Reduced Cortisol and Metabolic Responses of Thin Ewes to an Acute Cold Challenge in Mid-Pregnancy: Implications for Animal Physiology and Welfare

Background: Low food availability leading to reductions in Body Condition Score (BCS; 0 indicates emaciation and 5 obesity) in sheep often coincides with low temperatures associated with the onset of winter in New Zealand. The ability to adapt to reductions in environmental temperature may be impaired in animals with low BCS, in particular during pregnancy when metabolic demand is higher. Here we assess whether BCS affects a pregnant animal’s ability to cope with cold challenges. Methods: Eighteen pregnant ewes with a BCS of 2.760.1 were fed to attain low (LBC: BCS2.360.1), medium (MBC: BCS3.260.2) or high BCS (HBC: BCS3.660.2). Shorn ewes were exposed to a 6-h acute cold challenge in a climate-controlled room (wet and windy conditions, 4.460.1uC) in mid-pregnancy. Blood samples were collected during the BCS change phase, acute cold challenge and recovery phase. Results: During the BCS change phase, plasma glucose and leptin concentrations declined while free fatty acids (FFA) increased in LBC compared to MBC (P,0.01, P,0.01 and P,0.05, respectively) and HBC ewes (P,0.05, P,0.01 and P,0.01, respectively). During the cold challenge, plasma cortisol concentrations were lower in LBC than MBC (P,0.05) and HBC ewes (P,0.05), and FFA and insulin concentrations were lower in LBC than HBC ewes (P,0.05 and P,0.001, respectively). Leptin concentrations declined in MBC and HBC ewes while remaining unchanged in LBC ewes (P,0.01). Glucose concentrations and internal body temperature (Tcore) increased in all treatments, although peak Tcore tended to be higher in HBC ewes (P,0.1). During the recovery phase, T4 concentrations were lower in LBC ewes (P,0.05). Conclusion: Even though all ewes were able to increase Tcore and mobilize glucose, low BCS animals had considerably reduced cortisol and metabolic responses to a cold challenge in mid-pregnancy, suggesting that their ability to adapt to cold challenges through some of the expected pathways was reduced

Agonistic and sexual communication in the little blue penguins, Eudyptula minor.

The little blue penguin, Eudyptua minor, was used to examine three specific issues in animal communication. (1) Ethologists have traditionally viewed social repertoires as being fixed and invariable. In contrast, my analysis of agonistic behaviour of little blue penguins occupying two different habitats revealed significant variation in repertoire size and form. Cave-dwellers, which had large and complex repertoires, occupied open colonies characterized by high interaction rates. Burrow-dwellers, which had small repertoires, occupied colonies in which conspecifics were isolated from one another and rarely interacted. Despite higher interaction rates, cave-dwellers attacked one another less often and used overtly aggressive behaviours with shorter durations than did burrow-dwellers. The results suggest that the size and form of repertoires may be mediated by the social and physical properties of occupied habitats. Large repertoires may reduce the proportion of encounters leading to overt aggression where interaction rates are high. (2) Theoretical models of aggressive communication suggest that animals are unlikely to use aggressive displays to signal motivation. Using lag sequential analysis, I examined over 2000 agonistic interactions between cave-dwelling penguins. The results suggested that aggressive displays differ in how costly they are to perform (i.e. as measured by the risk of escalation) and that high cost displays were more effective in deterring opponents than low cost displays. I argue that animals can signal motivation by taking risks during interactions, as demonstrated by their choice of display. (3) The social facilitation of courtship behaviour is a widely assumed but rarely demonstrated process thought to be related to breeding synchrony. Using a playback experiment, I demonstrated that the acoustic components of penguin displays facilitated courtship behaviour from perceiving conspecifics. I argue that social facilitation may alter the availability of social stimuli and cluster acts of copulation, both of which may influence the timing and synchrony of breeding

Mean (sem) metabolic responses for LBC, MBC and HBC ewes between day 37 and 87 of pregnancy: (A) glucose and (B) FFA plasma concentrations.

<p>^Aeffect of BCS treatment (P&lt;0.01), ^bTime×BCS treatment interaction (P&lt;0.05). *Indicates a significant BCS treatment difference at individual time points (ANOVA).</p

Mean (sem) endocrine responses during the acute cold challenge for LBC, MBC and HBC ewes at day 85–87 of pregnancy: (A) plasma leptin and (B) T4 responses to the acute cold challenge.

<p>The horizontal line indicates the period of the cold challenge (0–360 min). ^aEffect of BCS treatment during the cold stress challenge, (P&lt;0.05), ^BTime×BCS treatment interaction during the cold stress challenge (P&lt;0.01), ^cEffect of BCS treatment during the recovery phase (P&lt;0.05, 480 and 1320 min), ^CEffect of BCS treatment (P&lt;0.01) during the recovery phase, ^DTime×BCS treatment interaction (P&lt;0.01) during the recovery phase.</p

Experimental timeline (D = day of gestation, BS = blood sample).

<p>Experimental timeline (D = day of gestation, BS = blood sample).</p

Mean (sem) live weight and BCS for LBC, MBC and HBC ewes between day 37 and 87 of pregnancy: (A) liveweight and (B) BCS.

<p>^AEffect of BCS treatment (P&lt;0.01). ^BTime×treatment interaction (P&lt;0.01), ^bTime×treatment interaction (P&lt;0.05).</p

Mean (sem) endocrine responses for LBC, MBC and HBC ewes between day 37 and 87 of pregnancy: (A) leptin and (B) insulin plasma concentrations.

<p>^Aeffect of BCS treatment (P&lt;0.01), ^BTime×BCS treatment interaction (P&lt;0.01). *Indicates a significant BCS treatment difference at individual time points (ANOVA).</p

Mean (sem) endocrine responses during the acute cold challenge for LBC, MBC and HBC ewes at day 85–87 of pregnancy: (A) plasma cortisol and (B) insulin responses to the acute cold challenge.

<p>The horizontal line indicates the period of the cold challenge (0–360 min). ^aEffect of BCS treatment on peak plasma cortisol concentrations during the cold stress challenge (P&lt;0.05, see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037315#pone-0037315-t002" target="_blank">Table 2</a>), ^Aeffect of BCS treatment during the cold stress challenge (P&lt;0.01), ^BTime×BCS treatment interaction during the cold stress challenge (P&lt;0.01), ^cEffect of BCS treatment during the recovery phase (P&lt;0.05, 480 and 1320 min).</p

Mean (sem) skin temperatures (°C) during the acute cold challenge for LBC, MBC and HBC ewes at day 85–87 of pregnancy: (A) ear skin temperature, (B) trunk skin temperature and (C) leg skin temperature.

<p>The horizontal line indicates the period of the cold challenge (0–360 min). ⁺Tendency for a BCS treatment effect (P&lt;0.1), ^bTime×BCS treatment interaction (P&lt;0.05).</p

Mean (sem) metabolic responses to the acute cold challenge for LBC, MBC and HBC ewes at day 85–87 of pregnancy: (A) Glucose, (B) β-HBA, and (C) FFA plasma responses to the acute cold challenge.

<p>The horizontal line indicates the period of the cold challenge (0–360 min). ^aEffect of BCS on AUC during the cold stress challenge (P&lt;0.05). For more detailed statistics see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037315#pone-0037315-t002" target="_blank">Table 2</a>.</p