Feeding Lactating Dairy Cattle Long Hay Separate from the TMR Can Maintain DMI During Incidents of Low Rumen pH
The objective of this study was to investigate effects of orchardgrass hay (H) quality and feeding method on rumen pH and feed preference in lactating dairy cows. Eight rumen-cannulated Holstein cows (104 ± 34 DIM, 601 ± 116 kg, and parity of 2.38 ± 1.69; mean ± SD) were used in a replicated 4 × 4 Latin Square. Each period encompassed 21 d divided into 5 phases: adaptation, d 1 to 14, ad libitum TMR; baseline, d 15 to 17, ad libitum TMR; restricted feeding, d 18, cows fed for 75% of baseline DMI; challenge, d 19, 4 kg (as-fed) fine ground wheat mixed into the digesta of each cow via rumen cannula before feeding; and recovery, d 20 to 21, ad libitum TMR. Cows were assigned to squares by parity and randomly assigned to treatments. Treatments were: corn silage (CS) with coarse H TMR (CC), CS and fine H TMR (CF; both hays chopped and included in TMR), CS TMR with 5.2% supplemental long coarse H (TMR+C), and CS TMR with 5.2% supplemental long fine H (TMR+F; both hays fed separate from TMR). Coarse H was 8.6% CP and 67.1% NDF, fine H was 14.4% CP and 56.2% NDF. Animals were housed individually, milked 2X/d, and fed 1X/d for 10% refusal rate. Data was analyzed using MIXED procedure of SAS. Rumen challenge decreased weighted average rumen pH from 5.72 to 5.51. Cows fed TMR+C had higher rumen pH compared to CC and TMR+F on d 19. During d 20, cows fed H had higher rumen pH than cows fed supplemental long H. Cows fed supplemental long H had greater DMI during baseline and challenge d compared to TMR H treatments. Minimal differences among diets were found for TMR particle size selection during challenge d; however, cows had a greater preference for fine long H during recovery d. Milk production averaged 38.3 kg/d and did not differ among treatments. Fat, protein, and lactose yields were also not different among treatments. Milk fatty acid profile was altered by treatment. The TMR+C and CF treatments increased production of conjugated linoleic acid (CLA) cis-9, trans-11 (P = 0.02). Results of this study indicate that feeding TMR plus supplemental long H can maintain DMI during incidents of and recovery from periods of low ruminal pH.
Keywords: subacute ruminal acidosis, ruminal pH, particle size