It’s easy for opinions or hypotheses that are repeated often enough to eventually morph into what passes as a fact and from there to a myth that’s difficult to eradicate. These are three commonly repeated, but wrong, horse feeding myths.
Constant access to hay buffers stomach acid/Feeding grain increases stomach acid. Damkel et al in a 2015 study fed horses either free choice hay, limited hay plus grain or the hay and grain diet with a pectin and lecithin supplement (75 g/100 kg of body weight). The horses had electrodes implanted in their stomachs to monitor pH. Diets were fed for 14 days before starting the experiment. Horses on the free choice hay had significantly lower (more acidic) pH values with a median pH of 2.69 over 24 hours compared to the the hay/grain diet (3.35) or the hay/grain diet with the supplement (3.4). Similarly, Nadeau et al 2000 found much lower pH in horses fed a grass hay diet than in those receiving corn and alfalfa. As a corollary myth, it has also been widely stated that alfalfa will reduce ulcers and buffer stomach acid but Vondran et al 2016 fed grass hay, alfalfa pellets or alfalfa chaff to weanlings and found no difference in ulceration in most areas but greatly increased ulceration at the pylorus in the weanlings fed alfalfa chaff.
Depriving horses of 24 hour access to hay causes cortisol to rise from the extreme stress. Gordon et al 2009 fed overweight horses a diet of either a high calorie pellet or reduced calorie, low carbohydrate weight control feed with 1% of their body weight in hay. Hay was only fed once a day, in the afternoon. Grains were fed twice a day. Some of the horses on weight control and restricted hay were also exercised. The unexercised weight control horses lost significant weight and also had a large drop in their cortisol levels from 11 ng/mL down to 1.8 ng/mL. Exercised also dropped from about 10.6 to 6 ng/mL (note: exercise increases cortisol naturally). The control horses that did not lose weight because of the high calorie grain had no significant change in cortisol with this feeding pattern (although it dropped a little in them as well.) Two other studies also found a drop in cortisol when feeding was restricted.
Feeding high glycemic index diets (i.e. grain) causes insulin resistance. Suagee et al 2013 fed nonobese horses feeds of 10%, 20% or 60% non-structural carbohydrate (primarily starch) for 90 days. They found no change in insulin sensitivity with the high carbohydrate diet. This study was important because other work looking at the effect of diet was done with horses that were obese or were deliberately overfed and became obese. Bamford et al 2016 also showed that feeding 1.5 g/kg body weight of glucose every day for 20 weeks did not alter insulin sensitivity even though it caused the horses to gain weight. In fact, feeding glucose actually improved insulin sensitivity in these non-IR horses.
Even if it seems to make sense it is always good to question what you think you know – and what other people think they know too.
Eleanor Kellon, VMD