In my country, driver schooling focuses on principles of moderate speed, correct safe distance, and maximum visibility. So here is my contribute answer.
If lowering beams hides the animal to your own eyes, keep high beams for a few more meters
Once you are able to track the animal, lower your beams
Do not horn or you will scare the animal more
I have found myself in similar situations, especially with cats. Once I hit one who first stayed still then crossed the street by the exact time my car approached him. First, use as much as high beam as possible. Travel is safer with them. It is better for you to see animals in advance than relying on them to avoid you. Humans are intelligent, expert and aware of dangers. They can elaborate escape routes. Animals rely on instinct.
You have to control your speed not just over the displayed/designated speed limit, but on your knowledge of the road, visibility and ability to brake. Ability to brake includes (picture displays snow) weather conditions and car status.
You will normally hit the speed limit, and travel as fastest as you are allowed, with full high beams on a straight way. By the time you notice reflections from wildlife eyes, you will have all the distance you need to slow down using the brakes without excessive force.
If you are on a curve, thus have reduced visibility, you are required to slow down as your beams will point to animals too late for breaking in safety.
Second part is how to handle the wildlife at short distance once you sighted them and slowed. You have to avoid the moose maneuver and keep it at last resort. Discussion here is whether to keep beams high or to lower them. My answer is: KEEP YOUR ANIMAL VISIBILE at all the time.
Do the above while braking, so I assume you will choose whether to lower beams while your foot is pushing the brake and speed gauge is reducing.
It may happen, on very dark roads/nights, that you may want to approach your animal with full beams at all the time. He will stare, his eyes will be stressed a lot, but you will probably save his life as soon as you slow down and gently turn him. Again, you have planned your speed in advance so you are aware of your braking distance. The vehicle behind you has planned his distance and speed and can react to you braking gently.
To make an idea, keep in mind that humans have 1 second lag to start braking. Assuming a 90km/h out-of-town speed limit, modern cars with ABS can slow down to 40 in 3 seconds in comfort (if you push the brake with your full body it will take less and scare passengers and following vehicles).
Avoid to moose if not forced to do so. Contributors correctly showed that choosing to surely hit wildlife with minor consequences or risking to fail to moose with severe consequences for driver, passengers and oppositebound traffic is a hard choice.
Traffic regulators may want to plan the mandatory installation of devices such as this one in all cars in the near future. Motor companies are already working on self-driving cars that need such kind of sensors.