Improving Fertility in Older Mares: Can the Effects of Aging be Reversed?

The University of Sydney

  • Project code: PRO-015542

  • Project stage: Current

  • Project start date: Saturday, January 14, 2023

  • Project completion date: Thursday, October 29, 2026

  • National Priority: HOR-Thoroughbred breeding


Early embryonic death is a major component of reproductive loss in horses and is mainly attributed to poor quality eggs ovulated by broodmares. The quality of the egg or oocyte is important for normal embryo development following fertilisation. This in turn impacts the establishment of a pregnancy, foetal development, and subsequent foal health.  Recent studies have revealed that the level of nicotinamide adenine dinucleotide (NAD+), an essential regulator of energy metabolism in all cells, is associated with egg quality and declines with advancing maternal age. Vitamin B3 supplements, including niacin and related NAD+ precursors, have been found to elevate the level of NAD+, improve egg quality and enhance embryo development, in aged mice. The “anti-aging” effects of these supplements are gaining increasing attention, especially for improving human health and fertility. This project will examine the effects of supplementing feed with niacin, also known as nicotinic acid, on mare fertility. Our previous studies in standardbred mares have determined the optimal daily dose of niacin and showed that feeding the supplement for several days prior to ovulation substantially altered the NAD+ precursor concentrations in the follicular fluid that surrounds the egg. The proposed study will examine the relationship between niacin supplementation and pregnancy outcomes, especially in older mares and “problem” mares that are difficult to get in foal. Targeted feeding with niacin promises to improve conception rates, reducing the time, effort and expense needed to get mares in foal, and extend the reproductive lifespan of older mares.


Thoroughbred Horses

Research Organisation

The University of Sydney

Objective Summary

In our previous studies in standardbred mares, concentrations of niacin and its related metabolites were found to be elevated in the circulating blood and ovarian follicular fluid (FF) following oral administration of niacin. Elevated concentrations of these metabolites are hypothesised to increase NAD+ production and improve energy metabolism in reproductive cells and tissues, thereby improving oocyte quality and embryo viability. An effective niacin dose and treatment period were determined in our previous trials, but further assessments are needed to determine the optimal dose and treatment period in thoroughbred mares. The proposed studies will target aged mares and problem mares that are difficult to get in foal because evidence indicates that the niacin supplement will be of greatest benefit to these groups of mares. The major objective of the project is to assess the capacity of a well-defined niacin supplemental feeding regimen to improve breeding efficiency in aged and problem mares.
 The specific objectives of the project are to:
1. Determine the optimal daily dose of niacin, given over 4 consecutive days prior to ovulation, in aged and problem mares.
2. Assess the effects of niacin dose on the FF levels of NAD+ metabolites and the blood levels of oestradiol.
3. Determine the optimal treatment period in aged and problem mares, using the optimal daily dose of niacin by assessing FF metabolite concentrations and oocyte quality.
4. Assess the effects of niacin treatment period on the FF levels of NAD+ metabolites and oocyte quality.
5. Determine the effect of the optimal daily dose of niacin and the optimal treatment period on conception and pregnancy rates in aged and problem mares.
6. Determine the effect of the optimal daily dose of niacin and the optimal treatment period on the health of newborn foals.