NEWS
How much blood?
Posted: Tuesday, November 14, 2006
The ability to perform at higher levels may be dependent on the individual's volume of blood
by Denise Steffanus
IF RESEARCHERS are correct, buyers may have another tool to use when selecting a prospective racehorse.
In Standardbred studies in the late 1960s, Swedish researchers drew a correlation between the amount of blood coursing through a horse's body and its ability to excel as an athlete. The studies were based on the principle of oxygen transport: The greater the number of red blood cells, the better the horse could deliver oxygen to its tissues and the more efficiently it could clear away waste products that cause a horse to tire.
Dean Householder, Ph.D., a former associate professor of animal science at the University of Kentucky and the president of the consulting firm Thoroughmotion, was intrigued by the studies, so he began an investigation to see if their results in Standardbreds held true for Thoroughbreds.
"Dr. Sunne Persson did the work in Sweden," Householder said. "He was one of the pioneers in sports medicine in horses. They were correlating blood volume in Standardbreds with exercise-tolerance tests and found basically that horses that had greater blood volume tended to work a given distance in a quicker time compared with the horses that didn't.
"It was known pretty much that blood volume probably varied among horses, even of the same size. When they did the work in Standardbreds, they found that given two yearling colts that both weighed 1,100 pounds, the blood volume could vary up to 10%, which meant one colt could have three to four liters more blood than the other."
Householder joined with Robert Douglas, Ph.D., managing partner of BET Labs in Lexington, to assess blood volume in 171 Thoroughbred yearlings from 15 Central Kentucky farms in the summer of 2002 and then follow those horses through their three-year-old season of racing to see how they performed. Householder and Douglas found that horses with below-average blood volume and those whose blood volume was in the lower 20% of those surveyed did not excel on the track.
"So we did the work in Thoroughbreds and virtually found out the same thing," Householder said. "When we plotted blood volume against highest performance of the horse, we found that performance dropped off when blood volume fell below a certain point."
Householder emphasized that assessing blood volume is not a selection tool per se, but rather a way to rule out horses whose below-average blood volume will create a disadvantage when they compete against horses that possess an average or above-average amount of blood.
"Yearlings that had average blood volume went on to perform just as well as those that had above-average values, so there would be no particular benefit in selecting just those with above-average values," he said.
He explained that many factors converge to create an outstanding racehorse--pedigree, conformation, husbandry, management of its racing career, training, the ability of its riders, and just plain luck. So it is a roll of the dice for anyone to predict which horse will be successful, even for an educated buyer. This is why he does not advocate using an upper-level blood-volume score as a reason to purchase a horse.
"It's a situation where, when you use parameters like this, you can't pick up the good horses, but you can eliminate ones that are at a disadvantage. And this mimicked virtually the same data that we collected [at EQUIX Biomechanics] when we looked at heart scores and stroke-volume scores on our horses."
(Stroke volume is the amount of blood the horse's heart pushes out of the ventricle and through the circulatory system with each beat. When the heart beats quickly, not enough time elapses between strokes to allow the ventricle to fill with blood, which results in a decreased stroke volume. A slower heart rate places less demand on the heart while it produces a greater stroke volume, which means the heart functions more efficiently.)
While Householder and his colleagues awaited performance results on the 171 yearlings, they took a look at some of the Kentucky broodmares and geldings that were retired racehorses to see how well blood volume correlated with their performance on the racetrack.
"A very high percentage of these broodmares were stakes horses," Householder said. "We wanted to see, in an elite population of older horses that are primarily stakes horses, is there any value in knowing what blood volume is. And when we ran blood volume against the performances of the population of primarily stakes horses, we again saw performance drop off in the bottom 20% with half of the non-stakes and several of the lesser stakes horses having a blood volume in the below-average range. This, coupled with the yearling data, indicated to us that blood volume was a pretty sound indicator of oxygen-delivery capacity."
Results of that yearling study found that horses with below-average blood volume had about one-third the chance to be stakes horses, and their earnings were cut in half compared with the rest of the population of the study.
Simple blood test
Blood volume is assessed by using the Evans blue-dye dilution technique. A small amount of marker is injected intravenously into the horse. Then, after allowing 15 minutes for the marker to permeate the horse's circulatory system, a sample of the horse's blood is withdrawn for assessment.
The less total blood volume a horse has, the more concentrated the marker will be in the sample, and vice versa. By using a dilution calculation based on the amount of marker found in the sample, the laboratory can determine the total amount of blood contained in the horse's circulatory system.
"[The marker] has been used in the medical profession for the past 60 years and has an excellent safety record," Householder said. "It's just a matter of sticking their horses."
A veterinarian performs the blood-volume test, which costs about $100 per horse.
Blood volume is inherent to the individual, Householder said. If a horse scores below average on the blood-volume test, nothing can be done to increase that volume, which remains relative to the horse's size throughout its life.
"No selection factor is 100%," Householder said. "Remember, blood volume is independent of other
performance-related factors such as conformation. So there will be the occasional horse with such good conformation and mechanical efficiency that his oxygen needs will be lower for a given amount of work. So, even if he has below-average [blood] volume, he can still be competitive at the stakes level, particularly at sprint distances."
Buyer-driven tool
Some sellers have been reluctant to accept blood-volume assessment as a screening tool for their yearlings. "I don't need another hoop for my horses to jump through," one high-profile farm manager told Householder.
"I agree 100%," Householder said. "If I were selling a yearling, I would be the same way." But he has found that most sellers who are reluctant to employ the technology will acquiesce if one of their regular buyers who is serious about a horse asks for the blood-volume test as part of a prepurchase examination.
But Householder said the test is beneficial for sellers, and most of the people in the industry who have utilized the test were consignors who were determining the reserve price to put on a sales yearling. In other words, if the horse is going to have less potential to excel based on a lower physical ability to transport oxygen to its muscles, it is better to let the horse go instead of incurring the added expense of keeping it another year and placing it in training for the two-year-old sales, only to find it cannot be competitive.
"The bigger farms with the nicer yearlings don't feel like they need to do that because they have plenty of pedigree and plenty of buyers," he said. "But the smaller farms with large numbers of horses, they'll cut [the reserve] down to how much they've got in the horse."
The Thoroughbred industry always has been resistant to change, and Householder and Douglas are finding reluctance rather than opposition to this new tool.
"It's kind of hard to educate the market because people are still of the opinion, 'I want you to tell me something to pick out a good horse,' but we just don't have any criteria to do that very effectively," Householder said. "But we can effectively eliminate ones that are at a real disadvantage, whether it be their heart scan or their blood volume or just profiling them at the barn.
"[Buyers] are not selecting horses as much as they're eliminating them, and their short list is really made up of horses they really can't eliminate. Those are the [group of] horses they're going to try to make a buy from."
The researchers try to explain to buyers that the selection process is not necessarily about picking a good horse; it is about crossing off horses until they arrive at a short list of potential candidates. Blood-volume testing is another tool to whittle down that list. According to Householder's results, one in five yearlings can be stricken from that short list based on below-average blood volume.
Denise Steffanus is a contributing editor of Thoroughbred Times who writes frequently on veterinary and farm management topics.
