Productive responses of lactating dairy cattle to supplementing high levels of ruminally protected lysine using a rumen protection technology

Abstract

Increased milk production requires high intakes of crude protein in the diet, and/or improved supply and profiles of amino acids (AA) delivered to the duodenum, in order to meet animal needs for milk and milk component synthesis. Our objective was to estimate the rumen escape of a ruminally protected lysine (RPL) product and determine effects of feeding it on dry matter (DM) intake, milk production and plasma AA profiles of high producing dairy cows. The study was two 2 × 2 crossovers ( i.e., early and mid-lactation dairy cows) with 28-d experimental periods. All cows were fed the same total mixed ration (TMR), calculated to be first limiting in lysine, with treatment pens receiving 17 kg/pen/d of the RPL supplement (to deliver 41 g of lysine/cow/d) mixed into the TMR. Extensive evaluation of the RPL suggested that this feeding level delivered 15–21 g/d of intestinally absorbable lysine. Control cows were fed the RPL without lysine ( i.e., the fat matrix) at the same level as the fat matrix which was fed to the RPL cows. Feeding the RPL did not influence DM intake in early lactation cows (26.8 kg/d), but production of milk (48.0 versus 50.0 kg/d), as well as milk fat, true protein and lactose, and energy, were higher (P<0.01) in RPL supplemented cows. In addition, cows supplemented with RPL gained body condition score (BCS) whereas control cows lost BCS during the 28-d period ( i.e., 0.020 versus −0.069 units/28 d; P=0.056). In mid-lactation cows, DM intake was not influenced, and only milk fat and energy outputs increased (P<0.05) with RPL feeding. BCS change was not influenced. Plasma lysine levels in mid-lactation cows were much higher (P=0.01) with RPL feeding, suggesting that the feeding level of RPL exceeded their lysine needs. However a lack of impact of RPL feeding on plasma lysine levels in early lactation cows suggests that lysine needs may not have been met with RPL feeding. In contrast to an earlier study by our group, with early lactation cows fed a similar diet where milk yield was not impacted by 7–10 g/d of lysine delivered to the intestinal absorptive sites, may support the unconventional hypothesis advanced in that study that body protein turnover is the first limiting AA priority in early lactation cows followed by milk component synthesis.