Blue LED light treatment of pregnant mares is not detrimental to gonadal development in their offspring

Abstract

A light program transmitted via blue LED light directed at one eye from individual light masks (Equilume, Kildare, Ireland) to pregnant mares from the middle of December onwards advanced the onset of foaling with birth of mature and healthy foals, but they were slightly smaller than foals from untreated control pregnancies (Lutzer et al., Domestic Anim Endocrinol 2022;78:106675). Differences, however, equilibrated within the first year of life. In this study we followed the hypothesis that light treatment of pregnant mares is without detrimental effects on body size and gonadal development of offspring after puberty. A total of 47 warmblood horses born and raised on the same stud farm to blue LED light-treated (17 males and 9 females) or control mares (14 males and 9 females) were included. At 24 months of age, their body weight, height at withers and cannon bone circumference was determined. In males, the external genitalia were examined, testis size was measured by transcutaneous ultrasound. The total testicular volume (TTV) was calculated. In females, a transrectal ultrasound examination of the genital tract was performed, the presence of corpora lutea was detected via plasma progesterone concentration and the antral follicle count (AFC) was assessed. Statistical comparisons weremade by analysis of variance (general linear model) with group (blue light vs. control) and sex (male vs. female) as between subject factors (IBM SPSS 27). Results are given as mean ± SEM. There were no group or sex differences with regard to bodyweight or height at the withers. The cannon bone circumference was larger in male vs. female horses (p<0.001) but not affected by blue light treatment during pregnancy. Testes were classified as normal in size and location (Love et al., J Reprod Fertil Suppl 1991;44:99-105) in 13 of 17 blue light and 11 of 14 control colts (n.s., chi2 analysis). The TTV was 232±14cm3 in the blue light and 218±11cm3 in the control group (n.s.). Abnormal testicular development was diagnosed in 7 males with unequal testicular size in 3 blue light and 2 control animals, both testes too small (1 blue light) or unilaterally cryptorchid (1 control). In females, no abnormalities were present. A corpus luteum (progesterone >1ng/ml) was present in 8 / 9 females from the blue light and 5 / 8 from the control group. The AFC was 20.6±2.5 in blue light and 22.1±3.7 in control females (n.s.). Results demonstrate that blue LED light treatment of pregnant mares has no detrimental effects on body and genital tract development of their offspring at two years of age.