Foal sex in Thoroughbred horses: related factors.
Abstract: Reproductive biotechniques in the equine species have advanced in the last decade and horse breeders have started to question the possibilities of interfering in the determination of foal sex. The aim of the present study was to verify whether the variables mares and stallion's age, side of the ovary containing the preovulatory follicle, preovulatory follicle diameter, time between breeding and ovulation, and ovulation inducing hormones influence the sex of the foal. A total of 259 reproductive cycles of 160 mares and 22 Thoroughbred stallions were used. Statistical analysis was performed using R software, including Pearson's chi-square test and logistic regression. Of the total foals born, 136 were males (52.51%) and 123 were females (47.49%). In mares that ovulated with -24h after ovulation induction, 104 foals (54.74%) were males and 86 (45.26%) were females, while in mares that ovulated with +24h, 32 foals (46.38%) were males and 37 (53.62%) were females. Stallions up to 15 years old had 44.14% (n=49) females and those over 15 years had 49.66% (n=73) females. The simple logistic regression model showed that mares and stallions under 15 years old, mares with ovulation time less than 24 hours and treated with Deslorelin had a higher probability of having male foals, but the Pearson's chi-square test showed that foals gender were not influenced by the variables studied.
Copyright © The Author(s).
Publication Date: 2024-08-05 PubMed ID: 39176003PubMed Central: PMC11340788DOI: 10.1590/1984-3143-AR2023-0073Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
The study focuses on the potential influencing factors on the sex determination of Thoroughbred horse foals, such as age of the parents, ovary side containing the pre-ovulatory follicle, preovulatory follicle diameter, hormones, and time between breeding and ovulation. However, the findings suggest that these variables may not significantly impact the sex of the foals.
Methodology
- Researchers conducted this study with 259 reproductive cycles involving 160 mares and 22 Thoroughbred stallions.
- The article seems to establish a correlation between the factors studied and the sex of the resulting foals.
- The data was analysed using R software, utilising Pearson’s chi-square test and logistic regression methods.
Findings
- Out of the total foals born, 136 were males and 123 were females–almost an even distribution.
- Mares that ovulated more narrowly after ovulation induction saw slightly more male foals, whereas there was a slight bias towards female foals in mares that ovulated later.
- Stallions up to the age of 15 had a smaller percentage of female offspring than stallions older than 15.
- However, the Pearson’s chi-square test suggested that the variables studied did not significantly influence the sex of the foals.
Discussion and Analysis
- Although some relationships were noted, such as a higher probability of having male foals among mares and stallions under 15 years old and mares with ovulation time less than 24 hours, these findings are not statistically significant.
- Eventually, this leads to a conclusion that the age of the parents, side of the ovary containing the pre-ovulatory follicle, preovulatory follicle diameter, hormones used for inducing ovulation, and the time interval between breeding and ovulation may not be significantly influential factors in determining the sex of Thoroughbred horse foals.
Conclusion
- The study points to further research needed to conclusively determine the factors that influence the gender of Thoroughbred horse foals, as the current study did not find the explored variables to be significantly influential.
Cite This Article
APA
Flores JG, Bueno VC, Bastos HBA, Rechsteiner SMDEF.
(2024).
Foal sex in Thoroughbred horses: related factors.
Anim Reprod, 21(3), e20230073.
https://doi.org/10.1590/1984-3143-AR2023-0073 Publication
Researcher Affiliations
- Histologia e Reprodução Equina (HISTOREP), Faculdade de Veterinária, Universidade Federal de Pelotas, Pelotas, RS, Brasil.
- Laboratório de Reprodução Animal (REPROLAB), Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
- Histologia e Reprodução Equina (HISTOREP), Faculdade de Veterinária, Universidade Federal de Pelotas, Pelotas, RS, Brasil.
- Laboratório de Reprodução Animal (REPROLAB), Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
- Laboratório de Reprodução Animal (REPROLAB), Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
- Histologia e Reprodução Equina (HISTOREP), Faculdade de Veterinária, Universidade Federal de Pelotas, Pelotas, RS, Brasil.
- Laboratório de Reprodução Animal (REPROLAB), Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
Conflict of Interest Statement
Conflicts of interest: The authors have no conflict of interest to declare.
References
This article includes 37 references
- Abecia JA, Arrébola F, Palacios C. Offspring sex ratio in sheep, cattle, goats and pigs: influence of season and lunar phase at conception.. Biol Rhythm Res 2016;48(3):417–424.
- Aurich C, Schneider J. Sex determination in horses - current status and future perspectives.. Anim Reprod Sci 2014;146(1-2):34–41.
- Ben-Rafael Z, Matalon A, Blankstein J, Serr DM, Lunenfeld B, Mashiach S. Male to female ratio after gonadotropin-induced ovulation.. Fertil Steril 1986;45(1):36–40.
- Cameron EZ, Linklater WL, Stafford KJ, Veltman CJ. Birth sex ratios relate to mare condition at conception in Kaimanawa horses.. Behav Ecol 1999;10(5):472–475.
- Cameron EZ, Linklater WL. Extreme sex ratio variation in relation to change in condition around conception.. Biol Lett 2007;3(4):395–397.
- Cameron EZ. Facultative adjustment of mammalian sex ratios in support of the Trivers-Willard hypothesis: evidence for a mechanism.. Proc Biol Sci 2004;271(1549):1723–1728.
- Edwards AW. The genetical theory of natural selection.. Genetics 2000;154(4):1419–1426.
- Giraldo AM, Hylan D, Bondioli KR, Godke RA. Distribution of sexes within the left and right uterine horns of cattle.. Theriogenology 2010;73(4):496–500.
- Gutiérrez-Adán A, Oter M, Martínez-Madrid B, Pintado B, De La Fuente J. Differential expression of two genes located on the X chromosome between male and female in vitro-produced bovine embryos at the blastocyst stage.. Mol Reprod Dev 2000;55(2):146–151.
- Gutiérrez-Adán A, Pérez-Garnelo, Granados J, Garde JJ, Pérez-Guzmán M, Pintado B, De La Fuente J. Relationship between sex ratio and time of insemination according to both time of ovulation and maturational state of oocyte.. Zygote 1999;7(1):37–43.
- Hall S, Jarrin-Yepez P, Schneider L, Klabnik-Bradford J, Riddle W, Friend W, Schnobrich M, Prado T. Influence of period between breeding and ovulation on foal sex ratio.. Clin Theriogenology 2022;14(1):18–31.
- Harlap S. Gender of infants conceived on different days of the menstrual cycle.. N Engl J Med 1979;300(26):1445–1448.
- Hosmer JR, David W, Stanley L, Rodney X. Applied logistic regression.. Hoboken: John Wiley & Sons; 2000.
- Hylan D, Giraldo AM, Carter JA, Gentry GT Jr, Bondioli KR, Godke RA. Sex ratio of bovine embryos and calves originating from the left and right ovaries.. Biol Reprod 2009;81(5):933–938.
- James WH. Evidence that mammalian sex ratios at birth are partially controlled by parental hormone levels at the time of conception.. J Theor Biol 1996;180(4):271–286.
- Krackow S. The developmental asynchrony hypothesis for sex ratio manipulation.. J Theor Biol 1995;176(2):273–280.
- Liu Y, Zhi M, Li X. Parental age and characteristics of the offspring.. Ageing Res Rev 2011;10(1):115–123.
- Martinez F, Kaabi M, Martinez-Pastor F, Alvarez M, Anel E, Boixo JC, de Paz P, Anel L. Effect of the interval between estrus onset and artificial insemination on sex ratio and fertility in cattle: a field study.. Theriogenology 2004;62(7):1264–1270.
- Navara KJ. Hormone-mediated adjustment of sex ratio in vertebrates.. Integr Comp Biol 2013;53(6):877–887.
- Nicolich MJ, Huebner WW, Schnatter AR. Influence of parental and biological factors on the male birth fraction in the United States: an analysis of birth certificate data from 1964 through 1988.. Fertil Steril 2000;73(3):487–492.
- Noorlander AM, Geraedts JP, Melissen JB. Female gender pre-selection by maternal diet in combination with timing of sexual intercourse--a prospective study.. Reprod Biomed Online 2010;21(6):794–802.
- Pinto CRF. Use of prostaglandin F2 alfa for controlling the mare’s estrous cycle. AAEP Annual Convention; 2013; Nashville: American Association of Equine Practitioners; 2013. pp. 337–341.
- Rath D, Moench-Tegeder G, Taylor U, Johnson LA. Improved quality of sex-sorted sperm: a prerequisite for wider commercial application.. Theriogenology 2009;71(1):22–29.
- Rezagholizadeh A, Gharagozlou F, Akbarinejad V, Youssefi R. Left-sided ovulation favors more male foals than right-sided ovulation in Thoroughbred mares.. J Equine Vet Sci 2015;35(1):31–35.
- Rorie RW, Lester TD, Lindsey BR, McNew RW. Effect of timing of artificial insemination on gender ratio in beef cattle.. Theriogenology 1999;52(6):1035–1041.
- Sakai N, Endo A. Effects of induced ovulation by pregnant mare’s serum and human chorionic gonadotropin on the sex ratio of mouse fetuses.. Gamete Res 1987;16(4):319–322.
- Saltz D, Rubenste D. Population dynamics of a reintroduced asiatic wild ass (equus hemionus) herd.. Ecol Appl 1995;5(2):327–335.
- Samper JC, Morris L, Peña FJ, Plough TA. Commercial breeding with sexed stallion semen: reality or Fiction?. J Equine Vet Sci 2012;32(8):471–474.
- Santos MM, Maia LL, Nobre DM, Oliveira JF, No, Garcia TR, Lage MC, de Melo MI, Viana WS, Palhares MS, da Silva JM, Fo, Santos RL, Valle GR. Sex ratio of equine offspring is affected by the ages of the mare and stallion.. Theriogenology 2015;84(7):1238–1245.
- Sartorelli EM, Mazzucatto LF, de Pina-Neto JM. Effect of paternal age on human sperm chromosomes.. Fertil Steril 2001;76(6):1119–1123.
- Scoggin CF. Not just a number: effect of age on fertility, pregnancy and offspring vigour in thoroughbred brood-mares.. Reprod Fertil Dev 2015;27(6):872–879.
- Silk JB. Local resource competition and facultative adjustment of sex ratios in relation to competitive abilities.. Am Nat 1983;121(1):56–66.
- Smith JM. A new theory of sexual investment.. Behav Ecol Sociobiol 1980;7(3):247–251.
- Stone BA, Alex A, Werlin LB, Marrs RP. Age thresholds for changes in semen parameters in men.. Fertil Steril 2013;100(4):952–958.
- Trivers RL, Willard DE. Natural selection of parental ability to vary the sex ratio of offspring.. Science 1973;179(4068):90–92.
- Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation: effects on the probability of conception, survival of the pregnancy, and sex of the baby.. N Engl J Med 1995;333(23):1517–1521.
- Zarutskie PW, Muller CH, Magone M, Soules MR. The clinical relevance of sex selection techniques.. Fertil Steril 1989;52(6):891–905.
Citations
This article has been cited 0 times.Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
