31 January 2008

3 minute read

Getting your dairy cows pregnant can prove less challenging when you supplement their diet with fats. Now researchers are finding that fine-tuning the type of fat can enhance herd reproductive performance even more.

Early-lactation cows may not get enough energy from a regular diet to meet their needs. Adding an energy-rich nutrient such as fat helps throughout the cow's body, especially in her reproductive system. The extra energy has been shown to provide improved conception rates.

During early stages of the estrous cycle, a group of small follicles grows on each ovary. Out of this group, a dominant follicle continues to grow while the others disappear. This can happen two or three times during a single estrous cycle. Detectable at three millimetres in length, dominant follicles grow upto 15 to 18 mm long before either disappearing or releasing their eggs into the oviduct for fertilization.

A recent University of Florida study considered whether influencing follicle size through nutrition actually impacted pregnancy rates. Researchers fed 54 cows two different fat sources, one an industry standard supplement and the other enhanced with flaxseed oil. The cows fed the flaxseed oil supplement had dominant ovarian follicles 1.5 mm longer than those of control cows.

A similar Canadian study looked at the impact of rolled flaxseed in dairy cow diets. At 28 days before breeding, researchers began feeding cows enough rolled flaxseed to supply 750 grams of oil per day. The dominant follicles for these cows averaged 2.8 mm larger than those of the control group.

In these two studies, cows fed fats enriched with essential fatty acids-omega-3 from the flaxseed-had larger dominant follicles. Why do larger dominant follicles lead to increased pregnancies? When the dominant follicle releases its egg into the oviduct, the ruptured follicle forms a corpus luteum on the ovary. This corpus luteum produces progesterone, a hormone important for pregnancy.

Progesterone prepares the uterus to receive the embryo, co-ordinates nutrients for development of that embryo and keeps the uterus in shape during the pregnancy. As well, cows that have more progesterone in their blood after insemination have shown better pregnancy rates than cows with lower levels.

The larger dominant follicle leads to a larger corpus luteum and provides more progesterone in the blood. So, larger follicles are associated with higher conception rates.

Cows fed flaxseed would have had larger ovarian corpus lutea. This would have made these cows better candidates for successful pregnancies.

The Canadian study also noted a reduced embryonic death rate in the group of cows receiving enriched fat. Pregnancy losses in the group fed rolled flaxseed were 9.8 per cent compared with a 27.6 per cent loss rate in the control group.

The influence of the omega-3 fat in the flaxseed may have accounted for it by reducing prostaglandin concentration in the blood. Prostaglandin-a hormone-like substance-can reduce the size of the corpus luteum after conception.

Lower prostaglandin levels would mean less effect on the corpus luteum so progesterone synthesis would be maintained and pregnancy sustained.

Other studies have suggested that feeding essential fatty acids from rolled flaxseed could provide a stronger cell membrane for the embryo.

Improved milk production, efficiency and reproduction are all benefits of adding energy-dense nutrients to the diet. Targeting essential fatty acids in this dietary addition further enhances performance, especially in the cow's reproductive cycle. Bigger dominant follicles appear to lead to increased pregnancy rates to term.

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