Effect of Defaunation and Amino Acid Supplementation on Growth and Amino Acid Balance in Sheep
by Wael G. Fahmy, Ali O. Bahaa, Michael R. Murphy, Siyabulela W. Nombekela, Robert N. Corley, III, and Jin S. Zhu
TAKE HOME MESSAGES
- Defaunation (elimination of rumen protozoa) increased the rate and efficiency
of body weight gain in growing sheep but did not affect feed intake.
- Rate of body weight gain was highest for defaunated sheep supplemented
with ruminally protected methionine and lysine.
- These results suggest that both treatments and their combination deserve
study in lactating dairy cows; however, development of a less stressful defaunation
procedure is needed before proceeding with this line of research.
The role of ciliated protozoa in the rumen has been the subject
of many studies. It has been established that ruminants can survive with or
without these organisms; however, manipulating their population may affect protein
metabolism in the rumen. This, in turn, may affect the availability of microbial
and dietary protein to the cow and her subsequent milk production. Chemical
defaunation is, at present, a risky procedure; therefore, we used young sheep
to study the effects of defaunation and supplementation of ruminally- protected
amino acids (methionine and lysine) on growth, wool production, and amino acid
MATERIALS AND METHODS
Twenty-eight sheep with an average initial body weight of 66 pounds
were divided into two groups, control and defaunated (using .5 ounces of alkanate
3SL3 daily for 3 days). Each group was further divided into two subgroups; one
fed a control diet and the other fed a similar diet designed to provide .12
ounces of ruminally- protected methionine and lysine per day. The diet was 62
percent concentrate and 38 percent forage on an as-fed basis, and averaged 17.3
percent crude protein (17.9 percent for the diet supplemented with ruminally-
protected amino acids), 28.8 percent neutral detergent fiber, 17 percent acid
detergent fiber, 8.4 percent ash, and 2.4 percent ether extract on a dry matter
Sheep were housed in elevated metabolic cages which allowed feces
and urine to be separated. Faunated and defaunated animals were in separate
rooms of the same building. Each sheep was offered 3.3 pounds of dry matter
daily. Water and trace-mineralized salt blocks were always available.
Growth rate was measured every 10 days over a 9-week period. All
sheep were shorn before starting and after completing the study. Amino acid
concentrations were measured in feed, feces, wool, and blood samples.
RESULTS AND DISCUSSION
The effects of defaunation and supplementation with ruminally-
protected methionine and lysine on dry matter intake, body weight gain, feed
conversion efficiency, and wool growth are presented in Table 1. The usual short-term
depression in feed intake following chemical defaunation was observed; however,
dry matter intake over the 10-week experimental period was not significantly
affected by defaunation or supplementation with ruminally-protected amino acids.
Wool growth was also unaffected by treatment.
Rate of body weight gain was affected (P < .05) by defaunation
and supplementation with ruminally-protected amino acids. Defaunated sheep supplemented
with amino acids gained weight most rapidly, .4 pounds per day; whereas, faunated
sheep fed the control diet gained weight most slowly (.15 pounds per day). The
surprisingly slow growth of faunated animals fed the control diet may have been
caused by protozoa in the rumen decreasing the flow of bacterial protein to
the small intestine. Others have reported data consistent with our results.
Efficiency of body weight gain, pounds of gain divided by pounds
of dry matter consumed, was highest for defaunated sheep (P < .05, Table
1). Supplementation of defaunated sheep with ruminally- protected amino acids
did not affect the efficiency of their body weight gain.
Amino acid digestibility data were consistent with the work of
others which has indicated that the presence of protozoa increases the degradation
of amino acids in the rumen. The wool of faunated sheep supplemented with amino
acids had the highest concentration of amino acids, perhaps an additional factor
helping to explain the slow growth of sheep in this subgroup. Defaunated sheep
also had higher concentrations of amino acids in their plasma than did faunated
sheep, although dietary supplementation with ruminally protected amino acids
did not increase their concentrations in plasma.
TABLE 1. Defaunation and amino acid supplementation
effects on growth of sheep.
| Protozoa Diet Measure
| Dry matter intake, pounds per day
| Body weight gain, pounds per day
| Efficiency of gain, pounds of gain per
pound of dry matter
| Wool growth, ounces per day
a,b,cMeans in the same row without
a common superscript differ (P < .05).