Expert Answers - June 20, 2014

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Q: What were some of the highlights of the Cornell/Miner Institute Advanced Dairy Nutrition Shortcourse?

A: The course had considerable focus centered around the science and modeling of amino acids, fatty acids and fiber digestion. Transition cows were touched on in many of the discussions, and attendees were given a tour of the recently opened Cornell Dairy Research Center.

Q: What were topics that really stood out on modeling dairy rations?

A: Advancements in nutritional modeling continue to allow the nutritionist to formulate rations for higher levels of production and greater efficiency. Improvement to the Cornell Net Carbohydrate and Protein System (CNCPS) model was one of the many topics covered. Several sessions focused on the predictability of metabolizable protein (MP) and amino acid (AA) flow by CNCPS, and rethinking the way we express amino acid requirements.

Q: Tell us more: What’s new with MP and AA? 

A: An article published several years ago in the Journal of Dairy Science showed that several commercial models predict essential amino acid flows with reasonable accuracy, and planned updates to CNCPS will further remove hurdles to adoption of essential amino acid (EAA) balancing in diets for dairy cows. One such improvement is updating the amino acid composition of feed ingredients, which is critical to the accuracy of prediction of MP from rumen undegradable protein (RUP), since one-half of the MP from today’s rations is derived from RUP.

If you want to check the accuracy or update the amino composition of feed ingredients in your library, NRC 2001 is a good place to start. The forthcoming amino acid updates to CNCPS’s feed library indicate that methionine is currently too low for most ingredients, and other EAA are a mixed bag of too high or too low.

In addition to changes on the AA supply side, changes to AA requirements were discussed. Efficiency of AA use is overestimated in the current model for most AA with Met and Lys at 97% and 82%, respectively. Future updates to CNCPS will have efficiencies for these two AA in the range of 66-69%, which is a considerable decrease. This will result in CNCPS’s amino acid requirements being more in-line with other nutrition models.

Q: What affect will these changes have on ration formulation?

A: The changes result in benchmarks changing slightly when the library is updated. Currently, to maximize milk protein yield the recommendation for methionine as a percentage of MP (MP-Met %) is 2.35 and lysine (MP-Lys %) is 6.93%. Suggested targets after update increase to 2.5% MP-Met and 7.0% MP-Lys. 

Q: Were there any new amino acid balancing strategies discussed?

A: Dairy NRC 1989 discussed an optimal ratio of nitrogen to energy in the rumen, and called this coupling microbial production with energy fermentation. In more recent years this concept has been extended to overall energy and protein supply with benchmarks of 44-46 g MP per Mcal of ME, indicating that when this ratio exceeds 46, nitrogen efficiency decreases, because energy is the most limiting nutrient; and when the ratio drops below 44, MP is the most limiting nutrient. Ryan Higgs, a graduate student at Cornell University, used similar logic and data analysis to show that metabolizable Met (mMet) and metabolizable Lys (mLys) should be formulated to levels relative to ME, with starting points of 1.1 g mMet per Mcal ME and 2.9 g mLys per Mcal ME. Higgs also noted that we tend to focus on milk protein yield or milk protein concentration as the outcome to amino acid balancing. However, the typical response to amino acid balancing also includes responses in milk flow and fat yield. So, amino acid and energy supplies are indelibly linked.

Q: You mentioned fiber. What’s new with laboratory fiber analysis, and how do we use it? 

A: Curt Cotanch of the Miner Institute discussed yet another laboratory NDF value and its use. Many of you may be getting undigestible NDF (uNDF) values on your forage analysis reports from labs. Terminology differs between labs with examples being 120 h uNDF, uNDF 240 h, and uNDF240. Undigestible NDF along with multiple NDFD time points can be used in the prediction of indigestible NDF and rate of NDF digestion. An optimal uNDF range may exist for rations since it has the potential to represent highly fermentable, low rumen structure rations for low uNDF rations and high fill, high structure rations for high uNDF rations. This could be another tool in the toolbox for nutritionists to strike a balance between achieving highly fermentable rations while maintaining rumen health. While Miner Institute continues research in this area, Cotanch recommended expressing uNDF240om as a percentage of body weight with 0.35% as a jumping off point.

Q: Finally, we heard something about ‘Mom’s signals’ in colostrum?

A: Mike VanAmburgh discussed the lactocrine hypothesis, which suggests that maternal programming extends beyond the uterus through the ingestion of milk-borne morphological factors present in colostrum. We typically focus on providing adequate passive transfer and essential nutrients through colostrum, but these milk-borne factors go beyond IgG and nutrients, and play a role in gut maturation and supply of hormones. Although antibody supplementation can achieve passive transfer, there are other factors present in colostrum that result in improved gain and feed efficiency. The cow is trying to communicate with her calf after birth, via colostrum, putting a new perspective on those 4 liters fed within the first 12 hours of life. 

Q: Where can I go to get more information?

A: Proceedings can be purchased by visiting Cornell University’s Dairy Management Extension proceedings and resources website. Click here to visit their site.

Patrick French, PhD, PAS
804-240-9190 | Patrick.French@feedcomponents.com | www.feedcomponents.com


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