Effect of dietary concentrate on rumen fermentation, digestibility, and nitrogen losses in dairy cows

Abstract

The objective of this experiment was to investigate the effect of level of dietary concentrate on rumen fermentation, digestibility, and N losses in lactating dairy cows. The experiment was a replicated 3x3 Latin square design with 6 cows and 16-d adaptation periods. Ruminal contents were exchanged between cows at the beginning of each adaptation period. Data for 2 of the diets tested in this experiment are presented here. The diets contained (dry matter basis): 52% (LowC; control) and 72% (HighC) concentrate feeds. Crude protein contents of the diets were 16.5 and 16.4%, respectively. The HighC diet decreased ruminal pH and ammonia concentration and increased propionate concentration compared with LowC. Acetate:propionate ratio was greater for LowC than for HighC. Rumen methane production and microbial protein synthesis were unaffected by diet. Dry matter intake was similar among diets, but milk yield was increased by HighC compared with LowC (36.0 and 33.2 kg/d, respectively). Milk fat percentage and yield and total-tract apparent NDF digestibility were decreased by HighC compared with LowC. More ruminal ammonia N was transferred into milk protein with HighC than with LowC. Urinary N excretion, plasma urea N, and milk urea N concentration were not affected by diet. The ammonia emitting potential of manure was similar between LowC and HighC diets. Increased concentrate proportion in the diet of dairy cows resulted in reduced ruminal ammonia concentration and enhanced ammonia utilization for milk protein synthesis. These effects, however, did not result in reduced urinary N losses and only marginally improved milk N efficiency. Increasing dietary concentrate was not a successful strategy to mitigate enteric methane production and ammonia emissions from manure.

Response of growing ruminants to diet in warm climates: a meta-analysis

“…= 2.30). The positive effect of CP on OMd, despite an increase in DMI as seen before, was likely the outcome of an increase in the activity of rumen microorganisms allowed by a greater N availability (Agle et al, 2010). The combined effects of dietary CP on DMI and OMd result in a large increase in DOMI, and therefore in ME intake as a response to dietary CP, which was also partly the outcome of the simultaneous increase of NDF as CP decreased.…”

Starch in ruminant diets: a review

“…Moreover, rapidly-fermenting diets reduce methane production by decreasing ruminal pH, which affects the growth of methanogens, protozoa (Hook et al, 2011) and cellulolytic bacteria (Sung et al, 2007), and increases passage rate, which reduces protozoans and, thereby, interspecies hydrogen transfer (Kumar et al, 2013). Agle et al (2010) reported that diets with higher proportion of non-structural carbohydrates (52 and 72%) resulted in numerically lower methane emissions (1.5 vs. 3.4 g/hour, respectively), although results showed no difference due to high variability. A recent study in grazing Holstein Friesian cows found that concentrate level (2, 4, 6, and 8 Kg/cow/day) had no impact on methane emissions (287,273,272, and 277 g/day, respectively).…”

Influence of glucogenic dietary supplementation and reproductive state of dairy cows on the composition of lipids in milk

“…The elevated propionate concentration induced by propylene glycol administration could also explain the elevated protein yield on day 8 post-estrus for the treatment group relative to the controls (Agle et al, 2010). One might assume that these changes in milk composition were due to changes in dry matter intake.…”