|Abstract or Summary
- The object of this study was to observe the effect of tallow plus
urea in vitro and in vivo. The study was carried out in three parts;
an in vitro fermentation study, a metabolism trial and a feedlot trial.
The in vitro study was conducted using a 4 x 2 x 2 factorial
design with readily available carbohydrate (RAC) levels of 30, 40, 50
and 60%; tallow levels of 0 and 3%; and urea levels of 0 and 2%. Pure
cellulose or soluble starch was used to dilute or fortify the basal substrate
to obtain the desired level of RAC. Treatment substrates were
fermented for 18 hr. and acetic, propionic and butyric acid production
and ammonia disappearance were measured. Acetic and propionic
acid production and ammonia disappearance increased as the level of
RAC increased from 30 to 50%. Tallow reduced acetic acid production
and ammonia disappearance while increasing propionic acid production.
Urea increased volatile fatty acid (VFA) production and ammonia
disappearance. There was a tallow x urea interaction for acetic, propionic and butyric acids and gross energy available from VFA's
as well as for ammonia disappearance. The interaction resulted in a
decrease in response for all parameters except propionic acid when
tallow and urea were added simultaneously.
The metabolism studies consisted of four separate experiments.
Trial one had the following treatments: basal, 5% tallow, 1. 5% urea,
and 5% tallow + 1.5% urea. Trial two had the following treatments:
basal; 3% tallow + 1.5% urea; and 5% tallow + 1.5% urea, The treatments
for trial three were 5% tallow + cottonseed meal; 5% tallow +
biuret; and 5% tallow + urea. Trial four had the following treatments:
5% tallow + 1. 15% urea; 5% tallow + 1.50% urea; and 5% tallow + 2.17%
urea. Twelve crossbred yearling wethers were used in each trial.
After a 10-day adjustment period urine and feces were collected for
10 days. Initial and final blood samples were taken to measure
changes in plasma urea and total plasma lipid. Trial 1 indicated that
tallow or tallow plus urea increased crude protein digestion and nitrogen
retention. When nitrogen retention was expressed as a percent
of dietary nitrogen retained, there were no treatment effects. The
addition of tallow to the rations improved fat digestibility. Tallow or
tallow plus urea increased plasma urea values. Trial 2 indicated that
the addition of urea increased crude protein digestibility and nitrogen
retention. Lambs receiving 3% tallow plus urea retained more nitrogen
than lambs receiving 5% tallow plus urea. Trial 3 indicated that 5% tallow plus cottonseed meal reduced dry matter and crude protein
digestion as well as nitrogen retention. Trial 4 showed that 1.5%
urea plus 5% tallow increased dry matter digestion. There was no
difference in crude protein digestibility between the three groups.
In all four trials urea had no effect on total plasma lipid.
The relationship between tallow and urea was studied in a feedlot
trial. Twenty steers averaging 282 kg were divided into four groups
and fed one of the following rations for 126 days; basal (I); basal +
1.5% tallow (II); basal + 0.75% urea (III); and basal + 1.5% tallow +
0. 75% urea (IV). The basal ration was made up of 10.5% alfalfa
pellets, 34.5% barley, 20.0% oats, 9. 0% wheat, 17.5% beet pulp,
7.5% molasses and 1.0% vitamin-mineral-antibiotic premix. Blood
samples were taken via jugular puncture 6 hr after the morning feeding
on days 0, 14, 42, 70, 98 and 126 and plasma urea and total plasma
lipid was measured. Average daily gain (kg) for the groups were: I,
1.13; II, 1.25; III, 1.44 and IV, 1.38. Group IV was the least efficient
in the conversion of digestible energy and digestible protein into gain.
After 14 days groups III and IV had higher plasma urea values than
groups I and II. Steers in group IV had the highest total lipid values
after 126 days.