Effect of Rumen-Degradable Protein Balance and Forage Type on Bulk Milk Urea Concentration and Emission of Ammonia from Dairy Cow Houses

Abstract

As the Dutch government and dairy farming sector have given priority to reducing ammonia emission, the effect of diet on the ammonia emission from dairy cow barns was studied. In addition, the usefulness of milk urea content as an indicator of emission reduction was evaluated. An experiment was carried out with a herd of 55 to 57 Holstein-Friesian dairy cows housed in a naturally ventilated barn with cubicles and a slatted floor. The experiment was designed as a 3 x 3 factorial trial and repeated 3 times. During the experiment, cows were confined to the barn (no grazing) and were fed ensiled forages and additional concentrates. The default forage was grass silage. The nutritional experimental factors were: (1) rumen-degradable protein balance of the ration for lactating cows with 3 levels (0, 500, and 1000 g/cow per d), and (2) proportion of corn silage in the forage ration for lactating cows with 3 levels (0, 50, and 100%) of forage dry matter intake. Several series of dynamic regression models were fitted. One of these models explained emission of ammonia by the nutritional factors and the temperature; another model explained ammonia emission by the bulk milk urea content and the temperature. The ammonia emission from the barn increased when levels of rumen-degradable protein balance increased. Furthermore, at a given level of rumen-degradable protein balance, the emission of ammonia correlated positively with the corn silage content in the forage ration. However, this correlation was not causal, but was the result of interaction between corn silage proportion and intake of ileal digestible protein. The bulk milk urea content and the temperature correlated strongly with the ammonia emission from the barn; the selected model accounted for 76% of the variance in emission. It was concluded that the emission of ammonia from naturally ventilated dairy cow barns was strongly influenced by diet. The emission can be reduced approximately 50% by reducing the rumen-degradable protein balance of the ration from 1000 to 0 g/cow per d. The milk urea content is a good indicator of emission reduction.

Effect of dietary crude protein on ammonia-N emission measured by herd nitrogen mass balance in a freestall dairy barn managed under farm-like conditions

“…In addition, we found a strong linear association between MUN and manure N. This relationship may reflect the strong association between MUN and urinary N reported in the literature (Kohn et al, 2002). The weak relationship between MUN E and NH 3 -N emission found here agreed with results of Powell et al (2008), but contrasted with those of van Duinkerken et al (2005). The latter study however, included dietary treatments with large excesses in dietary CP in the form of RDP primarily, resulting in wide ranges of MUN and NH 3 -N emission.…”

“…Unfortunately, feeding excess dietary CP may still be common in US dairy farms as dietary CP averaged 17.8 6 0.1% in a recent survey conducted in 106 large US herds (Caraviello et al, 2006). The work of Van Duinkerken et al (2005) suggested that milk urea nitrogen (MUN) could be used to predict NH 3 -N emission because bulk tank MUN was a good indicator of emission reduction when excess dietary CP was removed from the diet. There are ample evidences that MUN is an accurate predictor of dietary CP (Broderick and Clayton, 1997;Jonker et al, 1998;Kohn et al, 2002) and urinary urea-N excretion (Burgos et al, 2007) nevertheless, under farm-like conditions MUN is affected by management and other nonnutritional factors (Wattiaux et al, 2005).…”

The role of condensed tannins in ruminant animal production: advances, limitations and future directions

“…Rumen available N in excess of microbial growth requirements is absorbed as NH 3 , metabolized to urea in the liver, and either recycled or excreted in urine. High protein degradation rates increase urinary N excretion, which can negatively impact the environment (Powell et al, 2010), decrease N utilization efficiency, and impart a metabolic burden associated with increased urea synthesis and excretion that hinders animal performance (Van Duinkerken et al, 2005;Kohn et al, 2005) and fertility (Westwood et al, 2000;Tshuma et al, 2014).…”

In vitro protein breakdown by enzyme extracts of rumen origin: comparison with methods in situ and proteases of Streptomyces griseus

“…Measurement of degradation dynamics of feed proteins in the rumen represents a permanent challenge to optimize the protein nutrition, in order to control the excretion of nitrogen compounds to the environment and to improve the animal welfare (Van Duinkerken et al, 2005;Kaswari et al, 2007;Riasi et al, 2008). The quantitative assessment of the breakdown process is key to carry out an effective and sustainable nutrition of the productive ruminants (Givens et al, 2000;Monteny, 2000, quoted by Van Duinkerken et al, 2005.…”