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

Control of abomasal secretion in the sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in physiology at Massey University in the Department of Physiology and Anatomy

Preface: This thesis is concerned with an experimental investigation of abomasal secretion in sheep. The abomasum is the most caudal region of the ruminant stomach and is the only truly secretory part of it. The experimental work considered includes the study of hydrochloric acid secretion, the electrolyte composition and the peptic activity of abomasal secretion. Simultaneous observations have been made of abomasal acid secretion and motility of the reticulum and rumen recorded from partial exteriorisations of these structures. These observations have been made under a variety of conditions including periods when animals were feeding and fasted, and during rumination. The effect of intraduodenal infusions of fatty acids and oil on abomasal acid secretion and reticulum and rumen motility and of intravenous infusions of the same fatty acids has been studied Observations have also been made of the intravenous infusion of various substances reported to influence gastric secretion. Extracts exhibiting 'enterogastrone' activity have been tested; the effects of insulin studied; and the action of a synthetic gastrin ( ICI 50 , 123) which exhibits gastrin-like properties has been investigated. These observations were undertaken in the hope that it would be possible to elucidate further, factors which control or affect ab omasal acid secretion. An attempt has been made to determine whether any clear cut relation could be established between abomasal secretory activity and reticulorumenal motility. The observations presented below have been discussed in relation to the literature

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 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) 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 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) 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