Odd- and branched-chain fatty acids in milk fat from Holstein dairy cows are influenced by physiological factors.

Dairy products are the major source of odd- and branched-chain fatty acids (OBCFAs), a group of nutrients with emerging health benefits. The animal diet is known to influence milk fat OBCFAs of dairy cows; however, little is known about the effects of physiological factors. The objective of this study was to investigate the effects of parity and lactation stage on OBCFAs in milk fat of dairy cows. Holstein dairy cows (n = 157) were selected according to parity (first, second, third, or greater) and days in milk (DIM) (≤21 DIM, 21 < DIM ≤ 100, 100 < DIM ≤ 200, >200 DIM). All cows were fed the same total mixed ration for three weeks. Milk samples were collected during the last three days of each lactation stage for fatty acid (FA) analyses via gas chromatography. Results showed that first- and second-parity cows displayed significantly higher proportions and yields of iso-14:0, iso-15:0, iso-16:0, total iso-FA, and total branched-chain FA (P < 0.05) compared with other parities. The proportions of C17:0 and C17:1 cis-9 were also greater in first-parity cows (P < 0.05), while the yields of C17:0 and C17:1 cis-9 were similar among different parities (P > 0.05). The proportions of total OBCFAs were greater in first- and second-parity cows (P < 0.05), whereas the highest yield was observed in second-parity cows. Lactation dairy cows in ≤ 21 DIM group displayed lower proportions of iso-13:0, anteiso-13:0, C13:0, iso-14:0, C15:0, iso-16:0, total iso-FA, and total OBCFAs compared with that of the other groups (P < 0.05), and also lower yields of iso-14:0 and iso-16:0 (P < 0.05). In contrast, C17:0 and C17:1 cis-9 proportions and yields were higher in dairy cows with ≤ 21 DIM (P < 0.05). Iso-17:0 and anteiso-17:0 were not affected by lactation stage (P > 0.05). Taken together, our data showed that both parity and lactation stage have considerable effects on milk fat OBCFAs of dairy cows. In summary, first- and second-parity cows had higher milk OBCFAs compared with later parity cows, and OBCFAs with medium chain lengths were lower in dairy cows with ≤ 21 DIM, while C17:0 and C17:1 cis-9 were higher. These findings show that milk OBCFA contents are differentially modulated by physiological state. They will be useful in future studies that seek to alter OBCFA composition of Holstein dairy cow milk fats.