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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


  • 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 retention.


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 basis.

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.


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 Faunated   Defaunated
  Control Supplemented   Control Supplemented
Dry matter intake, pounds per day 2.28 2.16   1.92 2.22
Body weight gain, pounds per day .26b .15c   .29b .40a
Efficiency of gain, pounds of gain per pound of dry matter .11b .07c   .15a .18a
Wool growth, ounces per day .34 .31   .30 .36

a,b,cMeans in the same row without a common superscript differ (P < .05).

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