Risk factors, serum metabolite profiles, and productivity associated with periparturient metabolic stress in four maternal sheep breeds

Abstract Improved husbandry, genetic selection, or strategic crossbreeding can increase reproductive efficiency in sheep, which has corresponding effects on ewe nutrient requirements during the periparturient period. However, metabolic responses in prolific sheep populations are not well defined. The objectives of this study were to estimate periparturient metabolic stress risk factors and associations with ewe productivity in four maternal sheep breeds (Composite-IV [C-IV], Polypay, Katahdin, and Romanov). Serum concentrations of glucose, non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), Ca, K, Mg, and P were measured in 184 ewes across breeds at approximately -14, -7, 0, and 7 d relative to parturition. Serum values were analyzed as repeated measures within each breed, with fixed class effects of ewe age and periparturient timepoint, the linear covariate of litter birth weight (LBW), and all two-way interactions. Interactions among model effects were prevalent for several metabolites. Within Katahdins, glucose concentrations were greater at d 0 than other timepoints (P ≤ 0.02) for 5-yr and older ewes but no differences were observed between timepoints within younger ewes. Serum BHBA concentrations were lower at d -14 and -7 than d 0 and 7 within 2-yr-old Polypay ewes (P ≤ 0.01) and lower at d -14 than d 0 within 4-yr-old Polypay ewes (P < 0.01). At lambing (d 0), BHBA concentration increased with LBW in Romanov ewes (P < 0.01) and glucose concentration decreased with LBW in Katahdin ewes (P < 0.01), but values were unaffected by LBW at other timepoints. In Polypay ewes, Ca concentration increased with LBW in 2-yr-olds (P < 0.01) but decreased with LBW in 4-yr-olds (P < 0.001). Postpartum (d 7) serum energy metabolites (glucose, NEFA, BHBA) were categorized as HIGH or LOW based on median breed values to evaluate their effect on litter weaning weight (LWW). Polypay and Romanov ewes with HIGH NEFA had 8.4 kg and 12.8 kg greater LWW, respectively, than those with LOW NEFA (P < 0.05). Additionally, Polypay ewes with HIGH BHBA had 14.8 kg greater LWW (P < 0.001) than those with LOW BHBA. Results indicate that main and interactive effects of ewe age, LBW, and time relative to lambing contribute to periparturient metabolic stress in maternal U.S. sheep breeds. Understanding these risk factors for metabolic stress may enable targeted management to improve ewe productivity and health.