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!

Well, now we’re approaching the start of the breeding season, it’s time to start thinking about putting your mare in foal. We get asked a lot of questions about the hows, whys, and whens of the AI process, so here are a few pointers and ideas to get you thinking… (these apply mostly to fresh and chilled AI)

The goal of AI is to deposit semen into your mare’s uterus within 24-48 hours before she ovulates.

To best acheive this, you should order semen when a dominant follicle reaches 35-40mm in diameter, assuming that the mare also has an acceptable level of uterine oedema.

Administer hCG (Chorulon) or deslorelin (Ovuplant) when the semen is ordered, to help insure a timely ovulation. It’s a false economy to not use an ovulation-inducing agent! If your vet is not planning on using one of these drugs, ask why not, and strongly suggest that they rethink!

CHECK THE SEMEN ON ARRIVAL! If you or your vet don’t look at the semen when it arrives, you are potentially setting yourself up for repeated failed attempts, and a lot of money down the drain! If the semen has been heated up, has got too cold, is from a stallion whose semen does not chill well, or has been improperly processed packed it could have died in transit. If you put sperm with 0% progressive motility into your mare, you are extremely unlikely to acheive a pregnancy! Check it, and if it looks bad, call the stud!

Do not pre-warm the semen! Put it straight into the mare… her uterus is the best environment for the semen to be rewarmed to body temperature.

Check the mare for uterine fluid accumulation 12-24 hours after AI and treat as necessary with repeated oxytocin injections, and uterine lavage if more than 2.5cm of fluid is present.

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.

Older mares can be perfectly good candidates to be put in foal... with some precautions

Every year, we have tens of enquiries from owners who want to know if their mare is “too old” to have a foal. In most cases, there isn’t a “yes or no” answer to this question. Generally, when a mare is “too old” you will simply not be able to get her in foal. Although there is no such thing as an equine menopause, a mare’s reproductive system will often shut down when she is no longer capable of carrying a healthy foal to term. However, this is not always the case and sometimes you will have to make the decision as to whether or not you should try to put your older mare in foal.

There are no hard and fast rules in equine reproduction. However, in general if a mare is older than 12, then she is considered to be an “older” mare, and will need to be treated as such – with a combination of pre and post breeding treatments, and possibly a special insemination regime. Older maiden mares can be even more difficult, and may need further treatments and intervention in order to become pregnant.

The table below is a rough guide to whether or not a mare is too old to be put in foal, and what problems and treatments must be used with mares of different age groups.

This table is not comprehensive, and your mare may not fit the descriptions, but many will. The age-related problems and required treatments are not exhaustive, but should give you some idea of why older mares can be more difficult to get in foal, and the extent of the additional treatment that may be required for them to become pregnant.

If you are considering putting an older mare in foal, then you should get her fully checked out by a specialist reproductive/stud vet at the start of the season. This should include a uterine culture, cytology and biopsy. Use a reputable AI centre or stud, experienced in dealing with older mares, where the staff are able to discuss the possible problems associated with older mares with you. Some studs and AI centres offer an “older” or “problem” mare AI package which is a good sign that they are aware of the potential problems involved with trying to get older mares pregnant.

Has your mare been properly assessed for her breeding soundness? If not (or if any of the examinations listed below have not been performed), then we would recommend that you get a full soundness examination done before you start next breeding season. It really is a false economy not to get these tests done. They shouldn’t be that expensive either.

Conformation – perineal conformation, to make sure the mare’s vulva forms a tight seal, and does not allow air inside (pneumovagina), and does not become contaminated with faecal matter; these mares will probably need to be stitched up after breeding (Caslick’s procedure).

Vaginal inspection – to check for abnormalities, and to visually and digitally inspect the cervix

This mare has a large amount of fluid in her uterus, which must be treated (source: Equine-Reproduction.com)

Ultrasound – cysts, and any other abnormalities of the uterus should be mapped before breeding, as well as a general examination of the ovaries, and any follicular activity

Cytology & Culture – to check for infection (bacterial or fungal). Many AI centres, vets and studs offer a culture service, but do not perform cytology. One without the other is virtually worthless, as contamination of the culture swab can give a false positive, or infection can be missed by culture alone.

Biopsy – the biopsy consists of taking a small amount of tissue from the uterus (which is entirely painless for the mare), and having it assessed for signs of infection, damage, and/or age related changes. The biopsy will be graded I, IIa, IIb or III – with I being the healthiest, and III showing the mare has less than a 10% chance of carrying a pregnancy to term. There are plenty of treatment options for grades IIb & III.