In farm animals the need for improvements in reproductive performance is more urgent as there is usually a significant financial benefit either through fewer coverings, increasing litter sizes etc. Unfortunately the horse is nearly always the poor relation in terms of the amount of research that is conducted and so results from other species has to be “borrowed” from and applied to the horse wherever possible. The increased use of AI, particularly with frozen and chilled semen, has opened up more opportunities for stallion owners and has necessitated a better understanding of the factors affecting a stallion’s fertility. (photo left:Katie Lugsden,John Mansfield Chairman of the SSH and Sarah Howe,Scottish area representative)

Most of the research conducted with horses has focussed on the major components of the diet such as energy and protein levels. This provides fundamental information about fertility; like not letting a stallion get over weight as extra fat is stored around the testicles which increases the temperature, potentially reducing sperm viability. In other species investigations are being directed at smaller, but no less important, parts of the diet including fatty acids, anti-oxidants and minerals.

Altering Cell Membranes

Cell membranes contain lipids or fat which are made up of fatty acids. Research in other species such as the boar, is suggesting that altering the fatty acid composition of the spermatozoa cell membranes can improve fertilising capacity. One particular fatty acid, known as DHA (Docosahexaenoic Acid), is known to improve flexibility of a membrane and, perhaps not surprisingly, is located in the tail of spermatozoa. In trials with boars, increasing the percentage of DHA to replace another fatty acid known as DPA (Docosapaentoic Acid) resulted in a wide range of positive effects on sperm production and function including sperm concentration within an ejaculate. Marine oils appear to be the secret to manipulating fatty acid concentrations in the boar but, due to the considerable variation that exists in sperm characteristics between species, further investigation is needed to establish how best to alter the horse’s cell membrane composition.

Anti-oxidant Protection

The lipids in cell membranes are vulnerable to attack from harmful compounds known as free radicals or reactive oxygen species (ROS) that are produced in the mitochondria or “power stations” of a cell. The body has defence mechanisms against free radicals and ROS comprised of enzymes and nutrients that are referred to as anti-oxidants. Trace minerals such as selenium are vital components of anti-oxidant enzymes and vitamins such as E and C react with free radicals and ROS to protect the membranes.

It is logical to conclude that as the fatty acids in the sperm membranes are crucial to fertilising capacity, the nutrients that protect the fatty acids must be just as important. In theory, the horse should produce sufficient vitamin C itself but, during times of stress, it is known that it can’t always meet its requirements. This suggests that during the covering season supplemental vitamin C may be beneficial.

One of the key anti-oxidant minerals is selenium. It is incorporated into the enzyme glutathione peroxidase which is known to suppress the formation of free radicals and could be the answer to stopping a decline in fertility associated with age. The testes are a priority for selenium in boars, so much so that it may be diverted away from other areas of the body. Yet another study using boars found that the normal decline in fertility with increasing age was greater when the diet was inadequate in selenium. Supplementing with selenium may therefore help slow the decline in a stallion’s fertility and may be particularly important for the working stallion that is competing and covering.

Other Minerals Affecting Fertility

Zinc is a common feature in fertility supplements for men and no wonder really as a deficiency has been shown to result in smaller testicles. A zinc deficiency also causes abnormalities in the cells that produce testosterone and so can significantly affect libido.
· Chromium is not currently permitted by the EU for use in animal feeds but studies have indicated it could be useful in improving male fertility. Rats fed low chromium diets displayed a marked decrease in sperm count and fertility.

Feeding Strategies for Stallions

Until research is conducted that reveals how best to manipulate a stallion’s diet, it is a case of using what we know from work done using other species. The aim is to have a fit stallion that isn’t over weight with a balanced diet of essential nutrients. There are low calorie balancers such as Buckeye Gro’N Win, that provide the essential nutrients without additional calories and so are ideal for good doers. As there is basically no energy in them they shouldn’t cause over-excitable behaviour and so are useful for working stallions.

For stallions that don’t hold their weight there are a couple of options. You can use a conditioning feed and top-up with Gro’N Win or use a stud mix or cube. Stud cubes are probably more appropriate if you have an excitable stallion as they are usually free from whole oats whereas stud mixes are frequently oat-based.

If you have any queries regarding what to feed your stallion then please contact our feed helpline on 01371 850247.

User ID:

Password:

Search:

Name:

E-mail: