Where are we now? May 2021 – Part 2: More Rocks & Difficult Terrain

Introduction

Many owners and breeders, together with the Suffolk Horse Society and cogent input from the Rare Breeds Trust UK,  are still struggling to increase diversity using as many of the available breeding stock as possible.   Unfortunately there are variable results, since not all breeding stock  are being used.   Attrition rates continue to erode diversity in the small population of UK Suffolk Horse.    These include the continuing use of Elite Sires who dominate the numbers of progeny produced, both in number and over their timespan on the Licensed Stallion Lists.    Many more mares are covered, both by natural cover and AI, but resultant successful foal numbers hover round one third of coverings, and overall foaling numbers during the last decade are declining with a significant gender disparity. 

Looking at the overall picture – Total Population vs Effective Population Size N_e

To reiterate from Part 1:

‘Effective population size is a calculation which takes account 

1. 1. 1. 1. 1. 1. the total number of animals in a population, and
               2. the relative number of sires and dams (male and female parents).

Effective Population Size – N_e will only contain those animals who are deemed capable of breeding.   This excludes those too young and those too old.   It will, however, also exclude  colts whose semen has not been bio-banked prior to gelding. 

A minimum N₅₀ is required.    UK Suffolk Horse Society registered stock has had less than this apart from one year (2009) over decades.

• • • • • ‘A low effective population size signifies a greater likelihood of inbreeding and risk of loss of genetic diversity. A larger effective population size implies a lower risk of inbreeding and higher genetic diversity.’

The consistently  low Effective Population Size for the Suffolk horse is in itself one of the major drivers to attrition rates – that of low of genetic diversity

Attrition Rates

Attrition:

• • • • The process of reducing something’s strength or effectiveness through sustained attack or pressure.
      • Wearing down, wearing away, weakening, debilitation, enfeebling, sapping, attenuation, gradual loss

Attrition rates to successful foal numbers each year by both Mare and Stallion have been instrumental in the  precarious Effective Population Size N_e of the UK Suffolk Herd since 

1. Loss of Diversity

Figure 3 is an ongoing snapshot in time of a struggling  breed population with overall female foal numbers failing to recover and maintain their peak numbers in 2011 and 2013.          

For earlier versions, see:

https://suffolkpunchaustralia.com/index.php/the-suffolk-punch-draught-horse/the-clock-is-ticking-part-1/ Figure 1:    Two Decades of Foal Production Showing Actual Stallions Used 1988-2008 Compared to Total Stallions on Stallion List Against Two Optima for Genetic Diversity

Eroding Diversity – The Ongoing and Continual use of the  Elite Sires

Prior to the beginning of each year’s breeding season, The Suffolk Horse Society releases the Licensed Stallion List for that year.  The Stallion List is carefully compiled from data held by the Society and details a range of information as well as a colour photo of the horse from breeders.    The information is combined into a Booklet which  is downloadable from the Society’s website.  The Licensed Stallion List also appears in the Suffolk Horse Magazine in the Spring of each year, but without the five-generation pedigree and the number of progeny.

The Booklet lists important attributes of each stallion including:

The shaded areas in the layout of information above are helpful in deciding which stallion best appeals to the potential breeder, but also assist in understanding  the Effective Population Size for the year in tandem  with the all important SPARKS sheets for each mare and stallion. SPARKS – Selecting the Optimum pairing of Sire and Dam for the Maintenance of Genetic Diversity.*    

Some reminders

The following few paragraphs and with its Figure 1 are reproduced from 2009’s article:  ‘Running out of time?”   https://suffolkpunchaustralia.com/index.php/the-suffolk-punch-draught-horse

 ‘In 2007 the FAO stated that within-breed genetic diversity is being undermined by the use of a few highly popular sires for breeding. This has been problematic for the UK Suffolks as a scan through the Stud Books from 1960 onwards reveals.

‘Between 1993 and 2007, 71 registered and licensed stallions appear on the Stallion (or Breeding) Lists for those years. The total number of progeny from the foaling seasons to 2007 is 466 live foals. Some 19 of the 71 stallions, however, either never covered registered mares, or produced registered foals. This reduces the registered and licensed stallions producing mares within this period to 52.

‘In this time, 14 stallions produced 10 or more foals each, accounting for 295 live foals.

‘Within this group and period, two stallions produced 97 foals – just over 22% or just over a fifth of all live foals born 1994-2007.

‘Both stallions stood in 2008. One is standing for 2009 and also appears as either the sire or the dam’s sire in the pedigree of seven of the 25 stallions for 2009. The other stallion only appears once in the pedigrees of the 2009 stallions.

‘Further analyses of the Stallion Lists and foals produced for same period shows that 373 foals are the progeny of only 24 stallions (just over 75% of foals produced).’                                                      Exact from 2009 article, Bold Italics added 2021

Twelve years later as at 2021:  another decade – same problem

Figure 4 above shows results for the year 2020.  It is representative of the all the years from 2010 to 2020. The number of  stallions actually used from the Licensed Stallion List for any given year, is always markedly lower than of the total available stallions listed.

Figure 5 below illustrate the attrition of diversity over the period of 2010-2020, by failing to achieve the  minimum optimum of 25 stallions used with resultant progeny. 

In fact there were only two years (2011 and 2012) when the number of available stallions on the Licensed Stallion List reached or slightly exceeded the required minimum optimum stallion number.

It is not known how many of the remaining 109 stallions either were unsuccessful in mating, or were not chosen for breeding.  Some of the stallions may or may not have gone on to breed in later years.   In any given year, though, it is clear that access to the full gene pool was limited.   And it may be that the best suitable genetic match of  a  mare and stallion was not available in following years:  the stallion might be sold too far away for the mare to travel or in subsequent years, the mare might not be able to breed for a variety of reasons.   

A constantly repeating certainty, however, is that the  Elite Sires, (or as some prefer ‘Popular Sires)   dominated the gene pool.

Figure 6 and 7 above and below demonstrate how much diversity is threatened  with the  accumulated totals over the eleven years.   Between 2010-2020 a total of 258 stallions were listed, but only 149 stallions were used, with 109 stallions not used.

This does not mean that all those stallions are never used.      Some do loiter on the Stallion list for possibly two or three years, perhaps even less, with no takers for their charms.   Often their relative youth is against them:  stallions are inspected at two and may be added to the Licensed Stallion List around the end of that year or at age three.   As draught horses generally are slower to mature, their final adult conformation features are still a work in progress. 

Some stallions on the Stallion List  then go on to make very good geldings.   Others are slow to be chosen or produce, and then make up for lost time.    But each year’s total offerings are needed.    Refer to Figure 3 at the beginning of this Part 2, to see for each year what failing to meet the minimum optimum can mean not just for that year, but over time.  There is also the always difficult decision for the breeder to make:  has his/her stallion been on the Stallion List for too many years?

Figure 7 is representative of a loss of diversity.

The significance of individual timespans for Elite Licensed Stallions

Diversity is not only threatened by the number of progeny of each individual Elite Sire, but also by the length of time that Stallion appears on the Licensed Stallion List.

Some of these younger Sires will have foals born in 2021.

And even death is no obstacle to an Elite Sire continuing to influence the population dynamics of the UK Suffolk Herd, as frozen semen can continue to be used for years.  Indeed their range of influence  is extended globally  if they have been collected at Export Quality.   This is the case for the tiny numbers of mares in Australasia.   

One of the most prolific stallions has possibly produced more progeny by the use of his frozen semen since his death in 2003.

Too few other stallions havested for supplies of frozen semen

Table 8.2 above lists frozen semen from five stallions available domestically for 2021.    Three more have been collected to Export Quality.    Yet on the 2021 Licensed Stallion List there are 22 Stallions.    What needs to be in place for more  owners to put forward their stallions?

Repeated use of a successful paring of Stallion and Mare

Diversity in a tiny Effective Population Size is also threatened by repeat pairing of:

• • • a particular sire and dam  to produce two or three siblings

and/or

• • • the half or full sibling of the stallion to the same mare
    • the half or full sibling of the mare to the same stallion   

there are many and varied permutations.

A useful addition to either the published Stud Book, and the yearly booklet of Licensed Stallions standing at stud for the year, would be a list of named progeny, similar in the way that mares will have against an entry of a registered foal:  “The Mare has also bred: ….. then follows a list of named progeny with their registration numbers and years of birth.”   Such an addition would show up full siblings.

It may well be that the Elite Sires would require many column inches on the Pedigree Registrations pages for both fillies and colts.   Nonetheless, being able to see how many progeny are the result of one particular pairing would be useful.

It is to be hoped that the new  Suffolk Horse Society Stud Book in electronic form will incorporate the breeding history of both mare and stallion.   This as has been the case with for many years with The American Suffolk Horse Association (now renamed The North American Suffolk Horse Association).   Not only does the NASHA electronic stud book give lists for progeny (with the Sire or Dam for each individual horse) for both Sire and Dam but will also provide information on possible future breeding  by its ability to show results for theoretical crosses.  All at a tap of a button or two, saving hours of scrambling through assorted stud books with concomitant realms of paper lists.

At another tap of the keys, the NASHA e-stud book  also provides generation tables listing all the descendants down through the years, indenting as it goes, revealing an extraordinary range of familial relationships.   See: Table 6:  Progeny and Descendent Generations of Suffolk Punches exported to North America,  showing each animal’s contribution to both UK (a little) and North America (a lot) suffolkpunchaustralia.com/index.php/clock-ticking-part-2/how-far-have-we-got-considering-our-options-in-securing-the-future-of-the-suffolk-punch-in-the-united-kingdom/

For owners and breeders this is the sort of information combined with SPARKS,  that can only enhance their decisions on which stallion to which mare they wish to pair.    

Attrition Rates for the Mare

Historically it’s been the Stallion rather than the Mare who  inevitably has been promoted as representative of the breed.   Most Stud Books generally list the stallions first.    Perhaps not surprising because in any of the years that he’s been standing at stud, it is possible to see his influence on a range of foals who’ve arrived in any one year, whereas the mare’s natural contribution to one year of breeding produces the one foal.

Artificial breeding techniques can produce two foals per year from the mare, by using embryo transfer, as was the case when two filly foals resulted in 2013:  same Mare, but semen from two different Sires (Colony Edward 8781 and Donhead Hall Navar 8839).   (See also:  Artificial Breed Protocols  Suffolk Stud Books and the  new Owners’ Manual : https://suffolkhorsesociety.org.uk/horse-business/owners-manual/)

Attrition Rates – Gestational Foal Losses – Twinning

The ‘successful’ birth of twin foals is often heralded with great acclaim by media reports, eliciting many effusive comments from the non-horse breeding world.     The wastage rate of twin gestations is extremely high and can lead to serious consequences for the mare.

In her 2021 article Management of Twins in the Mare, Karen Wolfsdorf, DVM Dipl ACT in Mare Management, states:

‘Twin foals are rare, but also pose a greater risk to the mare:   it is estimated that twinning accounts 6-30% of abortions in the mare.  Surviving foals are usually weaker, more susceptible to infection and slower to develop than singletons.  The establishment and loss of twins, often results in a mare that is barren for a year and the associated economic loss.

“The incidence of twin births has been documented as occurring in 1-2% of the equine population with twinning accounting for 6-30% of abortions in the mare. When twins are present, gestation proceeds normally until the conceptuses begin to compete for uterine space or placenta.  With or without mummification, death of one foetus leads to abortion, usually between 5 and 9 months of gestation.

“Lactation commonly occurs after one foal dies and causes premature mammary gland development.

“Surviving foals are usually weaker, more susceptible to infection, and slower to develop than singletons. Fortunately, with the use of ultrasound and an increased understanding of the mechanisms involved in twinning, better approaches to twin reduction have been developed”.       https://info.selectbreeders.com/blog/management-of-twins-in-the-mare

Other Losses in Breeding the Mare

In 1998, 37 mares were covered by 9 stallions on a Licensed Stallion List of 18, resulting in 20 live foals.  14 mares proved not to be in foal, two mares aborted their foals, and another foal was born dead.

In 1999, 69 mares were covered by 15 stallions on the Licensed Stallion List of 18, resulting in 37 live foals.  30 mares proved not to be in foal, one mare aborted her foal, and another foal was born dead.

Fast forward to 2010 when 102 mares were covered resulting in 50 foals; 2011 saw 80 mares covered with 41 foals registered.  2012 the ratios were very similar:  67 mares were covered by natural service:  with 39 registered foals.

2010-2012 (3 years),  249 mares were covered, resulting in 130 foals born and registered.

In 2020 70 mares were covered, 55 scanned in foal, but only 30 registered foals resulted.

It may be stating the obvious, but Figures 9:1.2.3 are derived from what might appear to be randomly picked data* going back to 1999, some 22 years – two decades  ago and three 7-year horse generations later. It shows an average of 66% non-productive coverings, and an average foal registration of 34%. 

Something is serious amiss that the same pattern of coverings and foal outcomes consistently repeats.   Table 9.4 combines the five random years, to present the same picture.

*The  Suffolk Horse Society Stud books over the last few years do not always consistently reference breeding results, nor the factors that amplify them, such as: 

• • • • • • • mares of breeding age
            • available mares to breed
            • mares covered
            • mares scanned in foal
            • mares not in foal
            • foals aborted or stillborn
            • foals born but lost before registration complete

And the phrasing of such terms as “xx Number of Mares were Covered” does not distinguish between:

• • • • • • • how many times was the same mare covered by the same stallion in different cycles of the same breeding year
            • ….. by different stallion(s) in different cycles of the same breeding year after scanning showed the mare was not in foal

These differentials may appear pedantic.   They do however, provide owners and breeders, not just the Society, with tangible information , including that they are not alone in experiencing very limited success in achieving an ultimately successful foaling.   

Social media has resulted in the dissemination of worthwhile information, when responsibly used.    Testament to this is The Facebook page of The Suffolk Punch Horse Hub has grown to 3.1 subscribers in six or seven years.  Not only are topics under discussion covering matters important to breeding, but the page has useful ‘Files’ available and easy to access.    https://www.facebook.com/groups/233069560150525/?multi_permalinks=2526541894136602 

Why is there such a difference between the number of mares covered and the number of live and registered foals each year?

An Australian research article The effects of inbreeding on covering success, gestation length and foal sex ratio in Australian Thoroughbred Horses published in 2020 might give some useful pointers for interested Suffolk Horse owners and breeders to explore.   The extracted indented points are applicable to the Suffolk Horse Population in the UK.   

The researchers had the happy task of examining data from the breeding records of 27,262 Thoroughbred Mares.    Unsurprisingly with those numbers, they state that inbreeding had not measurable effect on foaling rate or gestational length in the mares being studied, whereas: 

“Populations that experience higher levels of inbreeding due to use of artificial reproductive technologies or extremely small population sizes may show a more pronounced reduction in natural foaling rate or gestation length. ”   

(Note:  all Thoroughbred Mares are bred by natural cover)  

“Genetic bottlenecks and inbreeding can increase the frequency of deleterious variants, resulting in reduced reproductive levels in a population.

“The long gestation period and short breeding season make the maintenance of good fertility rates in horse populations imperative to provide commercial returns for domestic breeds, and to increase the size of endangered populations.

“Deleterious genetic variants have accumulated in the genomes of modern horses as a result of population bottlenecks during domestication and breed foundation events.  In this process, also known as the “cost of domestication”, deleterious mutations increase in frequency by “hitchhiking” on selective sweep regions. These mutations can also increase in frequency through inbreeding, selective breeding and genetic drift in a population. The presence of these variants in a population can have negative consequences for overall fitness, including a decrease in fertility rates.

“Increased inbreeding levels were associated with reduced fertility in some domestic and wild horse populations  Impaired ovarian function resulting from high levels of inbreeding was reported in the Przewalski’s horse, the most closely related species to the domestic horse . It is possible that the effects of inbreeding on fertility may vary between different populations depending on the rate of increase in inbreeding, selective pressures and genetic diversity.

“…….. there is some evidence that increased inbreeding can skew secondary sex ratios (the sex ratio at birth) in animal populations . Variations in sex ratio exist due to an increased chance of early conceptus loss of one sex under different conditions . As maternal condition declines due to environmental stresses or inbreeding, the chance of producing a viable male conceptus may also decrease . Early female horse conceptuses produce more insulin like growth factor-1 than males, which may promote their survival in adverse conditions . It is possible that the environment at the time of conception or levels of inbreeding in horses may favour the survival of one sex.

“Foaling rate declined with increasing mare age, with mares over the age of 20 having less than 70% success    To optimise foaling rate, the breeding of older mares would need to be prioritised because they tend to have longer gestation lengths and lower foaling rates.

“Mares in a poor nutritional condition at conception have been reported to have an increased chance of successfully carrying a female foetus, with reports of female foal ratios up to 80%.”

Todd, E.T., Hamilton, N.A., Velie, B.D. et al. The effects of inbreeding on covering success, gestation length and foal sex ratio in Australian thoroughbred horses. BMC Genet 21, 41 (2020).     https://rdcu.be/ckBxw

The non-breeding mare

It is not known accurately how many non-breeding mares there are, both too aged and too young, but more importantly, those who are capable of breeding, but are not bred.   The 2020 Suffolk Horse Society Census is incomplete.*  Once (hopefully) all the returns are in, a clearer picture may emerge of the reasons owners are choosing not to breed their mares.    Despite the many difficulties of the COVID related lockdowns,  it is an expensive exercise to embark on a breeding mare.   Perhaps these Census returns will indicate that more funding from the Society is needed, in the way of all the grants for mare owners.                 * See Part 1 of this article for’Suffolk Horse Census by Jessica Ellis (Admin.Sec. Suffolk Horse Society) Suffolk Horse Magazine, P9, Issue 104 Spring 2021.

Other Attrition Rates

Yearly Foal Gender Disparity

From 2010 up to and including 2020,  351 foals were registered in the Stud Book, of which 188 were colts, and 166 were females.   In six of the years 2010-2020, colts have outnumbered fillies.  Although official Stud Book registrations will not be released until the publication of Volume 98 in 2022, unofficial foaling figures for 2021 demonstrate the same trend with an uneven ratio of 14 colts to 6 fillies.     

Figures 10.0 (above) and 10.1 (below)  will be amended when final results for the year are collated. 

  

What must be remembered is that foals born, as shown in ‘Foal Watch’ on the website of the Suffolk Horse Society during the current foaling year are not always the same as those registered in the following year’s Stud Book.    Official registration details in the Stud Book will sometimes include foals who were born late  the previous year and their registrations might not have been complete by the deadline for publishing.  In other cases foals born in the registration year, die after some weeks and any in-process registrations are not completed.  And although Suffolk Horse foals who are eligible for registration and are listed in the Stud Book for the years of their birth, their geographic location means that few (of the very few) will have influence on the UK Effective Population Size. 

Table 10 above  is obvious not a true reflection of the yearly losses of the UK Suffolk Horse population – how can it be when there is so little accurate information?   The columns, Mares/Females and  Potential Breeding Stock Loss are cases in point.   It is not known if these 54 / 66 animals for the years 2010-2020 were part of the Effective Population Size or not.

Attrition Rate:  One of the Unknowns – Gonadal Hypoplasia

It is not known how many more Suffolk Horses have been found with gonadal hypoplasia, in the almost four years since the previous report in 2017.    Review the Section Maintaining the Purity in the article The Clock is Ticking … … … Part 2 on the re-emergence of this disorder, together with the next Section in the same article The Curious Case of Stallion Z. (https://suffolkpunchaustralia.com/index.php/clock-ticking-part-2/)

Part 3 of this Article  – coming shortly –  continues this examination and discussion on ‘Where are we now?  May 2021 Update”

 

 

 

 

© Eleanor Yvonne Hatch, Suffolk Punch Australia 2021