You are misinterpreting what the lab was telling you. They are not telling you that it is bad or harmful to use manure over a long period of time. They are telling you that it is bad to use manure as the only thing you add to your garden.
Think of soil building as composting (because that's what it is). You want to maintain the same sort of C:N ratio as you do when composting. When you rely on manure as your only additive, you're unbalancing your soil. You're adding way too much nitrogen. It will have a similar effect to spraying a ton of NPK fertilizer. It will burn out the soil life and eventually make your soil less fertile. You can add manure to your garden every year, but you need to be adding carbon as well to off set all that nitrogen you're adding. You should be adding lots of mulch (hay, wood chips) and compost in addition to the manure.
Finally, manure is a good source of many nutrients. But it is by no means the source of all the nutrients your garden needs. Soil needs a hell of a lot more than just NPK and Mg/Ca to be healthy. In fact, we don't fully understand all the chemical reactions going on down there, let alone have the ability to optimize them. Your best bet is to -- as previously mentioned -- add manure and then add carbon. Compost any extra green matter on your land and add it back in. Plant nutrient accumulators and then use them for mulch. Also you can add other soil additives (like green sand, or kelp) to add various trace elements and nutrients.
Summary: There is nothing wrong with adding manure every year. But you should be mulching/composting on top of the manure to add carbon. You should also add other soil amendments to add what manure lacks.