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

## TL;DR

A lower omega-6 to omega-3 ratio in dairy cow diets increased milk production but had limited effects on early pregnancy development.

## Contribution

The study shows that increasing dietary omega-3 improves milk yield but has limited impact on early reproductive outcomes in dairy cows.

## Key findings

- Cows fed omega-3-enriched diets produced more milk and had higher lactose and protein yields.
- High omega-3 diets increased corpus luteum size and blood flow but did not affect hormone levels or conceptus development.
- No significant effects on cyclicity, oocyte quality, or postpartum reproductive parameters were observed.

## Abstract

Dietary fatty acids can influence milk production and reproductive function in dairy cows. Our objective was to evaluate whether reducing the dietary omega-6–omega-3 ratio by increasing omega-3 content would affect milk production and early pregnancy development in lactating dairy cows. Cows fed the omega-3-enriched diet produced more milk and showed changes in corpus luteum size and blood flow, without effects on hormone concentrations, conceptus-related parameters during early pregnancy, postpartum cyclicity, or oocyte quality. Overall, increasing dietary omega-3 had clear benefits for milk production, but its effects on early reproductive outcomes were limited. These results suggest that omega-3 supplementation can be considered a nutritional tool to improve milk yield; however, expectations for improvements in early pregnancy development should be conservative and require further investigation.

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.