Laminitis Conference Part 3

[bellajack]

The Royal Veterinary Laminitis Conference 24th March 2007
Part 3.

Metabolic Predispositions to Laminitis:
Obesity and Insulin Resistance

The speaker on this section was;
Raymond J Geor BVSc MVSc PhD Diplomate ACVIM
Dr Geor is the Distinguished Chair and Director of Research at The MARE Center and Professor of Large Animal Clinical Services, Virginia-Maryland Regional College of Veterinary Medicine. His research focuses on carbohydrate nutrition of horses in health and disease. Currant areas of study include the role of insulin and obesity in laminitis and the links between carbohydrate nutrition, insulin resistance and laminitis risk.


Metabolic abnormalities, notably obesity and insulin resistance (IR), have long been thought to be involved in the predisposition to laminitis.

Obesity and IR have now been proven to be important predisposing factors for laminitis. Identifying these conditions, particularly IR, means that management strategies can be implemented to assist in avoiding laminitis.

Horse with a condition score of more than 7, on a 9 point scale, are classified as obese.
However this does not take into account the distribution of fat.

It is well known that, in man, people who accumulate fat around the waist are at increased risk of heart disease, high blood pressure, diabetes, etc.

In the horse it would seem that some horses which are not clinically obese but have enlarged fat deposits on the crest, tail head, sheath/udder are predisposed to laminitis.

Research is ongoing in developing a 'cresty neck score', measuring the height and width of the crest and using it to assess laminitis risk.

IR is defined as a metabolic state in which normal concentrations of insulin do not result in a normal biological response in target tissues, such as an increase in cellular glucose uptake.

Compensated IR, evidenced by persistently raised levels of insulin but normal levels of glucose, is a common finding in IR horses.

Recent studies have shown that an IR phenotype (appearance) is strongly linked to a predisposition to laminitis. When studying the metabolic differences of 160 ponies on one farm, findings based on insulin sensitivity, compensated IR, and categorizing the ponies considered to be showing pre-laminitic metabolic syndrome (PLMS), enabled researchers to predict 11 of the 13 cases of laminitis that occurred in May of that year, meaning that the IR ponies were at 10 times higher risk of developing laminitis.

Cushings Disease may result from long term IR.

IR could cause laminitis in 3 possible ways:
1) IR might impair glucose delivery to the foot.
2) IR could alter blood flow to the foot.
3) IR could lead to a pro-inflammatory state, increasing MMP activity (the enzymes that destroy cells in the laminae when they are over- activated, causing separation of the pedal bone from the hoof wall).

There is evidence that high starch and sugar diets increase IR.
Horses thought to be of IR phenotype should be managed to increase insulin sensitivity (see next installment).

TAKE HOME MESSAGE:

If your horse is obese and has a cresty neck, or just has a cresty neck, BEWARE. It has the IR phenotype and is predisposed to laminitis.
It is likely that all horses have a laminitis threshold, but IR lowers this threshold.
IR is reversible, in the early stages at least.

[harveydales]

Once again, very interesting. Thanks for this. My goodness, you've been putting alot of work into these reports - much appreciated!

[bellajack]

BUMP to put back in right order.

[greydales]

Thanks again for this. I'm a bit unsure about the last statement - that if your horse is obese, it has the IR phenotype. Are they saying this applies to all horses who get fat on pasture?

[bellajack]

No, what I meant to put was obese and has a cresty neck, or just has a cresty neck, although obesity does predispose to laminitis, just not as much as IR does, or, worse still both, obese and enlarged fat deposits. Does that help?

[bellajack]

Have modified post to clarify above.

[bellajack]

More thoughts on this - feedback really helps - found a sentance I should have included:

'Obesity is now regarded as a chronic inflammatory state'.

It is not that a horse that gets fat on pasture is definately IR but that it is much more likely to develop IR. Nearly all horses could get fat on pasture, obviously, but if you allow them to do so then you decrease their sensitivity to insulin, and if you get them slimmer and fitter you increase their sensitivity to insulin. There are big similarities to Diabetes in people - you are more likely to become diabetic if you are overweight, and even more so if the excess fat is around your waist.

What I want to know is when the Doctor Green of my youth turned into the Doctor Shipman of today, and why?

[bellajack]

More thoughts on this:

I think that if Dr. Geor (lecturer above) came and looked at most of our Dales Ponies he would say that they have the IR phenotype. Mine scream it.

This doesn't mean that they will necessarily be clinically insulin resistant, just that they are more likely to become so.

Even if they do become IR that doesn't necessarily mean that they will get laminitis, just as not all overweight people will get diabetes or heart disease. It's all a massive gamble and about trying to stack the odds in our favour as the stakes are so high.

I think that the problem is that most of us are walking a tightrope (myself most definately included) with ponies carrying too much condition, on better grazing than they were ever designed for and doing far less work than they were bred for - and lets face it, Dales were bred to do an awful lot. We need to find a way to get off the tightrope and give ourselves a bit more margin for error.

It would be bad enough if the incidence of laminitis was static, but we all know that it is getting more and more common and no one really knows why.

In the case of overweight youngsters (mine included), even if it is apparently doing them no harm now, it could lead to Cushings Disease in 10 or 15 years time, and that is getting more common as well.

Having said all that, all any of us can do is the best we can, in the circumstances we are in, and pray that it is enough.

[harveydales]

I didn't realise that insulin resistance could be reversed if tackled early enough. From what you say, it looks like there is some kind of cut-off point then?

Quest was somewhat overweight for the 7 years I had him before he got Lami (and I didn't realise it!). He wasn't massively obese but did have a crest. He was clearly living on a knife edge and then several factors tipped him over into lami. Looking back, there was a 4 month period when he was starting to show odd signs that now would trigger alarm bells.

Anyway, he is now quite thin, probably on the underweight side but still has a bit of a crest - nothing like it was. I have been assuming that if he was insulin resistant when he first got lami, then he still is now but, from what you say, maybe he isn't? Not that it matters because I'm not taking any risks and will treat him as though he is insulin resistant.

The comment "Obesity is now regarded as an inflammatory condition" is an interesting one. This also links in to research I'd been told about on IR/obesitiy/lami/itchy psoriasis/sensitivity connections. It's all muddled in my brain now but I must check it out again - it was a real light bulb moment for me regarding Quest.

Reading your reports has spurred me on to do something about Harvey and his weight! Yesterday I got myself some more electric fencing and will sort my paddocks out this weekend. I'm also arranging for some cattle to graze the hay paddock this autumn - I'm not letting them out on all that grass next winter!

[bellajack]

I think it's a case of levels of insulin sensitvity. I think from what you say that experts would say that Quest has the IR phenotype and probably got laminitis because he became clinically IR, but hopefully you have now reversed that and increased his insulin sensitivity. Unfortunately we can't do anything about their phenotype, so laminitis risk will always be high, and the definitive tests for IR (allowing for compensated IR) are very expensive and not very available, but they are trying to develop some that are more practical.

I think the cut off point, as it were, to IR reversal probably depends on the length of time they have been IR for. There may be more on this in the next section, have to go back to notes!

[harveydales]

Good to know they are working on developing better tests for IR. At the time, I didn't think it was worth putting Quest through all the hassle of IR testing as it was then. it seemed more sensible to simply manage him as though he WAS IR.

[bellajack]

Definately, and the main thing is that if we treated them all as if they were IR; the overweight ones anyway, even if only slightly overweight, it could ONLY do them good. After all, being overweight has been shown to shorten the lifespan of nearly all species.

[greydales]

It's a huge management problem for many of us, especially those who (like me) have ex-dairy pasture. And I think as more and more farmers diversify into horses the problem will intensify.

I'm just thinking mine really ought to move off their winter field, but looking at the amount of spring grass I'm terrified of doing it! The girls have dropped off nicely, but the others are frighteningly fat for this time of year

Maybe I ought to move to the wilds of Scotland and buy a side of a mountain!!!

[bellajack]

I read someone somewhere saying that if they moved again they would look for a hard tennis court for their horse. Not a bad idea!!!!

Harveydales, sheep would be better than cattle if you can get them. Cattle leave it too long. Old saying "sheep rob horses, horses rob cattle".

[harveydales]

Bellajack - I use cows because the farmer who makes our hay has cattle and if I let him graze a few on our paddock August to November, he charges me very little for the haymaking.

I've found his cattle do a great job of grazing right down. I know sheep are supposed to be good but round here, I've noticed the reverse to the old saying. the horse paddocks grazed by sheep are far too lush looking for my liking and the horses seem to come down with lami. Maybe it's something to do with our heavy clay soil?

I didn't have the cattle last year because I simply couldn't cope with my ankle but I'm regretting it now, looking at the size of Harvey.