The objectives were to evaluate the effects of differential timing of supplementation of different Ca salts (CS) of fatty acids (FA) on FA profiles of cotyledonary-caruncular tissues, metabolic status, uterine health, pregnancy, pregnancy losses after two artificial inseminations (AI), and milk yield.

Holstein cows (n=1,380) were assigned randomly to be fed either CS of palm oil (PO) or safflower oil (SO) from 30 d prepartum until 30 d postpartum (dpp) and further randomized to receive either CS of PO or fish oil (FO) from 30 to 160 dpp. Supplementation of CS of FA was at 1.5 percent of dietary dry matter. Tissues (n=23) and blood (n=32) were collected from a subsample of cows. Blood was collected daily from parturition to 10 dpp and three times weekly thereafter until 30 dpp for analyses of PGF2α metabolite, nonesterified FA, β-hydroxybutyric acid, blood urea nitrogen, and glucose.

Cows were evaluated once between 8 to 10 dpp for cervical discharge type. At 43 dpp, cows received two injections of PGF2α 14 days apart, followed 14 days later by injections of GnRH at 7 d before and 56hours after an injection of PGF2α with AI at 16hours after the second GnRH injection. All cows received intravaginally a controlled internal drug-releasing device, containing 1.38g of progesterone, at 18 days after the first AI followed 7 days later by removal of the device and injection of GnRH. Nonpregnant cows at 32 days after AI were injected with PGF2α, followed 56hours later with a GnRH injection and second AI 16hours thereafter. Cows diagnosed pregnant after both AI were re-examined at 60 days of pregnancy to determine pregnancy losses. Milk weights were recorded monthly for all cows. Caruncular n-6:n-3 FA ratio was greater in cows fed SO. Plasma concentrations of metabolites and frequency of cervical discharge type did not differ between PO- and SO-fed cows. Plasma PGF2α metabolite was greater in SO-fed cows at 4 and 7 dpp. Pregnancy per AI at 32 and 60 days post first AI was not affected by diets, but pregnancy loss was less in FO-fed cows. At second AI, pregnancy was greater in FO-fed cows at 32 days and in SO-FO-fed cows at 60 days post AI. Pregnancy loss after second AI was not affected by diets. Overall pregnancy per AI was greater in cows fed SO followed by FO at 60 days of pregnancy and pregnancy loss was reduced in FO-fed cows. Monthly milk yield was greater (0.7 kg/d) in SO-fed cows.

In conclusion, strategic feeding of CS of FA during transition and breeding periods can benefit fertility and milk production of lactating dairy cows.