1586
Effects of forage particle size and corn oil supplementation related to milk fat depression in dairy cows consuming reduced-fat corn dried distillers grains with solubles
Four ruminally cannulated Holstein cows averaging (± SD) 116 ± 18 DIM and 686 ± 52 kg of BW were used in a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments to test the effects of forage particle size and dietary concentration of corn oil on milk fat depression (MFD). Cows were housed in individual stalls, milked twice daily and fed once daily to allow ad libitum access to feed. In each 28 d period each cow was offered 1 of 4 TMR that differed in forage particle size by inclusion of grass hay (LONG) or grass hay pellets (SHORT) and 0 or 2 % corn oil (OIL). Chewing activity was monitored visually every 5 minutes for 24 h on d 25. Total rumen evacuation was performed on d 27 and 28 of each period to determine rumen kinetics. Dietary treatments were: 0 % oil + short particle size (OIL0+SHORT); 0 % oil + long particle size (OIL0+LONG); 2 % oil + short particle size (OIL2+SHORT); and 2 % oil + long particle size (OIL2+LONG). Dry matter intake and milk yield were not affected by treatment averaging 26.5 ± 0.90 kg/d and 32.8 ± 3.25 kg/d respectively. There was a decrease (P < 0.01) in 3.5 % FCM due to oil inclusion resulting in 34.6 and 26.6 ± 2.6 kg/d for 0 and 2% oil diets. An oil × size interaction (P = 0.03) resulted in 2.26, 3.02, 3.62 and 3.62 ± 0.23 % milk fat for OIL2+SHORT, OIL2+LONG, OIL0+SHORT and OIL0+LONG. Fat yield was reduced (P < 0.01) from 1.22 to 0.81 ± 0.09 kg/d with 2% oil diets. An oil × size interaction (P < 0.01) affected yield of trans-10, cis-12 conjugated linoleic acid (CLA) resulting in 0.35 g/d for OIL2+SHORT and 0.11 g/d for OIL2+LONG. Long particles increased (P = 0.02) eating time from 169 to 198 ± 15 min/d, rumination time (P < 0.01) from 400 to 504 ± 35 min/d and reduced (P = 0.02) rate of passage of DM from 3.38 to 2.89 ± 0.42 %/h. These results demonstrate that dietary manipulations that modify rumen kinetics also impact milk fat production in dairy cows consuming TMR supplemented with corn oil, the effects of corn oil on MFD were less severe when cows consumed long particle size
Keywords:
Rumen kinetics
Biohydrogenation
Chewing activity