Cover crop (CC) grazing can be a potential strategy to support livestock and crop production while enhancing soil ecosystem services, but research on this potential multi-functionality of CCs is limited. We assessed 3-yr cereal rye (Secale cereale L.) CC grazing impacts on soil compaction, structure, water infiltration, fertility, and crop yields on an on-farm irrigated strip-till continuous corn (Zea mays L.) silage experiment on a sandy loam with <1% slope in west-central Nebraska. Treatments were: (a) non-grazed CC, (b) grazed CC, and (c) no CC. Across the 3 yr, cattle grazed CCs at 5.9 AUM ha −1 with grazing occurring over a 4-mo period during winter and/or spring, depending on the year. We measured soil properties within 5 d after grazing ended in spring before tilling and planting corn. Cattle grazing resulted in a 92% decrease of CC biomass, compared with non-grazed CCs. Grazing did not affect soil penetration resistance (compaction parameter), bulk density, aggregate stability, pH, and concentration of organic matter and nutrients except in the 2nd yr where it reduced cumulative infiltration by 80% and increased penetration resistance from 1.23 to 1.72 MPa but such increase was below root growth thresholds (<2 MPa). Cover crop grazing had no negative effect on corn silage yields although data were variable. Overall, CC grazing for 3 yr had small and variable effects on soils and crop yields, indicating that it can be a management option to support livestock production but more long-term data from different tillage and cropping systems, and climates are needed to further understand CC grazing implications. 1 INTRODUCTION Cover crop (CC) grazing can be a potential strategy to support crop and livestock production, diversify agroecosystems, enhance soil ecosystem services, and improve over-Abbreviations: AUM, animal unit month; CC, cover crop. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Chamberlain, D. G., Thomas, P. C., Wilson, W., Newbold, J., Macdonald, J. C. (1985). The effects of carbohydrate supplements on ruminal concentrations of ammonia in animals given diets of grass silage. Journal of Agricultural Science, 104 (2), 331-340.A total of 15 rumen-cannulated sheep and four rumen-cannulated goats (Expt 3) were used in five latin square experiments designed to investigate the effects of carbohydrate supplements on ruminal ammonia concentration in animals given grass silage diets. In Expt 1 barley supplements were given at the same time, 1 h before or 2 h before a meal of silage. The treatments were designed to alter the synchronization between energy release from fermentation of barley and ammonia release from the degradation of silage N compounds. As compared with the unsupplemented control diet, barley supplements reduced (P < 0?05) rumen ammonia concentration and increased (P < 0?01) the number of total protozoa, but the time at which barley was given was without effect. In Expt 2 animals receiving silage or silage-barley diets were defaunated chemically. This treatment led to a 20?25 % reduction in rumen ammonia concentration. In Expt 3 supplements of maize starch, glucose and sucrose were compared. Mean ammonia concentrations were 231 mg/1 for the control unsupplemented diet and 205, 155 and 160 mg/1 (S.E. 21) for the starch, glucose and sucrose treatments. Corresponding numbers of protozoa were 7?7, 15?1, 6?1 and 6?3 x 10s/ml (S.E. 1?8). In Expt 4 the diets were unsupplemented silage or the same diet plus supplements of sucrose or xylose. Xylose reduced ammonia concentration more than sucrose, the values (mg/1) being 236 (control), 206 (sucrose) and 125 (xylose) (S.E. 19). There was no difference between the supplements in numbers of protozoa. Xylose induced a smaller reduction in pH, a higher (P < 0?05) proportion of acetate and a lower (P < 0?05) proportion of butyrate in rumen fluid than did sucrose. Effects of rumen pH were examined in Expt 5 where supplements of sucrose were given alone or together with NaHCO3. Rumen pH values were 6?38 for the control unsupplemented diet and 5?99, 6?28 and 6?55 (S.E. 0?06) for the diets supplemented with sucrose, sucrose plus 50 g NaHC03 and sucrose plus 100 g NaHCO3. Corresponding values for ruminal ammonia were 193, 151, 93 and 41 mg/1 (S.E. 10). Differences in VFA proportions between sucrose treatments were small and significant (P < 0?05) only for butyrate. It is concluded that there are important differences between carbohydrate sources in their effects on nitrogen metabolism in the rumen. Differences between starch and sugars appear to relate to the influence of the carbohydrates on the microbial population of the rumen, as was indicated by the differential effects of the carbohydrate sources on the number of total protozoa; differences between sugars appear to depend in part on the rates of sugar fermentation and the associated reduction in rumen pH.Peer reviewe

Phosphorus is an expensive nutrient to supplement, and excess may lead to manure P challenges. Therefore, minimizing dietary P to meet requirements is important. Two experiments were conducted to determine the P requirement of finishing cattle (Exp. 1) and to evaluate the effects of feeding different P concentrations on the quantity and route of P excretion (Exp. 2). In Exp. 1, 60 heifers (BW = 278 kg +/- 17 kg) were individually fed 1 of 5 dietary P concentrations (0.10, 0.17, 0.24, 0.31, or 0.38% P). Cattle performance, plasma P concentration, bone characteristics, and bone P concentration were used to determine the P requirement. Intake and ADG increased quadratically (P < 0.01) as dietary P increased. Plasma P in heifers receiving the 0.10% treatment was less (P < 0.01) than the other treatments and suggested that these heifers were experiencing a P deficiency. Total ash weight of the phalanx bones increased linearly (P < 0.01) as dietary P increased. In Exp. 2 using a 5 x 5 Latin square design, 5 different diets varying in P concentration (0.12, 0.27, 0.42, 0.30, and 0.36% P) were fed to steers to evaluate route and quantity of P excreted. Steers excreted little (1.78 g/d on average) P in the urine as a percentage of total P excretion. Steers on the 0.12% P diet excreted very little P in urine (0.50 g/d). Excretion of P was less (P < 0.05) for the cattle fed 0.12% P compared with all other treatments. Results from cattle performance, plasma P concentrations, and bone characteristics indicate that the heifers fed 0.10% P were experiencing a deficiency and the P requirement of finishing heifers is between 0.10 and 0.17% P. Dietary P concentrations of 0.10 to 0.17% P resulted in decreased P excretion. Supplementation of mineral P is unnecessary in grain-based feedlot diets because dietary P will greatly exceed the requirements (<0.17%).

One experiment was conducted to evaluate the influence of glycerin (GLY) on animal performance and health when used as a partial replacement for roughage in receiving diets. The second experiment was conducted using ruminally and duodenally cannulated steers in a 4 × 4 Latin square to determine the site of nutrient digestion and ruminal fermentation characteristics when GLY replaced roughage at 0%, 2.5%, 5%, and 10% of diet DM. In Exp. 1, steers (initial BW = 245 ± 2.3 kg) were fed treatment diets over a 42-d period that consisted of a control diet based on steam-flaked corn with GLY inclusion in replacement of dietary roughage at 0%, 5%, and 10% of diet DM. A linear reduction in DMI was observed as GLY increased (P = 0.01). Glycerin incorporation tended to improve G:F in a linear manner (P = 0.07); efficiency was improved 5.4% and 4.7% at 5% and 10% GLY. The number of animals receiving treatment for bovine respiratory disease did not differ among treatments. Furthermore, there were no differences among treatments for mortality or the frequency of steers that were seropositive for serum antibody titers to infectious bovine rhinotracheitis on d 28. In Exp. 2, apparent OM and apparent and true starch digestibility increased linearly (P < 0.05) as GLY concentration increased, whereas true OM digestibility responded in a quadratic (P < 0.01) manner. Bacterial OM and bacterial starch flow responded quadratically (P ≤ 0.02), and flow increased from 0% to 5% GLY inclusion and decreased thereafter. Feed OM flow responded quadratically (P ≤ 0.05), where it decreased from 0% to 2.5% GLY and increased from 2.5% to 10% GLY inclusion. Feed starch (P = 0.02) and total starch (P = 0.02) flow from the duodenum decreased linearly as the concentration of GLY increased in the diet. Bacterial N flow to the duodenum responded quadratically (P < 0.01); it increased with increasing GLY in the diet up to 5% and then decreased from 5% to 10%. The acetate to propionate (A:P) ratio in the ruminal fluid decreased (P < 0.05) as the concentration of GLY in the diet increased, which could have implications on improved G:F. The decrease in the A:P ratio as GLY increased in the diet, coupled with the linear decrease in DMI and improvement in G:F with GLY addition up to 5% of DM in place of roughage, implies that GLY is a viable dietary ingredient in growing and receiving diets.

Cattle (Bos taurus) grazing intensifies production of the dryland wheat (Triticum aestivum L.)–sorghum [Sorghum bicolor (L.) Moench]–fallow (WSF) rotation in the U.S. Southern High Plains. Stubble‐mulch (SM) tillage controls weeds and counteracts soil compaction. No‐till (NT) increases soil water at planting and dryland crop yields, but added grazing effects are unknown. Our objectives were to quantify dryland winter wheat and sorghum yield responses to grazing and tillage practices. At the USDA‐ARS Conservation and Production Research Laboratory, Bushland, TX, we established all WSF rotation phases in triplicate ungrazed and grazed paddocks beginning 1999 on a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) using SM tillage. During spring 2004, NT or SM tillage were superimposed within grazing main plots. Cattle gain, soil water after fallow, and crop yield were compared during 2005 to 2009 using a split‐plot randomized complete block design. Cattle, stocked at 1.8 Mg ha−1, grazed sorghum stover and growing wheat an average of 29 d for a mean gain of 147 kg ha−1 Soil water at planting was unaffected by grazing, but increased from 14 to 28 mm with NT. Although grazing seldom reduced yield of wheat or sorghum, NT in ungrazed plots increased crop yields sufficiently (0.96–2.6 Mg ha−1) in 2008 and 2009 to offset any value added by grazing. We conclude that cumulative grazing effects in NT plots reduced soil water storage and depressed yield. We recommend post‐wheat‐harvest SM tillage to disrupt soil compaction and restore grazed soil productivity.