When biological experience determines individual adaptation: the role of parity in the efficiency of body reserves mobilization-accretion process in ruminants

The effects of parity [primiparous (PRIM) or multiparous (MULT)] on the efficiency of the body reserves (BR) mobilization-accretion process was evaluated in reproductive ewes belonging to two sheep breeds and contrasting in their productive purpose (dairy or dual) and rearing system (confined or grazing). The experiment was carried out throughout an entire year using 48 and 41 Lacaune and Romane ewes, respectively. Temporal changes in BR and profiles of related metabolites and metabolic hormones were monitored. Ewes were allocated to homogeneous groups according to body weight (BW) and body condition score (BCS), and distributed by parity (PRIM or MULT) and litter size (LSi) [lambing singletons (SING) or TWINS. The feeding system was based on the conventional system for each breed without intervention. Individual BW, BCS, plasma NEFA, β -hydroxybutyrate, glucose, insulin, leptin and triiodothyronine (T3) were monitored from 1.5 month before lambing until the end of next pregnancy at intervals of approximately 1 month. Mobilization of BR occurred from late pregnancy to the end of suckling, whereas BR accretion was performed from weaning until mating. Lipolysis was well illustrated by NEFA, ß-OHB, leptin and T3 kinetics which varied in function of the ewe energy balance but also due to the feeding situation. Overall, temporal changes in BR were directly affected by the evolution of physiological states and feeding levels while responses were predetermined by the ‘biological experience’ (parity) of the ewe [homeostatic (self-fishing) or teleophoretic behavior in PRIM and MULT, respectively]. In MULT, the readiness and magnitude of response was influenced by LSi. This work puts forward the interest of long-term studies about body reserves dynamics in ruminants. Monitoring the metabolic profiles enables one to obtain relevant insights about the individual nutritional status at a given point. The whole set of parameters allow the detection of sensitive and critical periods throughout the entire annual cycle, indicating new opportunities for management improvement, for example during physiological states usually underestimated like early and mid-pregnancy