If what Sir Robert Baker said is true, “A breeder is one who leaves the breed with more depth of quality than when he started. All others are but multipliers of the species,” then it could be that culling is a natural part of the process for breeders and not for multipliers.

David Trus, geneticist in the Animal Industry Division of Agriculture and Agri-Food Canada, added, “Modern animal breeding seeks to direct the natural evolutionary process.  Rather than fitness for survival in the wild, breeders seek to breed animals which are productive and excel at certain functions, are manageable, fit and healthy for the desired usage. Good breeding is most effectively achieved as a collective undertaking of many breeders having common goals, typically within a breed.  In the end, good breeding should be directed towards the collective goals of breeders, be beneficial to the well-being of individual animals, and be positive for the fitness and survival of the population.”

And, another appropriate quote, which is attributed to a friend’s grandfather: “Breeding animals is playing God and taking over the Garden of Eden. And a good garden needs to be weeded!”

These quotes point to the need for culling, but what does culling mean?

Defining Culling

According to Wikipedia, “the word comes from the Latin colligere, which means ‘to collect’. The term can be applied broadly to mean sorting a collection into two groups: one that will be kept and one that will be rejected. The cull is the set of items rejected during the selection process. The culling process is repeated until the selected group is of proper size and consistency desired.”

Cattle versus Horses

In cattle (beef or dairy) it is a common belief that the herd must be culled from time to time in order to maintain the genetics as well as profitability.

Dairy cow culling: Best practices and industry trends, as authored by J. Walker and published in the Journal of Animal Science (Volume 94, Issue suppl_5, 1 October 2016, Pages 132), states, “education, training and accountability will be the necessary drivers to secure change needed to demonstrate to consumers and customers alike that the welfare of cattle continues to be an industry priority.” The article can be viewed here: https://academic.oup.com/jas/article-abstract/94/suppl_5/132/4765998

From https://www.ncbi.nlm.nih.gov/pubmed/23911043 : “Complete breeding records were collected from 455 warmblood stallions serving between 1975 and 2010 at Marbach State Stud in Germany. The median length of life (18.0 years) was twice as long as the median length of service (9.0 years). However, both figures increased significantly over the time period examined (e.g., functional longevity increased from 5 years in the 1970s to 8 years in the 1980s to 12 years in the 1990s)… A more direct consideration of both functional and biological longevity in breeding programmes might help to further enhance both figures, and therefore welfare of the horses.”

A study in Icelandic horses – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1831549/ – shows, among other things, the distribution of causes of culling of 98 Icelandic horses.

Cause of culling	Number	(%)
Hind limb lameness	42	(42.9)
Other musculoskeletal disorders	11	(11.2)
Other diseases	6	(6.1)
Accidents	12	(12.2)
Temperamental disorders	16	(16.3)
Bad performance	11	(11.2)
Total	98

What is also interesting in this study was the number of horses that had radiographic evidence of bone spavin and/or lameness after flexion and the time frame until they were culled from riding. Amazing was the fact that culling from riding for these reasons usually meant being sold or being used for breeding. One has to wonder how much the horses culled due to bone spavin and then selected for breeding are contributing to bone spavin being a common issue within the breed.

When talking with people who breed both cattle and horses, it was clear that nearly all had a breeding plan and firm beliefs regarding the culling of their cattle. Curiously, when asked if they held the same standards for their horse breeding, most wavered. And, when asked why, the response tended to include an emotional element.

Cattle breeders would get laughed out of the stockyards if they said they bred a substandard cow because she was cute. However, horse breeders often say they bred their substandard mare because she was cute.

Cattle breeders seldom retain breeding stock just because there are famous relatives in the pedigree if the heifer, cow or bull does not exhibit the superior qualities of the famous ancestors. In general, they assess their stock far more objectively than many horse breeders do. Their culling policies are in keeping with strict breeding goals.

In the horse industry, it is quite common to market a young horse based on pedigree, even if the youngster does not resemble any of the horses of note in the ancestry. If it falls short of the expectations of the new owner and it is breedable, it enters the gene pool and likely propagates more descendants that do not resemble the superior ancestors.

Personal Experiences

During the 2018 breeding season, I was afforded the opportunity to go along when a stallion I had selected for sport was being collected for shipped semen. While the vet tech was preparing the semen for shipping, the vet was busy palpating client mares. The three mares (all with different owners) being palpated were to be inseminated via shipped semen from various stallions within their breeds, and, amazingly to me, all three were being bred because they could not perform in competition. No, they were not aged mares; in fact, they were young mares, just not athletic or not sound. That’s when it really hit home that the poorer quality horses are entering the gene pool earlier than the sound athletes, and therefore, have the potential to be more influential by number of foals produced. There is definitely something wrong with this picture when compared to the quotes in the first section of this piece.

I was disheartened, but I did find some solace in the following: The Importance of Culling Mares by Tom Reed (which can be found here:  http://www.morningside-stud.com/gpage30.html). “The goal we have set for ourselves of breeding and producing world-class athletes is a tough one. If we are to achieve this goal on a systematic basis we must use world-class stallions and mares in our breeding program and make informed, creative, and bold choices about which particular genetic endowments to combine each year to produce a foal. That’s the fun part: analyzing bloodlines, genotypes, phenotypes, and the actual production of mares and stallions to decide which stallions and mares are paired each year.

“The not-so-fun part is deciding which mares (and stallions) to remove from our breeding program.

“Each year we cull a minimum of 10% of our female herd (in practice we have been culling 10 – 15% each year). How do we decide which mares and fillies to cull?

“If a mare produces a foal that is in the bottom 10% (10th percentile) of its cohort in terms of athleticism, type, movement, and conformation the mare is put on a “watch list”. The following year if she produces a foal that is in the bottom 10% of its cohort the mare is culled. If she produces a foal that is between the 11th and 25th percentile of its cohort the mare is maintained on the “watch list” for another year. The next year if the produces another foal that is below the 25th percentile she is culled.

“If the foal she subsequently produces is an extraordinary filly — and apparently superior to its dam in terms of athleticism, type, movement, and conformation — we cull the mare from the breeding program and keep the filly foal.

“What do we do with our culled mares?

“If the mare produces correct foals but they are simply not good enough for Morningside Stud’s breeding and competition program we give the mare to a good friend whose breeding aspirations are not as high as ours. If the mare produces incorrect foals she is removed from the breeding population through euthanasia.

“We never sell culled mares to other breeders.”

And when I attended a sale for yearling Thoroughbreds and saw how few of the youngsters actually sold, I was on alert. Looking at the individuals and their pedigrees, it struck me that they were neither built for, nor bred for, racing in the local market. Wondering if this was the norm, I looked at pedigrees of the horses actually racing locally, where most races are 6 furlongs and a seldom-run long race is a mile – all on the dirt. What did I find? Tons of famous sires or grandsires (paternal and maternal) that won races such as the Breeders’ Cup Classic (1 ¼ miles) and the Kentucky Derby (1 ½ miles) or were distance turf horses in Europe. Where were the sprinter/miler pedigrees? It made no sense to me. Surprisingly, I found a similar situation while perusing the yearling sale catalogue from another small market with predominantly short races. Were the famous distance ancestors supposed to attract buyers? But then it occurred to me that the majority of the horses were on equal footing because they were racing against other horses with distance pedigrees even if they were ‘going short’.

Points to Ponder

Accountability includes everything from disposition to conformation to genetic diseases and encompasses the individual horses as well as the gene pool of the breed or registry. Breeding horses should not be taken lightly.

From https://equimed.com/diseases-and-conditions/reference/genetic-conditions

“Selective breeding and DNA testing are used to determine the chances of a foal being affected by a genetic condition. Careful attention to background of breeding stock, plus DNA testing when any questions arise as to whether or not a horse may be a carrier, can reduce the number of foals born with genetic conditions.”

Unfortunately, health and quality of life can easily be compromised when not closely guarded in the gene pool, and selecting for specific performance traits without considering the soundness and longevity of the horses produced is compromising.

From the Chronicle of the Horse forum: “The key is to have a clearly defined breeding goal and then to develop a clearly defined culling policy…and to avoid policy drift on either dimension.”

“Breeding is a RESPONSIBILITY. Culling is not ruthless; it’s kind and quite logical. It’s simply not continuing to breed combinations of mares and stallions that are not producing equal or BETTER than themselves. It requires an objective eye and a generous heart to stop breeding certain individuals, no matter how much you ‘love’ them. The kindest thing you can ever do is NOT breed horses that will put babies on the ground that for genetic or conformational or behavioral reasons will be [mistreated] for what they cannot possibly do in the proposed sport, through no fault of their own. Breed and market babies for that individual’s propensities. As a breeder, it should be an ethical obligation.”

So what is your breeding goal and what is your culling plan?