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The objectives of this study were to characterize the LH secretion pattern and the follicular development of anestrous beef heifers during early exposure (first 30 d of exposure) to androgenized steers (AS) and to determine if exposure to AS for 80 d (includes the first 30 d and 50 d more) advances the onset of ovarian cyclic activity. Twenty-nine anestrous Hereford heifers (20.2 ± 4.1 mo old and 257.5 ± 32.5 kg of BW) were allocated to 2 homogeneous groups according to their age and BW: 1) heifers exposed to AS (group EH; = 15) for 80 d and 2) control heifers, isolated from AS and any other male during all the course of the study (group CH; = 14). On d 0, 3 AS were joined with the EH group, which were removed and replaced with other 3 AS on Day 14. On d -10, 1, 10, 20, and 30, 8 heifers per group were housed in individual stalls and blood samples for LH were collected at 15-min intervals for 6 h. From d -10 to 30, the maximum follicle diameter (MFD) and the presence of a corpus luteum (CL) was daily recorded by ultrasound scanning and estrous behavior was detected twice daily. The emergence of follicular waves (FW), defined as the day when the dominant follicle of a wave was first observed (3-4 mm diam.), was retrospectively determined. Afterward, ultrasound scannings were performed weekly from d 32 to 60 and on d 70 and 80 to determine the presence of CL. After 10 d of male exposure, LH concentrations, either mean (1.67 vs. 0.88 ng/mL [SEM 0.09]) or basal (1.53 vs. 0.74 ng/mL [SEM 0.09]), were greater ( < 0.05) in the EH group than in the CH group. There was a treatment effect in MFD, as it was greater in EH than in CH ( = 0.05; 8.00 ± 0.16 vs. 7.52 ± 0.17 mm, respectively), but none of those follicles ovulated during the 40-d period. The MFD of the second FW was greater in EH than in CH, in coincidence with the transient increase on LH concentrations, which probably induced the greater follicular growth. Cumulative proportions of heifers that started to cycle were greater ( = 0.01) in EH than in CH on d 60 (33.3 vs. 0%), 70 (47 vs. 0%; < 0.005), and 80 (53 vs. 0%; < 0.001) of the exposure period. In conclusion, exposure of anestrous beef heifers to AS resulted in a transient increase on LH secretion after 10 d of male exposure and increased follicular diameter attained during the second FW. In addition, ovarian cyclic activity was advanced in exposed heifers.

We investigated the effect of genetic selection for temperament on the way that stressors affect the behaviour and the adrenal and reproductive axes of sheep. We tested three hypotheses: (i) isolation would increase cortisol secretion and decrease luteinising hormone (LH) secretion more in nervous sheep than in calm sheep; (ii) isolation combined with simulated human presence would increase cortisol secretion and decrease LH secretion more in nervous sheep than in calm sheep and (iii) isolation combined with stressors that were not specific to the selection process (i.e. non-selection stressors) would increase cortisol secretion and decrease LH secretion equally in calm and nervous sheep. Isolation alone increased cortisol secretion and decreased LH secretion in nervous sheep but not in calm sheep. Compared to calm sheep, nervous sheep were more agitated during the first 2 h of isolation but not during the second 2 h of isolation. Exposure to non-selection stressors increased cortisol secretion, decreased LH pulse amplitude and the mean plasma concentrations of LH in both calm and nervous sheep. We conclude that genetic selection for temperament affects the behavioural expression of the stress response and the secretion of adrenal and reproductive hormones during isolation, but has less impact on their reactivity to non-selection stressors.

The objective of this study was to compare the body weight (BW) and size, metabolic status, and reproductive development of dominant and subordinate prepubertal dairy heifers allocated in competitive dyads. Sixteen Holstein and Jersey × Holstein prepubertal heifers (means ± SEM; 250.8 ± 9.8 d; 208.5 ± 13.9 kg of BW) were assigned to 8 homogeneous dyads according to breed, age, and BW. Dyads were housed in pens separated 1 m from each other during 120 d, receiving a total mixed ration on a 5% restriction of their potential dry matter intake, and had access to the same feeder (60 cm) throughout the experiment. Dominant and subordinate heifers were defined based on the winning agonistic interactions in each dyad. Body development was recorded every 20 d in all heifers, and blood samples were collected on the same days to determine endocrine and metabolic status. The maximum follicle diameter, number of follicles >6 mm, and the presence of corpus luteum were observed weekly by ultrasound. Heifer BW (269.3 vs. 265.3 ± 1.5 kg) and average daily gains (0.858 vs. 0.770 ± 0.02 kg/d) were greater in dominant than subordinate heifers. On d 30, 37, and 53, dominant heifers had more follicles than subordinate heifers, and maximum follicle diameter was greater in dominant than in subordinate heifers (10.0 vs. 9.0 ± 0.3 mm). Dominant heifers achieved puberty earlier than subordinate heifers (313.9 ± 4.9 vs. 329.6 ± 5.7 d) with similar BW (279.4 ± 2.6 vs. 277.4 ± 5.8 kg). Glucose concentrations were greater in dominant than subordinate heifers (89.2 vs. 86.8 ± 1.2 mg/dL), but cholesterol concentrations were greater in subordinate than dominant heifers (86.1 vs. 90.2 ± 2.6 mg/dL). We concluded that, under continuous competitive situations, dominant heifers were more precocious than subordinate ones, achieving an earlier puberty. Dominant heifers had greater body growth and glucose concentrations than subordinate heifers, which may be responsible, at least in part, for the differences on reproductive development between heifers of different social status.