Adaptive responses of Mérinos d’Arles adult ewes submitted to nutritional and β-adrenergic challenges

Abstract En

Shortage and refeeding situations lead to switches in metabolic pathwaysinduced by undernutrition and body reserves (BR) replenishment cycles. In a 122-d experiment, we studied adaptive mechanisms in 36 adult non-pregnant Mérinos d’Arles ewes, selected with similar BW and BCS. Ewes were acclimated to diet ingredients (i.e., wheat straw, pelleted alfalfa and sugar beet pulp) and to the facility environment during 22 d. Then, the “diet challenge” (planes of nutrition; 12 ewes each) was applied during the first 50 d (normally fed, Control; underfed, Under; overfed, Over) and an individual monitoring (twice a week) of BW, BCS and energy metabolism was carried out. Then, a “refeeding challenge” was applied during the last 50 d (i.e., diets were adjusted using the same ingredients). The last day, the lipolytic activity was studied with a “β-adrenergic challenge” (4 nmol/ kg BW of isoproterenol) to the same ewes (BCS according to diet; i.e., Normal, Lean and Fat, respectively). The PROC MIXED with repeated measures of SAS package was used for data analyses. The NEFA response at each time after the β-adrenergic challenge was calculated as well as the area under the concentration curve at 5 min. time intervals during 1 h. Anabolic or catabolic responses were accompanied by synchronized metabolic regulations, leading to contrasting metabolic and BR profiles. Average BW and BCS were higher and lower in Over and Under ewes, respectively, which was proportional to BR dynamics (higher and lower BR mobilization in Under and Over ewes, respectively). Higher plasma NEFA were accompanied by lower insulin, leptin and glucose. Differences in leptin were consistent with energy load (Over > Control >Under). After refeeding, a rebound in BW and BCS was observed and NEFA was drastically reduced in Under ewes. No differences were detected in NEFA profiles at the end of the study but lipolytic activity was different and contrasted with adipose tissue mass (Lean > Normal ≈ Fat). Differences in those responses between ewes with the same BR status evidenced diversity among individual adaptive capacities. There is potential for a simplified β-adrenergic challenge protocol helping to characterize intraflock variability in adaptive capacity.