Dead Sperm Do Not Cause Greater Uterine Immune Response!

We know that sperm are the primary instigator for initiating the mare’s post-breeding uterine inflammatory response[1], but one not infrequently hears commentary to the effect of concerns that there may be a greater response if the insemination dose contains a higher number of dead sperm. Cousseau et al have however demonstrated this to not be the case.

20 clinically healthy, in estrus, breeding-sound mares – as evidenced by an absence of uterine fluid or uterine polymorphonucleocyte (PMN) inflammatory cell presence were selected. These mares all had uterine edema presence, and follicles ≥ 35 mm in diameter. Average age was 10.8 ± 0.9 years (range 6-20), with a body score exceeding 3 on a 1-5 scale. Two groups of 10 each were randomly selected to receive different quality of thawed frozen semen collected and pooled from two stallions. One group received semen which had been thawed normally, the other group received semen which had been thawed and then snap-frozen to kill the sperm prior to being thawed again and inseminated. Both groups received a 3-ml dose containing 900 million sperm. In the live group, the sperm were >35% progressively motile.

Four hours after the insemination, samples were recovered from the uteri by low-volume lavage (50 ml) and biopsy samples (3 sample sites – each horn and the body). The samples were then evaluated for Leukocyte and PMN concentrations.

Mares in the group inseminated with the dead sperm showed lower Leukocyte and PMN levels in all samples, thereby confirming that in these evaluations “dead sperm elicited a less intense inflammatory response 4 hours after AI compared to live sperm, suggesting that as with bacteria, the immune system may differentiate sperm according to viability.”

It is always interesting to see dogma destroyed by solid science!

(Cousseau SB, Cazales N, Fiala-Rechsteiner SM, Mattos RC. 2023. Influence of sperm viability on uterine leukocyte chemotaxis. JEVS 125:104704)

1: Troedsson, M.H.; Liu, I.K.; Crabo, B. 1998. Sperm transport and survival in the mare. Theriogenology 49:905–915