Goats

A goat is a browser rather than a grazer. Given the choice it eats woody and broadleaf growth - brambles, vines, tree seedlings - in preference to grass, so it will willingly eat the plants taking a piece of land back. Kept in rotated groups it turns that growth into milk and meat. The work is slow: woody plants within reach, up to about 1.8 m (6 ft), are stripped of leaves in a season, but vigour only declines over years and the brush returns if the animals leave.

What governs the system is a worm. The larvae that infect goats hatch in the droppings, stay within 30 to 60 cm (12 to 24 in) of them and climb only 5 to 8 cm (2 to 3 in) up a leaf or blade. An animal eating at head height off a bush barely meets them; the same animal on short grass eats them by the mouthful. The rules that follow are geometric rather than medical: never let them graze below about 5 cm (2 in), keep stocking near 20 to 25 head per hectare (8 to 10 per acre), and rest each paddock long enough for the larvae to die - roughly 35 days in hot humid weather and more than 65 where it is cooler. Running cattle over the same ground dilutes what is left.

Goats climb, lean and rub, so the fence is half the component. A perimeter runs five or six high-tensile wires, two or three of them live, on posts 6 to 12 m (20 to 40 ft) apart braced so they cannot be pulled out; woven wire needs a live strand inside it, and temporary netting has to be electrified to hold them at all. Unfenced they browse whatever is in reach, and a young fruit tree is in reach. Dosing is the second trap: goats break worming drugs down faster than sheep or cattle and need roughly double the dose, so an underdose fails and breeds resistant worms. Scoring each animal for anaemia through the warm season means treating the few that need it rather than the herd. The rest is daily milking, hoof trimming and a fence walked constantly.