All the hype and emphasis put on weight management in both people and horses is for good reason. Not liking it or trying to hide from it does us and our horses no favors.
Over the last few years, some very practical information has been published and medications developed for the management of hormone-dependent obesity in horses, as well as innovative equine feeds formulated for weight management in horses.
Being intentional in the weight management of our horses leads to obvious performance benefits simply from better health status, but it also goes a long way in preventing disease processes that are directly related to obesity.
Hepatic lipidosis, or fatty liver disease, is a prime example of obesity causing disease. Primarily a disease of miniature horses, pony breeds and donkeys, hepatic lipidosis can be a problem in Quarter Horse mares late in gestation or early in lactation after foaling.
It can also be a definite issue with geldings; however, the overweight Quarter Horse mare is a prime target.
The setup or risk factor in developing hepatic lipidosis is when an overweight horse goes into a negative energy balance.
Think of a body builder growing muscle mass being in a positive energy balance by putting nutrition into the system to gain weight in a positive way. That’s anabolic. Catabolic is the opposite, where you lose weight by the body scavenging protein and viable tissue for energy due to a lack of intake. That’s negative weight loss.
When a horse goes off feed for a short time — a few days — they still have energy requirements that must be met. So, when we see acute weight loss in a late gestation mare, one in heavy lactation or one fighting a systemic disease such as colitis, kidney disease or septicemia, the overweight horse has a high risk of going into a massive negative energy balance (catabolic).
Generally, these are the “ADR” horses. They “aren’t doing right.” There’s nothing specific; they’re just not right. They quickly lose weight, are depressed, do not eat, look weak and often have diarrhea. They can even have intermittent fevers and a distended abdomen with increased respiratory rate from a grossly enlarged liver.
It is the liver that becomes the problem. The simplified version of hepatic physiology that I understand enough to explain for us both starts with the liver making glucose from fatty acids and amino acids. This is stored as glycogen for later, an on-demand source of energy.
But, if the body uses up all the glycogen stores as a normal energy source because the horse isn’t eating due to the list of potential causes we mentioned earlier, a negative energy balance ensues and the body starts oxidizing fatty acids to fill the gap.
If your horse is overweight, then the fatty acid oxidation can proceed unchecked due to the excess of fat stores available. This creates a huge spike in blood triglycerides, free fatty acids and glycerol.
All this is shuttled to the liver, where the glyceride is converted to glucose for a Band-Aid supply of immediate energy. The free fatty acids are resyn- thesized through various steps into more triglycerides, which are stored in the liver.
So, if free fatty acids are mobilized and made into triglycerides faster than they can be oxidized into glucose for immediate use, then there is a net increase of fat deposited in the liver. Over a short amount of time — days to weeks — hepatic lipidosis, or fatty liver, occurs. The continual displacement of functional liver tissue by fat leads to liver failure.
The liver serves to filter numerous toxins from the blood and perform other important cellular operations; therefore, as it fails, symptoms often increase and progress to central nervous signs like severe depression, seizures and uncontrolled head pressing.
Diagnosis is made from a complete history and physical exam, combined with serum biochemistry evaluation of liver enzymes. Specific measurement of serum triglyceride and bile acid levels are simple blood tests that will definitively diagnose the condition and give insight as to the severity of the disease. Some blood samples may be so grossly lipemic (fat circulating in the blood) that you can see a hazy, opalescent discoloration of the blood within the redtop vial.
The prognosis for hepatic lipidosis is guarded, at best, as horses are often diagnosed in the later stages of the disease. If you are concerned about an overweight horse being a candidate for hepatic lipidosis, begin taking periodic serum triglyceride samples early and often. It is a simple and inexpensive blood test.
If your horse develops hepatic lipidosis from another primary disease, like an infection or colitis, treating the inciting disease will greatly reduce the likelihood of the condition becoming fatal.
However, if there is an idiopathic (unexplained) cause, it can be very difficult to manage, as there are no specific medications to treat fatty liver disease. You can only rely on dietary management to induce the body’s natural physiology to repair and reverse the damage we could have prevented a long time before.
This Breeding and Beyond column was published in the April 1 issue of Quarter Horse News. To purchase this issue, click here.