Data paper: Variability of milk fatty acid profiles across controlled dairy cow trials

This paper presents a curated compilation of milk fatty acid measurements assembled from 18 feeding experiments conducted over 12 years at the Department of Animal Sciences, Laval University. One experiment with two dietary treatments was considered as two separate units, and another with three treatments as three units, yielding 21 trials in total. All experiments were carried out in a tie-stall facility with Holstein cows milked twice daily. Cows received a total mixed ration in all but one experiment that used component feeding. During sampling periods, rations were either the baseline pre-experimental diet or a control diet without fat supplementation to maintain consistent background conditions. Milk samples were analyzed for individual fatty acids by gas chromatography with flame ionization detection using a 100‑m CP‑Sil 88 capillary column. For each fatty acid, means and pooled intra‑experiment SD were calculated across units, providing variance estimates that reflect within‑experiment variability under controlled housing, milking, and feeding practices. The compilation includes common short-, medium-, and long‑chain fatty acids, and selected isomers of 18‑carbon unsaturated fatty acids. This resource is designed to support power and sample‑size calculations, sensitivity analyses, benchmarking of new measurements, meta‑analytical aggregation, and simulation studies in dairy nutrition and physiology, thereby facilitating transparent planning and reproducible quantitative work.