Feeding measures to reduce nitrogen excretion in dairy cattle

Short communication: Evaluation of nitrogen excretion equations from cattle

Nitrogen excretion in dairy manure is a precursor for N2O and NH3 formation in livestock housing, manure storage facilities, and after manure is applied to land. Nitrous oxide is a major contributor to greenhouse gas emissions, and reducing N output from dairy production facilities can reduce the amount of anthropogenic N2O entering the atmosphere. The objective of the study was to conduct a comprehensive evaluation of extant prediction models for N excretion in feces and urine using extensive literature data. A total of 45 N excretion equations were evaluated for lactating cows, heifers, and nonlactating cows and steers. These equations were evaluated with 215 treatment means from 69 published studies collected over 20 yr from 1995 to 2015. Two evaluation methods were used: the root mean square prediction error and the concordance correlation coefficient. Equations constructed using a more rigorous development process fared better than older extant equations. Equations for heifers and nonlactating cows had greater error of prediction compared with equations used for lactating cows. This could be due to limited amount of data available for construction and evaluation of the equations. Urinary N equations had greater prediction errors than other forms of excretion, possibly due to high variability in urinary N excretion and challenges in urine collection. Fecal N equations had low error bias and reached an acceptable level of precision and accuracy.

Reducing nitrogen excretion and soybean meal use by feeding a lower rumen degradable protein balance and protected soybean meal to dairy cattle

To reduce N pollution by dairy cows, two levels of rumen degradable protein balance (RDPB) and the use of protected protein sources were studied in two feeding trials. Trial 1 investigated if the effect of lowering the RDPB, at a constant DPI (digestible protein in the intestine) supply, could be compensated by using protected protein sources (formaldehyde treated (= formolated) soybean meal (FSBM) or a combination of FSBM and formolated rapeseed meal at a ratio of 60:40). Trial 2 studied if FSBM is as effective as soybean meal (SBM) at a low RDPB level. Each trial was set up as a Latin square design, with three treatments and three periods, involving 18 lactating Holstein cows. Reducing RDPB from about 150 g/d to below -40 g/d resulted in small negative effects on the milk production, independent of the protein source (protected or not). However, N excretion per kg fat and protein corrected milk (FPCM) and N efficiency were both improved. At a low RDPB level, the performance of FSBM (35.0 kg FPCM) was no better than after feeding a combination of FSBM and formolated rapeseed meal (34.7 kg FPCM). The use of FSBM (32.8 kg FPCM and 34.2% N efficiency) was as effective as SBM (32.5 kg FPCM and 34.2% N efficiency). As such, SBM use can approximately be halved by using FSBM, possibly in combination with locally produced rapeseed meal.