Improving Nitrogen Efficiency of Dairy Cows and Its Environmental Impact
1. How much urea is fed in Holland?
Holland is a country with diets that are primarily grass-based. We have around 1 million hectares of grassland and about 230.000 ha of land for corn. However, in the southern and eastern part of the country, there are quite of lot of farms on sandy soils that have > 50% of corn silage in the basal forage ratio. The rumen degradable protein balance of these basal diets can be too low, resulting in the addition of rumen degradable protein (or NPN sources). What I see in common practice is that natural raw materials (such as soybean and rapeseed meal) are mostly used to balance the energy/protein ratio in these diets and that the use of urea is not common practice yet. I do not have quantitative data. However, marketing efforts of the industry (e.g., to promote the use of slow-release urea) may have a stimulating effect on the use of NPN in the future.
2. Did Kalsheur only look at gross CP levels, not amino acid of diets?
There is no focus on AA in this paper. Abstract of this paper: Three experiments were conducted to investigate the effect of crude protein (CP) concentration and ruminally undegraded protein (RUP) concentration on milk production and composition of dairy cows at three different stages of lactation. Experiments 1, 2 and 3 using 39, 40 and 39 Holstein cows were conducted for cows in early (wk 4 to 14 postpartum), mid (wk 19 to 29) and late (wk 34 to 44) lactation, respectively. Cows were assigned to one of four corn-based diets: high CP, medium RUP (control); low CP, low RUP; low CP, medium RUP; and low CP, high RUP. Percentages of CP in the high and low CP diets were, respectively, 17.4 and 15.2 for Experiment 1, 15.3 and 13.3 for Experiment 2 and 14.2 and 12.6 for Experiment 3. The RUP concentrations (percentages of CP) for low, medium and high diets averaged 35.5, 41.4 and 46.5%, respectively. For Experiment 1, production of milk, 4% fat-corrected milk, milk fat and milk protein were increased by the high protein diets versus the low protein diets. Production of milk and fat-corrected milk increased linearly as RUP in the diet increased. During Experiment 2, lactational responses were not affected by treatment. During Experiment 3, dry matter intake, body weight and body weight change increased for cows fed the high protein diets versus those same measurements for cows fed the low protein diets. Milk fat and milk protein percentage decreased linearly as RUP in the diet increased. Because there was no effect of diet on milk production, decreasing CP in diets fed to cows in mid or late lactation can reduce the cost of the diet and waste N excreted from the cow.
3. What did MUNs look like on the organic farms that were milking 34kg and being fed 15% protein?
The book chapter of Bannink and Dijkstra does not provide data on MUN content. My experience is that with levels of 15% CP, milk urea content is around 20 mg/100 g milk, translated to MUN that would be 9 to 10.
4. What about the yield drag you would have on the grass with less nitrogen fertilizer?
Valk (2002) reported a negative effect of level of N fertilization on grassland (kg N/yr) on the milk yield (see figure) based on zero grazing experiments with grass cut at DM yield per cut between 1,500 and 2,000 kg per hectare per cut.
5. What kind of NUE is possible with DDGS? How about with rumen protected amino acids adding to DDGS?
The talk of Paul Kononoff probably provided the answers to these questions: pp 15-18 of the proceedings.
6. How high do you think we can realistically go on NUE?
The paper of Powell et al. gives a very good overview of all relevant matters and interactions concerning NUE: Powell, J. M., C. J. P. Gourley, C. A. Rotz and D. M. Weaver. 2010. Nitrogen use efficiency: A potential performance indicator and policy tool for dairy farms. Environmental Science & Policy 13:217-228. Furthermore, according to Chase (2003), feed-NUE of less than 20% can be defined as very low; 20–25% indicates substantial improvement can be made; 25–30% is a range that encompasses most on-farm and some experimental feed-NUE; 30–35% is above average; and greater than 35% is excellent.
7. Why do we continually see tank variations in MUN levels on the same farm day to day with TMR feeding?
It is assumed a priori that large day-to-day variability in MUN will occur (Rajala-Schultz and Saville, 2003), particularly because of fluctuations in pasture grass composition, feed intake and grazing conditions. In common Dutch dairying practice, the milk bulk tank is emptied every 3 d (generally after 6 milkings). Clear milking-to-milking variation in milk urea concentration has been observed within one milk delivery period of 3 d in experiments of van Duinkerken et al. (2011). In this study, the p.m. milking generally showed a higher milk urea concentration than the a.m. milking. Furthermore, Spek et al. (2011) performed a literature review and concluded that variation in milking and feeding frequency, and variation in the distribution of feed intake over time affect the diurnal variation in MUN.
8. To improve NUE, should we target feeding individual cows or pens of cows?
In practice, an increase in NUE is not the only farm objective and the feeding strategy is chosen on multifactorial grounds (available labor, costs for equipment, flexibility of housing systems, availability of forages, raw materials, feedstuffs, etc.). If NUE would be the only relevant issue (which is a theoretical situation), individual feeding would provide better opportunities to achieve highest NUE.