1) This is not clear but I can suggest the following idea for the moment. If we look in Rashi (Temurah 30a, DH Mechad) we find that what he brings here in Bechoros from "the Moreh" he calls in Temurah "Lashon Yerushalmi." Now we find in Rashi (Temurah 6b, DH Hachi Garsinan L'A) that he cites two Leshonos but says there is no difference between them but simply one is the Lashon of the Bavli and the other is the Lashon of the Yerushalmi. Also in Temurah (23b, DH Milsa d'Pesika, in the L'A) he cites two Leshonos and writes that they are identical but the second is simply a Yerushalmi version.

2) So it seems that in Maseches Temurah there are different versions but sometimes they work out to be the same. Since the Sugya here in Bechoros 57a really originates from Temurah 30a, this rule might apply here too, so according to this there might not be a difference between Rashi's Pshat and the Pshat of the Moreh. This requires further study.

Kol Tuv,

Dovid Bloom

1) Here is another way of understanding how it could be that there is no essential difference in Lamdus and Sevara between the Pshat of the Moreh and the first Pshat in Rashi. The Mishnah in Eduyos 1:3 states that a person is obligated to say things in the same way as his teacher. The Tiferes Yisrael (#20) cites the Vilna Ga'on who explains that as a result of this rule, Hillel added a totally superfluous word in the Mishnah. The word that Hillel wanted to use was "Hin," the measure of drawn water which renders a Mikvah invalid. However, the problem was that Avtalyon, who was Hillel's teacher, could not articulate the letter "Heh" properly because he was a Ger Tzedek. If Avtalyon would have said "Hin" it might have sounded as if he said "In" and people might have misunderstood his intention and thought that Avtalyon said, "Ein Mayim She'uvim Poslin ha'Mikvah" -- "water which has been drawn does not invalidate the Mikvah." This would be a serious misunderstanding which Avtalyon was careful to avoid by adding an extra word ("Melo Hin" -- "a full Hin") to make sure that he was understood properly. Now it was clear that the Halachah is that only a full Hin of drawn water can Pasul the Mikvah. When Hillel reported later Avtalyon's Halachah it was not actually necessary for him to say "Melo Hin," because Hillel had no problem pronouncing the word "Hin," but even so he continued to say "Melo Hin" because those were the words he heard from his Rebbi. Similarly, we can say that Rashi reports the exact numbers that his Moreh said, because of the rule, "A person is obligated to use the same words as his teacher."

2) It is worth adding a comment to elaborate a little on what I wrote in my first reply, that what Rashi cites here in the name of the Moreh he calls in Temurah 30a, "Lashon Yerushalmi." The Teshuvos Sho'el u'Meshiv (first edition, 3:144) writes that the way of Rashi in Kodshim, especially in Maseches Temurah and Kerisus, is that whenever he cites two explanations, he calls one of them "Lashon Yerushalmi." The Sho'el u'Meshiv writes that we do not know whether Rashi possessed a Talmud Yerushalmi on Kodshim or not.

I also saw that Rashi in Kerisus (beginning of 4b) writes, "This Loshon is opposite, it is the Loshon of Girsa Yerushalmis." The Teshuvas Mefane'ach Ne'elamim (#2) writes that what Rashi means to say is that this is the way of speech of the people in Eretz Yisrael and it is opposite to the way they speak in Bavel.

I was thinking (and this couild be relevant for us nowadays, too!) that Rashi is pointing out that sometimes they say the same thing in Eretz Yisrael as they do in Chutz la'Aretz, but they use an opposite way of speaking. This may be a reason why it is worth keeping track of the different ways they said things -- so that we can know that even though it sounds different, in essence it comes down to the same Pshat.

3) However there is a simpler answer to your question, Daniel.

a) It is based on what I saw that Rabeinu Gershom writes in Temurah 30a, where our Sugya also appears. He writes that the second Lashon explains the "additions" of the first Lashon.

b) It seems that this means as follows. If you look at Rashi's own Pshat, he does not actually give concrete numbers. He writes that that 9 out of the 10 sheep are worth more than the 9 sheep together with the dog, and that the dog is worth the value of the 10th sheep plus 9 times the small amount that the 9 of the 10 sheep are worth more than the 9 sheep together with the dog. But Rashi does not put actual numbers as an example onto this. It is only in the Pshat of his Moreh that he gives real numbers: 4 and a tenth for each of the 10 sheep against the dog, 5 for the dog, and the 9 together with the dog are worth 4 each, which is a total of 36.

Kol Tuv,

Dovid Bloom