Stage of maturity at harvest and mechanical processing affect the nutritive value of corn silage. The change in nutritive value of corn silage as maturity advances can be measured by animal digestion and macro in situ degradation studies among other methods. Predictive equations using climatic data, vitreousness of corn grain in corn silage, starch reactivity, gelatinization enthalpy, dry matter (DM) of corn grain in corn silage, and DM of corn silage can be used to estimate starch digestibility of corn silage. Whole plant corn silage can be mechanically processed either pre- or postensiling with a kernel processor mounted on a forage harvester, a recutter screen on a forage harvester, or a stationary roller mill. Mechanical processing of corn silage can improve ensiling characteristics, reduce DM losses during ensiling, and improve starch and fiber digestion as a result of fracturing the corn kernels and crushing and shearing the stover and cobs. Improvements in milk production have ranged from 0.2 to 2.0 kg/d when cows were fed mechanically processed corn silage. A consistent improvement in milk protein yield has also been observed when mechanically processed corn silage has been fed. With the advent of mechanical processors, alternative strategies are evident for corn silage management, such as a longer harvest window.

Experimentally inoculated sheep and cattle were used as models of natural ruminant infection to investigate the pattern of Escherichia coli O157:H7 shedding and gastrointestinal tract (GIT) location. Eighteen forage-fed cattle were orally inoculated with E. coli O157:H7, and fecal samples were cultured for the bacteria. Three distinct patterns of shedding were observed: 1 month, 1 week, and 2 months or more. Similar patterns were confirmed among 29 forage-fed sheep and four cannulated steers. To identify the GIT location of E. coli O157:H7, sheep were sacrificed at weekly intervals postinoculation and tissue and digesta cultures were taken from the rumen, abomasum, duodenum, lower ileum, cecum, ascending colon, descending colon, and rectum. E. coli O157:H7 was most prevalent in the lower GIT digesta, specifically the cecum, colon, and feces. The bacteria were only inconsistently cultured from tissue samples and only during the first week postinoculation. These results were supported in studies of four Angus steers with cannulae inserted into both the rumen and duodenum. After the steers were inoculated, ruminal, duodenal, and fecal samples were cultured periodically over the course of the infection. The predominant location of E. coli O157:H7 persistence was the lower GIT. E. coli O157:H7 was rarely cultured from the rumen or duodenum after the first week postinoculation, and this did not predict if animals went on to shed the bacteria for 1 week or 1 month. These findings suggest the colon as the site for E. coli O157:H7 persistence and proliferation in mature ruminant animals.For many years it has been known that healthy ruminants transiently harbor the human pathogen Escherichia coli O157:H7 in their gastrointestinal tract; however, the conditions that lead to its acquisition, persistence, and clearance from that site are not clearly understood (18,30). Elucidating the relationship between cattle and E. coli O157:H7 may impact the development of interventions to curb its presence in ruminants and thereby reduce the incidence of human infections with this pathogen.The hallmark of human disease with E. coli O157:H7 is a hemorrhagic colitis that is most often self-limiting (2, 18). However, among reported outbreaks, as many as 25% of infected individuals have been hospitalized, 6% have developed life-threatening sequelae, the hemolytic uremic syndrome, and 1% have died from their infection. For children infections are even more severe, with 5 to 10% progressing to hemolytic uremic syndrome and a 3 to 5% mortality rate (2, 6, 18). E. coli O157:H7 is transmitted by ingestion of contaminated bovine food products, contaminated drinking water or fruit juice, contact with contaminated recreation water or culture-positive animals, and in rare cases, human-to-human transmission via the fecal-oral route (2,3,18,24).Although healthy cattle (5, 9, 15, 21, 37), sheep (9, 26, 28), deer (16, 34), and goats (9, 32) have been shown to transiently harbor E. coli O157:H7 naturally, cattle are the main source of human infections ...

In situ and in vitro studies with a 3 x 2 x 5 factorial arrangement of treatments with an added untreated control evaluated three enzyme preparations, two levels of enzyme, and five moisture conditions of grass forage. Enzyme preparations predominantly contained cellulase and xylanase and will be designated as enzyme 1 (E1), enzyme 2 (E2), and a 50:50 combination of E1 and E2 (E1E2). The five moisture conditions included fresh, wilted, dried and rehydrated to fresh, dried and rehydrated to wilt, and dried grass. Addition of the high level of E1E2 to dried grass improved (P < .05) in vitro DM (43.5 vs 38.7%) and NDF (31.1 vs 26.0%) disappearance (48 h incubation) compared with the control treatment. Also, IVDMD was greater (P < .05) for the low level of E1 applied to wilted grass compared with the control. No other enzyme application improved in situ or in vitro disappearance of substrate over the control. In vivo responses of enzyme treatments found most likely to be effective from degradability studies were measured using four ruminally cannulated steers in a 4 x 4 Latin square experiment. Treatments examined were E1 applied to fresh forage, then dried; E1 applied to wilted forage, then dried; E1E2 applied to dry forage immediately before feeding (E-dry), and untreated forage (control). All forage treatments were harvested as dry hay. Total diet and hay DM intakes were greater (P < .05) for the E-dry than for the control diet. Rate of in situ NDF disappearance and total tract DM and NDF digestibility were greater (P < .05) for the E-dry than for the other treatments. Ruminal fluid ammonia N concentration, total VFA concentration, and pH were not altered (P > .10) by dietary treatment. Ruminal particulate passage rate was greater (P < .05) and ruminal retention time was shorter (P < .05) for the E-dry than for the control treatment. Data from this study suggest that addition of fibrolytic enzymes to grass hay before feeding has the potential to enhance intake and digestion.

In trial 1, 30 midlactation (213 d in milk) Holstein cows were randomly assigned to a control or enzyme treatment in a two-period crossover design and were fed a total mixed ration based on alfalfa hay and silage. Cows on the enzyme treatment received an enzyme solution containing cellulases and xylanases, which was sprayed on the forage component of the ration at a rate of 1.65 ml/kg of forage dry matter (DM) between 8 and 24 h prior to feeding. Cows consuming the forage treated with enzyme produced more milk (27.2 vs. 25.9 kg/d) and digested more DM per day than did cows fed the control forage. In trial 2, 40 early lactation Holstein cows were assigned to one of four treatments for 16 wk. Following a 2-wk covariate period, cows were assigned to 1) no enzyme treatment, 2) a low (1.25 ml/kg of forage DM) enzyme treatment, 3) a medium (2.5 ml/kg of forage DM) enzyme treatment, or 4) a high (5.0 ml/kg of forage DM) enzyme treatment. Enzymes were a 2:1 combination of cellulase and xylanase diluted in water and sprayed on a combination of alfalfa hay and silage and whole cottonseed immediately before mixing with a concentrate based on barley. Dry matter intakes were similar for cows on treatments 2, 3, and 4 and were greater than those for cows on treatment 1. Production of milk, 3.5% fat-corrected milk, and energy-corrected milk was greater for cows on treatment 3 than for cows on treatment 1. Fibrolytic enzymes applied to the forage portion of the rations prior to feeding improved lactational performance of early and midlactation cows.

A study was conducted to examine the method of delivery of a solution containing cellulases and xylanases on the digestion of a forage-based diet. Five ruminally cannulated beef steers (536 kg BW) were randomly assigned to a control (CON) or one of four enzyme treatments in a 5 x 5 Latin square experiment. Steers were fed a 70:30 (DM basis) grass hay:barley diet. Enzyme-treated rations contained a solution of fibrolytic enzymes at the rate of 1.65 mL/kg of forage DM. Enzyme application treatments were 1) enzyme to forage 24 h before feeding (F-24), 2) enzyme to forage 0 h before feeding (F-0), 3) enzyme to barley 0 h before feeding (B-0), and 4) enzyme infused ruminally 2 h after feeding (RI). Dry matter and NDF intakes were not different (P > .10) across treatments. Ruminal pH was lower and total VFA concentration at 16 h after-feeding was greater (P < .10) for steers fed enzyme treatments compared with CON. Rate of NDF disappearance was greater (P < .05) for enzyme-treated than for untreated grass substrate. Ruminal infusion of enzymes compared with F-24 and F-0 produced lower disappearance of DM at 8 and 32 h (P < .10), NDF at 32 h (P < .10), and DM and NDF at 96 h (P < .05). Rate of DM disappearance of enzyme-treated grass hay was greater (P < .10) for steers fed B-0 than for those fed F-24 and F-0 and for CON than for F-24 and F-0. Total tract digestibility of DM, NDF, and ADF was greater (P < .10) for F-24 and F-0 than for CON. Forage transit time was shorter (P < .10) for B-0 than for F-24 and F-0; however, all other contrasts for particulate passage did not differ (P > .10). Results from this study indicate that direct application of enzymes to forages is capable of improving forage digestion.