J Anim Sci. 2016 Sep;94(9):3851-3863. doi: 10.2527/jas.2016-0491.
Abstract
Two
experiments were performed to evaluate the effects of 1) increasing
supplementation doses of a 50:50 (as-fed) liquid supplement of molasses
and crude glycerol (M:G) on ruminal fermentation parameters and blood
urea nitrogen (BUN) in beef steers consuming Tifton 85 bermudagrass (
spp.) hay and
2) different proportions of molasses and crude glycerol in a liquid
supplement on in vitro fermentation and gas production kinetics. For
Exp. 1, 8 ruminally cannulated, Angus-crossbred steers were used in a
duplicated 4 × 4 Latin square design, had ad libitum access to Tifton 85
bermudagrass hay,
and were randomly assigned to 1 of 4 treatments: 1) CTRL, no
supplementation; 2) SUP1, 0.45 kg/d (as fed) of 50:50 M:G; 3) SUP3, 1.36
kg/d (as fed) of 50:50 M:G; and 4) SUP5, 2.27 kg/d (as fed) of a 50:50
M:G. For Exp. 2 in vitro batch cultures were conducted to test the same
treatments from Exp. 1 and effects of different proportions of a M:G
mixture (100:0, 75:25, 50:50, 25:75, and 0:100) when added to a hay substrate simulating the proportions of hay
and liquid supplement used in SUP5. In Exp. 1, increasing doses of
liquid supplement linearly decreased ( < 0.001) concentrations of
NH-N, BUN, and acetate molar proportions, whereas propionate ( = 0.002)
and butyrate ( < 0.001) molar proportions increased linearly.
Treatment × time interactions were observed for ruminal pH ( <
0.001), where the greatest decrease was observed at 3 h postfeeding for
animals consuming SUP5 (from 6.82 at 0 h to 6.32 at 3 h). In Exp. 2,
decreases in acetate molar proportions ( < 0.001) and increases (
< 0.001) in propionate and butyrate molar proportions were also
observed for either increasing doses of a 50:50 mixture or increasing
proportions of glycerol in the mixture. Total VFA and in vitro organic
matter digestibility were increased linearly ( < 0.001) as doses of a
50:50 mixture increased. Increasing doses of 50:50 M:G to growing beef
heifers consuming bermudagrass hay
caused a shift in VFA profile toward increases in propionate and
decreases in acetate molar proportions. This was also confirmed in
vitro, as the proportions of crude glycerol increased in a
molasses:crude glycerol mix. Thus, molasses and crude glycerol combined
seem to be useful to enhance performance in growing cattle consuming
forage-based diets.