What hormones do to females varies bitch by bitch, but, heat cycles can most certainly affect them and their work in the field. Some before, some after, some not so much, there's just no hard or fast rule as to when, and for how long. A few of mine get a little sharper, but mostly, they suddenly can't find a single on a cut hayfield, can't run straight for 20 yards, fall apart if nicked on a 1, and pretty much make me threaten to spay every one of them before they return to normal. But, seriously, it does vary by female, both affect and duration.