EFFECT OF ALFALFA SILAGE STORAGE STRUCTURE AND ROASTING CORN ON PRODUCTION AND RUMINAL METABOLISM OF LACTATING DAIRY COWS

Authors: KRIZSAN, S - NORWEGIAN UNIV OF LIFE; Broderick, Glen; Muck, Richard; PROMKOT, C - KHON KAEN UNIV-THAILAND; COLOMBINI, S - UNIV OF MILANO-ITALY; RANDBY, A - NORWEGIAN UNIV OF LIFE

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2007
Publication Date: 10/1/2007
Citation: Krizsan, S.J., Broderick, G.A., Muck, R.E., Promkot, C., Colombini, S., Randby, A.T. 2007. Effect of alfalfa silage storage structure and roasting corn on production and ruminal metabolism of lactating dairy cows. Journal of Dairy Science. 90:4793-4804.

Interpretive Summary: In the U.S., alfalfa usually is fed to dairy cows as silage rather than hay because harvesting silage is much more rapid and requires less manual labor. Among the common silo structures used to ensile alfalfa are plastic bags, bunkers and oxygen-limiting silos. However, it is not known whether there is a clear advantage to using any one of these 3 different silos for conserving the feeding value of alfalfa. Moreover, there is an additional problem with alfalfa silage in that its protein is extensively degraded in the rumen, the first compartment of the cow's stomach. The rumen microbes both form and degrade protein; generally, they reduce the value of the protein in alfalfa silage because they form less protein than they degrade. Dietary energy stimulates protein formation by the rumen microbes. Corn grain is the principal dietary energy feed for U.S. dairy cows. If roasting increased the availability of corn energy to the rumen microbes, then more protein would be formed in the cow’s rumen and milk and protein yield improved. This study examined the value of roasting corn that was fed as energy supplement to cows eating alfalfa ensiled in plastic bags, bunkers or oxygen-limiting silos. Yield of milk and milk fat was greater, and there was a trend for greater milk yield per unit feed consumed, when cows were fed alfalfa silage from the oxygen-limiting silo compared with alfalfa silage from the bag or bunker silos. Also, there was smaller wastage of silage with the oxygen-limiting silo versus the other 2 silos. Feeding roasted corn resulted in small improvements in feed intake and milk protein yield. These results indicated that ensiling alfalfa in the oxygen-limiting silo resulted in greater recovery of alfalfa’s nutrients for feeding to dairy cows, as well as improved production of milk and milk fat. Depending on the relative costs of these 3 silos, this would result in improved profit for the dairy farmer. Greater milk yield per unit feed consumed would mean better protein utilization and reduced nitrogen pollution in the environment. Because roasting of corn increased milk protein yield only as much as feed intake, these results suggested that corn roasting would not result in an economic or environmental advantage for dairy farmers.

Technical Abstract: A study was conducted to determine if feeding roasted corn as principal concentrate source, would improve production and nutrient utilization when supplemented to lactating cows fed one of 3 different alfalfa silages (AS). Forty-two lactating Holstein cows, including 6 fitted with ruminal cannulas, were blocked by days in milk and parity, and assigned to 2 cyclic change-over designs, with 3 x 2 factorial arrangements of treatments. Treatments were AS, ensiled in bag, bunker, or O2-limiting tower silo supplemented with ground shelled corn (GSC) or roasted GSC (RGSC). Silages were prepared from second cutting alfalfa, field-wilted an average of 24 h, and ensiled over 2 days. Production and N utilization were evaluated in 36 cows during four, 28-day periods and ruminal fermentation was evaluated with 6 cows during five 21-d periods. Experimental diets contained 40% AS, 15% corn silage and 35% of either GSC or RGSC on dry matter basis. Although chemical composition of the 3 AS was similar, feeding AS from the O2-limitied tower silo elicited positive production responses (P < 0.01). Yields of 3.5% FCM and fat were increased 1.7 kg/d and 150 g/d, and milk fat content was increased 0.3% when cows were fed diets based on AS from the O2-limiting silo compared with the other 2 AS. The responses in milk fat corresponded with an average increase in ADF digestibility of 300 g/d for cows fed AS from the O2-limiting tower silo. However, ruminal concentrations of lipogenic VFA were unchanged with AS source. Cows fed RGSC consumed 0.6 kg/d more DM and yielded 30 g/d more protein and 50 g/d more lactose than cows fed GSC diets (P = 0.02). There was no evidence of increased total tract digestibility of OM or starch, or reduced ruminal NH3 concentration, when feeding RGSC. Free AA increased, and isovalerate decreased in rumen fluid from cows fed RGSC diets (P < 0.01) suggesting an AA sparing effect with diets containing roasted corn. However, responses in production with roasted corn were mainly due to increased DMI, which increased the supply of energy and nutrients available for synthesis of milk and milk components.