What is the origin of "weighing the pig doesn't make it fatter"

What is the origin of "weighing the pig doesn't make it fatter"

There are multiple versions of this saying:

Weighing the pig doesn't make it [any] fatter.

Weighing the pig doesn't make it grow [any faster].

Weighing the pig doesn't make it gain weight.

Weighing the pig doesn't fatten it.

Weighing a pig doesn't make it heavier.

But I noticed a couple of odd things about this bit of down-home wisdom. First, a Google Books search reveals that the oldest match for either "Weighing the pig doesn't" or "Weighing a pig doesn't" is from the year 2000. From British Records Association, Archives, volume 25 (2000):

Most of the information contained in these pages suggests that the PRO is doing pretty well in setting and meeting targets. But the farming analogy that 'weighing the pig doesn't make it any fatter' is one that springs to mind.

The second odd thing is that most of the 30 or so Google Books matches for "weighing the pig doesn't" and "weighing a pig doesn't" come from books and articles on on education. It seems fairly clear that the controversy over focusing on standardized testing as a means of gauging the quality of education that a school offers has caused this small geyser of pig-weighing analogies.

Even so, a Google Books search does turn up one significantly older instance of the expression "Weighing a pig doesn't fatten it"—from Housecraft, volume 51 (1978) [combined snippets]:

The reader may appreciate one or two cautionary notes here. First, the only reason for carrying out evaluation activities as outlined is to become a most efficient professional. If the evaluation activities of the teacher do not make her effective as a teacher, then they are a waste of time. Secondly, and just as important, it is timely to remember that 'weighing a pig doesn't fatten it'. The evaluation role is a weighing role. Essentially, teaching is a fattening activity on terms of the analogy.

And it finds one truly old instance of the expression "Weighing a pig doesn't make it grow any faster"—from The Swine World (July 5, 1919), involving a story about a child in Iowa who told his father that he wanted to weigh his pig every day:

"Why," the father replied, "you can't do that for we haven't any scale. Anyway, weighing a pig doesn't make it grow any faster." But the boy insisted he was going to find a way to weigh that pig and do it right there at home. Finally his father said, “Well, I've got no objections to your weighing the pig, but there's no way to do it but to take the pig to town, and you can't do that. But go ahead, and if you can weigh your pig I'll furnish all the feed it eats this summer and not charge you a cent for it."

He had made a safe offer, for the only scale on the farm was a small kitchen balance that might weigh as much as fifteen pounds. But the boy didn't quit and the next day he weighed his pig. This is how he did it: First, he selected a strong piece of 2x4 and balanced it over a 2-inch plank in the barn-lot fence. Then he hung a box on each end of the 2x4 and balanced it carefully. Then he put the pig in one box and into the other box piled stones until it just lifted the pig's box on the other end. Then he took the old kitchen balance and, a few at a time, weighed out the stones, added up their total weight and he had the weight of his pig.

That perseverance won the summer's feed for his pig, but best of all he had done something worth while and done it by himself.

Somehow I doubt that the lesson that the education commentators want to draw from their invocation of the pig-weighing proverb has much to do with the moral of the 1919 story in The Swine World, which might be summarized as

"Weighing a pig doesn't make it grow any faster, but figuring out how to weigh it could win you free pig feed for the whole summer."