המקושרות. פירש"י כתרגום מבוכרות ואין לו עד במקרא. ונראה שהוא ל' קשר שהיה מנהג באותן הימים שהיו קושרין על הבכורות מפני חביבותן קשר כדי להכירן ושלא להחליפן כמו שהיו עושין לבכור אדם שנא' ותקשור על ידו שני לאמר זה יצא ראשונה שגם בדורינו דרך בני אדם לחבב הבכורות ולהחיותן ולהניח להם יותר מן האחרים מהר"ם: המקושרות, “the sturdier ones;” According to Rashi the meaning of the word is: מבכירות, “the ones liable to give birth early in the season because they conceived without difficulties.” Although he attributes this interpretation to Targum Onkelos, he was unable to quote proof, and neither did Onkelos quote proof. I believe that the word is connected to the root: קשר, “knot.” It was the custom in those days to tie a knot to the firstborn animal of each mother, in order to be able to identify these animals later on as they were presumed to be stronger, or at any rate preferred by their owners to those born later. This would prevent them from being confused with animals born by the same mother animal in subsequent years. We know from Genesis 38,28, that the midwife of Tamar also tied a knot to the twin that appeared to be born first from its mother’s womb. The author quotes the Maharam from Rotenburg as saying that in his time fathers also displayed preferences for firstborn sons.