Effect of Licking Molasses-Urea Block on Weight Gain, Rumen Fermentation and the Main Microbe Populations of Grazing Sheep during Grass Withering Period

Introduction

Sheep were grazing in grassland for 6-7 months during withering period in north China. Crude protein (CP) of grass decreased dramatically, crude fiber (CF) increased significantly, and pasture digestibility decreased by 50% in this period. Sheep grazing these pasture as the sole diet may not be able to consume sufficient energy to meet the requirements for a preferred level of performance (Moore and Kunkle, 1995).The pasture can also be low in soluble nutrients and unbalance of energy and nitrogen (Johnson et al., 2001), causing producers to rely on grain or protein products to make up for the nutritional shortfalls. This experiment studied the effect of molasses-urea on rumen fermentation and microbial populations in grazing sheep during grass withering period.

Materials and methods

70 sheep, with similar body weight, were divided into 2 groups: 40 served as experimental group and 30 served as control group. The experimental group were fed molasses-urea after grazing. The experiment last for 60 days. At the beginning and finishing period body weight of each animals was measured. 6 sheep from each group were selected and rumen fluid was collected through oral in morning in the first 3 days and last 3 days of experimental period. Rumen fermentation parameters, including pH, MCP, NH₃-N, were measured. In addition, the population of the Selenomonas ruminantium (Srmm), Anaerovibrio lipolytica (Anal), Fibrobacter succinogenes(F.S), ruminococcus flaveciens(R.F), ruminococcus albus (R.A)were investigated by real-time PCR.

Results and discussion

The average daily molasses-urea consumption was 43.18g per sheep, the average daily gain was 64.83g for experimental group, whereas it was 30.92g for control group, and the difference was significant between two groups (p<0.05). There were no significant difference in pH value between two groups, MCP concentration tended to be increased in experiment group as compared with control group. NH₃-N significantly increased in experiment group (18.2±0.36mg/100ml) as compared with control group (16.2±0.53mg/100ml) (p<0.05).At the end of experiment, the population of Srmm，Anal，F.S，R.F，R.A in experimental group were significant higher than that of control group (p<0.05). These changes can affect fiber digestion, possibly by decreasing the rumen pH and inhibiting cellulolysis (Piwonka and Firkins, 1996). These data corroborate that population of rumen bacteria can be improved by the addition of molasses-urea to a diet (Kostenbauder et al., 2007).

Conclusion

Molasses-urea block provides NPN and sugar for rumen microorganism, and promoted growth and reproduction of microorganism, then improved the nutrients digestibility.