GetBreeding

Wikipedia states: “Lies, damned lies, and statistics” is part of a phrase attributed to Benjamin Disraeli and popularised in the United States by Mark Twain: “There are three kinds of lies: lies, damned lies, and statistics.” The statement refers to the persuasive power of numbers, the use of statistics to bolster weak arguments…

A quick flick through February or March’s horse magazines will show you how statistics are used to bolster arguments. Quite often the statistics are useful, and meaningful. However, looking at the stallion and stud adverts in Horse Deals, and Horse and Hound, I am struck by two things:

1) Not a single stallion advert (as far as I can see) shows reliable/meaningful fertility statistics.

2)Those adverts that do have a “statistic” (if we can call it that), have used a misleading and essentially meaningless number to “bolster” their advert.

For fertility statistics to be meaningful, we need to know how many mares the stallion was bred to, and how many attempts/cycles it took for those mares to become pregnant. Now, these figures are most usefully represented by showing the number of mares (as a perecentage) who became pregnant on the first cycle, or as the average number of cycles it took each mare to become pregnant. Here are some -rough- averages to see what you might expect:

Type of breeding   /    Average first cycle pregnancy rate  /   Average number of cycles for pregnancy

Natural cover or Fresh AI   / 70%   /   1.6 cycles

Chilled semen /  60%  /   2 cycles

Frozen semen  / 40%  /    3 cycles

These are rough averages, and what you might expect of each type of breeding.

I would imagine that if you’ve seen fertility statistics you’ve seen figures like (and I’m quoting these from Horse Deals) “100% in foal success rate” or “99% conception rate” or “high conception rate”. These statistics are not worth the paper they are printed on. Why do I say this? Because these numbers give you no idea of how many mares have been bred to that particular stallion/at that AI centre, and you have no idea how many cycles it took for those mares to become pregnant.

For example… Say the pretend stallion “Mr Dudd” covers 1 mare in 2008 via natural cover. She gets pregnant on the 5th cycle. What figure does the stallion owner quote? “Oh, well 100% of Mr Dudd’s mares went in foal last year” or “Mr Dudd has a 100% conception rate”. If they quoted the statistics properly, it would be an average 1st cycle conception rate of 0 (ZERO) and an average of 5 cycles for the mare to become pregnant. Now obviously, the stallion owner won’t want to quote that (and the number of mares makes the statistic almost totally meaningless (although you would question why it took 5 cycles, right?)), but quoting the “100% conception rate” figure is VERY misleading. The owner could quote:

“100% of mares pregnant within 5 cycles. Of those, each pregnancy required an average of 5 cycles. The overall percentage of cycles resulting in pregnancies was 20%”.

Let’s go for another example… Mr Dudd’s hypothetical sire, “Fye Ring Blanks” is actually quite popular, and covered 20 mares in 2008. 5 mares became pregnant on the first cycle, 5 mares on the 2nd, 5 mares on the 3rd, 2 on the 4th and 3 mares didn’t get in foal at all. Now, old Fye’s owner likes to give the impression that he’s still pretty fertile… so she looks at the numbers. 17/20 in foal… that’s 85% overall. So again, she quotes “85% fertility” which still sounds pretty good. Right? Wrong. His first cycle pregnancy rate is (5/20) 25% which is pretty low.  On average it takes 2.24 cycles to get a mare pregnant, which isn’t so bad. (Don’t forget, all these figures are totally hypothetical, so you’re unlikely to see that combination of numbers). It would be fair for the owner to quote the 2.24 cycles average, but not “85% fertility” because that leads mare owners to believe that they have an 85% chance of their mare being in foal after the first cycle, which is simply not the case. This owner could quote:

“85% of mares pregnant within 4 cycles. Of those, each pregnancy required an average of 2.24 cycles. The overall percentage of cycles resulting in pregnancies was 34%”.

So… the next time you see “100% conception rate”, “99% fertility”, or “all mares in foal in 2008″, have a think about what these statistics are actually saying. Ask the stallion owner or stud what a stallion’s fertility figures were “per cycle” last season. If they can’t give you an answer, they either don’t keep good enough records, don’t understand fertility statistics, or they know the rates are low and don’t want to tell you. Any of these reasons should be cause for concern!

Statistics can be very misleading!

Well, we’ve certainly written about this before, but it’s worth covering again before we get going with the bulk of the AI work this season.

So, you have a couple of attempted cycles of AI… and it looks like you’re one of the unlucky ones. Your mare isn’t pregnant. You’re talking to the vet/AI technician/stud staff and they say:

“I think she’s having a reaction to the extender”

or

“The semen has been extended with an egg yolk extender and she’s having a reaction”

Well, it sounds kind of plausible initially, but actually some very nice research from last year suggests that this really isn’t the case. Palm et al (2008) infused phosphate buffered saline,  seminal plasma, milk-based extender, and egg-yolk based extenders into the uteruses of 8 mares over four cycles, changing what was infused on each cycle, in alternating order. They then used lavage and biopsy to look at the immune response to each different infusion.

The results were very interesting. Similar immune responses were seen after uterine infusion with PBS, seminal plasma, and milk-based extender. The least pronounced immune response was seen after infusion with egg-yolk-based extender. Essentially, an immune response is a natural response to any substance getting into the uterus. Whether it’s semen, extender, or saline, an immune response (”reaction”) is perfectly natural.

The only thing that might cause any sort of adverse reaction in a semen extender might be the antibiotics contained in the extender. In fact, we heard a very interesting piece of anecdotal evidence this week about a mare we were working with last year. The mare failed to conceive on several consecutive cycles. A reaction to the egg yolk extender was eventually blamed, and the mare conceived when inseminated with raw semen directly after a collection. This year, the mare has been treated for a minor infection, and has been found to be extremely sensitive to a range of antibiotics. Almost all commercially available semen extenders contain a broad-spectrum antibiotic, and it is fairly likely that this factor was the main cause of her failure to conceive; due to an allergic reaction of the endometrium to antibiotics.

Milk and egg yolk are fairly innocuous, and it’s really not plausible that they would cause an allergic reaction in the endometrium. If you’ve ruled out other problems, then consider an antibiotic sensitivity, but don’t blame the semen extender!

Researchers from the Department of Reproduction Obstetrics and Herd Health at Ghent University (Govaere et al, 2008) have published a paper describing the abortion of monozygotic twins in a Warmblood mare.

Normally equine twins are dizygotic (non-identical). This means they are produced because two separate eggs (ova) were fertilised by different sperm cells from the same ejaculate. These twins were monozygotic (identical). They were produced because, for some reason the embryo split in two in the early stages of development. It is extremely rare for horses to ever have monozygotic twins. Even if monozygotic twins are produced, one is normally manually reduced, and it is then impossible to prove wheteher or not the twin embryos were monozygotic or dizygotic.

Sadly, these twins were aborted at 260 days gestation, one a fresh foal and the other a mummified foal. Understanding the mechanisms behind monozygotic twin production could have future ramifications for embryo transfer, and perhaps even improving cloning technologies.