reproductive hormonal profiles in pelibuey ovine females raised in Southern Sonora

Abstract

Objective of this study was to evaluate the effect of year season, heat stress and female age on hormonal reproductive performance in pure breed females raised in southern Sonora. The study included 20 Pelibuey ovine females in good body condition, from 1 to 3 years of age (primiparous and multiparous). Blood samples were collected form each female during 26 weeks through a vein jugular punction. All samples were centrifuged to 25000 RPM during 45 min. The serum was aspirated and poured into 2 ml eppendorf tubes, and then transported to the endocrine lab to measure serum level of reproductive hormones such as Thyroxine (T4), Progesterone (P4) and Prolactin (PRL) using radioimmunoassay (RIA). Serum levels of T4, P4 and PRL differed (P<0.0001) according to the season of the year (i.e. summer and fall); however, only serum T4 (P<0.0007) and PRL (P<0.0001) differ according to the parity of the females. The effect of the heat stress on reproductive hormone levels was only significant in T4 and PRL (P<0.0001) for every stress level (i.e. no stress, moderate stress and high stress); however, P4 levels only were different under high stress versus moderate or no stress. These results suggest that Pelibuey females raised under environmental conditions from southern Sonora are season breeding, because their reproductive hormone profiles are associated to photoperiod. In addition, the heat stress influenced negatively the reproductive hormone levels in this females as well as their reproductive performance.