Relationship Between Content of Crude Protein in Rations for Dairy Cows and Milk Yield, Concentration of Urea in Milk and Ammonia Emissions

Abstract

During recent decades, efforts have been made in several countries to diminish the negative environmental influence of dairy production. The main focus has been on nitrogen and phosphorus. Modern dairy production in Western Europe is often based on imported feed-stuffs, mostly protein-rich feeds. In Sweden at least, it is wished that the use of imported feedstuffs in animal production will decrease due to the risk of contamination with Salmonella and the ban of using GMO crops in Swedish dairy production. An experiment was carried out to investigate whether a lower content of crude protein in the diet would decrease the ammonia release from cow manure and whether a well-balanced diet using only feedstuffs of Swedish origin would maintain milk production. Five treatments were arranged in a Latin square design. Two different protein supplements made of ingredients of Swedish origin were each fed at two protein levels, and a fifth imported commercial protein mix was fed at the higher level. The treatments with low protein levels (13.1 to 13.5%) had a significantly lower milk yield, kilograms of ECM, but, on the other hand the net profit, milk income minus feed cost was nearly the same in all treatments except diet C, which had lower feed cost but also lower net profit due to lower milk yield. The content of urea in milk was higher with diets high in crude protein (17%) content. A decreased protein level in the diets did not influence the content of casein or whey protein, but the commercial concentrate showed a tendency to give lower values than the Swedish mixtures. The low protein diets gave significantly lower ammonia release from manure compared with the high protein diets. There were no production differences between the diets of Swedish feeds compared with the imported control. The readily fermentable beet pulp should have helped cows use the higher N diet more efficiently and increased the response. This gives the rumen microbes a possibility to match the inflow of protein with carbohydrates. Income over feed costs shows that it is possible to compile diets using products of Swedish origin and still be competitive. On the other hand, this structure may change quickly due to altered world market prices.

Responses of milk urea nitrogen content to dietary crude protein level and degradability in lactatingHolsteindairy cows

“…The lack of responses in milk production and milk composition was consistent with others' observations that these did not change when dietary protein varied from 16.7 to 18.4% (Davidson et al, 2003), from 16.4 to 20.4% (Mulligan et al, 2004), from 16.4 to 18.0% (Wattiaux and Karg, 2004), and from 14.6 to 18.3% (Castillo et al, 2001). While some researchers observed significant differences in milk yield or composition with dietary protein from 13.1 to 17.0% (Frank and Swesson, 2002), it has been reported that milk production benefits from > 15% protein, but increasing the protein above 17% has no further effect (Groff and Wu, 2005), and dietary protein has only a low effect on milk fat and protein concentration (Sutton, 1989). The effect of dietary protein level on MUN content is shown in Figure 1.…”

Low degradable protein supply to increase nitrogen efficiency in lactating dairy cows and reduce environmental impacts at barn level

“…Moreover, as both milk protein concentration and yield were not significantly affected by the diet (P > 0.05, Table 3), it seemed that the animals were able to achieve a better use of nutrients with a lower amount of feed ingested, as illustrated by the food conversion ratio that tended to be higher for the LowN diet (1.24 v. 1.22, P = 0.05, Table 3). This could represent a certain economy for farmers and act as compensation for the slight loss in milk production (Frank and Swensson, 2002). For example, changing the diet from 16% to 14% CP by replacing soya bean meal and urea by grains was estimated to bring a benefit of 12 €/cow per year, provided balanced supplies of PDIN and PDIE were maintained (taking into account milk yield and milk protein concentration reductions in winter; Pellerin et al, 2013).…”

Effect of Incremental Urea Supplementation of a Conventional Corn Silage-Based Diet on Ruminal Ammonia Concentration and Synthesis of Microbial Protein

“…Concentrations of MUN were expected to increase because CP concentrations of the diets increased. The direct relationship between MUN and dietary CP concentrations is well documented (Frank and Swensson, 2002;Nousiainen et al, 2004).…”