Maternal influence on feeding site selection of male and female lambs.

We conducted an experiment to determine whether early-life social learning of feeding site selection in lambs was sex-specific. Sixteen ewes and their new born lambs were used in a controlled experiment. Eight ewe-lamb pairs included a male lamb and the remaining eight a female lamb. All pairs were individually exposed to an experimental arena containing a safe and unsafe artificial feeding site (SFS, UFS) each consisting of nine bowls which contained either ground Bermuda grass hay (SFS) or ground alfalfa hay (UFS). The bowls in UFS were surrounded by bright orange traffic cones (visual cues). Half the ewes were trained with controlled electric shock to avoid UFS. Thus, pairs were randomly assigned to: (1) shock aversion training (SAT) to mothers of male lambs (MS); (2) SAT to mothers of female lambs (FS); (3) no aversion training (NAT, control) to mothers of male lambs (MC); and (4) NAT (control) to mothers of female lambs (FC). None of the lambs were subjected to SAT. During training, testing, extinction, and retraining ewe-lamb pairs were exposed to the arena together. Ewes were then removed from the experiment and two additional extinction phases were conducted with weaned lambs alone. Fear conditioning elicited UFS avoidance of both the trained ewes (means±s.e.m. % times observed in UFS during testing phase: FC=95.3±1.70; MC=94.4±4.87; FS=1.6±1.63; MS=0 ±0; P<0.01) and their naïve lambs (FC=83.8±6.07%; MC=76.6±6.56%; FS=30.4±7.90%; MS=33.9±9.23%; P<0.01). UFS avoidance in lambs occurred regardless of sex and tended to persist after weaning (% times observed in UFS during 1st post-weaning extinction phase: FC=92.6±4.50%; MC=89.8±6.09%; FS=45.1±10.57%; MS=43.5±10.42%; P=0.06). Fear conditioning in mothers appeared to alter sex-related differences in mother-infant behavioral synchrony by increasing and decreasing feeding synchrony of male and female lambs, respectively (FC: r=0.52, P<0.01; MC: r=-0.02, P=0.86; FS: r=0.14, P=0.26; MS: r=0.46, P<0.01). During the extinction phase mothers of ram lambs were observed feeding more often (FC=85.0±2.33%; MC=92.7±1.45%; FS=47.3±8.81%; MS=72±5.68%; P=0.02) and standing less often than ewes with daughters (FC=7.3±2.40%; MC=2.7±0.83%; FS=39.3±9.04%; MS=18.0±5.29%; P=0.06). This study suggests that social conditioning at an early age could be a viable tool to induce learning of feeding site avoidance in female and male lambs alike.

Technical note: comparison of salivary and serum cortisol concentrations after adrenocorticotropic hormone challenge in ewes.

An ACTH challenge was conducted to determine if salivary cortisol concentration reflects serum cortisol concentration in ewes. Twelve yearling ewes (64.0 +/- 1.2 kg) were administered ACTH (100 IU, intravenously) or saline. Serum and salivary samples were collected at 30-min intervals for 2 h before ACTH administration, at 15-min intervals for 2 h after treatment, and at 30-min intervals for an additional 3 h, and cortisol concentration was determined by RIA. Although ewes responded to ACTH and saline, cortisol concentration was greater (P < 0.001) in ACTH-treated ewes from 15 to 120 min and tended to be greater (P = 0.054) at 150 min after challenge in serum. In saliva, cortisol concentration was greater (P < 0.001) in ACTH-treated ewes from 30 to 120 min and tended to be greater (P = 0.092) at 15 min after challenge. No difference was observed between ACTH-treated ewes and controls for time to peak serum cortisol concentration (P = 0.126) and time to peak salivary cortisol concentration (P = 0.109), or between saliva and serum for time to peak cortisol concentration (P = 0.220) and return to baseline cortisol concentration (P = 0.341). The serum (P = 0.009) and salivary (P = 0.050) cortisol areas under the curve between 0 and 150 min were greater for ACTH-treated ewes than controls, and serum (P = 0.002) and salivary (P < 0.001) cortisol return to baseline concentration was longer for ACTH-treated ewes. The correlation coefficient between serum and salivary cortisol concentrations was 0.88 (P < 0.001). These data indicate that salivary cortisol concentration is closely related to serum cortisol concentration and that the former may represent a suitable noninvasive alternative to blood collection for measurement of cortisol in sheep.