Apparent ruminal degradation and rumen escape of lysine, methionine, and threonine administered intraruminally in mixtures to high-yielding cows.

Abstract

We studied the kinetics of lysine, methionine, and threonine in six high-yielding dairy cows at peak lactation (stage 1) and 6 mo later (stage 2). The cows were fitted with cannulas in the rumen and duodenum and were automatically fed every 4th h. The three amino acids (AA) were administered intraruminally in mixtures at dosages of 100, 200, 300, and 400 mmol of each, together with polyethylene glycol (PEG) as a liquid marker. Mean rumen liquid pools at stages 1 and 2 were not significantly different. The mean liquid outflow decreased from 13.6 to 9.5 L/h, and there was a significant linear increase in the liquid outflow with increasing dosages of AA. No significant interaction was found between feeding levels and AA dosages on rates of apparent degradation and rumen escape values. Expressed as percentages of the dosage, all three AA studied showed a significant linear decrease in degradation and a significant increase in rumen escape values with increasing dosage. At the feeding levels in stages 1 and 2, the highest relative degradation rates (percentage of dosage) were observed for threonine. The relative degradation rate of methionine was significantly lower than of lysine at the high feeding level but significantly higher at the low feeding level. The mean rumen escape values of threonine, methionine, and lysine across dosages and feeding levels were 16.7, 22.1, and 20.5%, respectively. The flow of the administered AA into the duodenum during an 8-h period after administration increased with increasing dosages, with peak concentrations after 1 h. Thus, the amounts of rumen escape of the three AA were considerable at all dosages, even when the AA were administered in unprotected form.

Effect of rumen-protected protein supplemented with three amino acids on milk yield, composition and fatty acid profile in dairy cows

“…Volden et al (1998) found that the mean rumen escape values of threonine, methionine and lysine given intraruminally in non-protected form were 16.7, 22.1 and 20.5%, respectively. The response to feeding protected amino acids reported in the literature is variable depending on the source of protein in the basal diet.…”

Rumen escape of methionine and lysine administered intraruminally to growing double-muscled Belgian Blue bulls

“…Feeding crystalline AA could be economically attractive when their ruminal escape rates exceed 20 to 25% [11]. Such rates, observed with dairy cows with high AA administration [22][23][24], have not previously been reported for fast-growing bulls. However, the main factor influencing the proportional ruminal escape of free AA is their concentration in the ruminal fluid, which depends on its volume and the dose of AA.…”

“…Total ruminal outflow of free Lys did not differ when it was supplied with or without Met (P = 0.08) and reached, respectively, 26.6 ± 5.5 and 27.5 ± 5.5 g. In this study, high ruminal escape of Met and Lys were observed despite dietary conditions favourable to AA degradation. High concentrate diets actually induce an efficient growth of microorganisms [16] and a selection of amylolytic bacteria that utilise high proportions of AA [24]. However, more than 65% of the total amounts of free Met and free Lys that escaped ruminal fermentation did so during the first 4 h. According to Velle et al [23], ruminal escape of free AA is increased when they are administered with larger amounts of other AA.…”

“…The ruminal escape of free AA has been shown to vary with AA [22], dietary conditions [16], amount supplied [24], and whether the AA is administered individually or with other AA [23]. To our knowledge, only Campbell et al [2] has investigated free AA supplementation for growing cattle, and observed no effect on animal performances although the amounts supplied were modest.…”

“…Dietary incorporation of free AA may be a practical way to improve the AA pattern of metabolisable protein in dairy cows [24]. The ruminal escape of free AA has been shown to vary with AA [22], dietary conditions [16], amount supplied [24], and whether the AA is administered individually or with other AA [23].…”