30 October 2015
I've already had a few rants on social media as to why it's important to thoroughly read the whole of a scientific journal article and not just the abstract when writing a journalistic article. Let alone, having some good knowledge of what is already known about in the area you are writing about. Many of you may have already read about the research on how feeding a high starch / low fibre diet can have negative effects on the behaviour of horses. Good research that gives horse owners food for thought and keeps us on our toes, because we all want to do the best by our four hooved friends. But research needs to be put into perspective when writing journalistic reports, and this is just what I've been ranting on about the last week!
In October 2015 an interesting article was published in the peer-reviewed journal "Physiology & Behaviour" by Alexandra Destrez1 and colleagues: “Changes of the hind gut microbiota due to high-starch diet can be associated with behavioural stress response in horses". This research report was picked up on by the horse media and has been doing the rounds on social media. The problem is, some media reports seem to be missing the point somewhat, maybe because the authors of these reports didn't take the time to actually read the whole journal article? This is a shame because the research gives us some interesting information, when read in its entirety and put into the context of what we know about feeding horses. To make matters even worse is that so far as I can tell, the Dutch media report in the Hoefslag2 seems to be an almost exact translation of a report in the US publication TheHorse.com3.
Enough digression, let's shine some light in the research and put some perspective on the findings:
The aims of this study were (and I quote directly from the authors): "The aim of the present study was to investigate to what extent behavioural changes are associated with changes of the microbiota through an alimentary stress in horses." The aims of this study were thus not to investigate how much starch you need to feed your horse in order to elicit a change in the flora of the large intestine; it was to see if such changes were associated with changes in behaviour. Research on how much starch is needed to change the intestinal flora has been published, some by this group and elsewhere and is used a background to this study design.
So now we know the aims of this study were, we can fill in vital information contained in the publication that might help horse owners put this research into perspective. Instead of making drastic or unnecessary changes to their own horses diet due to some media outlets not using enough background information to substantiate their reports. Please note: this is not a discussion about whether or not your horse needs extra energy in the form of concentrates; we'll save that for another time ;-).
In this study, the horses were first fed a high fibre diet (100% hay) to meet 100% of the energy requirements for a 3-week period (period 1). There then followed a transition period of 5 days where the horses were introduced to a very low fibre (60% hay) high starch (40% barely) diet. During the next three weeks, period 2, the horses were fed a very low fibre (57% hay) high starch (43% barley) diet. In period 3 the horses were transferred back to the high fibre diet for the rest of the study period for 3 weeks. The amount of dry matter from the 100% hay diet (2.2kg DM/day/100kg body weight) was substantially decreased to just 0.8kgDM/day/100kg body weight coming from hay and 1.4kgDM/day/100kg body weight coming from barely during period 2. During all three periods, two behavioural tests were carried out: a sociability test with an unfamiliar horse and novelty test with a strange object placed in front of the horses feed container. The results of these tests demonstrated that vigilance behaviour (a behavioural stress indicator) was significantly positively correlated with the negative disturbances in the intestinal bacteria when on the high starch diet.
In their conclusions, the authors suggest that changes in intestinal bacteria can be associated with behavioural stress response in horses and that vigilance might reflect a negative emotional state such as intestinal discomfort. In addition, that these behavioural signs may be useful indicators of alimentary stress.
Information that might help horse owners put this type of diet in perspective is that whilst on the high starch diet the horses received a morning feed containing 2.5g starch per kg body weight (BW) in a single meal. This is equivalent to approximately 3kg for a 500kg horse of an average performance cereal-based concentrate for sport horses (30% starch) in a single meal. The evening meal contained 1.26g starch /kg BW.
Horses have a limited capacity to digest starch due to the limited production of α-amylase, the enzyme responsible for breaking down starch in the small intestine. This is in sharp contrast to humans and many other species. The products of starch digestion by α-amylase, the simpler sugars, are further digested by the enzymes maltase and sucrase in the small intestine. The pancreas of horses produces adequate amounts of α-amylase for the digestion of starch from a diet containing a high proportion of forage. However, the activity and production of α-amylase by the pancreas in horses limits the amount of starch that can be completely digested in the small intestine in a single, high starch, grain based meal. Undigested starch leaves the small intestine and enters the large intestine stimulating fermentation by undesirable bacteria leading to a lowering of the intestinal pH and disturbances in the normal bacterial ecosystem, which may increase the risk of diarrhea, colic and laminitis. A commonly accepted recommendation is to limit starch intake to <2g/kg BW/meal to avoid starch overload in the large intestine4. A more recent recommendation is not to feed more than 1g/kg BW/meal5.
From this background information, you can see that the horses in this study received much more starch in a single meal than is currently recommended: 2.5g/kg BW/meal as opposed to a recommendation of <1g/kg BW/meal. This was actually an intentional part of the study design, the researchers expected to induce changes in the flora of the large intestine. They elicited this change in order to produce an alimentary stress in horses so they could access to what extent behavioural changes are associated with such stress. The researchers also measured the number of granulocytes (white blood cells that play a role in inflammatory processes), as these changes are also associated with acidification (drop in pH) in large intestinal disturbances and alimentary stress. Interestingly the actual acidity (pH) of the large intestine was not measured, although one of the authors has previously reported a decrease in pH in horses fed similar diets6.
So how do these recommendations compare to common feeding practices and the amount of starch in many cereal-based concentrates?
This is actually quite a difficult question as not all starches are as equally digestible, and processing of cereal grains also affects starch digestibility4. However, I hope I can at least shed some light on the matter. If you look at the starch content of cereal-based concentrates for sport horses from various feed manufacturers you will see that they contain varying amounts of starch, ranging on average from 25 to 35%. Thus, a kg of concentrate with 30% starch will contain 300g of starch. The next step is to take a look at how much the feed manufacturer recommends feeding per day. Most seem to recommend feeding 2 to 3 kg per day for a 400-600kg horse depending on the amount of work. So let's take a 600kg horse and feed it 3 kg of concentrates containing 300g of starch per kg (or 30% starch), and divide that 3kg over two meals per day. We end up giving this horse 450g of starch per meal or 0.75g starch/kg BW/meal. Thus well within the <1g/kg BW/meal recommendation and well below the amount of starch fed to the horses in the research by Alexandra Destrez and colleagues. The take-home message here seems to be to stay within the limits that feed manufacturers recommend and remember that adding extra straights such as oats or barely will significantly increase the starch content of a meal.
I hope that this summary helps put this research into perspective. The authors of this research have contributed widely to our knowledge of nutrition and digestion in horses, not only through this publication. Research continues to answer many of the questions that we as horse owners have when it comes to safely feeding our horses. But research needs to be read carefully and put into a context that is useful to everyone, and not just in the interest of creating sensation-seeking headlines in the popular media.
1. Changes of the hindgut microbiota due to high-starch diet can be associated with behavioral stress response in horses.
Destrez, A., Grimm, P., Cézilly, P., & Julliand, V. 2015
Physiology & Behavior 149; 159–164
http://www.sciencedirect.com.ezproxy.is.ed.ac.uk/science/article/pii/S0031938415003339
2. High-Starch Diets’ Effects on Stress Reponse in Horses
Casie Bazay, NBCAAM
TheHorse.com 19 October 2015
http://www.thehorse.com/articles/36571/high-starch-diets-effects-on-stress-response-in-horses
3. Zetmeelrijk voer versterkt waakzaam gedraag
Hoefslag, 19 October 2015
http://www.dehoefslag.nl/laatste-nieuws/algemeen/zetmeelrijk-voer-versterkt-waakzaam-gedrag.html
4. Starch digestion in horses: The Impact of feed processing
Jullian, V., De Fombelle, M. & Varloud, M. 2006
Livestock Science 100(1); 44-52
5. Andrea Ellis, personal communication 2015
http://www.unequi.co.uk/
6. Julliand, V., de Fombelle, A., Drogoul, C. & Jacotot, E. 2001
Feeding and microbial disorders in horses: part 3 – effects of three hay:grain ratios on microbial profile and activities.
Journal of Equine Veterinary Science 21; 543-546
I've already had a few rants on social media as to why it's important to thoroughly read the whole of a scientific journal article and not just the abstract when writing a journalistic article. Let alone, having some good knowledge of what is already known about in the area you are writing about. Many of you may have already read about the research on how feeding a high starch / low fibre diet can have negative effects on the behaviour of horses. Good research that gives horse owners food for thought and keeps us on our toes, because we all want to do the best by our four hooved friends. But research needs to be put into perspective when writing journalistic reports, and this is just what I've been ranting on about the last week!
In October 2015 an interesting article was published in the peer-reviewed journal "Physiology & Behaviour" by Alexandra Destrez1 and colleagues: “Changes of the hind gut microbiota due to high-starch diet can be associated with behavioural stress response in horses". This research report was picked up on by the horse media and has been doing the rounds on social media. The problem is, some media reports seem to be missing the point somewhat, maybe because the authors of these reports didn't take the time to actually read the whole journal article? This is a shame because the research gives us some interesting information, when read in its entirety and put into the context of what we know about feeding horses. To make matters even worse is that so far as I can tell, the Dutch media report in the Hoefslag2 seems to be an almost exact translation of a report in the US publication TheHorse.com3.
Enough digression, let's shine some light in the research and put some perspective on the findings:
The aims of this study were (and I quote directly from the authors): "The aim of the present study was to investigate to what extent behavioural changes are associated with changes of the microbiota through an alimentary stress in horses." The aims of this study were thus not to investigate how much starch you need to feed your horse in order to elicit a change in the flora of the large intestine; it was to see if such changes were associated with changes in behaviour. Research on how much starch is needed to change the intestinal flora has been published, some by this group and elsewhere and is used a background to this study design.
So now we know the aims of this study were, we can fill in vital information contained in the publication that might help horse owners put this research into perspective. Instead of making drastic or unnecessary changes to their own horses diet due to some media outlets not using enough background information to substantiate their reports. Please note: this is not a discussion about whether or not your horse needs extra energy in the form of concentrates; we'll save that for another time ;-).
In this study, the horses were first fed a high fibre diet (100% hay) to meet 100% of the energy requirements for a 3-week period (period 1). There then followed a transition period of 5 days where the horses were introduced to a very low fibre (60% hay) high starch (40% barely) diet. During the next three weeks, period 2, the horses were fed a very low fibre (57% hay) high starch (43% barley) diet. In period 3 the horses were transferred back to the high fibre diet for the rest of the study period for 3 weeks. The amount of dry matter from the 100% hay diet (2.2kg DM/day/100kg body weight) was substantially decreased to just 0.8kgDM/day/100kg body weight coming from hay and 1.4kgDM/day/100kg body weight coming from barely during period 2. During all three periods, two behavioural tests were carried out: a sociability test with an unfamiliar horse and novelty test with a strange object placed in front of the horses feed container. The results of these tests demonstrated that vigilance behaviour (a behavioural stress indicator) was significantly positively correlated with the negative disturbances in the intestinal bacteria when on the high starch diet.
In their conclusions, the authors suggest that changes in intestinal bacteria can be associated with behavioural stress response in horses and that vigilance might reflect a negative emotional state such as intestinal discomfort. In addition, that these behavioural signs may be useful indicators of alimentary stress.
Information that might help horse owners put this type of diet in perspective is that whilst on the high starch diet the horses received a morning feed containing 2.5g starch per kg body weight (BW) in a single meal. This is equivalent to approximately 3kg for a 500kg horse of an average performance cereal-based concentrate for sport horses (30% starch) in a single meal. The evening meal contained 1.26g starch /kg BW.
Horses have a limited capacity to digest starch due to the limited production of α-amylase, the enzyme responsible for breaking down starch in the small intestine. This is in sharp contrast to humans and many other species. The products of starch digestion by α-amylase, the simpler sugars, are further digested by the enzymes maltase and sucrase in the small intestine. The pancreas of horses produces adequate amounts of α-amylase for the digestion of starch from a diet containing a high proportion of forage. However, the activity and production of α-amylase by the pancreas in horses limits the amount of starch that can be completely digested in the small intestine in a single, high starch, grain based meal. Undigested starch leaves the small intestine and enters the large intestine stimulating fermentation by undesirable bacteria leading to a lowering of the intestinal pH and disturbances in the normal bacterial ecosystem, which may increase the risk of diarrhea, colic and laminitis. A commonly accepted recommendation is to limit starch intake to <2g/kg BW/meal to avoid starch overload in the large intestine4. A more recent recommendation is not to feed more than 1g/kg BW/meal5.
From this background information, you can see that the horses in this study received much more starch in a single meal than is currently recommended: 2.5g/kg BW/meal as opposed to a recommendation of <1g/kg BW/meal. This was actually an intentional part of the study design, the researchers expected to induce changes in the flora of the large intestine. They elicited this change in order to produce an alimentary stress in horses so they could access to what extent behavioural changes are associated with such stress. The researchers also measured the number of granulocytes (white blood cells that play a role in inflammatory processes), as these changes are also associated with acidification (drop in pH) in large intestinal disturbances and alimentary stress. Interestingly the actual acidity (pH) of the large intestine was not measured, although one of the authors has previously reported a decrease in pH in horses fed similar diets6.
So how do these recommendations compare to common feeding practices and the amount of starch in many cereal-based concentrates?
This is actually quite a difficult question as not all starches are as equally digestible, and processing of cereal grains also affects starch digestibility4. However, I hope I can at least shed some light on the matter. If you look at the starch content of cereal-based concentrates for sport horses from various feed manufacturers you will see that they contain varying amounts of starch, ranging on average from 25 to 35%. Thus, a kg of concentrate with 30% starch will contain 300g of starch. The next step is to take a look at how much the feed manufacturer recommends feeding per day. Most seem to recommend feeding 2 to 3 kg per day for a 400-600kg horse depending on the amount of work. So let's take a 600kg horse and feed it 3 kg of concentrates containing 300g of starch per kg (or 30% starch), and divide that 3kg over two meals per day. We end up giving this horse 450g of starch per meal or 0.75g starch/kg BW/meal. Thus well within the <1g/kg BW/meal recommendation and well below the amount of starch fed to the horses in the research by Alexandra Destrez and colleagues. The take-home message here seems to be to stay within the limits that feed manufacturers recommend and remember that adding extra straights such as oats or barely will significantly increase the starch content of a meal.
I hope that this summary helps put this research into perspective. The authors of this research have contributed widely to our knowledge of nutrition and digestion in horses, not only through this publication. Research continues to answer many of the questions that we as horse owners have when it comes to safely feeding our horses. But research needs to be read carefully and put into a context that is useful to everyone, and not just in the interest of creating sensation-seeking headlines in the popular media.
1. Changes of the hindgut microbiota due to high-starch diet can be associated with behavioral stress response in horses.
Destrez, A., Grimm, P., Cézilly, P., & Julliand, V. 2015
Physiology & Behavior 149; 159–164
http://www.sciencedirect.com.ezproxy.is.ed.ac.uk/science/article/pii/S0031938415003339
2. High-Starch Diets’ Effects on Stress Reponse in Horses
Casie Bazay, NBCAAM
TheHorse.com 19 October 2015
http://www.thehorse.com/articles/36571/high-starch-diets-effects-on-stress-response-in-horses
3. Zetmeelrijk voer versterkt waakzaam gedraag
Hoefslag, 19 October 2015
http://www.dehoefslag.nl/laatste-nieuws/algemeen/zetmeelrijk-voer-versterkt-waakzaam-gedrag.html
4. Starch digestion in horses: The Impact of feed processing
Jullian, V., De Fombelle, M. & Varloud, M. 2006
Livestock Science 100(1); 44-52
5. Andrea Ellis, personal communication 2015
http://www.unequi.co.uk/
6. Julliand, V., de Fombelle, A., Drogoul, C. & Jacotot, E. 2001
Feeding and microbial disorders in horses: part 3 – effects of three hay:grain ratios on microbial profile and activities.
Journal of Equine Veterinary Science 21; 543-546
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