Relationships between measures of feed efficiency and transmitting ability for milk of Holstein cows

Abstract

Feed efficiency measures, gross energy (solids corrected milk/estimated energy intake) and nitrogen (milk nitrogen/nitrogen intake) utilization, and apparent digestibilities of ration dry matter, nitrogen, acid detergent fiber, and starch were calculated for 134 samples of 75 daughters of 31 Holstein sires. Nitrogen balance trials were conducted during the first and second trimesters of lactation of cows fed ad libitum corn silage-based complete rations formulated to meet average nutrient requirements. The objective was to test the hypothesis that feed efficiency diminishes as milk increases from selection. The sample of cows closely approximated the distribution of genetic ability for milk of the Holstein breed. Nonsiblings of the same parity (1, 2, (GREATERTHEQ) 3), calving within two weeks of each other and differing by (GREATERTHEQ) 140 kg estimated transmitting ability were paired in nitrogen balance trials.Evidence for diminishing returns to increased transmitting ability for milk was nil for any measure of feed efficiency. Energy efficiency showed linear increases when regressed on cow transmitting ability for fat corrected milk, but other measures of dietary utilization were unrelated to milk yield.