Lower Omega-6–Omega-3 Ratio Increased Milk Production and Had Limited Effects on Early Pregnancy Development in Dairy Cattle

The aim of this study was to evaluate the effect of the linoleic-α-linolenic acid ratio (LA:ALA) on cyclicity, oocyte quality, early pregnancy parameters, milk yield, and composition. Holstein cows were randomized to a 6:1-LA:ALA diet (Low-OMG3: n = 3 pens; 11 primiparous, 14 multiparous) or a 2:1-LA:ALA diet (High-OMG3: n = 3 pens; 10 primiparous, 14 multiparous). Diets were isocaloric and isonitrogenous and fed between 15 and 140 days in milk (DIM). Data were compared using linear mixed models. As expected, omega-3 concentrations in milk and blood increased in the High- compared to Low-OMG3 cows. No effect of diet was observed on cyclicity by 45DIM or oocyte quality at 50DIM. High-OMG3 cows had larger corpus luteum size (11-32 d post-timed artificial insemination TAI) and greater blood flow (32-60 d post-TAI) than Low-OMG3 cows. However, there was no effect of diet on progesterone, pregnancy-associated glycoproteins, or conceptus size. High-OMG3 cows produced more milk throughout the study, had greater lactose, and tended to have greater protein yield at 50DIM. In conclusion, decreasing the LA:ALA dietary ratio in lactating dairy cows did not provide evidence of effects on cyclicity, oocyte quality, or other early pregnancy-related parameters, but affected corpus luteum size and blood flow, enhanced milk production, and partially increased protein and lactose yields.