'Elevated white count' is pretty nonspecific, in and of itself; yes, it would make one think about a possible infection, but the magnitude of the elevation and distribution of the different populations of white blood cells would be more informative.
I'd have to know *how much* of an elevated WBC count - and distributions of the different cell types.
If normal range is, say (I'm just making up these numbers), 8,000-16000, well, a count of 16,500 is elevated, but it's not high enough that I'm going to get very bent out of shape about it - could be high 'normal' for that animal.
Terminology often gets in the way here, too. These six 'first-calf heifers' - are they bred heifers that will be delivering their first calves in the fall, or are they actually cows that have calved, bred back, and will calve in the fall? I've seen folks here (and elsewhere) refer to animals in both categories as 'first-calf heifers'. In either case, this is a production group that is still growing, 'building' a calf, and are probably less aggressive about pushing in for their fair share of the feed. That alone could be grounds for less than desirable improvement, even in the face of increased feed supplementation.