3. Feed high-lysine protein supplements to achieve a level of lysine in metabolizable protein that comes as close as possible to meeting the optimal concentration. If protein supplementation is required, select high-quality, high-Lys protein supplements (e.g., soybean and canola meals, blood meal, and fishmeal). In this case, "high quality" refers to consistency in distribution of RDP and RUP and highly digestible RUP where one is certain that RUP-Lys digestibility is not compromised. Feeding low-Lys feeds such as corn gluten meal and distiller's grains as sources of additional protein is not consistent with balancing for AA. Purposely selecting high-Lys protein supplements has been the only option, at least until the recent release of the first rumen-protected Lys sources on the market, to at least partially compensate for the low content of Lys in the RUP fractions from forages, grains and distiller's grains. Achieving target formulation levels for Lys in MP will become easier, and the value of lower Lys protein supplements extended, if these rumen-protected Lys products can be demonstrated to be cost effective sources of MP-Lys.
4. Feed a "rumen-protected" methionine supplement in the amounts needed to achieve the optimal ratio of lysine and methionine in metabolizable protein. Feeding a rumen-protected Met supplement, in conjunction with one or more of the aforementioned high-Lys protein supplements, is almost always necessary to achieve the correct Lys/Met ratio in MP. We continue to be surprised with first time evaluation of diets how often we see Lys to Met ratios in MP of 3.3 or higher ... values as high as 3.5 and 3.6 are not uncommon. "Out of balance" Lys to Met ratios lowers the efficiency of use of MP for protein synthesis and the more "out of balance" the ratios, the less efficient the use. To achieve the desired predicted ratio of Lys to Met in MP, and to ensure full use of the available MP-Lys for protein synthesis, one MUST use a realistic estimate for the amount of metabolizable Met provided by the Met product that you are feeding. Over-estimating the bioavailability of some of the Met supplements has been way too common. This is unfortunate because it leads to disappointing production outcomes, and more often than not, leaves the nutritionist and dairy producer believing that balancing for Lys and Met has minimal impacts on animal performance.
5. Don't overfeed rumen undegradable protein. There are several disadvantages to overfeeding RUP. These include:
- Lowered concentrations of Lys and Met in MP [because most sources of supplemental RUP are deficient in Lys, Met or both (fish meal is the only exception).
- Lowered milk production (because surplus RUP usually replaces fermentable carbohydrates in the diet, the primary substrates for synthesis of milk components).
- A more-expensive diet (because most sources of supplemental RUP are more expensive than most sources of NFC).
- Increased urinary and fecal N (because of lowered conversions of feed protein to milk protein).