"Sheep in Winter" was written by John Clare, who has been called “the quintessential Romantic poet" as well as "the greatest nature poet in the English language," according to the Poetry Foundation. "Sheep in Winter" is a fairly accessible poem and displays key characteristics of Romanticism. Immediately noticeable should be the poem's focus on animals and nature rather than humans. The beauty and power of nature are extremely important to Romantic poets like Clare.
"Sheep in Winter" also uses a fairly standard rhythm and meter, not only for the Romantic era, but for poetry in general: the poem is written in iambic pentameter. If you are new to figuring out a poem's rhythm and meter, a good place to start is to count the syllables in multiple lines. If you do that with this Clare poem, you discover that the lines have ten syllables. Ten divides by two evenly, so that should clue you in to the direction of the iambic and trochaic foot, because they are both two-syllable units. Clare could be using a three-syllable foot like an anapest and always adding an extra syllable, but that is not common (nor is it what he used in this poem).
In this poem's case, Clare uses the iambic foot. The iambic unit is composed of an unstressed syllable followed by a stressed syllable. Words like "attain" and "describe" are good examples of how the second syllable is the stressed syllable. Let's apply the iambic foot to a line of Clare's poem. I'm using line 2 because it's easier to "feel" the iambic foot in the two-syllable "upon" than it is in the two-syllable "many" from line 1. I'll bold the stressed syllables.
And bear / a load / of snow / upon / their backs,
Notice that there are five uses of the iambic foot within this line. This means the line is written in iambic pentameter, which is what Clare uses throughout the poem.