UC Davis

Objective: Our objectives were to evaluate milk production and constituent responses to changes in the diet for pens of cows over time and whether differences in response were attributable to fibrolytic enzymes and dairy. Materials and Methods: A multiherd trial used 7,507 cows in 8 control and enzyme-treated (750 mL/t of DM feed) replicates (16 pens) on 3 dairies. Feed composition and milk production and constituents by pen (n = 12) were analyzed weekly. Time-series cross-correlation estimates by pen of feed component intakes (kg/d) and milk responses were pooled to produce effect size (ES) estimates. Results and Discussion: We observed differences between treatment and control pens for soluble protein (ES = 0.249) in the same week, acid detergent–insoluble CP (ES = 0.293) and lignin (ES = 0.237) 1 wk before with milk protein percentage, and acid detergent–insoluble CP (ES = 0.276) and lignin (ES = 0.246) 1 wk before with milk protein yield. These differences are consistent with enzymes improving feed digestibility, particularly for protein and fiber fractions. Differences in production responses to intake of feed components among dairies were observed. More significant and larger differences occurred among dairies than for treatments. The dairy that increased milk production most with treatment had an estimated MP excess from the diet, whereas the least responsive had an estimated MP-deficit diet and was the highest producing. Implications and Applications: We provide evidence for variability in enzyme response and that changes in dietary feed components influence production outcomes immediately and up to 3-wk later.