With normal conception and pregnancy, SAA level in broodmares is comparable to that in other healthy horses. That includes the time of ovulation through early pregnancy1 and throughout the final trimester up to parturition2,3. Artificial insemination may induce negligible SAA production, but levels stay within normal physiological limits.
Although the majority of SAA is produced by the liver, local production by the endometrium likely contributes to systemic SAA elevation in pathological states.5 Elevation early in pregnancy may indicate an increased risk of early embryonic death (EED), whereas any spike in mid-to-late-term should raise concern for ascending placentitis and abortion risk. In clinical application, other potential causes of increased SAA must of course also be considered, as elevation can occur due to other infections or pathological conditions.2,6 However, SAA should remain normal in an otherwise healthy pregnant mare.
Elevated SAA at the time of ovulation reflects a greater risk of experiencing EED, possibly due to some degree of subclinical endometritis. EED may occur in these individuals despite the continued presence of an intact corpus luteum and maintenance of normal progesterone levels.1
In other mares with EED, SAA may be normal at ovulation but increase as early as 3 days post-ovulation. These cases are generally associated with excessive PGF2 and subsequent lysis of the corpus luteum, leading to EED. SAA typically remains elevated for at least 2 weeks, and sometimes up to 2 months.1
For greatest utility in early pregnancy, SAA should be evaluated around the time of ovulation and then rechecked at 7-14 days. At either of these timepoints, even mild elevations of SAA (20-100 µg/mL) should be considered significant and warrant closer evaluation and monitoring.
Monitoring SAA in mares with a history of high-risk pregnancy can provide valuable information, as it increases rapidly with ascending placentitis. This is in contrast to fibrinogen or white blood cell count, which do not appear to be useful markers for this condition.3
Following a diagnosis of placentitis, tracking SAA can help monitor risk of impending abortion.2,3 It increases on average 2-6 days prior to abortion from ascending placentitis and continues to rise until abortion occurs.2,3 Treatment should lead to a decrease in SAA if the pregnancy is effectively preserved, and persistent elevation indicates a high likelihood of impending abortion.2
Normal parturition is an acute inflammatory event, and as such may increase SAA to a mild degree (<100 µg/mL). However, after normal foaling it should return to normal within 2-3 days.2 More drastic or persistent elevation may indicate a medical issue requiring further investigation and care.
1 Krakowski L, Krawczyk CH, Kostro K, et al. Serum levels of acute phase proteins: SAA, Hp and progesterone (P4) in mares with early embryonic death. Reprod Dom Anim 2011;46:624-629.
2 Coutinho da Silva MA, Canisso IF, MacPherson ML, et al. Serum amyloid A concentration in healthy periparturient mares and mares with ascending placentitis. Equine Vet J 2013;45:619-624.
3 Canisso IF, Ball BA, Cray C, et al. Serum amyloid A and haptoglobin concentrations are increased in plasma of mares with ascending placentitis in the absence of changes in peripheral leukocyte counts or fibrinogen concentration. Am J Reprod Immunol 2014;72:376-385.
4 Wojtysiak K, Ryszka W, Stefaniak T, et al. Changes in the secretion of anti-inflammatory cytokines and acute phase proteins in the uterus after artificial insemination in the mare. Animals 2020;10(12):2438.
5 Christoffersen M, Baagoe CD, Jacobsen S, et al. Evaluation of the systemic acute phase response and endometrial gene expression of serum amyloid A and pro- and anti-inflammatory cytokines in mares with experimentally induced endometritis. Vet Immunol Immunopathol 2010;138(1-2):95-105.
6 Canisso IF, Loux SC, Lima FS. Biomarkers for placental disease in mares. Theriogenology 2020;150:302-307.
7 Ball BA. Embryonic loss in mares. Incidence, possible causes, and diagnostic considerations. Vet Clin North Am Equine Pract 1988;4(2):263-290
8 Giles RC, Donahue JM, Hong CB, et al. Causes of abortion, stillbirth, and perinatal death in horses: 3,527 cases (1986-1991). Am Vet Med Assoc. 1993;203(8):1170-1175