The objective of this study was to investigate effects of offering dry hay of different quality and length on rumen pH and feed preference in lactating dairy cows.

Cows were assigned to squares by parity and randomly assigned to treatments comparing hay (high and low quality) fed within a TMR and supplemented separate from the TMR. Animals were housed individually, milked twice per day, and fed once per day for 10% refusal rate. Data were analyzed using PROC MIXED of SAS (SAS Institute Inc., Cary, NC).

Cows fed supplemental long hay had greater dry matter intake during baseline and challenge days compared with when hay was chopped and included in the TMR. Minimal differences among diets were found for TMR particle size selection during the challenge day; however, cows had a greater preference for high-quality long hay during recovery days. Milk production did not differ among treatments. Fat, protein, and lactose yields were also not different among treatments. Milk fatty acid profile was altered by treatment.

Results of this study indicate that feeding TMR plus supplemental long hay can maintain dry matter intake during incidents of and recovery from periods of low ruminal pH.

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