One of the golden rules of feeding is to feed according to work done and it is very important to bear in mind when feeding your horse. 
It is particularly important at this time of the year when the nights are getting lighter, weather improves and workloads, very often, increase.
Feeds are generally classified by the level of work they are designed for and whether or not your horse needs more or less condition. There are a whole host of feeds available within each of these categories which can lead to some confusion. 
The first thing to remember is that feeding the wrong ‘class’ of feed can lead to problems – some more serious than others. 

Behaviour issues
Overfeeding by using feed for harder working horses can lead to undesirable behaviour. This may manifest itself as out of character ‘fizziness’ or spookiness, or just general bolshiness. 
The horse is basically experiencing the effects of having too much energy and is using it up at the first given opportunity (ie, when you get on him to go out for a nice, quiet hack). 
Some of this is not just due to the amount of feed, but also to the type of feed. 
Feeds formulated for higher levels of work will tend to have a higher starch content, which provides fast release energy. Indeed, explosive energy. 
A change to a feed formulated for the appropriate, lower level of work, will make life much easier for you and your horse and will generally be a lot easier on your pocket too. 
Look for feeds that are high in oil and fibre (eg, Harbro Horse and Pony Nuts and Mix). 
At this time of year there is the added issue of the effects of spring grass to deal with too, so don’t automatically assume because your horse’s workload has increased that he suddenly needs a higher energy feed or more feed. The extra energy from the grass may mean that you don’t need to increase your feeding and may actually have to look at using a lower energy feed or the use of a balancer pellet instead.

Work level
Ascertaining what level of work your horse is doing is one of the first steps to getting your feeding sorted out. The below table should give some indication as to what category your horse falls into but if in doubt make use of one of the many help-lines available to you and ask the question.
Resting    also includes very light hacking

  1. Light work 1 hour hacking 5 days a week, novice dressage and show jumping
  2. Light-medium 1-2 hours hacking/fittening, pre-novice/novice eventing, up to medium level dressage
  3. Medium  Advanced dressage, intermediate/1* eventer, A&B show jumper
  4. Medium-hard  Advanced/2* eventer; international show jumper
  5. Hard Racing, 3 and 4 * eventer

Selecting a feed
Once you have ascertained the amount of work your horse is doing, it makes it easier to select an appropriate feed. The use of a weigh tape will help you to decide what amount of feed is required and, used on a weekly basis, will soon alert you to any increases or drops in weight enabling you to adjust feed levels before there is a big issue. 
Remember to feed by weight and not volume and this in itself will prevent any over or under feeding. Also remember that 1kg of one feed type does not necessarily come up to the same level on your scoop as another type, weigh each feed individually. All horses are individuals and what works for one horse won’t necessarily suit another, even if they are the same weight and doing the same work level. 
Laid back horses may require a feed containing instant release energy sources (higher cereal content feeds eg, coarse mixes) whereas fizzier types will require feed containing slow release energy sources (high in fibre and oil and generally nuts/cubes). Stand back and look at your horse and ascertain if you need to make any adjustments according to the amount of work he is doing, his current condition, his breed, his current energy level and his temperament. Help is only a phone call away. 

Weighty issues
A more serious consequence of over feeding or incorrectly feeding your horse is that it can lead to him being over conditioned or, at the extreme, obese. Horses seem to be kept at a higher condition score now than they were 10-20 years ago and, whatever the cause, it is a worrying trend. 
Fit not fat, always used to be the watch phrase used to describe a fit healthy horse, now there seems to be a growing number of fat and fairly fit horses out there. This is most likely a consequence of feeding diets which are over specified for the activity of the horse, and the growth in popularity of the ‘cobby’ type, with the realisation that they make a fantastic and sensible all-rounder. 
They are also, in the main, incredibly good doers. Like humans, carrying too much weight can put excessive strain on joints and major organs (heart, lungs etc) and potentially shorten the working life of a horse. There is also the concern about laminitis in overweight horses. 
Imagine how much better and livelier you feel for shedding a few pounds. For many horses it is possibly the amount of extra weight that they are carrying which makes them lethargic and ‘lazy’. Feeding them more feed will only exacerbate this problem. Before running to the feed shop to change your horses feed to make him more lively make sure he is not carrying excessive weight and that he is fit enough for the job expected of him. Most good doers thrive well on chaff plus a balancer pellet (to ensure they are receiving all the protein, vitamins and minerals they require) topped up with a small amount of oats (if extra oomph is required), and oil for stamina if needed.