Abstract
The objective of these studies was to determine the effects of feeding a novel rumen-protected Lys (RP-Lys) product on plasma AA, lactational performance, and Lys bioavailability. To evaluate RP-Lys on lactation performance a corn-based diet (42.5% of corn silage and 21.9% of corn and corn by-products, on DM basis) was formulated to be Lys deficient but adequate in Met, energy, and metabolizable protein. Thirty-six lactating Holstein cows were fed either a Lys-deficient control diet (CON) with no added RP-Lys, or diets containing 0.3% of RP-Lys (0.3RP-Lys) or 0.6% of RP-Lys (0.6RP-Lys) for 8 wk. There were no effects on dry matter intake (mean ± SD; 26.1 ± 0.58 kg/d), milk yield (37.9 ± 0.72 kg/d), or milk composition to the RP-Lys supplementation. No effect was observed on plasma AA concentrations except for His. Plasma His was linearly reduced by Lys feeding (42.6, 41.2, 30.0 ± 4.09 μM, for CON, 0.3RP-Lys, and 0.6RP-Lys, respectively). Calculated efficiency of Lys utilization decreased linearly with RP-Lys supplementation. In the companion study, 3 rumen-cannulated lactating dairy cows were used in a 3 × 3 Latin square design to assess the bioavailability of the RP-Lys. Free Lys (HCl-Lys), RP-Lys, and water were administered separately by postruminal bolus dosing. The Lys bioavailability was assessed by the ratio of area under the curve of Lys plasma concentration for RP-Lys compared with HCl-Lys and discounted for the area under the curve for water bolus dose. The estimated bioavailability of the RP-Lys was 24.4% ± 4.61. In summary, increased supplemental doses of Lys had no effect on Lys plasma concentration and lactational performance when fed to dairy cows on a corn-based diet, although altered Lys as % of essential AA was observed. However, the lack of effects should be considered in light of the lower-than-expected bioavailability of the RP-Lys.
Highlights
The ideal protein provides the perfect balance of biologically available AA relative to the animal’s physiological needs
We evaluated the effect of incremental amounts of a lipid-coated RP-Lys product on plasma AA concentration, milk production and composition in a diet designed to be deficient in digestible Lys (dLys) for mid-lactation dairy cows
Diets supplemented with RP-Lys were formulated to contain similar ingredient levels as the control diet
Summary
The ideal protein provides the perfect balance of biologically available AA relative to the animal’s physiological needs. Greater precision in meeting the AA needs of lactating dairy cows may increase productivity, reduce N excretion to the environment, or result in a combination of both factors (Castillo et al, 2000; Godden et al, 2001). Improved knowledge of protein and AA profiles of conventional feed ingredients combined with an understanding of the value of AA supplements in current feeding systems is necessary to advance feeding management strategies toward greater precision in meeting AA requirements for lactating cows. When corn and corn products comprise a significant proportion of the diets, dairy nutritionists have formulated rations using rumen-protected sources of Lys to meet Lys requirements for high-producing cows. Despite recognizing Lys is likely limiting, there is still a scarcity of research demonstrating consistent responses to rumen-protected (RP) Lys supplementa-
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