Ruminal escape and apparent degradation of amino acids administered intraruminally in mixtures to cows.
The apparent ruminal degradation and escape of amino acids (AA) administered in 9 different mixtures of essential AA and 8 different mixtures of nonessential AA were studied using two cows fitted with ruminal cannulas. The 600-mmol AA mixtures, which were administered intraruminally using polyethylene glycol as a liquid marker, contained equal amounts of two, four, or eight AA. The amounts of each of the AA in the mixtures were 300, 150, and 75 mmol, respectively. Ruminal degradation and escape were compared with values previously reported for AA administered individually. Across doses, the mean rate of initial degradation (degradation during the 1st h after administration) of essential AA was 26% when the AA were administered in mixtures and 45% when the AA were administered individually. For nonessential AA, the corresponding values were 34 and 54%. Across doses, mean ruminal escape during the first 8 h after essential AA administration was 22% when the AA were administered in mixtures and 16% when the AA were administered individually. For nonessential AA, the corresponding values were 13 and 11%. After intraruminal administration of AA, both individually and in mixtures, significant negative correlations were found between rates of degradation during the 1st h and ruminal escape during an 8-h period. Some AA mixtures caused a net increase in the concentration of other AA in ruminal fluid 1 h after administration. Twelve of the mixtures that did not contain Ala caused a considerable net increase in the concentration of this AA, and 3 AA mixtures containing Arg and Ala caused a marked net increase in the concentration of Trp.
Hydroxymethyl lysine is a source of bioavailable lysine for ruminants.
Experiments were conducted to evaluate the availability to ruminants of lysine from hydroxymethyl lysine, a product potentially resistant to ruminal degradation yet able to release free lysine when subjected to the acidic environment of the abomasum. An in vitro ruminal fermentation assay that led to ammonia production from free lysine was used for initial assessments, but the hydroxymethyl lysine was inhibitory to lysine degradation at the concentrations tested in vitro; therefore, an in vivo assay with sheep, using plasma lysine concentrations as the response criterion, was used for assessment. twelve mature sheep were fed graded amounts of lysine from either a commercially available ruminally protected lysine product with known availability or from hydroxymethyl lysine. the protected lysine product provided 3 or 6 g/d of metabolizable lysine, whereas the hydroxymethyl lysine provided 3 or 6 g/d of total lysine. Plasma lysine concentrations increased linearly in response to both the ruminally protected lysine product and hydroxymethyl lysine. by slope ratio analysis, the bioavailability of lysine in hydroxymethyl lysine was estimated to be 94% of that for the commercially available product. We concluded that hydroxymethyl lysine may be used as an effective means of supplementing lysine to ruminants.
Sulphur metabolism and excretion studies in ruminants. 8. Methionine degradation and utilization in sheep when infused into the rumen or abomasum.
Methionine (2 g/day) was continuously infused either abomasally or ruminally into two groups of sheep (four per group) over a 6-week period. After a further 6 weeks on the basal diet, which supplied daily 900 g dry matter, 18· 3 g nitrogen, and 1· 45 g sulphur, the infusion treatments were reversed. A control group of four sheep did not receive infusions. After 13 days on each treatment L-[35S}methionine was continuously infused, along with the carrier methionine, for 5 days during which the sheep were fed at 2-hourly intervals.