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

摘要

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), 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.