Just another reminder that these conditions in the Southwest can set up your horse to easily become dehydrated which can lead to an impaction.
Your first line of defense? SALT! An adult horse needs about an ounce of plain white salt a day added to feed for maintenance - about four teaspoons or a small handful. This will ensure an adequate "thirst response" as long as fresh clean water is available. Most horses can't get enough salt solely from a block, although a plain white block or brick should always be kept available in their feeder and/or turn out area.
Next in our line of defense is monitoring water intake. My horses consistently are drinking ten to twelve gallons each now that the weather has cooled down, and a little more when daytime highs go up into the 80's (I just love living in Arizona!) I long ago got rid of my automatic waterers and switched to large muck buckets for water, along with a 100 gallon tank in the turn out area. If you use automatic waterers, they need to be checked every day to ensure they are working properly and not freezing up during the night; providing a bucket of water also is good insurance but not always possible if you board. You should also do a hydration check on your horse daily - squeeze a fold of skin between your index finger and thumb, it should snap back flat in less than three seconds, and check that the gums are moist, not dry or sticky.
As horses age they make less saliva when they chew; this can be aggravated if water intake is inadequate. Combined with worn or missing teeth hay can become difficult to chew into digestible lengths which will pass easily through the digestive system leading up to an impaction.
Consider using a leaf mulcher to chop hay into finer lengths and/or wetting the hay down. Getting the older horse used to accepting concentrates as a mash, with wetter and soupier consistency as it's accepted, is a good way to get more water into these older campaigners. Hay pellets and beet pulp shreds will hold many times their weight in water and the fineness of the grind makes them a good option.
Caution with beet pulp pellets - unless they're soaked for several hours, beet pulp pellets can retain a hard center which may cause a problem for some horses. I've been finding much more consistency in the beet pulp shreds I purchase now (cleaner, more consistent chop) than when I first started feeding beet pulp fifeen years ago, plus they soak up water quickly, eliminating the need for a long soak.
Feeding the mash in a large muck bucket will also encourage whoever is doing the feeding to add more water than if the feed is mixed up in a small bucket. I mix the beet pulp shreds, Timothy hay pellets, supplement (AZ Copper Complete), salt and any other add-ins in easy to carry buckets out to the stalls, then dump it into the large muck buckets and soak it all with a hard spray setting with a hose to thoroughly mix, using at least a gallon of water per horse. The muck buckets are easy to keep clean and don't tip easily - at least not until they're down to licking up every last drop!
Bottom line - plain white salt is likely the most essential supplement you can provide to your horse - along with lots of clean, fresh water and quality forage.
Stay warm and enjoy your horses!
in warm sunny Vail AZ - until the weekend (Brrrrrr)
AZ Copper Complete - http://horsetech.com/arizona-copper-complete
Leaf Mulchers - http://www.bestreviews.guide/leaf-mulchers?
Large muck buckets -http://www.tractorsupply.com/tsc/search/muck%20bucket