Comparison of Brown Midrib Sorghum with Conventional Sorghum Forage for Grazing Dairy Cows

A brown midrib (BMR) sorghum pasture was compared with normal sorghum for its effects on performance of Holstein cows in midlactation in terms of milk production and composition at grazing over three periods (Period 1: 20/01 to 31/01, Period 2: 17/02 to 28/02, Period 3: 19/03 to 30/03). Forty Holstein cows were grouped according to pre-experimental milk production (22.4 ± 4.2 kg/d milk), live weight (530 ± 25 kg) and lactation stage (127 ± 63 days) and assigned randomly to one of the two experimental pasture. Pasture was assigned on equal basis at an allowance 25 kg DM/cow/day (above 10 cm), assuming a 65% forage utilization and cows received 4 kg of concentrate per day. Simultaneously, both pastures were evaluated with sheep, to analyze digestibility at every grazing period. The BMR sorghum supported higher FCM than normal sorghum (18.5 vs. 17.8 l/day, P < 0.05). Additionally, production of milk components was greater (+52 g/day/cow and +36 g/day/cow for fat and protein respectively, P 0.05), with fewer intake of concentrate (-0.4 kg/day/cow, P 0.05) when compared with cows grazing normal sorghum. Those results are in accordance with greater (P 0.05) total digestive tract DM, OM and NDF in vivo digestibilities for BMR sorghum (65.0, 67.1, 65.9 respectively) than for normal sorghum (60.3, 62.0, 61.3 respectively). The increased digestibility of BMR sorghum must be associated with the compositional differences on fiber which allowed a higher cell wall digestion. Results of this study indicate that the BMR sorghum hybrid outperformed the normal sorghum hybrid resulting in a higher performance per cow with lower concentrate consumption compared with normal sorghum.

Intake, Energy Expenditure and Methane Emissions of Grazing Dairy Cows at Two Pre-Grazing Herbage Masses

A grazing experiment was undertaken to assess the effects of two levels of herbage mass (HM) on herbage DM intake (DMI), fat and protein corrected milk yield (FPCM), grazing behaviour, energy expenditure (HP), and methane emissions (CH4) of grazing dairy cows in spring. Treatments were a low HM (1447 kg DM/ha;LHM) or a high HM (1859 kg DM/ha;HHM). Pasture was composed mainly of cocksfoot (Dactylis glomerata) and lucerne (Medicago sativa), offered at a daily herbage allowance of 30 kg DM/cow, above 5 cm. Eight multiparous Holstein cows were used in a 2 × 2 Latin Square design in two 10-day periods. Despite the differences in pre-grazing HM between treatments, OM digestibility was not different (P = 0.28). Herbage mass did not affect DMI or FPCM. Grazing time was not different between treatments, but cows had a greater bite rate when grazing on LHM swards. However, HP did not differ between treatments. Daily methane emission (per cow), methane emission intensity (per kg FPCM) and methane yield (as percentage of gross energy intake) were not different. The lack of effect of the amount of pre-grazing HM on energy intake, confirms that the difference between HM treatments was beyond the limits that impose extra energy expenditure during grazing.