馬や羊が放牧されてて、牧羊犬もいるわ。一度訪ねてみてはどうかしら？

、。？

There are horses and sheep grazing, and even sheepdogs. Why don't you visit sometime?

Literal

Horses [and-や] sheep [subject-が] pastured, sheepdogs [also-も] exist [feminine-わ]. Once visiting try how-about [feminine-かしら]?

放牧されてて is the casual contracted passive progressive (放牧されていて). 牧羊犬 (ぼくようけん, 'sheepdog') is a specific compound. いるわ uses the feminine sentence-final わ. 一度訪ねてみてはどうかしら uses the suggestion pattern ~てみてはどう ('how about trying') with the feminine かしら ('I wonder'). The speaker is a woman enthusiastically recommending a pastoral outing.