They grow faster, they require less fertilizer, they produce fewer weeds, they erode less. In rotational grazing they get healthier. They are outdoors, moving and grazing normally. They have less lameness, fewer infections, less trouble with breeding and calving. With bGH, cows are more prone to infection, especially mastitis, and they have trouble breeding.
Some experts expect bGH to reduce a cow's productive lifetime from about four lactations to two.
Not with rotational grazing. There are uncertainties here. Artificial bGH is slightly different from the cow's bGH and might produce some allergic reactions. Health troubles in the cow could result in milk containing antibiotics or a slightly different nutrient composition. These possible effects are exaggerated by bGH foes, minimized by bGH proponents, and not yet tested by neutral scientists under farm conditions.