Jennifer Little BSc Hons MSc RNutr PgCert
Independent Equine Nutritionist


Choosing to breed from your mare can be a very exciting time. But, as a pregnancy progresses there are several nutritional factors that need to be considered, especially during late gestation. It is in the later phase of pregnancy, where the foetus’s growth rate is the most rapid, and when the mares requirements for several nutrients including protein and total energy (calories) increase. Unfortunately this is the same time that the size and location of the foetus starts to negatively impact on the efficiency of the mares digestive system (figure 1). The capacity of the digestive system becomes reduced, especially for the hindgut. It is within the hindgut where bacteria (known as the gut biome) convert fibre into energy. This energy source is then absorb through the gut wall, to become available for the horses body and bodily functions. The impact on the hindgut and the reduced action of gut biome can also reduce a mares apatite. The combination of reduced digestive efficiency and apatite with increased nutritional requirements, means that mares during this phase often require diet changes. There are multiple commercially available options, specifically formulated for brood mares. In addition to providing a suitable balanced diet, research has shown that the addition of the probiotic, Saccharomyces cerevisiae, can support the mare and subsequent foal.

Late Gestation

Anatomical location of foal - late pregnancy


Anatomical location digestive system - non pregnancy


Figure 1:
A: Anatomical location of foal – late pregnancy.
B: Anatomical location digestive system – non pregnancy [1]

Saccharomyces cerevisiae
This probiotic is a live, yeast based, micro-organisms, which has the ability to live within the horses hindgut. Supplementation of Saccharomyces cerevisiae helps to ensure its presence in the hindgut, creating an environment favourable for other types of beneficial bacteria [2:3]. Improving the efficiency of the digestive system, and potentially mitigating some of the impacts of pregnancy [4].

Supporting the mare
Supplementing a mares diet with Saccharomyces cerevisiae from 4 weeks before foaling through to 8 weeks post foaling has been shown to improve the nutritional value of both the forages and hard feeds ingested. This is achieved by increasing the mares ability to digest and absorb certain nutrients. Specifically multiple components of fibre, calcium, phosphorus and total dietary energy [4]. The mares ability to digest her forage and feeds can directly influence the qulaity of the colostrum and milk that she produces following the birth of the foal [5;6].

Colostrum – supporting foal immunity
Colostrum is the first milk that a mare produces, and it is the foals source of antibodies, know as imunoglobulins. In mares colostrum the most abundent imunoglobulin is imunoglobulin G (IgG) [5]. While a foal should be born with a functioning imune system, at the time of birth they have not recived any antibodies via the placenta. The foal is dependent on the mares colostrum to provide sufficient imunolglobins, especially IgG, to achieve a passive transfer of immunity. A failure of passive transfer results in foals being at a high risk of developing potentially fatal sepsis [7;8]. One measure that can be employed to improve the quality of the colostrum produced is the supplementation of the mare with Saccharomyces cerevisiae for at least the last month of grestation [5].

Following ingestion of the colostrum foals born from supplemented mares have been shown to achieve significantly higher levels of IgG within their blood serum, compared with foals born from unsupplemented mares [5].

Influencing the mares milk & supporting foal growth
After the colostrum the mare goes on to produce milk, the quality of which directly impacts the growth rate and weight gain of the nursing foal. Supplementating the mare with Saccharomyces cerevisiae from 4 weeks before birth to 8 weeks post foaling has been shown to significantly stimulate milk production at the onset of lactation [6]. In addition to the increased volume of milk produced, the quality of the milk can also be influenced. Milk produced from supplemented mares has significantly higher levels of fat, protein, sugar, amino acids and total energy in comparison to unsupplemented mares [6].

Foals nursing from mares supplemented with Saccharomyces cerevisiae (from 4 weeks before birth to 8 weeks post partum) have demonstrated 24% more efficient growth, with higher weight gains by week 4, and greater growth at the withers by 6 weeks of age [6].

Preparing for the safe arrival of a foal, ensuring the health of the mare, and thriving of the subsequent foal, requires multiple considerations. However, choosing to supplement the mares diet with Saccharomyces cerevisiae during late pregnancy and early lactation has been shown to;
• Improve the efficiency of the mares digestive system
• Increase the transfer of antibodies (IgG) to the foal, via the colostrum
• Increase the quantity and quality of the mares milk produced
• Increase the growth rates and weight gains of the nursing foal.


[1] Chaucheyras-Durand, F., Sacy, A., Karges, K., Apper, E. 2022 Gastro-Intestinal Microbiota in Equines and its role in health and disease: the black box opens. Microorganisms (10) 2517
[2] Linderberg,F, Krych,L., Kot,W., Fielden, J., Frokiaer,H., van Galen,G., Nielsen,D.S, Hansen,A.K. 2019 Development of the equine gut microbiota. Sci. Rep. (9) 14427
[3] Mach, N., Ruet, A., Clark, A., Bars-Cortina, D., Ramayo-Caldas, Y., Crisci, E., Pennarun, S., Dhorne-Pollet, S., Foury, A., Moisan, M.P, 2020 Priming for welfare: gut microbiota is associated with equitation conditions and behaviour in horse athletes. Sci. Rep. (10) 8311
[4] Perricone, V., Sandrini, S., Irshad, N., Comi, M., Lecchi, C., Savoini, G., & Agazzi, A., 2022 The role of yeast saccharomyces cerevisiae in supporting gut health in horses: An updated review on its effects on digestibility and intestinal faecal microbiota. Animals 12, 3475
[5] Coverdale, J.A., 2016. Horse species symposium: can the microbiome of the horse be altered to improve digestion? J. Anim. Sci. (94) 2275-2281
[6] Geor, R.J., Harris, P.A., & Coenen, M., 2013 Equine Applied and clinical nutrition. Health welfare and performance. Saunders Elsevier, 575-576
[7] Valigura, H.C., Leatherwood, J.L., Martines, R.E., Norton, S.A., White-Springr, S.H., Dietary supplementation of a Saccharomyces cerevisia fermentation product attenuates exercise-induced stress markers in young horses. J. Anim Sci 99, 199
[8] Newbold, C.J., Wallace, R.J., McIntosh, F.M., 1996 Mode of action of the yeast Saccaromyces cerevisiae as a feed additive for ruminants Br. J. Nutr. 76, 249-261
[9] Respondek,F., Goachet,A.G., Julliand,V. 2008 Effects of dietary short-chain fructooligosaccahrides on the intestinal microflora of horses subjected to a sudden change in diet. Journal of Animal Science. 86 (2) 316-323
[10] Zhao, W., Chen, L., Tan, W., Li, Y., Sun, L., Zhu, X., Wang, S., Gao, P., Zhu, C., Wang, L., Jiang, Q. 2023 Mannan Oligosaccharides promoted skeletal muscle hypertrophy through the gut microbiome and microbial metabolites in mice. Foods, 12, 357
[11] Lyte, M. 2013 Microbial endocrinology in the microbiome-gut-brain axis: How bacterial production and utilization of neurochemicals influence behaviour. PLoS Pathog (9) e1003726

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