The prohibition of muzzling an animal while it is threshing applies to all types of animals.
A worker may eat from the produce that he is working on whether he is working on produce that is attached to the ground or has been harvested. (1)
It is forbidden to muzzle an ox while it is working whether it is working on unpicked produce or produce that has already been harvested.
A worker may only eat from produce that grows from the ground but if he is milking an animal or making cheese he may not eat.
A worker may only eat from unpicked produce if he is doing the Gmar Melachah (harvesting) but if he is weeding or pruning the produce he may not eat. (2)
A worker may only eat from harvested produce it is not yet the Gmar Melachah for Ma'aser and therefore if he is separating dates or figs that are stuck together he may not eat from the fruit.
If dates are picked from the tree before they are ripe and they are placed in a basket to ripen if the workers are separating the dates prior to their ripening they may eat from the fruit because it is not yet the Gmar Melachah.
If workers are working on produce which has a Chiyuv Chalah the workers may eat if it is not yet the Gmar Melachah for Chalah and therefore if they are kneading or shaping the dough or baking the dough they may not eat.
The fourteen years that Klal Yisrael conquered and divided Eretz Yisrael the produce that was harvested was Chayav in Chalah and Patur from Ma'aser.
Workers may not singe produce over the fire in order to sweeten it if it will take them away from Melachah but if it doesn't take them away from Melachah it is a Safek. (3)
A Baal ha'Bayis may give his workers wine to drink in order to suppress their appetite and the workers may dip their bread in brine in order to whet their appetite.
The workers may refrain from eating grapes until they reach the ends of the rows of the vineyard. (4)
Workers may not warm up the produce in hot earth or to bang it on a rock if it will take them away from Melachah but they may pass it from hand to hand.
Workers who are harvesting fruit may eat the fruit without separating Ma'aser.
Workers may not eat the fruit with their bread without permission from the Ba'al ha'Bayis because it will cause them to eat a lot.
If workers are hired to hoe and cover roots under olive trees they may not eat the olives. (5)
If workers made a condition with the Ba'al ha'Bayis that they may eat from the produce it is akin to a purchase and they must separate Ma'aser if they eat two fruit at a time. (6)
If the workers eat two fruit at a time they may not scatter salt on them without separating Ma'aser even if they did not make a condition with the Ba'al ha'Bayis that they may eat from the produce. (7)
A BIT MORE
1. If it is not yet harvested he may eat from it if it is the Gmar Melachah and if it is harvested he may eat from it if it is not yet the Gmar Melachah for Ma'aser.
2. Even if he is picking the edible smaller produce to make extra space for the bigger produce since it is not the Gmar Melachah and he may not eat.
3. Workers may not dip grapes in salt in order to give it a better taste so that they will eat a lot and the Safek is if singing grapes over the fire the same as dipping it into salt, however the Safek is only if their family members are available to singe it for them but if not it is forbidden because it will taken them away from their work..
4. The grapes at the ends of the rows are more expose to the sun and are sweeter.
5. Because workers who are working on unpicked produce may only eat if they are doing the Gmar Melachah and hoeing and covering roots is not a Gmar Melachah.
6. The produce is Chayav in Ma'aser when it is reaches the stage of Goren (granary) and one fruit at a time is not considered a Goren and they may eat without separating Ma'aser, but if they eat two fruit at a time it is considered the Goren and it is the Gmar Melachah for Ma'aser and a purchaser may not eat without separating Ma'aser.
7. Even though workers may eat from the produce without separating Ma'aser if they did not make a condition with the Ba'al ha'Bayis, however scattering salt on the produce is Kove'a and it is regarded as a Gmar Melachah for Ma'aser and if it reaches the stage of Goren it may not be eaten without separating Ma'aser and when two fruit are eaten together it is regarded as a Goren and Ma'aser must be separated.