Influence of feeding free lysine to early lactation dairy cows on ruminal lysine escape, rumen fermentation and productivity

The primary objective was to quantitate ruminal escape of lysine fed to cows in a free form. However since it was expected that a substantial proportion of the lysine would be degraded in the rumen, other objectives were to determine if this lysine impacted ruminal fermentation as well as determine impacts on the performance of the cows, including intake of dry matter (DM). Four multiparous Holstein cows, fitted with large diameter plastisol rumen cannulae between 6 and 8 weeks prior to their projected calving date, were assigned in a 4 × 4 Latin square design experiment between 2 and 4 weeks post-partum. All cows were fed the same total mixed ration (TMR) and treatment differences were achieved by manually incorporating l-lysine HCl into each cow's individually weighed allocation of TMR at the time of feeding to deliver 0, 1, 2 or 3 g of l-lysine from l-lysine HCl/kg of DM intake. However actually delivered lysine values were about 20% higher. The DM, neutral detergent fibre and crude protein (CP) intakes increased only numerically (P = 0.09-0.11), in a linear fashion, with increased feeding of l-lysine. Rumen pH and volatile fatty acid concentrations were not influenced by lysine feeding, although both total N and ammonia N concentrations in rumen fluid increased linearly (P < 0.05). The latter contrasts with the CP levels of rumen ingesta DM, which were not affected by lysine feeding. Other organic components of rumen ingesta, as well as those of isolated rumen bacteria, were also unaffected by lysine feeding as was rumen volume and liquid turnover rate. As expected, average rumen free lysine concentrations increased linearly, but only at P = 0.07, due to increased feeding levels of lysine. Production of milk, and its components, was unaffected by lysine feeding. Feeding increasing levels of free lysine to lactating dairy cows, in three levels up to 85 g/day, resulted in an estimated ruminal escape of lysine of 72 g/kg of lysine fed, a level that is only about 1/3 of those reported in previously published studies based upon short term pulse dosing and/or feeding studies.