Effects of dietary essential fatty acid supplementation on reproductive health and function (Proceedings)

Supplying fat in dairy cattle rations has become a common practice on commercial dairies, as it is an effective way to supply energy to the cow. In recent years, research has been conducted on different fat sources, more specifically on the types of fatty acids provided through those various sources and their consequent effects on cow production, health, and reproductive status. Two fatty acids, linoleic (C18:2, an omega-6) and linolenic (C18:3, an omega-3) have become a major focus of fat research, as they are essential fatty acids (EFA) and must be supplied through the diet.

These EFA have double-bonds in their molecular makeup, and as such are susceptible to biohydrogenation by rumen microbes. These microbes break the double bonds, resulting in the conversion of the EFA to stearic and other long-chain fatty acids before the EFA can reach the small intestine for absorption. One means of avoiding biohydrogenation is to couple the EFA with calcium salts of long-chain fatty acids (Ca-LCFA), effectively making the EFA rumen inert. This allows a larger portion of the EFA to reach the small intestine with double bonds intact, and to be absorbed and circulated to virtually every tissue in the body (Schauff and Clark, 1992; Allred et al., 2006). This paper will focus on the effects of EFA supplementation on hormone production, tissue repair and function, and immune function of multiparous Holstein cows.

Role of EFA in hormone and prostaglandin production

Essential fatty acids are precursors to steroid hormones, via cholesterol. The corpus luteum (CL) uses cholesterol to produce progesterone (P4 ), and P4 itself is a precursor of estradiol (E), although it is an inhibitor of E secretion from follicles. Linoleic acid is also a proven inhibitor of cyclooxygenase in endometrial tissues, and can subsequently suppress prostaglandin (PG) secretion from the uterus (Haag, 2001). Staples et al. (1998) state that this action might be aided by the effect fat has in curbing E secretion, therefore further decreasing PGF2α production and reducing the sensitivity of the CL to PGF2α. Consequently, the life and functionality of the CL is extended and allows for increased P4 concentrations.

Progesterone is frequently referred to as the pregnancy hormone. The higher the concentration of P4 after conception, the greater the probability the animal will remain pregnant. Fonseca et al. (1983) and Shemesh et al. (1983) both reported that higher pre-breeding P4 concentrations correlated linearly with increased conception rates. For each ng/mL serum [P4] increased on d 12 of the estrous cycle prior to AI, the conception rate improved 12.4% (Fonseca et al., 1983). Additionally, Staples et al. (1998) cited that cattle with increased [P4] at the end of the estrous cycle demonstrated stronger signs of estrus. Stronger signs of estrus lead to more accurate head detection and correctly timed breeding.

Essential fatty acids are also key elements in the synthesis of certain biological signaling factors, including PG and leukotrienes (Haag, 2001). Linoleic and linolenic acids are precursors to three classes of PG, including PGF2α and PGE. Exogenous PGF2α is commonly utilized by producers to synchronize the estrous cycle or to treat reproductive problems. Prostaglandins have several functions, including resumption of cyclicity, causing ovulation via regression of the CL, and increasing blood flow to the ovaries to promote follicular development (Senger, 2005). PGF2α and it's metabolite, 13,14-dihydro-15-keto-PGF2α (PGFM) have been used and validated in several ruminant species as a marker in peripheral circulation for uterine health, cyclic status, parturition indicator and for degree of uterine involution (Risco et al., 1994; Mishra and Prakash, 2005). Cows with retained fetal membranes had higher PGFM concentrations, increased rates of contraction postpartum and increased interval from calving to completion of uterine involution (Risco et al., 1994).

Role of EFA on immune response and uterine involution

The most commonly detected immune response cells are polymorphonuclear leukocytes (PMN), also known as neutrophils. LeBlanc (2006) stated that PMN are the primary immune cells immediately postpartum for the breakdown of the cotyledon/caruncle connection, allowing fetal membranes to be expelled with the lochia. Retained fetal membranes are often seen in cows with subprime immune responses, and those cows frequently develop metritis, which negatively impacts subsequent fertility (Senger, 2005).

Estradiol17 is the principal hormone involved in the stimulation of the immune response, both postpartum and during the follicular phase of the estrous cycle, physically resulting in increased fluid production, endometrial and glandular changes and cervical muscle relaxation. At the cellular level, vascular porosity and circulating populations of PMN are increased to combat bacteria, viruses, and cellular debris introduced during parturition and breeding (Tomlinson et al., 1992; Hammon et al., 2006). During the luteal phase of the estrous cycle, the reproductive tract and local immune response are under the direct influence of P4, resulting in barrier mucous production by the cervix. Cellularly, vascular permeability and PMN presence are greatly reduced. It is important that the presence of immune cells in the uterus be minimal to prevent the dam's immune system from attacking and rejecting the conceptus and risking lasting immunity to future embryos, as well (Robertson, 2005).

University of Arizona trials

Two separate trials were conducted on two large, commercial herds to evaluate the effects of supplemental Ca-LCFA (MEGALAC®, Arm & Hammer Animal Nutrition, Princeton, NJ) compared to Ca-LCFA with higher concentrations of linoleic and linolenic acids (MEGALAC®-R) on the reproductive outcomes and health of multiparous Holstein cows. Trials 1 (Jones, 2006) and 2 (Bowen, 2008) were designed similarly, with both randomly assigning cows blocked by previous milk production and parity, and treatment diets were formulated to be isocaloric. At 21 d prepartum, all cows in Trial 1 were fed 0.11 kg/d of Ca-LCFA until parturition, when they were placed into one of two treatment groups and fed either 0.16 kg/d of Ca-LCFA or Ca-LCFA+EFA until confirmed pregnant or 150 DIM. On Trial 2, cows were fed 0.11 kg/d of Ca-LCFA or Ca-LCFA+EFA from 21 d prepartum to parturition, and then fed 0.23 kg/d of the same supplement until 60 DIM. In both trials, real-time ultrasonography was conducted to monitor ovarian activity in subsets of cows before 20 and 30 DIM. In Trial 1, milk samples were collected twice weekly on subsets of cows for P4 analysis. In Trial 2, blood serum concentrations of PGFM were evaluated for DIM 10, 20, and 30. Incidence of metritis was recorded, in both trials by the herd veterinarian's prescription of prostaglandins to treat uterine abnormalities, and additionally in Trial 2 by uterine cytology swabs with evaluation for neutrophils. The herd veterinarian was blind to treatment.

Results

Ovaries evaluated via ultrasonography by trained technicians (SonoVet 2000, Medison, Cypress, CA) were categorized as follows: Class 1 (majority of follicles measuring 1-3 mm diameter), Class 2 (majority of follicles 3-5 mm), Class 3 (at least one follicle ≥6 mm or presence of CL not attributed to previous pregnancy), or Inactive (no follicles or CL present). Pearson's chi-square was used for statistical analysis (Moore and McCabe, 1999). The combined ultrasound results showed a significant effect of Ca-LCFA+EFA on number of Class 3 ovaries before 20 DIM, shown in Table 1. At 30 DIM, Ca-LCFA+EFA-fed cows showed significant improvement by having more Class 3 ovaries and fewer Class 1 and Inactive ovaries than those cows fed Ca-LCFA (Table 2).

Table 1. Trials 1 and 2 combined ovarian status confirmed by ultrasound, ≤20 DIM.

Incidence of metritis was reduced in cows supplemented with EFA. Table 3 shows the number and percentage of cows treated <60 DIM with exogenous PGF2α. A significant result was seen in Trial 1, with a tendency towards the same result in Trial 2.

Table 2. Trials 1 and 2 combined ovarian status confirmed by ultrasound, 21-30 DIM.

In Trial 1, P4 concentrations were utilized to obtain the number of estrual cycles of cows prior to the VWP of 60 d. An estrous cycle was counted as such if P4 concentrations declined below 4 ng/mL, followed by a rise above 4 ng/mL. Four ng/mL was pre-determined as the value at which a CL was fully functioning, as P4 concentrations in milk are generally double those found in serum (Schams and Karg, 1986). A significant effect was seen in EFA-supplemented multiparous cows for number of cycles by the VWP compared to Ca-LCFA fed cows (2.76 vs. 2.0 cycles/cow respectively; p<0.03) using the PROC-mixed procedure of SAS with parity and milk as covariates (SAS Institute, Cary, NC).

Table 3. Effects of Ca-LCFA+EFA supplementation on number of cows treated with PG for uterine health issues by the herd veterinarian, combined results of Trials 1 and 2.

Diet also proved to have an impact on levels of PGF2α metabolite. In Trial 2, there was a tendency for cows fed Ca-LCFA+EFA to have lower [PGFM] at 10 DIM, and a significant decrease in [PGFM] at 20 and 30 DIM compared to Ca-LCFA-fed cows (Table 4). Over that time period, [PGFM] were decreasing twice as fast for EFA supplemented cows compared to Ca-LCFA only. As PGF2α contributes to the expulsion of fetal membranes, lochia and the early stages of uterine involution, the results show that the significant decrease in [PGFM] is indicative of improved uterine recovery in early postpartum cows.

Table 4. Trial 2 serum concentrations (pg/mL) of PGFM from 10-30 DIM.

Conclusion

Feeding supplemental fat to dairy cows not only can provide those cows with more dietary energy, but also with essential nutrients (linoleic and linolenic acids) that have direct effects on reproductive health and efficiency. Cows fed Ca-LCFA+EFA had more ovulations early postpartum, more estrous cycles by the voluntary waiting period and fewer incidences of metritis than cows fed an isocaloric ration containing Ca-LCFA. These events all point to improved fertility early in the postpartum period.

Acknowledgements

The authors thank Goldman Dairy (Coolidge, AZ), Shamrock Farms (Stanfield, AZ), Church & Dwight (Princeton, NJ), Pfizer (New York), Merial (Duluth, GA), Dr. Tony Martin (Dairy Veterinary Services, Chandler, AZ), as well as Mr. Dean Fish, Mr. Jay Faircloth, Mr. Tyler Dewey, and Dr. Bilby and Dr. Duff.References

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