Let’s discuss mismatched twin lambs. It was a learning experience for us this lambing season when Hestia gave us mismatched twins. Mismatched twins is when one twin is born markedly larger than the other twin. I’ve scoured the web for explanations as to why, but it really boils down to a difference in caruncles or cotyledons between the two lambs, possibly caused by poor feeding during pregnancy. This article, More Than One Cause of Mismatched Lambs, by Joanne Marshall, Farmnews.co.nz, sums it up best.
The way I understand it is sheep (and most all ruminants) have a cotyledonary placenta, which means they have numerous small placentae instead of one big placenta that connects the fetus to the uterine wall. A cotyledon (fetal side of placenta) and caruncle (maternal side of placenta) together make up a placentome, with multiple placentomes connecting the fetus to the uterine wall. If one lamb fetus hooks up with, let’s say, 50 placentomes, but the other lamb fetus hooks up with 20 placentomes – that’s how you end up with mismatched twins. The lamb fetus hooked up to more placentomes will receive more nutrients, and will grow faster and larger. See Placentation in Ruminants, by R. Bowen, Colorado State.
I will mention that Hestia is a shy eater and may just be less thrifty than the other sheep. Every other sheep in this flock can body score at a 4 (quite fat), and Hestia will score at a 2 (skinny), even when she scores healthy on her FAMACHA. That is her way. However, she has produced a strapping ram lamb each year for two years in a row.
The smaller twin, the runt (Ixora), true to form, has been the scrappiest, most tenacious lamb of the whole gang from the very beginning. She must have known she needed to work harder since she was smaller. When she was born, she seemed like she was the size of a kitten! She’s fat now, and is catching up quickly to the rest. She’s been the cutest little bonus lamb.
The bigger twin, a large ram-lamb (Fennel), will have great horns like his sire, Tzatziki. He will be epic, and has been left in tact. He is outpacing everyone in growth since he had such a big head-start! Ixora loves her brother, Fennel, and he watches over her.