Comparative Analysis of Fatty Acid Distribution in Milk Triacylglycerols of Even-Toed and Odd-Toed Ungulates

Lipid in milk plays a crucial role in mammalian nutrition, particularly for young offspring. The positional distribution of fatty acids (FAs) in milk triacylglycerols (TAGs) has been linked to enhanced digestion and absorption in neonates. For example, palmitic acid is largely distributed the β-position avoiding solidification after digestion in the infant intestine in human milk TAGs. Meanwhile, short-chain (SC) FAs, such as butyric and caproic acids, are primarily distributed at the α-position of TAGs in cattle and goat milk, major contributors to the dairy industry. However, the FA distribution in milk TAGs of other even-toed and odd-toed ungulates remains poorly understood. This study analyzes FA distribution in milk TAGs from various herbivores using Joint JOCS-AOCS Official Method Ch 3a-2019, a validated method for assessing milk fat containing SCFAs.

The lipid content of herbivore milk varied significantly among species. Sheep milk exhibited the highest lipid content (~20%), while black rhinoceros milk displayed the lowest (0.1%). Odd-toed ungulates generally had lower milk fat content compared to even-toed ungulates.

Analysis of FA distribution revealed that even-toed ungulates typically had SCFAs at the α-position of milk TAGs. An exception was camel milk, which contained little SCFAs at the α-position, while the FA composition of β-position was similar to that of other even-toed ungulates. Odd-toed ungulate milk TAGs were characterized by medium-chain FAs and negligible SCFAs, without significant positional unevenness. Camel milk exhibited unique characteristics with lower SCFA content at the α-position, though camel is an even-toed ungulate.

Authors thank Tama Zoological Park, Kyoto City Zoo, Hiroshima City Asa Zoological Park, Hokkaido Agricultural Research Center (NARO), and Himeji Central Park, for providing milk samples.