A brief review of some recent findings related to ACTH levels in horses and its use as a diagnostic test for PPID.
Clear breed differences in ACTH levels in normal horses
A normal autumn seasonal rise in ACTH was observed in ponies, Andalusian horses and Standardbreds however the greatest increases were seen in ponies (range 45.5-146pg/ml) and Andalusian horses (range 38.7-84.8pg/ml) [1]. Interestingly, one pony had an ACTH of 146pg/ml in mid-Autumn but had returned to 17.9pg/ml by late autumn.
Diet can impact the result of ACTH values
In aged horses (18-24 years old) not displaying clinical sign of PPID, researchers found that on a starch-rich diet, horses had elevated ACTH levels (60.0 ± 10.7 pg/mL) compared with adult horses (5-13 years old) on the same diet (15.7 ± 12.0 pg/mL) [2]. The same aged horses on the control diet, fiber-rich diet and sugar-rich diet did not show significantly higher ACTH levels as compared to the horses in the 5-13 years of age group.
Stress may influence ACTH results
Travel for 40 minutes caused ACTH levels in horses to increase and remain higher up to 30 minutes post-unloading [3].
References
Read more from the 4th Global Equine Endocrine Symposium 2020 https://sites.tufts.edu/equineendogroup/files/2020/01/GEES_2020_Proceedings.pdf
[1] Bamford, N.J., Harris, P.A., Bailey, S.R. (2020) Seasonal variation in adrenocorticotropic hormone (ACTH) concentrations and dexamethasone suppression tests in ponies and Andalusian horses compared with Standardbreds. In: 4th Global Equine Endocrine Symposium 2020, Gut Ising, Bavaria, Germany p12.
[2] Jacob, S.I., Geor, R., Weber, P.S.D., Harris, P.A. and McCue, M.E. (2017) Effect of dietary carbohydrates and time of year on adrenocorticotropic hormone (ACTH) and cortisol concentrations in adult and aged horses. Domestic Animal Endocrinology 63.
[3] Haffner, J.C., Hoffman, R.,. and Grubbs, S.T. (2020) The Effect of Trailering and Dentistry on Resting Adrenocorticotropic Hormone Concentrations in Horses. In: 4th Global Equine Endocrine Symposium, Gut Ising, Bavaria, Germany.
Meet The Author: Samantha Potter, MSc
In 2009, Sam completed a Bachelor of Equine Studies and it was during this time she developed an interest in equine nutrition. Pursuing this passion, Sam went on to complete her Honours followed by her Masters degree in equine nutrition at The University of Melbourne. Since 2015, Sam has worked as an independent nutritionist and enjoys supporting horse owners manage their horse’s nutrition in her role with FeedXL. To learn more about Sam and to ‘meet’ the rest of the FeedXL team, check out our About Us page here.
Do you have a question or comment? Do you need help with feeding?
We would love to welcome you to our FeedXL Horse Nutrition Facebook Group. Ask questions and have them answered by PhD and Masters qualified equine nutritionists and spend time with like-minded horse owners. It’s free!
Weight loss in easy keepers can seem like an impossible task and is often the cause of frustration for owners, but feeding straw to your horse could be a potential solution. Despite a strict hay only diet, many easy keepers can still maintain their body condition. Owners are also faced with the dilemma of not restricting intake too much (to avoid colic) while trying not to add too much energy to the diet. A study published recently investigated the effectiveness of adding straw to ponies diets to assist with weight loss. The outcomes provide some hope of weight loss for those with easy keepers.
This study looked at 40 native-type ponies at pasture in the UK over winter. The ponies were split into two groups; supplementary fed hay alone or a 50:50 ratio of hay and barley straw. The ponies were weighed regularly over a 4 month period. Over this period, all ponies in the straw fed group lost an average of 27kg. Only 3 of 15 ponies in the hay group lost weight, and overall the group gained weight (average +6kg).
Why feed straw to your horse?
Straw is lower in energy as compared with most grass hays, therefore substituting up to 50% of grass hay in the ration with straw, creates a less energy dense ration whilst maintaining adequate forage intake. This means that intake does not need to be severely restricted to achieve weight loss. In addition, the time horses spend eating per day is extended, which keeps them satisfied and at less risk of gastric ulcers due to prolonged periods without food.
Considering the risk of colic when feeding straw
The addition of straw into diet can be problematic due to the risk of colic. However, in this study there were no reports of colic. Care needs to be taken when choosing the right type of straw, and introduction to the diet should be done gradually over 14-21 days until a 50:50 ratio is achieved with hay to straw.
What type of straw is best for horse feed?
Oaten or barley straw is generally softer (less indigestible fibre) than wheaten straw and is therefore more commonly used for feed. If you have a feed analysis performed, look for an NDF of less than 65. You can also scrunch the straw in your hand to check the coarseness (technical I know!) – you’re feeling that the straw scrunches easily (stems are soft) and the sharp ends don’t prick your palm ie. we want to avoid bedding type straw.
While most straw is low in sugar and starch, a feed analysis to confirm this is a good idea. If a feed analysis is not practical for you, visually inspect the straw to ensure it doesn’t contain intact heads of cereal grains which may make the straw high in starch. Straw will be lower in protein than grass or cereal hays. Therefore, attention should be paid to supplying a good quality protein source within the diet as well as meeting mineral and vitamin requirements.
The difference between straw and hay
Straw vs. hay – for cereal crops, hay is the name given to a crop that is cut for hay when the grain is still maturing. Straw is a by-product which is cut after the plant has matured and the grain has been harvested from the plant.
Reference
Dosi, MCM., Kirton, R., Hallsworth, S., Keen, JA., Morgan, RA. (2020) Inducing weight loss in native ponies: is straw a viable alternative to hay? Veterinary Record Published Online First: 03 May 2020. doi: 10.1136/vr.105793
Meet The Author: Samantha Potter, MSc
In 2009, Sam completed a Bachelor of Equine Studies and it was during this time she developed an interest in equine nutrition. Pursuing this passion, Sam went on to complete her Honours followed by her Masters degree in equine nutrition at The University of Melbourne. Since 2015, Sam has worked as an independent nutritionist and enjoys supporting horse owners manage their horse’s nutrition in her role with FeedXL. To learn more about Sam and to ‘meet’ the rest of the FeedXL team, check out our About Us page here.
Do you have a question or comment? Do you need help with feeding?
We would love to welcome you to our FeedXL Horse Nutrition Facebook Group. Ask questions and have them answered by PhD and Masters qualified equine nutritionists and spend time with like-minded horse owners. It’s free!
Confusion around what form of flaxseed (linseed) is best/safest to feed our horses is nothing new. While many of us thought the concerns around cyanide poisoning for horses were laid to rest, recent safety issues around flaxseed supplementation in human diets, more specifically for toddlers and children, has warranted us to look at this again (EFSA CONTAM Panel, 2019).
There are very few published research studies available in horses around the safety of feeding flaxseed. And there are no published reports of cyanide poisoning that we are aware of. Most safety information is extrapolated from other species including humans, rats, dogs, cattle and pigs. Although information is limited, we aim to answer three questions for you:
Should we be concerned about the potential of cyanide poisoning in horses?
What is the safest form of flaxseed to feed our horses?
Does form then affect the fatty acid composition of flaxseed?
How is flaxseed commonly fed to horses?
Currently, whole and freshly ground flaxseed are the most common ways of feeding flaxseeds to our horses.
Whole flaxseeds are deemed relatively safe from the point of view of cyanide poisoning as the two things (more scientifically, the precursors for cyanide production; cynanogenic glycosides and the glycosidase enzyme) that combine to produce cyanide are contained separately within the intact whole seed. Once eaten, the chewing action grinding the seeds can allow for cyanide production, but it is thought that this is quickly halted once the flaxseed reaches the stomach and the enzyme becomes deactivated by the gastric acid.
Anecdotally horse owners have found that whole flaxseeds can pass undigested through the gastrointestinal tract presenting in manure, with some finding flaxseed plants growing in their paddocks (great for biodiversity in the pasture, but not so much benefit to our horse in getting those added fatty acids in the diet as we had hoped).
Freshly ground flaxseed has become popular for this reason – with limited time for cyanide to form, preservation of fatty acids and to ensure our horses could access all the goodness within the seed coat freshly ground flaxseed is an excellent option.
Realistically, what is the likelihood of cyanide poisoning in horses?
It appears not likely.
Extrapolated from other species, a horse’s maximum ‘safe’ intake of cyanogenic precursors is 0.4mg/ kg body weight… or 200mg for a 500kg (1100lb) horse (Dusica, I. et al., 2012).
So, even if a flaxseed product contained the highest concentration of cyanogenic precursors reported in the European Food Safety Authority database (407mg/kg) (EFSA CONTAM Panel, 2019), it can be still be safely fed at up to 500g (~1 lb) per day for a 500kg horse.
How much flaxseed can I feed safely?
There is no established recommendation, but we can be guided by amounts that have been safely fed in a few horse-specific studies.
In a Canadian study, horses were fed 100g (3.5 oz) per 100kg (220 lb) body weight per day (500 grams for a 500 kg horse). This study looked at the supplementation of flaxseed for reducing skin reactions like ‘sweet itch’ (O’Neill, W. et al., 2002). The authors reported no negative effects of feeding milled flaxseed at this level and reported reduced skin reactions in response to the induced skin irritation in the flaxseed supplemented horses.
Other studies in 2009 & 2012, fed a much lower amount of milled flaxseed, estimated to be 150-165g (5.5-5.8 oz) per day. Between these two studies, positive changes in blood and muscle omega 3 content and improved immune function were reported in those supplemented with flaxseed compared with control groups (Vineyard, K. et al., 2009; Hess, T. et al., 2012).
Based on these few studies and figures extrapolated from other species, up to 100g (3.5 oz) per 100kg (220 lb) or 500 grams for a 500 kg horse per day can be fed safely.
Most horses (65% according to Facebook Poll conducted on the 15 October 2020 by FeedXL Horse Nutrition Calculator) receive 100-250g (3.5-8.8 oz) flaxseed per day.
If you are concerned about cyanide toxicity, what can you do?
Research has shown that heating flaxseed can reduce the amount of cyanogenic precursor present.
One study showed microwaving flaxseed for just over 4.5 minutes on microwave power of 400W reduced precursor by 25% (Dusica, I. et al., 2012). Beware though, you can burn flaxseed in the microwave! Microwave power > 560W for 6 minutes caused samples to burn.
Other studies have also shown that microwave roasting achieved the highest level of precursor reduction (83.3%) in flaxseed (Feng et al. (2003).
Happily, this study also showed that there were no major changes in the main nutrient and fatty acid profile caused by microwave treatment.
Similarly, extrusion (140 degree Celsius) significantly reduced cyanogenic compounds (84%) but did not significantly change the fatty acid content – even after storage for 60 days (Imran, M et al., 2015). Limited information is available on micronized flaxseed specifically.
Interestingly, the perception that fatty acids in raw ground flaxseed deteriorate quickly is not supported by various studies, all showing minimal difference in fatty acid composition after 2-4 months storage (Khalesi, S., et al. 2011).
What about oil?
The good news is that oil doesn’t contain the cynangenic compounds of whole or ground flaxseed. It can be less stable in terms of fatty acid composition, therefore must be stored correctly and used in a timely manner. But if the reason you are feeding flaxseed is for the oil content, then using the oil may be an option worth considering.
With flaxseed oil products though, you do not get the benefit of other nutrients whole, ground or milled flaxseed provides to a diet including like protein, fibre, minerals & vitamins.
Summary
So, are we any closer to knowing what is the best and safest form of flaxseed to feed our horses? Honestly, we think it comes down to personal preference.
With cyanide toxicity appearing to be less of an issue for horses due to the low amounts commonly fed in comparison to body weight – whole or ground flaxseed is acceptable. Due to anecdotal evidence of whole flaxseeds passing undigested through the gut, freshly ground flaxseed is favourable to ensure fatty acids can be absorbed.
Ground flaxseed also offers the benefit of providing the wonderful fibre and other nutrients along with the omega 3 fatty acids compared with flaxseed oil.
Practically, freshly grinding flaxseed is not for everyone. If this is the case for you, using a stabilised (pre-heat treated) flaxseed product may be a better option.
If you are still concerned about cyanide poisoning, microwaving your flaxseed should significantly reduce the cyanogenic precursor and is unlikely to affect the fatty acid content. Be careful microwaving though to make sure you are not burning the flaxseed.
And do your own research on the safest way to microwave them based on your specific microwave. As a guide you should be able to safely microwave them at 400W for 5 minutes. But the quantity you microwave at any one time will have an effect on the appropriate time you should use.
Feeding rates will vary depending on a horse’s energy requirement and amount of omega 3 within the diet however up to 100g per 100kg body weight appears safe…the economics of feeding this much we are less sure about!
References
Dusica, I., Kokic, B., & Tea, B., Colovic, R., Vukmirovic, D. & Slavica, S. (2012). Effect of microwave heating on content of cyanogenic glycosides in linseed. Ratarstvo i povrtarstvo. 49. 63-68.
EFSA CONTAM Panel (EFSA Panel on Contaminants in the Food Chain), Schrenk, D., Bignami, M., Bodin, L., Chipman, J.K., del Mazo, J., Grasl‐Kraupp, B., Hogstrand, C., Hoogenboom, L.R., Leblanc, J‐C., Nebbia, C.S., Nielsen, E., Ntzani, E., Petersen, A., Sand, S., Vleminckx, C, Wallace, H., Benford, D., Brimer, L., Mancini, F.R., Metzler, M., Viviani, B., Altieri, A., Arcella, D., Steinkellner, H. & Schwerdtle, T., (2019). Scientific opinion on the evaluation of the health risks related to the presence of cyanogenic glycosides in foods other than raw apricot kernels. EFSA Journal 2019;17(4):5662, 78.
Feng, D., Shen, Y. & Chavez, E. (2003). Effectiveness of different processing methods in reducing hydrogen cyanide content of flaxseed. Journal of the Science of Food and Agriculture. 83. 836 – 841.
Hess, T., Rexford, J., Hansen, D. Harris, M., Schauermann, N., Ross-Jones, T., Engle, T., Allen, K. & Mulligan, C. (2012). Effects of two different dietary sources of long chain omega-3, highly unsaturated fatty acids on incorporation into the plasma, red blood cell, and skeletal muscle in horses. Journal of Animal Science. 90. 3023-31.
Imran, M., Anjum, F., Ahmad, N., Khan, M., Mushtaq, Z., Nadeem, M. & Hussain, S. (2015). Impact of extrusion processing conditions on lipid peroxidation and storage stability of full-fat flaxseed meal. Lipids in health and disease. 14. 92.
Khalesi, S., Jamaluddin, R. & Ismail, A. (2011). Effect of raw and heated flaxseed (Linum usitatissimum L.) on blood lipid profiles in rats. International Journal of Applied Science and Technology. 1(4). 84-9.
O’Neill, W., McKee, S. & Clarke, A. (2002). Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. Canadian journal of veterinary research = Revue canadienne de recherche vétérinaire. 66. 272-7.
Ratnayake, W., Behrens, W., Fischer, P., Labbe, M., Mongeau, R. & Bearerogers, J. (1992). Chemical and nutritional studies of flax-seed (Variety Linott) in rats. Journal of Nutritional Biochemistry. 3. 232-240.
Vineyard, K., Warren, L. & Kivipelto, J. (2009). Effect of dietary omega-3 fatty acid source on plasma and red blood cell membrane composition and immune function in yearling horses. Journal of Animal Science. 88. 248-57.
Meet The Author: Samantha Potter, MSc
In 2009, Sam completed a Bachelor of Equine Studies and it was during this time she developed an interest in equine nutrition. Pursuing this passion, Sam went on to complete her Honours followed by her Masters degree in equine nutrition at The University of Melbourne. Since 2015, Sam has worked as an independent nutritionist and enjoys supporting horse owners manage their horse’s nutrition in her role with FeedXL. To learn more about Sam and to ‘meet’ the rest of the FeedXL team, check out our About Us page here.
Do you have a question or comment? Do you need help with feeding?
We would love to welcome you to our FeedXL Horse Nutrition Facebook Group. Ask questions and have them answered by PhD and Masters qualified equine nutritionists and spend time with like-minded horse owners. It’s free!
