"A total of 84 Holstein cows in mid-lactation were studied in three experiments. The study was a crossover design with 2 treatment periods. Treatments were a high forage-low starch diet (HF; 36%NDF, 19% starch) and a low forage-high starch diet (LF; 26%NDF, 32% starch). Forage comprised 70% of the DM in HF and 47% in LF. Collected data included: dry matter intake (DMI), milk yield (MY), body weight (BW), body condition score (BCS), and milk components. Statistical analysis was performed using the MIXED or GLM procedures (SAS 9.4). An RFI value was calculated for each cow when fed each treatment diet then, cows were ranked as high RFI (HRFI), medium RFI (MRFI) or low RFI (LRFI) for each treatment diet. The HF diet resulted in a decrease of 10% DMI, 5% ECM and 1% BW compared to the LF diet. Rate of BW accretion was 60% lower for cows fed HF compared to for cows fed LF. Milk fat yield, and BCS were not altered by treatments. RFI was relatively repeatable (r=0.54) across the two diets. Of all animals, 56% maintained their group ranking across treatments whereas 38% changed ranking by 1 group. Only 6% moved in ranking from the HRFI to the LRFI group or vice versa. In conclusion, although dietary treatments significantly altered intake, milk production, and energy partitioning, RFI was relatively repeatable for cows fed two diets with different forage concentrations. Thus, genomic breeding values of RFI estimated from cows fed a lower forage (higher starch) diet should still be useful when they are fed a higher forage diet containing less starch."--Page ii.
Read
