"We have some very friendly calves/steers which are always licking and pushing me with their heads. A few even came close to 'mounting' me. Any clue as to why they might be doing this?"
They certainly sound very friendly! A bit too friendly, in fact. While this seems really cute now, it's not going to be so cute when those steer calves are double the size and continue to do the same to you (or the person who did the right thing by asking this question).
The reason they're doing this is because they're not being disciplined to not do this. They're allowed to be overly friendly, which is not good. Boundaries and discipline with these calves must start immediately, before someone or the person asking this question gets themselves hurt when those calves are much bigger.
This person must find a way to get them to learn that they have boundaries that ought not to be crossed, and that that person must be respected as the head of the herd, not as a mere play thing. That may mean getting a little "mean" with them to get the point across that they're not a toy nor a subordinate to be easily dominated.
See, the licking is fine, but the pushing around and attempting to mount or "bulling" are actually signs of calves, in their bovine-way, learning how they can establish dominance. That's not a good thing for a human who will never get as big and powerful as those calves will become in a year or so.
What must this person do, then? The first thing to realize is that moving away from them is a BIG No-No. That will just encourage those calves to come back for more; that moving-away action is a sign of subordination to them, and that they're well and truly the dominant ones! I've watched countless times the struggle for dominance among cattle, and the one that loses the fight, and therefore becomes subordinate to the one he or she was battling, always turns and moves away as a sign of defeat.
This person will need to do a bit of pushing back, probably some chasing (if it comes down to it), a lot of saying a stern "No!" at the right time and place--but not too frequently, otherwise they'll just learn to ignore it--and a huge amount of time, persistence, and patience. Calves can be a bit hard because they're young, they love to play, and will often test boundaries, just because they can. That's where the patience will come into play, and where this person cannot allow themselves to get angry or frustrated, and end up doing something that they will regret which could cause distrust in the calves' part. The art of disciplining is a fine line to walk.
The Bovine Practicum Q&A "blog" is an informative, just-for-fun section where I find a variety of questions that are often (and not-so-often) asked by inquisitive people like you, and answer them to the best of my ability. Much of the questions have come from a wide variety of reaches from the Internet.
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