de Ridder, K. A. G., Farmer, C., de Lange, C. F. M., Shoveller, A. K. and Luimes, P. H. 2014. Plasma amino acids, prolactin, insulin and glucose concentrations in lactating sows following venous infusion of isoleucine, leucine, lysine, threonine or valine. Can. J. Anim. Sci. 94: 323-330. The amino acid supply to lactating sows affects their milk yield, and the current study aims at establishing whether this is mediated via increases in concentrations of insulin and prolactin, two hormones that are important for lactation. Six multiparous Yorkshire sows (252.8±18.5 kg body weight) were fitted with an ear vein catheter and were used in a 6×6 Latin square design experiment from days 7 to 10 of lactation (am and pm infusions on 3 consecutive days). Sows were fed a commercial corn and soybean meal diet (17.1% crude protein) three times daily (1.5 kg at 0600 and 1200, 3.0 kg at 1830). Starting 2 h after the 0600 or 1200 feeding, sows received an infusion of saline (control), isoleucine, leucine, lysine, threonine or valine at a rate of 33 mL min^-1 during 30 min. The infused dose was equivalent to 18±0.9% of true ileal digestible intake for each of the amino acids. Serial blood samples were taken, starting 30 min prior to infusion and until 240 min after infusion. Plasma concentrations of amino acids, prolactin, insulin, and glucose were determined. Data were analyzed as repeated measurements and also using areas under the curve. Intravenous infusion with each of the five amino acids studied increased the corresponding free plasma amino acid concentrations (P<0.05). However, concentrations of prolactin, insulin, and glucose were not affected by infusion of any of the amino acids studied (P>0.10). Therefore, supplying intravenously 18% of the daily intake of isoleucine, leucine, lysine, threonine or valine brings about expected increases in amino acids, but does not alter the short-term response in prolactin, insulin or glucose concentrations of lactating sows.