Alfalfa cut at sundown and harvested as baleage increases bacterial protein synthesis in late-lactation dairy cows

Abstract

Alfalfa (Medicago sativa L.) cut at sundown (p.m.) has been shown to have a greater concentration of total nonstructural carbohydrates (TNC) than when cut at sunup (a.m.). Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were used in a crossover design (24-d periods) to investigate the effects of alfalfa cutting time on digestibility and omasal flow of nutrients. Alfalfa was cut at sundown or sunup, field-wilted, and harvested as baleage (530 +/- 15.0 g of dry matter/kg of fresh matter). The difference in TNC concentration between p.m. and a.m. alfalfa within each pair of bales fed daily during the 10 d of data and sample collection varied from -10 to 50 g/ kg of dry matter. Each pair of bales was fed for ad libitum intake to cows once daily with no concentrate. During the 3 d of omasal sampling, intake (+0.8 kg/d) and omasal flow of organic matter (OM; +0.42 kg/d) tended to be greater when cows were fed p.m. vs. a.m. alfalfa, but no differences were found for ruminal and postruminal digestion of this nutrient. Similarly, N apparently digested ruminally and postruminally did not differ when feeding p.m. vs. a.m. alfalfa. However, N truly digested in the rumen, as a proportion of N intake, was significantly greater in cows fed p.m. (79%) vs. a.m. alfalfa (74%), thus suggesting that longer wilting time of alfalfa cut at sundown increased forage proteolysis. Supply of rumen-degradable protein did not change (2,716 g/d) when averaged across treatments, whereas omasal flow of non-NH(3) nonbacterial N was significantly decreased (-29 g/d) when feeding p.m. vs. a.m. alfalfa. Omasal flow of total bacterial non-NH(3)-N (NAN) increased (+21 g/d) significantly when cows were fed p.m. vs. a.m. alfalfa possibly because bacteria from cows fed p.m. alfalfa captured significantly more NH(3) than those from cows fed a.m. alfalfa. Therefore, greater availability of fermentable energy as TNC appears to increase the capacity of microbes to uptake NH(3)-N and convert it to microbial protein. Enhanced OM intake can also explain the observed increase in bacterial protein synthesis with p.m. alfalfa. Efficiency of bacterial protein synthesis, expressed on a fermented OM basis or as grams of bacterial NAN per gram of rumen-degradable N, did not differ between p.m. and a.m. alfalfa. Conversely, bacterial efficiency, as grams of bacterial NAN per gram of N intake, was significantly increased when cows were fed p.m. baleage. No significant difference between forage treatments was found for the omasal flow of total AA from omasal true digesta, suggesting no benefit of daytime cutting management on the passage of total AA to the lower gastrointestinal tract. Enhancing energy intake and TNC concentration of alfalfa by shifting forage cutting from sunup to sundown increased protein synthesis and NH(3) uptake by ruminal bacteria indicating an improvement in N utilization.

Supplementing lactating dairy cows with a vitamin B12 precursor, 5,6-dimethylbenzimidazole, increases the apparent ruminal synthesis of vitamin B12

“…The fluid-associated bacteria (FAB) and particle-associated bacteria (PAB) were isolated from the daily 420-ml composites from each cow on each of the 2 sampling days using filtration and differential centrifugation as described earlier in detail (Brito et al, 2009). The resulting FAB and PAB pellets were stored at −20°C, lyophilized, ground with a mortar and pestle, and finally pooled by cow per period by mixing equal amounts of dry matter for later analysis.…”

“…The resulting FAB and PAB pellets were stored at −20°C, lyophilized, ground with a mortar and pestle, and finally pooled by cow per period by mixing equal amounts of dry matter for later analysis. The 4.8-l pooled omasal composites were thawed at room temperature, separated into the three omasal phases (LP, SP and FP) Vitamin B 12 synthesis in rumen as described by Brito et al (2009), and stored at −20°C until lyophilized. After lyophilization, these samples were ground through a 1-mm screen before analyses of digesta markers.…”

“…Concentrations of Cr, Yb and indigestible NDF in LP and SP and Cr and Yb in FP were determined using the methods detailed earlier (Brito et al, 2009). Marker concentrations were used to physically recombine DM from the lyophilized FP, SP and LP in the correct proportions to reconstitute the omasal true digesta (OTD) flowing out of the rumen using the triple-marker method of France and Siddons (1986).…”

“…Extracts from OTD samples were prepared and analyzed for ammonia-N (NH 3 -N) as described by Brito et al (2009).…”

Supplementation with non-fibrous carbohydrates reduced fiber digestibility and did not improve microbial protein synthesis in sheep fed fresh forage of two nutritive values

“…In addition, water-soluble carbohydrates and CP were greater in early than in late phenological stage of forage. In fact, Brito et al (2009), feeding dairy cows with silage from alfalfa cut at sundown, with greater sugar concentration than when cut at sunup, observed an increased capacity of microbes to uptake N-NH 3 and convert it to microbial protein. Therefore, it seems that the impact of the diets on microbial protein production and EMPS was mainly related to the pattern of supply of the forage fermentable carbohydrates (as also proposed by Hall and Huntington, 2008), and that the NFC supplementation and the consequent increased DOMI did not improve these parameters.…”