I found this information published by Horse & Rider interesting, I hope you do too! Keep in mind that the more vigorously you perform these exercises, the more you’ll maximize the calorie burning* benefits.

Vigorously curry your horse, using a circular arm motion
Time spent: 10 minutes
Calories burned: 68

Vigorously brush your horse (Tip: alternate arms)
Time spent: 10 minutes
Calories burned:46

Walk a 10-foot circle, as you lunge your horse
Time spent: 20 minutes
Calories burned:79

Briskly hand-walk your horse
(Tip: add wrist or ankle weights for increased calorie-burning and aerobic benefits)
Time spent: 20 minutes
Calories burned:91

Muck/rebed stall
Time spent: 20 minutes
Calories burned: 159

Push 50-pound load in wheelbarrow
Time spent: 10 minutes
Calories burned: 63

Ride at the walk
Time spent: 20 minutes
Calories burned: 57

Ride at the trot
(Tip: Posting at a medium trot will burn more calories than sitting at a jog)
Time spent: 10 minutes
Calories burned: 74

Ride at the lope
Time spent: 10 minutes
Calories burned: 93

Sweep/rake
(Tip: For a great waist trimmer, twist your upper body with each stroke, rather than using only your arms. When sweeping with a push broom, slightly bend your knees, to push off with your legs into each stroke.)
Time spent: 20 minutes
Calories burned: 91

Unload/stack 100-pound hay bales
(Tip: Protect your back by bending at the knees, and using your legs to lift the load. Consider a back support brace when lifting heavy loads)
Time spent: 20 minutes
Calories burned: 249

Unload/stack 50-pound straw bales
Time spent: 20 minutes
Calories burned: 181

Lift/heft 20 pounds (feed/water)
Time spent: 30 minutes
Calories burned: 153

Lift/heft 40-pound Western saddle on/off horse
Time spent: 10 minutes
Calories burned: 56

Lift/heft 20-pound English saddle on/off horse.
Time spent: 10 minutes
Calories burned: 46

*Calories burned per exercise for a person who is 5’8″ and weights 150 lbs.
If you have a smaller frame and weight, you’ll burn slightly fewer calories; you’ll burn slightly more if you have a larger frame and weigh more.