Feeding nicotinic acid to mares will likely reduce embryo losses – study

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Australian researchers believe short-term supplementation has the ability to improve pregnancy outcomes.
Image by Rebecca Scholz

Providing mares with nicotinic acid in their diets during a crucial phase of their reproductive cycle will likely reduce early embryonic loss during pregnancy, the findings of fresh research suggest.

The reproductive efficiency of mares is much lower compared to other livestock species, Charley‐Lea Pollard and her fellow researchers noted in the journal Animals.

This, they said, is largely due to the sacrificing of reproductive potential through the selection of stallions and broodmares based on their pedigree and athletic performance.

Analysis of Thoroughbred and Standardbred breeding records revealed that pregnancy rates are greatly affected by maternal age and reproductive status. Embryonic losses as high as 20 to 30% have previously been reported.

Repeated services or inseminations are often required in mares, elevating the risk of stress and injury associated with breeding, which can drastically increase the economic costs involved in achieving a successful pregnancy.

The Australian research team said there are many factors that can cause embryonic losses, largely attributed to defective embryos, inadequate maternal factors and external environmental factors.

Maternal nutrition is increasingly recognised as playing a role in embryonic losses and may provide a non‐invasive method of manipulating fertility, they said.

Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor involved in many cellular processes, including energy metabolism, cell survival, DNA repair and, more recently, aging. There is a need to constantly replenish NAD+ stores to keep these processes functioning within cells.

NAD+ is synthesised through three methods: The metabolism of dietary niacin (nicotinic acid, vitamin B3); through conversion of the amino acid tryptophan; and through the salvage of nicotinamide.

In women and mice, miscarriage and embryonic death have been linked with a deficiency in NAD+, relating back to a lack of dietary niacin.

“Very little is known regarding the NAD+ requirements for optimum reproductive function in horses,” the researchers said.

They set out to determine the effect of nicotinic acid supplementation on the composition of NAD+ metabolites in the blood and follicular fluid of mares. Nicotinic acid is a form of niacin often supplemented in horse diets.

Six Standardbred mares aged 13 to 17 and one 7‐year‐old Thoroughbred mare were included in the study. All had healthy body condition scores and were in good physical health.

The mares were housed in a large paddock and maintained on a forage diet comprising pasture and some lucerne hay.

A crossover study design was employed, with all mares serving as their own control.

Blood samples were collected before and after a minimum of three consecutive days of supplementation of nicotinic acid at a rate of 3 grams a day during the follicular phase of their oestrous cycle. Samples of follicular fluid were also collected.

Samples were processed and analysed by mass spectrometry.

The results painted a picture of the absorption and metabolism of nicotinic acid in the blood plasma and follicular fluid of mares following the short supplementation regime.

Testing showed that multiple examined NAD+ precursors were elevated in the follicular fluid of the mares at the end of the feeding period. This, they suggested, would be expected to better promote the maturation of good quality oocytes (developing eggs), especially in older mares.

“Given that supplementation of NAD+ precursors, particularly nicotinamide mononucleotide, has been found to enhance oocyte quality and embryo development in other species, it is tempting to propose that the observed changes in the follicular environment may translate to improved oocyte viability and mare fertility,” they said.

The researchers acknowledged that their study used a small number of animals, with large variations seen between animals in the concentrations of some metabolites.

“This suggests that the absorption and metabolism of nicotinic acid varied considerably between individual mares, possibly due to differences in the mares’ metabolic demands and/or enzyme activities. These differences were not attributed to age in this study,” they said.

Studies segregating a larger number of mares by age would provide more definitive results regarding the metabolic demands of aged mares.

Future studies are needed to assess the quality of oocytes collected from mares fed nicotinic acid, they said.

The researchers said the findings of their study will aid future investigations into the effects of orally administered nicotinic acid on equine oocyte developmental competence and provide insights into its use to improve reproductive outcomes in older mares.

The study team comprised Pollard, Zamira Gibb, Jennifer Clulow, Agustin Ruiz, Alecia Sheridan, Mohammad Bahrami, Aleona Swegen and Christopher Grupen, affiliated with institutions including the University of Sydney, the University of Newcastle, the Scone Equine Hospital, the Newcastle Equine Rehabilitation and Reproduction Centre, and Oxford University in England.

Pollard, C.-L.; Gibb, Z.; Clulow, J.; Ruiz, A.; Sheridan, A.; Bahrami, M.; Swegen, A.; Grupen, C.G. Supplemental Nicotinic Acid Elevates NAD+ Precursors in the Follicular Fluid of Mares. Animals 2022, 12, 1383. https://doi.org/10.3390/ani12111383

The study, published under a Creative Commons License, can be read here

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