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

Laura Astigarraga,Ricardo Mello,Ana Bianco,Dana Montedónico

doi:10.4236/ajps.2014.57108

Abstract

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.

Highlights

Sorghum [Sorghum bicolor (L.)Moench.] is an important forage crop for grazing dairy cows in many milk producer regions of the world as frequent drought and high summer temperatures reduce forage production from pastures
The Brown midrib (BMR) Sorghum hybrid has an average forage accumulation (1695 kg dry matter (DM)/ha) and a morphological composition similar to the CONTROL hybrid at the entrance to grazing. Those results contrast with data reported previously [1] [14], that the BMR trait is associated with a decrease in forage yield
That the BMR sorghum was not compare to its correspondent normal one and so, the effect of the specific mutation is confounded with hybrid.Gross Energy (GE) content was not significant different between sorghum types

Summary

Introduction

Sorghum [Sorghum bicolor (L.)Moench.] is an important forage crop for grazing dairy cows in many milk producer regions of the world as frequent drought and high summer temperatures reduce forage production from pastures. Brown midrib (BMR) mutants were originally induced and described in sorghum by Porter et al [2] This trait is associated with reduced lignin content and/or an increase in forage digestibility expressed in both sorghum and sudangrass [3] and their hybrids [4] [5]. In situ and in vitro digestion studies have shown that BMR forages have greater extent of NDF digestion than their conventional counterparts [6] [7]. Such increases in digestibility are associated with increased animal performance. To date, there is no study with dairy cows conducted using brownmidrib sorghum as grazing forage

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