Dietary fatty acids and how they affect reproduction

Over the years, I’ve had the opportunity to work with and provide technical support to numerous dairies here in the U.S. and internationally. One of the most common questions asked pertains to feeding fats, fat sources and the hoped-for effects on milk volume, components and reproduction.

Fats have long been fed to dairy cows to increase the energy density of the diet, thus increasing milk volume. More recently, a shift in focus has turned toward feeding more specific, essential fatty acids to modify component production. With this, another area of attention has been the possible effects of feeding essential fatty acids on reproduction.

This goes beyond improving energy balance to modifying the supply of fatty acid components shown to provide the base molecular components for reproductive hormones, particularly progesterone. Research and subsequent meta-analyses have revealed responses that have included but are not limited to:

Initiating ovulation
Resumption of cycle
Improving visible signs of estrus
Increasing blood flow to the ovaries to promote follicle growth

These responses are largely influenced by prostaglandins (PG), the most well-known of which is prostaglandin F-2 alpha (PGF2α). The production of PG is a multi-step process which commonly begins with the synthesis of cholesterol from poly-unsaturated fatty acids (PUFAs).

One of the most widely recognized of these is linoleic acid (18:2). The physiological basis by which linoleic acid may improve reproductive performance lies with its influence on the metabolism of progesterone.

Progesterone, synthesized and secreted by the corpus luteum on the ovary, not only prepares the uterus for implantation of the embryo but also helps maintain pregnancy by providing nourishment to the fetal tissues. Increased concentrations of plasma progesterone have been associated with improved conception rates of lactating dairy cows.

Additional studies have reported dairy cows fed supplemental fat (tallow, calcium salts of long-chain fatty acids [Ca-LCFA], prilled fatty acids, whole cottonseed, etc.) had elevated concentrations of blood progesterone.

The production sequence beginning with PUFAs proceeds as follows:

PUFAs -> Cholesterol -> Pregnenolone -> Progesterone -> Testosterone -> Estradiol -> Luteinizing hormone secretion

Of course, this pathway is more complex than this illustration and includes both positive and negative feedback components. This pathway, in general, illustrates the role fatty acids play in this process as an initial building block. Overall, this helps us see improvements in dietary levels of certain fatty acids can have a direct effect on critical steroidal hormone production and thus can enhance the various processes involved in reproduction.

It’s complicated

Ongoing research has shown modifying fat levels and specific essential fatty acid (EFA) levels in the diet can have a direct effect on a variety of reproductive processes. However, there are several challenges to the feeding process.

A large number of fatty acids can be delivered to the animal in the diet. While analyses can define the fatty acid profile of a given feed ingredient, additive or supplement, the ability to pass these fat sources through the rumen unaffected by microbial activity is often not possible or, at best, highly variable. In other words, depending on the source, the fatty acids we feed may be changed by the time they pass through the rumen.

An example of this is the feeding of certain vegetable ingredients (oils), which are sources of PUFAs. As shown previously, PUFAs are precursors to various prostaglandins. The challenge is: We may feed sources of PUFAs, but ruminal bacteria action may “bio-hydrogenate” these fatty acids.

This converts them to a monounsaturated or completely saturated fatty acid (stearic acid, 18:0), which are less absorbable and, potentially, more poorly utilized.

By using the fatty acid profiles of ingredients, we can formulate diets specific for the fatty acids of concern or those shown to provide the greatest responses in the animal. Using these values, it is possible to increase the amounts of EFAs such as linoleic acid (18:2). Research has shown positive effects on reproduction from feeding an enhanced 18:2 level. Researchers in 2009 provided a review of some of these trials. These results included:

1. In several studies, lactating cows fed a base diet containing whole cottonseed (about 9 percent C18:2) and further supplemented with Ca-LCFA (about 8 percent C18:2) exhibited better rates of conception or pregnancy than cows fed the diet containing only whole cottonseed.

2. Lactating cows fed tallow (4.3 percent C18:2) at 3 percent of dietary dry matter tended to have a better conception rate by 98 days in milk than cows not fed tallow.

3. Grazing dairy cows supplemented with soybean oil soap stock (53 percent C18:2) at about 2 percent of dietary dry matter experienced a greater pregnancy rate than controls (62.5 versus 22.2 percent).

4. Beef heifers also have experienced greater pregnancy rates (94, 90, 91 and 79 percent) from being fed rolled and cracked safflower seeds, soybeans or sunflower seeds, all high in C18:2 concentration.

5. Protection of dehulled cottonseed (about 9 percent linoleic acid) with protein-aldehyde complexes delivered approximately 175 grams per day of linoleic acid to the lower gut of lactating Hereford cows. Overall pregnancy rates were improved from 63 to 79 percent.

These are some of the most obvious and measurable effects. EFAs have been found to function other specific areas that contribute to the net result of improving reproductive performance.

Immune response. There are relationships with immune system function and the recovery of the uterus postpartum. The reproductive tract, as well as the immune system, utilizes EFAs for signaling, chemical marking and precursors for enzyme and hormone activity. In the uterus, the function of EFAs results from the incorporation of these fats into endometrial cell membranes for conversion to PG.
Placental effects. The placenta has been shown to integrate EFAs preferentially into cell membranes, thus increasing activity and efficiency of several metabolic pathways, altering the hormone profiles produced by the fetal membranes and contributing to a decreased incidence of retained fetal membranes postpartum. This has been found to be directly related to a preferential use of linoleic acid and concentrations and proportion of EFAs in the diet.
EFAs early postpartum. Since EFAs are precursors for steroids and PG, they are related to the re-establishment of cycling after calving. Increased levels of both linoleic and linolenic acids in the diet have been shown to double the incidence of ovulations by 30 days postpartum. This also contributed to almost a full additional cycle and a significant improvement in uterine health by 60 days. These responses have been shown to reduce services per conception and days open.
Pregnancy recognition and maintenance. Pregnancy recognition in cows generally occurs between day 15 and 18 after estrus. It is estimated as much as 40 percent of embryonic death loss occurs during days eight to 17 after estrus, largely due to an inability to maintain the corpus luteum by conceptus activity.

There is evidence indicating the length of the conceptus is directly related to the production capacity of interferon-tau. Inclusion of omega-3 PUFAs (i.e., linolenic acid) in the diet through Ca-LCFA increases the length of the conceptus, which should improve the synthesis of interferon-tau. This enhances the likelihood pregnancy recognition through maintenance of the corpus luteum will occur.

Research and practice is making it clear feeding supplemental fat and, specifically, EFAs to dairy cows is no longer only for improving energy density. Essential fatty acids, in particular linoleic and linolenic acids, have direct effects on physiological processes such as cellular membrane integrity, hormonal pathways and immune function.

Clearly, they are important to uterine health, and that is accompanied by earlier ovulations postpartum and more cycles during the voluntary waiting period. These events lead to improved fertility earlier in the postpartum interval because they reduce services per conception and days open.

A key concern, however, is the need to define the actual requirements of the animal for specific EFAs. With this information, we can fine-tune ration formulation and increase accuracy of feeding for improved performance and reproduction.