Craig, Aimee-LouiseGordon, AlanHamill, GregoryFerris, Conrad2022-08-022022-08-022022-07-11Craig, A.-L., Gordon, A.W., Hamill, G. and Ferris, C.P. (2022) ‘Milk Composition and Production Efficiency within Feed-To-Yield Systems on Commercial Dairy Farms in Northern Ireland’, Animals. MDPI AG. doi:10.3390/ani12141771.2076-2615 (electronic)https://doi.org/10.3390/ani12141771Publication history: Accepted - 5 July 2022; Published - 11 July 2022.This study examined the relationships between milk yield and diet composition, nutrient intakes, milk composition, and feed use efficiency when concentrates were offered using a feedto- yield (FTY) approach. The study was conducted on 26 dairy farms in Northern Ireland. Cows (n = 3471) were fully housed and were offered concentrates on an FTY basis. Individual cow genetic information was obtained for 18 herds. Concentrate intakes of individual cows were either obtained from the farms or calculated, while milk yield and milk composition data were obtained from test-day milk recording. Mean test-day milk yields during months 2 to 5 post-calving were calculated for each cow, and cows within each lactation were placed into one of six equal-sized milk yield (kg/cow/day) groups. Diet effects and performance responses to milk yield groups were tested for linear and quadratic effects. Total dry matter intakes increased with increasing milk yield. Milk fat and milk protein concentration declined as milk yield increased, which could be attributed in part to genetics and diet. As milk yield increased, nitrogen and energy use efficiency was improved. However, concentrates offered per kg of energy-corrected milk also increased at higher milk yields, indicating an increased reliance on concentrates for these cows.en© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).dairy cattlefeed-to-yieldmilk compositionconcentrate use efficiencynitrogen efficiencyArticle