Effects of Supplementing High or Low Quality Forages with Corn or Corn Processing Co-Products Upon Digestibility of Dry Matter and Energy by Steers

A digestibility trial, utilizing eight crossbred steers weighing initially 741 lbs. was conducted in an 8 x 8 Latin square design. High-fiber corn by-products were compared with corn as energy sources when fed in mixed diets with either lowor high-quality forage. Ground, dry corn stover and ground alfalfa hay were both fed alone or with corn grain, dried corn gluten feed (CGF), and dried corn distillers grains plus solubles (DDG) in a 1:1 ratio (dry basis). Total tract dry matter digestibility (DMD) was increased for both forages when fed with concentrates. Total tract DMD was similar in stover-based and alfalfa-based diets fed with CGF and DDG. However, stover+corn was lower in DMD than either stover+CGF and stover+DDG. Conversely, alfalfa+corn was higher in DMD than alfalfa+CGF or alfalfa+DDG. Feeding stover with corn tended to decrease digestibility of neutral detergent fiber (NDF), while feeding stover with CGF or DDG increased NDFD. There was no effect upon NDF digestion of alfalfa-based diets when fed with any of the concentrates. Feeding either forage with a concentrate increased digestible energy (DE). Stover+CGF and stover+DDG were similar in DE and were both higher in DE than stover+corn. Alfalfa+DDG tended to be higher than alfalfa+CGF and was similar to alfalfa+corn in DE. Alfalfa+CGF was lower in DE compared with alfalfa+corn. Results are interpreted to indicate that stover is more susceptible to negative feed interactions caused by corn grain than is alfalfa. Additionally, highfiber corn co-products fed with stover resulted in a positive associative effect but essentially had no associative effect when fed with alfalfa.

The Effects of High-Oil Corn or Typical Corn with or without Supplemental Fat on Diet Digestibility in Finishing Steers

Two 3 x 3 latin squares were utilized in an 84-day digestion trial with ruminally- and duodenallycannulated steers. Diets consisted of 73 to 78% whole corn grain, 12.3% corn silage and 2.0% N, with treatment differences being high-oil corn- (HOC), isogenetic typical-corn- (TC), or isogenetic typical-corn + fat- (TC+F) based diets. The HOC and TC+F diets were formulated to provide the same ether extract (EE) content. All diets were fed at 90% of ad libitum intake. Chromic oxide was used as a digestibility marker. Total tract dry matter (DM) (P=.08), organic matter (OM) (P=.08) and nitrogen (N) (P=.06) digestibilities tended to be greater for TC than HOC diets, whereas starch neutral detergent fiber (NDF), acid detergent fiber (ADF), and ether extract digestibilities were similar (P>.10). There were no differences (P>.10) in total tract dry matter, organic matter, starch, NDF, ADF, ether extract, or nitrogen digestibilities between TC+F and HOC diets or TC and TC+F diets. Ruminal digestion of dry matter, organic matter, starch, NDF, ADF, and feed nitrogen was similar (P>.10) among treatments. Microbial-nitrogen flow and efficiencies were also similar (P>.10) among treatments. Results indicate finishing steer diets composed of primarily HOC are equally or less digestible than similar diets composed of TC, and adding fat to TC diets did not affect the digestibility of the diet when fed to finishing steers.

An Evaluation of Effective Fiber in Beef Feedlot Finishing Diets

A study was designed to collect a database of Iowa feedlot rations for determination of effective neutral detergent fiber (NDF) in complete diets from fiber analysis and particle size determination of individual feed ingredients and compare this with particle size determination of mixed wet rations. Seventy-one beef finishing total mixed rations were collected by ISU Extension Beef Field Specialists across Iowa. Producers were asked to complete a form assessing the acidosis risk associated with each ration. The average NDF of these diets was 25.9%. Of the total mixed rations 1.33 % remained in the top tray (>.75 in.), 47.27 % remained in the middle tray (>.31 in.), and 50.88 % was smaller than the .31 in screen. The effective NDF (eNDF) calculated from the eNDF of the ingredients averaged 10.56%. Estimated eNDF from total diet NDF and the percentage of the total diet in the top and middle trays averaged 12.47%. The calculated eNDF from non-grain sources alone averaged 3.6%. The percentage of digestive deads was weakly related to the percentage of the ration in the bottom tray (r=.19), the percentage in the top tray (r=- .46) and the effective NDF of the ration (r=-.23). The percentage of bloat was related to the total NDF of the diet (r=.28) and the effective fiber from non-grain sources (r=-.23). The number of off-feed incidences was related to the dry matter of the ration (r=.38), the apparent eNDF (r=-.28) and the percentage of ration in the bottom tray (r=.24). This study confirms that there is some relationship between effective NDF of the diet, effective NDF from non-grain sources or diet particle size; and acidosis indicators. These relationships are weak, however, indicating that other factors such as feedbunk management, feed processing, feed presentation and feed mixing likely also play a role in the incidence of acidosis in feedlot cattle.

Effects of Chemical Composition on Forage Intake of Heifers Fed Hays of Different Species

Alfalfa, smooth bromegrass, and big bluestem hays harvested at two maturities differing by four weeks were fed at mature-to-immature hay ratios of 1:0, 2:1, 1:2, and 0:1 to yearling heifers in an experiment with a three 4 x 4 Latin square design with 14 day periods. Concentrations of in vitro digestible dry matter and crude protein were greater and concentrations of neutral detergent fiber, acid detergent fiber, and indigestible neutral detergent fiber (determined by either a manual method with a 96 hour incubation or an automated method with a 48 hour incubation) were less in alfalfa hay than in the two grass hays and in smooth bromegrass hay than in big bluestem hay. Concentrations of in vitro digestible dry matter and crude protein decreased whereas those of neutral detergent fiber, acid detergent fiber and indigestible neutral detergent fiber increased with increasing forage maturity. Consumptions of dry matter, digestible dry matter, in vitro digestible dry matter, and crude protein were greater for heifers fed alfalfa hay diets than those fed the two grasses. Consumptions of total neutral detergent fiber and indigestible neutral detergent fiber, determined by the automated method with a 48 hour incubation, were greater by heifers fed diets containing big bluestem than those fed alfalfa or smooth bromegrass diets. Consumptions of acid detergent fiber and indigestible neutral detergent fiber, determined by a manual method with a 96 hour incubation, were greater for heifers fed alfalfa or big bluestem hay diets than those of heifers fed smooth bromegrass diets. Consumption of dry matter, in vivo or in vitro digestible dry matter, crude protein, neutral detergent fiber, acid detergent fiber and automated indigestible neutral detergent fiber decreased as the mature-to-immature hay ratio decreased. Diet digestibility was not affected by forage species, but increased as the mature-toimmature hay ratio decreased. Fecal excretion of dry matter and neutral detergent fiber did not differ between forage species or mature-to-immature hay ratios. Forage dry matter intake expressed as a percentage of body weight was significantly related to the concentrations of in vitro digestible dry matter (r2=.14), crude protein (r2=.17), neutral detergent fiber (r2=.20), and manual indigestible neutral detergent fiber (r2=.18) of the hays and the concentration of digestible dry matter of the diets (r2=.43).

Nutritive Value of the Crop Residues from bt-Corn Hybrids and Their Effects on Performance of Grazing Beef Cows

One non bt-corn hybrid (Pioneer 3489) and three btcorn hyrids (Pioneer 34RO7, Novartis NX6236, and Novartis N64-Z4) were planted in replicated 7.1-acre fields. After grain harvest, fields were stocked with 3 mature cows in midgestation to be strip-grazed as four paddocks over 126 days. Six similar cows were allotted to replicated drylots. All cows were fed hay as necessary to maintain a condition score of 5 on a 9-point scale. Cows were condition-scored biweekly and weighed monthly. Forage yield and weathering losses were determined by sampling one 4-m2 location per grazed or ungrazed paddock in each field with a minimum total of 2 locations of grazed or ungrazed forage per field. To measure forage selection during grazing, samples of grazed forage were collected from the rumen of one fistulated steer that grazed for 2 hours after ruminal evacuation. Non-bt-corn hybrids had greater (P<.05) infestation of corn borers in the upper stalk, lower stalk and ear shank than bt-corn hybrids. However, there were no differences in grain yields or dropped grain between hybrids. Crop residue dry matter, organic matter and in vitro digestible dry matter yields at the initiation of grazing did not differ between corn hybrids. Dry matter, organic matter and in vitro digestible dry matter losses tended (P<.10) to be greater from the NX6236 and N64-Z4 hybrids than from the 3489 and 34RO7 hybrids and were greater (P<.05) from grazed than non-grazed areas of the fields. At the initiation of grazing, dry matter concentrations of the crop residues from the NX6236 and N64-Z4 hybrids tended to be lower than those from the 3489 and 34RO7 hybrids. Crop residues from the NX6236 and N64-74 hybrids had lower concentrations of acid detergent fiber (P<.05) and acid detergent lignin (P=.07) and higher concentrations of in vitro digestible organic matter than the 3489 and 34RO7 hybrids. Over the grazing season, corn hybrid did not affect mean rates of change in forage composition. The concentration of in vitro digestible organic matter in forage selected by steers after two weeks of grazing did not differ. However, steers grazing corn crop residues consumed forage with higher (P<.05) concentrations of neutral detergent fiber, acid detergent fiber, and acid detergent insoluble nitrogen than steers fed hay. The acid detergent fiber concentration of forage selected by steers grazing the 3489 and N64-Z4 hybrids was lower (P < .05) than concentrations from the 34RO7 and NX6236 hybrids. In order to maintain similar body condition score changes, cows grazing crop residues from the 3489, 34RO7, NX6236, and N64-Z4 hybrids required 650, 628, 625, and 541 kg hay DM/cow compared with a hay requirement of 1447 kg hay DM/cow for cows maintained in a drylot.

The Effect of Heat Treatment of Forages on Degradation Kinetics and Escape Protein Concentration

An in situ study was conducted to evaluate the effects of heat treatments on the degradation kinetics and escape protein concentrations of forages (alfalfa and berseem clover). Alfalfa collected at 4 and 7 weeks post-harvest and berseem clover collected at 5 and 7 weeks postharvest were freeze-dried and then heated to 100, 125, and 150o C for 2 hours. Heat treatment effects were determined by placing two bags of sample (for each treatment, maturity, and forage species for a given incubation times) into the rumen of one fistulated steer fed alfalfa hay. Bags were incubated for periods of 0 to 48 hours. Increasing levels of heat treatments of forages increased concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent insoluble nitrogen (ADIN) and non-degradable protein (NDP), potentially degradable protein proportion (PDP), and protein escaping rumen degradation (PEP) while decreasing water soluble protein (WSP) and the rates of crude protein (CP), except immature berseem clover and cell wall (CW) degradation. PEP was greater and rate of CP degradation was lower at 100 and 150o C compared to 125o C in immature berseem clover.

The Effect of Maturity and Frost Killing of Forages on Degradation Kinetics and Escape Protein Concentration

Two consecutive in situ studies were conducted to determine the effects of maturity and frost killing of forages (alfalfa and berseem clover) on degradation kinetics and escape protein concentrations. Four maturities (3, 5, 7, and 9 weeks after second harvest) of forages collected from three locations were used to determine the effects of maturity. Four weeks after a killing frost (-2o C), berseem clover was harvested from the same locations previously sampled. To evaluate maturity, 336 DacronÒ bags containing all maturities of either alfalfa or berseem clover were placed into the rumen of two fistulated steers fed alfalfa-grass hay. Frost killing effects of berseem clover were compared with maturecut berseem clover by placing DacronÒ bags into the rumen of one fistulated steer fed alfalfa hay. Bags were incubated for periods of 0 to 48 hours. With increasing maturity, the proportion of non-degradable protein (NDP) and the rate of crude protein (CP) degradation increased in both forages. While the rate of neutral detergent fiber (NDF) degradation and potentially degradable protein proportion (PDP) increased with increasing maturity in alfalfa, the rate of NDF degradation and PDP proportion decreased and proportion of water soluble protein (WSP) increased in berseem clover. The proportion of protein escaping rumen degradation (PEP) was greater in berseem clover than alfalfa, but was not affected by maturity. Frost killing of mature berseem clover decreased WSP proportion and increased PDP proportion compared to mature berseem clover harvested live. Even though ADIN concentration was higher for frost-killed berseem clover, PEP and total escape protein concentration (CEP) was also higher for frostkilled berseem clover than mature berseem clover harvested live, due to decreases in the rate of ruminal N degradation with frost-killing.

Changes in Chemical Composition and Digestion Kinetics of Stockpiled Kura Clover in Late Fall

Stockpiled kura clover samples harvested on three different winter dates were used to determine changes in chemical composition and N digestion kinetics. Kura clover was harvested from four different plots at 14 d intervals and analyzed for neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), acid detergent insoluble nitrogen (ADIN), and in vitro digestible dry matter (IVDMD), and in situ digestion kinetics of N. Crude protein concentrations decreased, but ADIN concentrations increased with later date of harvest. Digestible N pool-size and the rate of digestion was the lowest in third-harvest kura clover. Although the proportion of protein that is soluble or nondigestible increased, proportion of protein that is potentially digestible decreased with maturity.