Production of lambs' resilience to Haemonchus contortus

Haemonchus (H.) contortus infection in sheep is a major health problem in tropical and sub-tropical regions that cause great economic losses. Our previous studies have shown that improved uterine environments during pregnancy can improve postnatal growth and health performance of the offspring, indicated by lower mortality and morbidity. In the present experiment, we evaluated the resistance and resilience to H. contortus of lambs born to ewes injected with pregnant mare's serum gonadotropin (PMSG) prior to mating. Improvement of the uterine environment was conducted by increasing endogenous secretion of estrogen and progesterone as pregnancy hormones during pregnancy by injecting the ewes with PMSG prior to mating. A total of 16 lambs, regardless of sex, at the age of 5 months were assigned into a 2 × 2 factorial experiment with 4 replications. The first factor was PMSG injection, consisting of two levels, i.e., lambs born to ewes without PMSG injection (Non-PMSG lambs) and those born to PMSG-injected ewes (PMSG lambs). The second factor was the infection of lambs with H. contortus at the age of 5 months, consisting of two levels, i.e., lambs without infection (Non-infected lambs) and lambs infected with H. contortus (Infected lambs). Non-infected lambs were administered with distilled water in a capsule without infective larvae. Infected lambs were individually infected with a single dose containing 1200 L3 of H. contortus. Compared to non-PMSG lambs, PMSG lambs tended to have better prenatal growth indicated by greater birth weights (P = 0.06). The improved prenatal growth during pregnancy improved the postnatal growth and health performance of the lambs. Three months after infection of H. contortus, non-PMSG lambs and PMSG lambs had similar worm counts. However, the PMSG lambs showed significantly higher resilience to H. contortus as indicated by the lower fecal egg counts 6-10 weeks after infection. The higher resilience of the PMSG lambs was shown by the positive growth rate during infection, while non-PMSG lambs had a negative growth rate after infection. Prior to infection, PMSG lambs showed a higher segmented neutrophil percentage with lower lymphocyte numbers. Three months after infection, PMSG lambs had significantly higher lymphocyte and thrombocyte numbers as well as mean corpuscular hemoglobin concentration (MCHC) with lower neutrophil and monocyte numbers. The conclusion of this study is that the improvement of the uterine environment during pregnancy could be used to produce superior offspring with high resilience to the infection of H. contortus.