Oxidative Status of Kangal Ewes Under Accelerated Versus Conventional Reproductive Management: A Cross-Sectional Comparison at Day 40 of Lactation.

Abstract

In sheep farming, distributing reproductive and lactation periods throughout the year is of great importance for increasing farm profitability. Hormone-supported oestrus induction protocols applied during the anoestrous period enable a second pregnancy and lactation to be achieved within the same year. Whether this accelerated management pattern is associated with an altered oxidative status has not been examined in ewes. In this cross-sectional study, 20 multiparous Kangal ewes that had lambed a single lamb in the early months of the year and were subsequently subjected to a short-term (7-day) synchronisation protocol (flugestone acetate sponge, eCG and cloprostenol) during anoestrus, and which entered a second lactation in the same year (Group 1, accelerated management), were compared with 20 contemporaneous ewes that received no hormonal treatment, were not mated and were therefore in the dry period at sampling (Group 2, conventional management). All ewes in Group 1 again reared a single lamb. Blood was collected from both groups on the same calendar date, corresponding to Day 40 ± 4 of the second lactation in Group 1. Serum malondialdehyde (MDA) and the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were measured and compared by Mann-Whitney U test. SOD activity was significantly lower in Group 1 than in Group 2 (60.55 ± 0.876 vs. 70.19 ± 0.476 U/L; p < 0.0001), and MDA concentration was modestly higher (10.30 ± 0.363 vs. 8.99 ± 0.619 nmol/mL; p = 0.035); CAT and GPx activities did not differ (p > 0.05). The MDA difference was of moderate magnitude and did not withstand correction for multiple comparisons (q = 0.070), whereas the SOD difference did. Because the groups differed simultaneously in lactational status, hormonal exposure and recent gestation, these differences cannot be attributed to any single component of the protocol, and the single time point precludes inference about the trajectory of oxidative change. What the data show is that accelerated reproductive management returns the ewe to a pro-oxidant lactational state during a period in which she would otherwise be dry and recovering. Whether the repeated loss of this recovery window has cumulative consequences requires a longitudinal, within-animal design. In conclusion, accelerated reproductive management was associated with lower SOD activity and modestly higher MDA at Day 40 of lactation, but did not increase the intensity of oxidative stress beyond the level previously reported for conventional lactation; what this management system changes is the duration of lactational exposure rather than its intensity.