Introduction:-
Linseed (otherwise known as flaxseed) is a traditional ingredient in equine rations and it has been fed to horses for many years.
It provides numerous nutritional benefits, including delivering additional energy and promoting a shiny, healthy coat.
What is linseed?
Linseed is classified as a lipid.
The natural-occurring lipids in forages and cereal grains exist as a mixture of ‘simple lipids’ and ‘complex lipids’. (Geor, 2013). By comparison, lipids added to equine diets consist mostly of triacylglycerols, which are commonly referred to as ‘triglycerides’. These are three fatty acids joined to a glycerol ‘backbone’ and can vary in length from 2 to 28 carbons.
The length of a fatty acid, it’s degree of ‘unsaturation’ and its molecular structure, all dictate its biological function.
What function do they perform in the equine body?
Certain types of fatty acids are essential in the ration because horses cannot synthesise them themselves within the equine body. These essential fatty acids are Linoleic Acid (Omega-6) and Alpha Linolenic Acid (Omega-3).
There have been many studies and much recent interest in the biological impact of different types of fatty acids supplied by various lipid sources. In particular, Omega-3 and Omega-6 fatty acids have received attention for their roles in maintaining the cell membrane and integrity, receptor and ion channel function, gene expression, neural and retinol development, correct absorption of fat-soluble vitamins (A, D, E and K), inflammation and immunity. (Geor, 2013).
Linseed, forages, fish oil and some algae, are typically rich sources of Omega-3 fatty acids, whereas cereal grains, vegetable oils and rice brans are high in Omega-6 fatty acids.
What are the nutritional benefits of feeding lipids?
Lipid supplemented rations can deliver:-
Increased levels of digestible energy (DE) when metabolised in comparison to any other food source, on a like-for-like basis. Research has shown that lipids deliver 2.5 times more energy when metabolised compared to the same weight of cereals (Pilliner & Davies, 2004). (As the break-down of one molecule of fatty acid produces more energy than one molecule of glucose, as fat is very energy-dense).
An increased ability for the equine to utilise body fat stores and hence, spare precious muscle glycogen stores. This is known as a ‘muscle glycogen sparing’ effect. When feeding between 10 – 20% of the total dietary energy intake in the form of lipids, it has a ‘training effect’ on the musculature. As such, the horse effectively becomes more efficient at mobilising, transporting and oxidising fat during exercise. This has the knock-on effect of ‘sparing’ muscle glycogen stores and ultimately, potentially delaying the onset of fatigue. (This effect is only an advantage during low and moderate intensity exercise, however).
Delays in blood glucose decline and an accelerated rate of recovery of resting pulse and respiration rates. (Hintz et al. 1978a, cited in Frape, 2004)
Reduced heat burden for exercising horses, when compared to providing that energy from starch, since the body utilisation of the products of starch digestion produces more heat. (MacLeod, 2007)
Lipid quality
Omega-3 and Omega-6 fatty acids are present in varying amounts in all lipids. In simple terms, Omega-6 fatty acids, on their own tend to aggravate inflammatory responses in the body. Omega-3 fatty acids help to balance the effects of these Omega-6 fatty acids, such that we should aim to be supplying at least twice as much Omega-3 as Omega-6 in a ration.
Linseed is one of the richest plant sources of linolenic acids, or in other words, Omega-3 fatty acids.
Nutritional differences between different forms of linseed that we can feed to our horses.
The main nutritional differences derive from the form (or substrate state) that we feed linseed in – this can either be:-
- as a liquid (i.e., in an oil form) or,
- as a solid (i.e., as a fat in the form of linseed meal).
Linseed Oil
The horse’s ability to digest lipids is highest (60 – 95% digested) when lipids are included in the ration in their liquid form, i.e., as an oil. (Marlin, 2020)
Linseed oil delivers approx.. 40 MJ/kg of DE (Digestible Energy) when metabolised, or 3.7 MJ/kg per 100 g or 100 ml oil fed. (ibid., 2020)
However, oils are said to add ‘empty calories’ to an equine ration, as they deliver no other nutritional benefits, (i.e., they are devoid of protein and minerals). So, ‘top-dressing’ an equine’s ration with additional linseed oil, can cause nutrient imbalances.
Linseed Meal
Linseed meal is commonly sold as ‘micronised linseed meal’ or ‘cooked linseed meal’.
Micronising is an infra-red, high-speed, high-temperature cooking process, which causes minimal degradation of the constituents. As such, it contains useful minerals and trace elements such as, Calcium, Phosphorus, Magnesium, Copper and Selenium, all of which are essential for metabolic processes.
As with feeding linseed oil, when metabolised, Digestible Energy levels are high, at approx. 16 – 19 MJ/kg of DE. However, linseed meal, (unlike linseed oil) also delivers high levels of crude protein (19 - 22%).
As it is virtually starch-free (less than 3%) and also contains very low amounts of sugar (less than 5%), it is suitable for equines with clinical nutritional diseases, such as PPID / Cushing’s Disease or EMS (Equine Metabolic Syndrome).
Conclusion
In today’s equine nutrition industry, the inclusion of lipid sources in horse’s rations has become commonplace. It is perhaps the biggest change to horse feeding that has happened over the last twenty years.
One of the main reasons for this is that equines can metabolise lipids in their diet very well. Recent studies have shown that up to 20% lipid in the overall diet is well-tolerated. (Barfoot, 2010). In addition, lipids are particularly good if feeding for condition improvement. In a recent study, adding 10% extra energy as lipid proved to be twice as effective as cereals at improving weight gain – and without any associated side-effects. (ibid., 2010)
Be aware however, that depending on how you feed that lipid – in the case of linseed, either as a liquid (in the form of linseed oil) or as a solid (in the form of linseed meal) will have differing nutritional benefits for your horse.
References:-
Barfoot, C., (2010) Need Oiling, Horse & Rider. October 2010. Pg. 87-88.
Frape, D., (2004) Equine Nutrition and Feeding, 3rd Edition, Oxford, Blackwell Publishing.
Geor, R.J., Harris, P., Coenen, M., (2013) Equine Applied and Clinical Nutrition. London, Elsevier.
Marlin, D., (2020) Feed Materials In Focus – Why and How to Feed Oil to Horses, drdavidmarlin.com.
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