Rachael Alexandra filly by Bernardini with nurse mare Ojos. Image: Ray Paulick Report.
A nurse mare foal is the by-product of a nurse mare. A nurse mare is an equine wet nurse. Nurse mares are needed to nurse foals whose natural mother has been taken away to be re-bred.
They call them "Junk Mares". Yes "junk" as in debris, trash, worthless and possessing utility but lacking in substance. These are the horses of the nurse mare industry.
The tradition of breeding mares to ordinary studs lacking any significant commercial value to induce lactation has been practiced for many years primarily by, but not limited to, the horse breeding/thoroughbred racing industry.
Originally, these mares served to nurture rejected foals or those whose mothers died in childbirth; basically a benevolent thing which over the years has progressively deteriorated into a reprehensible industry as a result of the lucrative quest to breed the ultimate horse with rejection of the masses.
Over breeding is now pandemic and has created an exponential rise in a most insidious disease called "horse slaughter".
Once the mares have foaled, they are leased out to highly profitable breeding farms to act as surrogate mothers to "expensive and promising" foals. You may ask why this is necessary and who is responsible?
First and foremost, The Jockey Club and their archaic rules are accountable for these crimes.
"To be eligible for registration, a foal must be the result of a stallion’s Breeding with a broodmare (which is the physical mounting of a broodmare by a stallion with intromission of the penis and ejaculation of semen into the reproductive tract) . . . . A natural gestation must take place in, and delivery must be from, the body of the same broodmare in which the foal was conceived. Without limting the above, any foal resulting from or produced by the processes of Artificial Insemination, Embryo Transfer or Transplant, Cloning or any other form of genetic manipulation not herein specified, shall not be eligible for registration." 
In essence, a quality highly valued mare who has produced champion foals in the past is repeatedly bred with equally impressive stallions to maximize profits.
Given that the gestation period is 11 months and after giving birth she is in heat 7-10 days later she must be re-bred to ensure she produces another potential champion foal in 11 months. This unremitting cycle pushes the mare to extreme biological limits, clearly equine exploitation at the hands of the negligent thoroughbred industry.
Since the mares can only be impregnated naturally and not by artificial insemination, for example, they must be transported to the farm housing the stallion to be live bred. Due to the value of her foal and insurance purposes the foal cannot travel to the breeding shed with her.
Having left her own foal behind, the mare will now nurse the “privileged” thoroughbred and at the end of her "duty" be re-bred to resume the chronic cycle.
Many of these mares are not well cared for and just as the thoroughbred and PMU mares, used for the Premarin® industry, they are relentlessly pushed beyond their natural physical capacity. Effectively "pack mules" of a malignant industry rife with overzealous greed.
Perhaps in the "good old days" of racing prior to the explosion of over breeding this was legitimate and respectful protocol but in today’s frenzy of unregulated breeding and unmitigated overpopulation of horses, it is no longer viable.
Looking more closely at the situation, one realizes that the real tragedy of this procreative process is not only the fate of the nurse mares but more piteously their foals – the unwanted and forgotten by-products; simply waste for disposal.
Similar to the fate of the foals of the PMU industry, these innocent creatures face an even gloomier destiny. They are more or less taken from their mother immediately at which time the horror begins. Many are simply killed by clubbing or other means, some are starved to death and others are sold to the tanning industry for their hides also known as "pony skin". Since it is illegal to send foals under six months to slaughter, they skin them to manufacture high-end leather products.
Some are lucky and are rescued by horse advocacy groups but like the PMU industry some eventually make it to the slaughterhouse ultimately ending up on a high-priced foreign menu as a delicacy item. Are you unwittingly carrying a "pony skin" handbag or sitting comfortably on a couch made of "Cordovan" leather – the product of nurse foal hides?
What is really overwhelming to think about is the state of thoroughbred breeding practices in this day and time and what this implies in terms of these by-product foals.
"Based on RMBs (Report of Mares Bred) received through Oct. 13, 2009, The Jockey Club reports that 2,409 stallions covered 45,317 mares in North America during 2009. The annual statistics include the number of mares bred to each stallion and represent approximately 92 percent of the mares that eventually will be reported as bred in 2009. According to historical trends, The Jockey Club expects to receive RMBs representing an additional 4,000 to 5,000 mares bred from the 2009 breeding season." 
Let’s do the math. 45,317 + 4500 (an average estimate) = 49,817 mares bred in 2009. Looking at the worst case scenario, this means there are about 50,000 mares and 50,000 by-product foals on average per year that the racing industry is accountable for. This is an atrocity in light of their claim to be a reputable and responsible organization.
Well, it is dedicated all right; to the "prominent" thoroughbred owners and breeders and their bulging pocketbooks, certainly not to the welfare and safety of the horse.
So, what can be done to end this poignant, thoughtless multi-million dollar enterprise that prospers on equine exploitation?
Awareness of this industry has in fact increased but this does not stop the rampant over breeding we continue to witness.
Although horse racing is not the only contributor to the nurse foal industry they are the major player in this "game" of death.
Horses are dying in anguish simply to line the pockets of the wealthy. Will the abuse and neglect ever end?
The most endangered species of all, the innocent.