Effect of Altering the Dietary Ratio of n-6 to n-3 Fatty Acids on Luteolytic Mechanism in Dairy Cows

Abstract Text: Objectives were to evaluate the impacts of altering the ratio of dietary n-6 to n-3 fatty acids (FA) on timing of luteolysis, uterine production of prostaglandin F_2α, and endometrial fatty acid profile and gene expression in dairy cows. Diets were supplemented (1.43% DM) with a mixture of Ca salts of fish oil, safflower oil and palm oil to create different ratios of n-6 to n-3 FA; 4, 5 and 6 parts of n-6 to 1 of n-3 FA (R4;R5;R6). Cows were blocked by milk production from 6-10 DIM and then assigned randomly to one of the three dietary treatments. Cows had the estrous cycle synchronized starting at 40 DIM. An indwelling catheter was inserted in the tail vessel on d 15 of the estrous cycle and blood was sampled every 2 hours from estrous cycle d 16 to 23. Progesterone and 13,14,dihydro-15-keto-PGF_2α metabolite (PGFM) were measured in plasma. Cows had the estrous cycle resynchronized and endometrial tissue was collected for biopsy on d 8 of the cycle. Gene expression and FA profile were measured. Data were analyzed using MIXED procedure of SAS. Treatment did not influence the length of the estrous cycle or concentrations of progesterone in plasma. Basal PGFM concentrations did not differ (P=0.66) among treatments. The number of PGFM pulses decreased (P=0.05) as the ratio n-6 to n-3 FA increase, and they averaged 5.6, 4.3, and 3.8 pulses, for cows fed R4, R5 and R6, respectively. The area under the curve of the largest PGFM pulse increased as the ratio n-6 to n-3 increased (P=0.02) and were 764, 958, and 1953 pg/h per mL, for cows fed R4, R5 and R6, respectively. The concentrations of arachidonic acid increased (R4=8.09, R5=10.35, and R6=11.04% of the identified FA; P=0.01) and of eicosapentaenoic acid decreased linearly (R4=2.29, R5=1.90, and R6=1.83% of the identified FA; P=0.03) in the endometrium by altering the ratio of n-6 to n-3 from R4 to R6. Of the genes evaluated, expression of the oxytocin receptor, estrogen receptor and steroidogenic acute regulatory protein linearly increased as the diet change from R4 to R6. Altering dietary ratio of n-6 to n-3 FA of lactating dairy cows influenced the pattern of prostaglandin synthesis, the FA profile, and gene expression of the endometrium but did not influence the length of the estrous cycle.

Keywords: Dairy Cow; Fatty acid; Luteolysis