Experiments using periparturient Holstein cows were conducted to evaluate how supplemental fat sources enriched in specific fatty acids affected production, immunity, hepatic gene expression, and metabolism of periparturient dairy cows. In Experiment 1, fat supplements enriched with C18:1 (sunflower oil), Ca salt of trans C18:1, C18:2 (Ca salt of palm and soybean oils), or C18:3 (linseed oil) were fed (1.35 to 1.75% of dietary DM) in isolipid diets from 30 d before to 105 d post calving to 22 primiparous and 32 multiparous animals. Cows fed C18:3 tended to produce more 3.5% fat-corrected milk due to an improvement in concentration of milk fat compared to cows fed the C18:2 source. Supplementation with trans C18:1 increased trans C18:1 in plasma, milk fat, and liver fat. Supplementation with C18:2 increased C18:2 in plasma and milk fat. Supplementation with C18:3 increased C18:3 in plasma, milk fat, and liver fat. Animals fed C18:3 had greater plasma NEFA concentrations at wk 2 and 5 postpartum which were accompanied by upregulation of mRNA pyruvate carboxylase and phosphoenolpyruvate carboxykinase in the liver during this same time period. Concentrations of plasma IGF-1 and expression of hepatic IGFBP-3 mRNA increased at a faster rate postpartum for animals fed C18:2 or C18:3 compared to those fed cis or trans C18:1; this was accompanied by a faster rate of increase for plasma insulin of multiparous cows fed C18:2 or C18:3 sources. Primiparous cows supplementated with C18:3 had fewer neutrophils in the uterine flushing at 40 d postpartum. Trans C18:1 may have had immunostimulatory effects as evidenced by increasing concentrations of plasma acid soluble protein and haptoglobin of primiparous cows compared to those fed cis C18:1.

In Experiment 2, fat supplements enriched with C18:2 (Ca salt of safflower oil) or C20:5 and C22:6 (Ca salt of palm and fish oils) were fed (1.5% of dietary DM) as well as a no-fat supplement control diet from 34 d before to 49 d post calving to 16 primiparous and 29 multiparous animals. Animals fed fish oil tended to consume less DM (% of body weight) and produce less milk fat compared to animals fed C18:2. Mean values for dry matter intake prepartum, milk yield, milk protein yield and concentration, body weight, body condition score, and plasma concentrations of glucose, nonesterified fatty acids, beta hydroxybutyrate, and prostaglandin F metabolite were unchanged across the 3 diets. Concentrations of plasma progesterone increased earlier in primiparous cows fed fish oil compared to safflower oil fed cows and return to first ovulation was improved by 6 day across parities. Consumption of fish oil appeared to have immunosuppressive effects. A greater proportion of the animals fed fish oil were diagnosed with a more severe case of metritis at 5 and 10 d postpartum, had lower blood concentrations of white blood cells and neutrophils and had circulating neutrophils that consumed fewer E. coli per neutrophil on -18, 0, 7, and 40 d postpartum. Primiparous cows fed fish oil had lower plasma concentrations of ceruloplasmin. In addition, animals fed fish oil had circulating lymphocytes that produced fewer cytokines when isolated and stimulated in vitro on 10, 20, and 30 d postpartum. On the other hand, the C18:2 fat source had immunostimulatory effects. Cows had a greater humoral response of IgG concentrations in serum postpartum to repeated ovalbumin injections, did not experience the decrease in concentration of blood neutrophils at 7 d postpartum that occurred in the other treatments, and multiparous cows had increased fibrinogen concentrations in plasma. Based upon greater plasma concentrations of acute phase proteins, primiparous cows were under greater stress from parturition and lactation compared to multiparous cows.

In conclusion enrichement of the diet with specific fatty acids during the periparturient period were reflected in the incorporation of these fatty acids into different tissues. Omega-3 fatty acids attenuated immune responses compared to omega-6 supplementation and shortened return to first ovulation.