Weimaraners, like most sporting dogs, tend to be high energy dogs that need a lot of human interaction and a high level of training. They're not bad dogs but as was pointed out they ARE highly intelligent and as such if left to their own for long periods of time are prone to getting into trouble.
I've known of a couple of different weimaraners that actually knew how to open the fridge and ate all the food that was in the fridge, including those that were enclosed by tupperware or other like storage containers (the dogs figured out how to open or otherwise puncture the containers to get at the food).
I'm not entirely sure the weimaraner would be a good dog to have around livestock. They're natural hunters and will point at everything that enters their field but at the same time I've also heard of them being very prey driven and will also give chase to anything that runs from them too - this includes larger animals like livestock.
They are however very alert dogs and can be great early warning systems for intruders onto your property and home albeit it would have to be within the confines of a front/back yard and your home itself. I would not give this type of dog hundreds of acres to roam freely. That gives the dog too much freedom and as such it can and will most certainly get into trouble and perhaps get injured. While a weimaraner is a larger dog and very athletic too it can and would be severely injured if it encountered a pack of coyote. These and other sporting dogs should not be left unsupervised for any long length of time unless they're confined in a kennel or crate while you're gone. Even at that these dogs don't do well in such confined spaces (their high intelligence gets to them in confined spaces) so you'll have to give them plenty of chew toys while they're confined and I wouldn't leave them for too long.
These dogs are however known for their great stamina and can work (running, hunting, tracking etc) for long periods of time. A long brisk walk is only one of the things that will be required to keep this breed of dog calm and relatively inactive while indoors. They are also prone to bloat, rapid excessive growth - which can lead to joint, circulatory and other medical problems, and hip dysplasia. Be aware of this and when buying a puppy make sure to only buy from a reputable breeder who can give you a good health guarantee. Make sure you have documentation that the parents are healthy and have good temperaments too. As with sporting breeds there is a field line and a show line. The field lines tend to have higher energy levels and higher prey drive while the show lines tend to be of lower energy levels and lower prey drive. Regardless be aware of the fact that you ARE getting a hunting/sporting dog and even if it were a show line you will still have a dog with a higher energy level and higher prey drive.
If you're looking for a dog that you can have on a farm that would be good with livestock, be alright if left alone (and unsupervised) for long periods of time AND also be a good alert/guardian dog for your home I'd strongly suggest a Great Pyrenees. They make excellent livestock guardian dogs, learn their boundaries quickly and even with hundreds of acres to roam will not leave the boundaries they have been taught. They are excellent dogs for children although they can be somewhat aloof with adults. They won't be disruptive of cattle or other livestock, preferring to stay around the fringes of the herd and keeping an eye out for predators. They don't herd animals and will not make attempts to herd them, rather they just hang around waiting for possible predators and danger. The one thing about them that you might not like is that they are extremely distrustful of strangers. If you as the owner have not welcomed visitors each and every time they come onto your property the Great Pyrenees might look at them as intruders and will start to treat them as such... with shows of aggression trying to get the intruders to vacate the property until either they leave or you as the owner come to greet them and welcome them in. Then the dogs seem to have an instinctive understanding that if their leader welcomes the intruders in they are ok. Again one of those pack mentality things. When inside the home Pyrenees are for the most part sedentary. They'll prefer to lay in a spot they choose and stay there unless called or till they decide they need to move (which may not be for hours on end). They're quite accepting of children and children can play with and on them but when they are done playing with the children they will simply get up and walk away to lay down elsewhere.
In any case make sure you purchase from a reputable breeder and do your research on the breed you're going to purchase. Neither breed of dog is good for bouncing from home to home so choose wisely and make it a life long commitment.
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