
looking at your location your in Scotland right? if so id check the Land Reform (Scotland) Act 2003 to see if your land would come under the act, if it does people are allowed access to it for recreational use.
Some highlights from the Scottish Outdoor Access Code, from reading this it sounds like your field comes under the places where people are allowed access, so tecnaly they are not trespassing but they shouldn't damage your fencing and should keep dogs under control be either on sort lead or keeping it close around live stock.
http://www.snh.gov.uk/docs/A309336.pdf"You can exercise these rights, provided you do so responsibly, over most land and inland water in Scotland, including mountains, moorland, woods and forests, grassland, margins of fields in which crops are growing, paths and tracks, rivers and lochs, the coast and most parks and open spaces."
"You can exercise access rights for recreational purposes (such as pastimes, family and social activities, and more active pursuits like horse riding, cycling, wild camping and taking part in events), educational purposes (concerned with furthering a person's understanding of the natural and cultural heritage), some commercial purposes"
"Provided you do so responsibly (see Parts 3 and
5 of the Code), you can exercise access rights in places such
as:
*hills, mountains and moorland;
* woods and forests;
* most urban parks, country parks and other managed open
spaces;
* rivers, lochs, canals and reservoirs;
* riverbanks, loch shores, beaches and the coastline;
* land in which crops have not been sown;
* on the margins of fields3 where crops are growing or have
been sown;
* grassland, including grass being grown for hay or silage
(except when it is at such a late stage of growth that it is
likely to be damaged);
* fields where there are horses, cattle and other farm animals; <---- Asume your field come under this
* on all core paths agreed by the local authority4;
* on all other paths and tracks where these cross land on
which access rights can be exercised;
* on grass sports or playing fields, when not in use, and on
land or inland water developed or set out for a recreational
purpose, unless the exercise of access rights would
interfere with the carrying on of that recreational use;
* golf courses, but only for crossing them and providing that
you do not take access across greens or interfere with any
games of golf;
* on, through or over bridges, tunnels, causeways, launching
sites, groynes, weirs, boulder weirs, embankments of canals
and similar waterways, fences, walls or anything designed
to facilitate access (such as gates or stiles)."