Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 1997
Publication Date: N/A
Interpretive Summary: Cattle and sheep have a four chambered stomach. The largest is the rumen. Many microbes live in the rumen and are responsible for digesting the feed that the animal eats. Without these microbes, a dairy cow can not convert the feed they are fed to milk. However, some of these microbes are not very efficient at converting the feed the cow eats to compounds that she can use. Some of these microbes digest protein faster than the cow can use them and make excess amounts of an endproduct known as ammonia. An experiment was conducted using artificial rumens to determine the effect feeding an antibiotic (chlortetracycline) at very low levels and different protein levels on the microbial activity of the rumen microbes. We used the microbes from animals that were fed either a diet containing 10% or 13% protein and gave one group the antibotic and another none. When the artificial rumens were fed the antibiotic with the 13% protein diet, the microbes did not make as much ammonia as they did when they didn't receive the antibiotics. Additionally, the low level of the antibiotics decreased the amount of acetate (one of the microbial endproducts used by the cow for energy) and increased propionic acid production (another microbial endproduct used by the cow for energy). Under these circumstances, the use of the antibiotic led to similar ammonia concentrations when used at both the protein levels, indicating a sparing of dietary protein.
An in vitro ruminal fermentation study was used to investigate the influence of feeding sub-therapeutic levels of chlortetracycline (CTC) at two levels of dietary protein (PRO) on ruminal fermentation characteristics. Rumen fluid was obtained at slaughter from steers fed one of four treatments (- or + CTC and 10% or 13% PRO) and used to initiate continuous culture artificial rumens. CTC and 13% PRO resulted in lower (P < .001) ammonia. However, CTC and 10% PRO had similar (P > .05) concentrations of ammonia. CTC with 13% PRO resulted in higher (P < .001) pH and acetate, as well as, lower (P < .001) acetate, iso-butyrate, iso-valerate, n-valerate, and total VFA. Fermentors receiving 10% PRO and CTC had similar (P >.05) pH, and total VFA. When CTC was added to fermentors receiving 10% PRO, acetate, iso-butyrate, iso-valerate and the acetate to propionate ratio were lower (P < .001). Propionate was higher (P < .001) when CTC was fed with 10% PRO, but was similar (P > .05) when fed with 13% PRO. Acetate to propionate ratio was decreased (P < .001) by addition of CTC at both PRO levels, with the 10% PRO being lower (P <.001) than 13% PRO. Under these circumstances, CTC maintained similar ammonia concentrations at both 10% and 13% PRO, indicating a sparing of dietary protein.