DUODENAL INFUSIONS OF PALMITIC, STEARIC OR OLEIC ACIDS DIFFERENTLY AFFECT MAMMARY-GLAND METABOLISM OF FATTY-ACIDS IN LACTATING DAIRY-COWS

The effect of dietary lipids on the fatty acid (FA) profile of cows' m irk fat is mainly dependent on digestive processes and mammary gland u ptake and metabolism of FA. The objective of this study was to determi ne the separate effects of high arterial concentrations of 16:0, 18:0 and cis-18:1 (n-9) on uptake, synthesis and 18:0 desaturation rate in the mammary gland of lactating dairy cows, via arterio-venous differen ces and mammary gland balance of FA. In a 4 x 4 Latin square, four lac tating Holstein cows with cannula in the proximal duodenum were infuse d duodenally with a mixture providing dairy 0 (C treatment) or 500 g F A with mainly 16:0 (P treatment), 18:0 (S treatment) or cis-18:1(n-9) (O treatment). Significantly higher arterial concentrations of infused FA in arterial plasma nonesterified FA and triglycerides (NETGFA) wer e observed with P and O treatments, but the effect of the S treatment was much lower. Arterio-venous differences of NETGFA increased with ar terial concentrations. The number of synthesized FA in the mammary gla nd was not significantly affected by duodenal infusion of FA. Mean cha in length was significantly reduced by P and O treatments, suggesting an effect of mammary gland uptake of long-chain FA on the termination process of mammary gland synthesis of FA. Across air treatments, 4:0 m ammary gland balance increased linearly (r = 0.67, P = 0.004) with mam mary gland FA uptake. Mammary gland desaturation of 18:0 to cis-18:1(n -9) averaged 52% and was not significantly affected by treatments, but was reduced by trans-18:1 mammary gland uptake. Uptake, synthesis and desaturation of FA by the mammary gland of dairy cows are affected by arterial concentrations of 16:0, 18:0 and cis-18:1(n-9).