Escape protein for beef cows: II. Source and level in ammoniated wheat straw-corn silage diets

Two experiments, using Angus x Hereford spring-calving beef cows in mid- or late lactation nursing Simmental-sired calves, were conducted to evaluate the relative value of a corn gluten meal-blood meal mixture (CGM-BM; 50% of supplemental protein from each source). In Exp. 1 (78 d), cows in late lactation were assigned to one of three treatments: control at 8.2% CP (C), soybean meal at 10.4% CP (SBM), or CGM-BM at 10.3% CP. Diets were calculated to be isocaloric at 55% TDN. In Exp. 2 (65 d), cows in mid-lactation were assigned to four treatments: urea, SBM, low CGM-BM (LM), and high CGM-BM (HM). Diets in Exp. 2 were isonitrogenous (9.5% CP) and isocaloric (55% TDN). Diets in both experiments were based on ammoniated wheat straw and corn silage. Weight gains of cows and cow-calf pairs were greater (P less than .06) when protein was supplemented in Exp. 1. Gains were lower for cows fed urea (P less than .03) in Exp. 2 but were similar when cows were supplemented with SBM vs either the low or the high level of CGM-BM. Performance of calves did not differ among dietary treatments.     

Productivity of cow-calf pairs grazing tall fescue pastures infected with either the wild-type endophyte or a nonergot alkaloid-producing endophyte strain, AR542

The nonergot alkaloid-producing endo-phyte, AR542, has been shown to improve the persistence and yield of tall fescue pastures without causing the animal disorders commonly associated with tall fescue toxicosis. A 3-yr grazing study was conducted to compare effects of AR542-infected tall fescue pastures with wild type endophyte-infected (E+) tall fescue pastures on cow-calf performance. Replicated 7.3-ha pastures of each treatment were grazed by cow-calf pairs (16 pairs per pasture replication) each year from March to weaning in September. The cows were exposed to breeding on their respective pasture treatments from April 1 through June 15. The treatment groups were compared for reproductive performance, ADG, BCS, calf growth rate, and weaning weight. Blood samples were also collected for serum prolactin (PRL) analysis. There were no significant differences in calving rate (P = 0.98) or calving interval (P = 0.62) between pasture treatments. Cows that grazed the AR542 pastures subsequently gave birth to calves that were heavier (P < 0.05) than calves from cows that had grazed the E+ pastures. Cows grazing the AR542 pastures had higher (P < 0.05) BCS at the end of the grazing period, and had higher ADG during the grazing period. Calves raised on the AR542 pasture had higher (P < 0.05) ADG and weaning weights than calves of the same sex raised on the E+ pastures. Serum PRL concentrations were decreased (P < 0.05) in both cows and calves on the E+ pastures compared with serum PRL concentrations in cows and calves grazing the AR542 pastures. The results indicate that grazing tall fescue pastures infected with the AR542 endophyte may give significant advantages in cow-calf growth rates and BCS over grazing E+ pastures. However, there did not seem to be any benefit in reproductive performance in this trial. There was a small, but significant increase in birth weight in cows grazing AR542 pasture.     

Effects of season and inclusion of corn distillers dried grains with solubles in creep feed on intake, microbial protein synthesis and efficiency, ruminal fermentation, digestion, and performance of nursing calves grazing native range in southeastern North Dakota

Nine ruminally and duodenally cannulated (145 +/- 21 kg of initial BW; Exp. 1) and sixteen intact (181 +/- 36 kg of initial BW; Exp. 2), commercial, Angus, nursing, steer calves were used to evaluate the effects of advancing season and corn distillers dried grains with solubles in creep feed on intake, digestion, microbial efficiency, ruminal fermentation, and performance while grazing native rangeland. Calves were assigned to 1 of 2 treatments: a supplement containing 41% soybean meal, 26.25% wheat middlings, 26.25% soybean hulls, 5% molasses, and 1.5% limestone (control) or a supplement containing 50% corn distillers dried grains with solubles, 14.25% wheat middlings, 14.25% soybean hulls, 14% soybean meal, 5% molasses, and 1.5% limestone (CDDGS). Calves were offered supplement individually (0.45% of BW) once daily. Three 15-d collection periods occurred in June, July, and August. In Exp. 1, there were no differences in OM intake, or OM, N, NDF, or ADF digestion between control calves and those fed CDDGS. Forage and total OM intake increased (P < 0.03), whereas OM digestion decreased (P < 0.01), with advancing season. Duodenal microbial N flow (g/d) was not affected (P = 0.50) by treatment and increased linearly (P = 0.003) as season progressed. Calves consuming CDDGS had decreased (P < 0.01) ruminal acetate:propionate ratio, increased (P < 0.01) molar proportion of butyrate, and decreased (P < 0.001) molar proportions of isobutyrate and isovalerate. In Exp. 2, supplement OM intake (% of BW) was less for CDDGS compared with control calves, but there were no differences in performance or subsequent carcass composition between treatments. Inclusion of 50% corn distillers dried grains with solubles in a creep supplement for nursing calves produced similar results compared with a control creep feed based on soybean meal, soybean hulls, and wheat middlings.     

Influence of Urea Alone or Combined with Fish Solubles,Fish Meal,or Feather Meal in Liquid Supplement with and Without L-Carnitine on Performance and Ruminal and Metabolic Parameters of Weanling Calves

Using growing calves (n = 368) grazing mature forage in three 84-d experiments, one objective was to compare the effects of feeding molasses-based liquid supplements containing urea (U) alone or combined with fish solubles (FS), fish meal (FM), or feather meal (FE) on performance, and blood metabolites. Another objective was to evaluate the effects on these criteria of adding carnitine to these supplements to provide 1 g·h⁻¹·d⁻¹ L-carnitine. Including FM or FE in the mixture improved (P<0.05) supplement consumption in two experiments and improved growth rate in all experiments. Carnitine improved the growth rate when U was the only protein source, but reduced growth rate when FM was included in the liquid supplement (P<0.05). During the growth phase, plasma ammonia N (PAN) was higher (P<0.05) when U was the only protein source as compared with FM or FE. Carnitine did not influence these metabolic parameters. During the metabolic phase of each experiment, calves similar to those used in the growth phase were dosed via stomach tube with 3 g liquid supplement/kg BW. Ruminal and blood samples were collected at 0, 0.5, 1, 2, and 4 h after dosing. Ruminal ammonia N, PAN, and plasma urea N (PUN) concentrations were higher (P<0.05) when calves were dosed with U or FS supplement than when dosed with FM or FE supplements. Calves dosed with liquid supplement containing carnitine had lower (P<0.05) concentrations of ruminal ammonia N and PAN. Carnitine reduced (P<0.05) PUN in one experiment and increased (P<0.05) PUN in another. Branched-chain volatile fatty acids were increased (P<0.05) by dosing with FS or FM supplements. Including ruminally undegradable protein sources (FM or FE) in liquid supplement improved intake and performance and was related to reduced ruminal ammonia N, PAN, and PUN. Carnitine fed in liquid supplement also reduced ruminal ammonia N and PAN concentrations.     

Winter-annual pasture as a supplement for beef cows

In each of two experiments, 120 pregnant beef cows were stratified by body condition score, BW, breed, and age, randomly divided into six groups of 20, and assigned to one of six 5.1-ha bermudagrass (Cynodon dactylon [L.] Pers.) pastures (two replicates/ treatment) in early January to evaluate the use of winter-annual pasture as a supplement. All cows in Exp. 1 and 2 had ad libitum access to bermudagrass/dallisgrass (Paspalum dilatatum Poir.) hay plus three treatments: 1) a concentrate-based supplement fed 3 d/wk, 2) limit grazing on winter-annual pasture 2 d/wk (7 hr/ d; 0.04 ha x cow(-1) x grazing d(-1)), or 3) limit grazing on winter-annual pasture 3 d/wk (7 hr/d; 0.04 ha x cow(-1) x grazing d(-1)) sod-seeded into a portion of the pasture until mid-May. The seeded portion of pastures in Exp. 1 was planted with a mixture of wheat (Triticum aestivum L.) and rye (Secale cereale L.), but annual ryegrass (Lolium multiflorum Lam.) was added to the seed mixture in Exp. 2. In mid-May, cows were blocked by treatment and the previous sorting factors, randomly assigned to six new groups of 20, and placed on the six perennial pastures until calves were weaned. Groups of cows were exposed to a bull for 60 d beginning in mid-May. In Exp. 1 and 2, limit-grazing winter-annual pasture compared to the concentrate-based supplement or limit grazing 2 vs 3 d/wk did not affect (P > 0.15) cow BW. In Exp. 1, cows limit grazed on winter-annual pasture had a lower (P = 0.05) body condition score than cows fed the concentrate-based supplement in the early spring. However, in Exp. 2, cows limit grazed on winter-annual pasture had higher (P < or = 0.07) body condition score than cows fed the concentrate-based supplement. The conception rate of cows in Exp. 1 and 2 did not differ (P > 0.22) between cows fed concentrate-based supplements and cows limit grazed on winter-annual pasture. In Exp. 2, cows limit grazed 2 d/wk tended to have a greater (P = 0.10) conception rate than cows limit grazed 3 d/wk. In Exp. 1 and 2, birth weight, total gain, BW, and ADG of calves were not affected (P > 0.15) by treatment. We conclude that wheat and rye pasture is a marginal supplement for lactating beef cows. However, cows limit grazed 2 d/wk on winter-annual pasture of wheat, rye, and annual ryegrass as a supplement maintained BW and body condition score as well as cows fed the concentrate-based supplement. But, grazing pasture 3 vs 2 d/wk did not seem to affect performance of cows.     

Dried poultry waste for cows grazing low-quality winter forage

Two trials conducted in 1996-97 measured BW and body condition score changes of cows fed different sources of degradable intake protein, including dried poultry waste and soybean meal, while grazing low-quality winter forages. In Trial 1, 60 spring-calving cows (5 yr; 555 kg) were used in an individual supplementation trial. Cows were gathered three times a week, sorted into individual pens, and fed their respective supplement. Cows grazed dormant native Sandhills winter range (common pasture) and were assigned to one of six supplemental treatments: 1) no supplement, 2) urea, 3) 22% dried poultry waste + urea, 4) soybean meal, 5) 22% dried poultry waste + soybean meal, or 6) 44% dried poultry waste. All supplements were based on wheat middlings and soybean hulls and were formulated to contain 44% CP. Thirty-six cows were selected randomly (six per treatment) for a 5-d measurement of forage intake from December 16 through December 20, 1996. Cows receiving supplements gained more weight (P < 0.001) and maintained greater body condition (P < 0.001) than unsupplemented cows. Cows receiving urea gained less (P < 0.10) than cows receiving a source of natural protein, but body condition remained similar. No differences were found in daily forage or total organic matter intake (P > 0.10). In Trial 2, cows grazed corn residues. Forty-eight spring-calving cows were group-fed supplements in one of six 4-ha paddocks. Cows received supplements containing either soybean meal or dried poultry waste that were the same as the soybean meal and 44% dried poultry waste supplements fed in Trial 1; gains were not different (P > 0.10). Under the economic conditions that existed at the time of these experiments, the supplement containing dried poultry waste resulted in a savings of $.04 per cow per day and a total savings of $3.20 per cow over an 80-d period. Feeding a supplement containing dried poultry waste resulted in performance similar to that when feeding a more conventional supplement containing soybean meal.     

Value of a molasses mixture containing natural protein as a supplement to brood cows offered low-quality forages

In a 4-yr study, molasses (M; 6% CP), molasses-urea (MU; 17.5% CP; 92% molasses, 4% urea and 4% water) and molasses-cottonseed meal-urea (MCSM; 17.5% CP; 73% molasses, 25% cottonseed meal, 1% urea and 1% water) were compared as winter supplements for Braford cows (514 matings) consuming low-quality forage. Cows were fed 1.35, 1.50 and 1.27 kg.head-1.d-1 of the respective supplements for 127 d beginning in December. Cows were wintered on bahiagrass pasture (avg 8% CP) and stargrass hay (avg 5% CP). Quantity of hay offered averaged 7.6 kg.cow-1.d-1 over 109 d. Cows were exposed to bulls for 90 d beginning on March 1. Supplementation treatment did not affect cow live weight, live weight change or condition score (P greater than .05). However, pregnancy rate was higher (P less than .05) for cows fed MCSM (79.0%) than for cows fed M (67.8%). The pregnancy rate of cows fed MU (76.3%) was intermediate to, but not different (P greater than .05) from, that of cows fed either M or MCSM. Supplementation treatment did not affect calf performance as measured by birth weight, survival rate or weaning weight (P greater than .05). However, calves from cows fed MCSM were 6 d older (P less than .05) at weaning than calves from cows fed M. For 3-yr-old cows, pregnancy rate was considerably higher (P less than .05) for cows fed MCSM (69.6%) than for cows fed M (37.5%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of an early and normal weaning management system on cow and calf performance while grazing endophyte-infected tall fescue pastures

A 3-yr study used 16 cows and their spring-born calves (yr 1) and 48 first-calf heifers (yr 2, n = 24; yr 3, n = 24) and their spring-born calves in a completely randomized design. All cows and heifers were Angus x Beefmaster, and calves were sired by Angus bulls. Cow-calf pairs were assigned randomly to one of two management systems: 1) an early-weaning system, in which steer and heifer calves were weaned at 108 d of age and fed a postweaning growing diet (EW), or 2) a normal weaning system, in which calves were weaned at 205 d without supplementation (NW). Before early weaning and within each management system, calves and their dams were maintained in two 1.4-ha, endophyte-infected tall fescue pastures for 35 d (yr 1) or 14 d (yr 2 and 3). Early-weaned calves and cow-calf pairs were then randomly allotted to 1.4-ha, endophyte-infected tall fescue pastures with two (yr 1) or three (yr 2 and 3) calves or cow-calf pairs per pasture (four pastures per management system). Cow weights and BCS changes and calf gains were measured from early to normal weaning. Dietary intakes and nutrient digestibilities by EW and NW calves were determined during two periods of yr 1 and three periods of yr 2 and 3. Total gains and BCS changes were greater (P < 0.01) for cows that produced EW calves in all years. Calf ADG from early to normal weaning did not differ (P = 0.32). Similar to ADG, BW of calves at normal weaning were not different (P = 0.11). Forage intake was greater (P < 0.01) by NW calves during Periods 2 and 3 of yr 1 and Periods 1 and 2 of yr 2 and 3; however, total DM and CP intakes were greater (P < 0.01) for EW calves in Periods 2 and 3 of each year. Intakes of NDF tended (P = 0.11) to be greater by EW calves across all years. Estimates of CP and NDF digestibilities were higher (P < 0.01) for EW calves during yr 1 and 2; however, all components of the diet consumed by NW calves in yr 3 were more digestible (P < 0.05) than those consumed by EW calves. These results show the condition of cows with EW calves was improved by early weaning and gains by calves weaned at 108 d to pasture plus a commercial grower diet were comparable to those by calves continuing to nurse dams until weaned at 205 d.     

Programmed Feeding for Maintaining Gestating Beef Cows in the Southeastern United States

To evaluate programmed feeding of beef cows fed high concentrate diets as an alternative to hay, 160 spring calving cows (average BW = 510 ± 11 kg) were stratified by age, body condition score (BCS), and BW. The cows were randomly distributed into 10 drought-stricken pastures (16 cows per pasture) on September 11, 1998. Cows on eight pastures were fed one of four diets (two pastures per diet) formulated with corn or corn gluten feed (CGF) and 20% cottonseed hulls (CSH) or rice hulls (RH) for 87 d and compared with cows on two pastures that were allowed free-choice hay plus a supplement. Diets were fed in amounts to meet requirements for NE_m and had similar metabolizable protein yields (corn and CSH, 1.8, 17; corn and RH, 2.0, 14; CGF and CSH, 1.5, 23; and CGF and RH, 1.7, 21 NE_m/kg and CP percentage, respectively). Data were analyzed in a completely random design by ANOVA; pasture was the experimental unit. Programmed feeding decreased (P<0.08) BW compared with hay diets. By d 87, cows fed RH diets weighed less (P<0.05) than did cows fed CSH diets, and cows fed corn diets weighed less (P<0.05) than did cows fed CGF diets. Body condition score did not differ (P>0.20) among treatments over the feeding period. The cows fed hay plus supplement cost approximately $1.03/d, but the cost of the program-fed cows averaged $0.54/d. After cows were returned to forage-based diets, no differences (P>0.25) were detected among treatments in BW, BCS, calving date, or calf performance. Programmed feeding of high concentrate diets to gestating cows during forage shortages is a viable alternative to feeding hay. Also, when grain prices are favorable, feed costs to maintain gestating cows are lower with grain than with hay plus supplement.     

Evaluation of hay-type and grazing-tolerant alfalfa cultivars in season-long or complementary rotational stocking systems for beef cows

Alfalfa (Medicago sativa L.) persistence and forage and cow-calf production were evaluated on pastures containing smooth bromegrass with or without grazing-tolerant or hay-type alfalfa cultivars rotationally stocked in either a season-long or complementary system. In 1997, six 2.02-ha pastures were seeded with smooth bromegrass, a mixture of a grazing-tolerant alfalfa (Amerigraze variety) and smooth brome-grass, or a mixture of a hay-type alfalfa (Affinity variety) and smooth bromegrass to be used in season-long stocking systems. Four 2.02-ha pastures were seeded with smooth bromegrass on 1.21 ha of each pasture, and mixtures of either the grazing-tolerant or hay-type alfalfa cultivars and smooth bromegrass on the 0.81 ha of each pasture to be used in complementary stocking systems. All 10 pastures were divided into 10 paddocks and rotationally strip-stocked at 1.98 cow-calf units/ha with crossbred cows and calves for 120 and 141 d starting May 18, 1998 (yr 1), and May 6, 1999 (yr 2), respectively. Each year, first harvest forage was harvested as hay from 40% of all 10 pastures, this being the portions of the pasture seeded with the alfalfa-smooth brome-grass mixtures for pastures with the complementary stocking systems. In yr 1 and 2, the remaining 60% of each pasture was grazed for the first 44 and 54 d, and 100% of each pasture was grazed on d 45 to 120 and d 55 to 141, respectively. Proportions of alfalfa in the live dry matter of pastures seeded with the grazing-tolerant and hay-type alfalfa cultivars decreased by 70 and 55% in paddocks stocked season-long and by 60 and 42% in paddocks used for complementary stocking (alfalfa cultivar, P < 0.05; stocking system, P < 0.05) in yr 1, but decreased by 72% across cultivars and stocking systems in yr 2. Total (P < 0.08) forage masses in September of yr 1 and in August of yr 2 were greater in pastures in which alfalfa paddocks were stocked season-long than in those with complementary alfalfa stocking. Grazing of alfalfa in grass mixtures increased calf and total cow/calf weight gains in comparison with grazing of smooth bromegrass, but alfalfa persistence, measured as a proportion of the live dry matter, was not affected by alfalfa cultivar.     

A comparison of native tallgrass prairie and plains bluestem forage systems for cow-calf production in the southern great plains

The objective of this study was to compare an introduced warm-season perennial grass (plains bluestem, Bothriochloa ischaemum) to native tallgrass prairie for cow-calf production. Three systems were used, two based on tallgrass prairie with two different forms of protein supplementation and one based on plains bluestem as the primary forage. The systems were as follows: 1) native tallgrass prairie with pelleted oilseed meal as the winter protein supplement (native-control); 2) native tallgrass prairie with limited access to wheat pasture as the winter protein supplement (native-wheat); and 3) plains bluestem with limited access to wheat pasture as the protein supplement (bluestem-wheat). Oilseed meal protein supplements were fed twice weekly. Cows grazing wheat pasture were allowed 6 h of grazing twice weekly. Ninety-nine cows per year were used over the 3-yr study. Cows were sired by either Charolais, Gelbvieh, Angus, or Hereford bulls out of commercial Angus-Hereford dams. Calves were sired by Simmental bulls. Calving and weaning rate increased over time but did not differ among systems or breed types. System did not influence the size or body condition score of cows or the performance of calves, but changes in the weight and condition scores of cows were greater on either native system than on the bluestem-wheat system. Cows from Charolais and Gelbvieh bulls were taller (P < 0.05), and heavier (P < 0.05), and weaned heavier (P < 0.05) calves than cows from Angus or Hereford bulls. The weight of cows on the bluestem-wheat system tended to decrease over time, whereas cows grazing on the native systems tended to gain weight over time. The native-control system was the most profitable system based on cow production. If excess hay produced from the bluestem-wheat system was sold as a cash crop, then this system was the most profitable. In general, we conclude that limit-grazing wheat pasture is a viable alternative to oilseed meal as protein supplement for wintering dry cows. Although the bluestem system had 2.5 times the carrying capacity of the native prairie systems, increased productivity was offset by increased production costs. All systems were equal on a cow basis for providing nutrients for the cow-calf production system.     

Bioavailability of magnesium in beef cattle fed magnesium oxide or magnesium hydroxide

Two experiments were conducted to compare Mg bioavailability from Mg oxide (MgO) vs Mg hydroxide (Mg(OH)2) fed in either a completely mixed diet or a mineral supplement. In Exp. 1, these Mg sources were incorporated into completely mixed diets and offered to 15 steers (282 kg) allotted to three treatments: control diet containing .19% Mg, control plus .2% added Mg as MgO, or control plus .2% added Mg as Mg(OH)2. Each calf was fed 5 kg/d of the respective diet during 10-d adjustment and 7-d collection periods. Blood samples were collected on d 1, 3 and 7. Mg supplementation increased (P less than .01) fecal and urinary Mg excretions, whereas apparent Mg absorption (%) and retention were similar (P greater than .10) for all treatments. Plasma Mg concentrations were similar (P less than .10) for calves supplemented with MgO and Mg(OH)2 but were higher (P less than .05) for Mg supplemented than for control calves on d 7. In Exp. 2, these Mg sources were incorporated into mineral supplements and offered free choice to 30 spring-calving beef cows gazing tetany-inducing pastures from March 6 to May 1. Each of three groups of 10 cows was assigned to a 5.7-ha tall fescue pasture and offered either a control supplement or a supplement containing 40% MgO or Mg(OH)2. Blood samplers were collected on d 0, 7, 14, 28, 42 and 56. Plasma Mg concentrations were not different (P greater than .10) for cows offered MgO and Mg(OH)2 but were higher (P less than .01) for Mg-supplemented than for control cows on d 28, 42 and 56.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cow and calf performance on Coastal or Tifton 85 Bermudagrass pastures with aeschynomene creep-grazing paddocks

Cow and calf performance was determined in a 2-yr, 2 x 2 factorial, grazing experiment using Coastal or Tifton 85 (T85) replicated Bermudagrass pastures (4 pastures each; each pasture 4.86 ha), without or with aeschynomene creep-grazing paddocks (n = 4, 0.202 ha each, planted in May of each year, 13.44 kg/ha). On June 10, 2004, and June 8, 2005, 96 winter-calving beef "tester" cows and their calves were grouped by cow breed (9 Angus and 3 Polled Hereford/group), initial cow BW (592.9 +/- 70.1 kg, 2-yr mean), age of dam, calf breed (Angus, Polled Hereford, or Angus x Polled Hereford), calf sex, initial calf age (117 +/- 20.1 d, 2-yr mean), and initial calf BW (161.3 +/- 30.4 kg) and were randomly assigned to pastures. Additional cow-calf pairs and open cows were added as the forage increased during the season. Forage mass was similar for all treatment pastures (P > 0.70; 2-yr mean, 6,939 vs. 6,628 kg/ha, Coastal vs. T85; 6,664 vs. 6,896 kg/ha, no creep grazing vs. creep grazing). Main effect interactions did not occur for performance variables (P > 0.10; 2-yr means), and year affected only the initial and final BW of the calves and cows. The 91-d tester calf ADG was greater for calves grazing T85 than Coastal (0.94 vs. 0.79 kg; P < 0.01), and for calves creep grazing aeschynomene compared with calves without creep grazing (0.90 vs. 0.82 kg; P < 0.03). Calf 205-d adjusted weaning weights were increased for calves grazing T85 compared with Coastal (252.9 vs. 240.3 kg; P < 0.01) and for calves with access to creep grazing (249.9 vs. 243.3 kg; P < 0.05). The IVDMD of esophageal masticate from pastures had a forage x creep grazing interaction (P < 0.05; Coastal, no creep grazing = 57.4%; Coastal, creep grazing = 52.1%; T85, no creep grazing = 59.1%; T85, creep grazing = 60.0%), and IVDMD was greater (P < 0.05) for T85 than for Coastal pastures. Cows were milked in August 2004, and in June and August 2005, with variable milk yields on treatments, but increased milk protein (P < 0.05) for cows grazing T85 compared with Coastal pastures in August each year, contributing to increased calf gains on T85 pastures. These results complement previous research with T85 and indicate increased forage quality and performance of cattle grazing T85 pastures. Calf gains on T85 pastures and for calves on creep-grazed aeschynomene paddocks were high enough to influence the efficiency of cow-calf operations.     

Growth Performance by Stocker Steers Fed Magnesium-Mica During a Grazing and Feedlot Period

Two experiments were conducted to determine the effects of Mg-mica supplementation on grazing and feedlot performance of stocker steers. In Exp. 1, eight groups of six steers were fed a basal diet of 80% ground grain sorghum, 15% corn silage, and 5% control protein supplement (DM basis) or a supplement containing Mg-mica (9% of supplement; 4.5 mg/kg diet DM) for 141 d. Marbling scores tended (P<0.10) to be greater, and the percentage of carcasses grading USDA Choice or higher was greater (P<0.05), from steers fed Mg-mica than from those fed the control supplement. In Exp. 2, eight groups of nine head each were offered either a control grain sorghum-based supplement or one containing 34 g/d of Mg-mica (2.7 g Mg) while grazing smooth bromegrass pastures for 112 d. Pasture groups were then placed in feedlot pens for 120 d and fed a basal diet similar to that described above. Two groups fed each pasture supplement received a control supplement, and two received a supplement containing Mg-mica (10% of supplement; 5 mg/kg diet DM). Steers fed Mg-mica during the pasture phase tended to have heavier (P=0.11) hot carcass weights, higher (P<0.05) dressing percentages, numerically (P>0.10) higher marbling scores, and a higher percentage of carcasses grading USDA Choice than steers fed the control supplement during the pasture phase. Therefore, adding Mg-mica to pasture supplements or feedlot diets appears to have no impact on grazing or feedlot performance, but may improve carcass quality.     

Effects of Supplemental Undegradable Protein During Early Lactation on the Performance of Beef Cows Grazing Native Range

Two experiments were conducted (Exp. 1, n = 63; Exp. 2, n = 72) using Angus x Hereford cows grazing Oklahoma dormant tallgrass prairie to determine the effects of increasing supplemental undegradable intake protein (UIP) on performance. In each experiment following parturition (February and March), cows were blocked by body weight, body condition score (BCS), and calving date and randomly assigned to one of four dietary treatments. For Exp. 1, supplements provided 396 g/d of degradable intake protein (DIP) with increasing amounts of UIP (211, 274, 337, and 400 g/d, respectively). For Exp. 2, supplements provided 281 g/d of DIP with 142, 196, 248, and 301 g/d UIP, respectively. Cows were individually fed 1.59 kg supplement 6 d/wk. Body weight and BCS were determined biweekly until the end of supplementation (Exp. 1, 37 + 1.5 d; Exp. 2, 45 + 1.2 d). Milk production was estimated 30 and 45 d postpartum. Plasma progesterone concentrations were quantified weekly to determine interval to first normal luteal function (PPI). Weight loss, BCS, and PPI were not influenced by treatment. In Exp. 2, there was a linear (P<0.08) decrease in weight gain of calves post-treatment to weaning as supplemental UIP increased, and a quadratic effect (P<0.06) of additional UIP on milk production at 30 d postpartum. In these experiments, metabolizable protein requirements were met by microbial protein, forage UIP, and a minimum of 142 g of supplemental UIP.     

Canola Meal Compared with Urea in a Barley and Potato Processing Residue Finishing Diet for Feedlot Steers

Five combinations of canola meal and urea were compared in a titration study using yearling beef steers (n = 120, initial weight = 383 kg ± 6.25) consuming barley and potato processing residue-based diets. The steers were allotted to 20 pens in a randomized block design and fed for 86 d. Diets were formulated to contain 30% potato processing residue, 45% barley, 15% corn silage, and 10% supplement (DM basis). Nitrogen source was the only difference in the diets. Supplements were formulated to be isonitrogenous with the N source being either urea or canola meal (C) to provide a calculated dietary CP of 11.5%. Treatments were: 100% urea supplement (0C); 25% canola meal supplement, 75% urea supplement (25C); 50% canola meal supplement, 50% urea supplement (50C); 75% canola meal supplement, 25% urea supplement (75C); and 100% canola meal supplement (100C). Average daily gain and DMI were similar for all treatments (P>0.05). Gain to feed ratio was larger (P<0.05) for 75C than 0C (163.2 vs 151.5 g/kg). Marbling scores were greater (P<0.05) from steers fed 0C than from those fed 50C or 75C. Longissimus muscle area and hot carcass weights were greater for 25C than 0C (P<0.05). Longissimus muscle area for 100C was also larger than 0C (P<0.05). The yield grade of 25C steers was lower (P<0.05) than that found in the 0C, 50C, and 100C steers (P<0.05). The 25C treatment had the highest apparent NDF digestibility of all treatments (P<0.05). Additional return of $14.50 per steer fed canola was found (P>0.05). The changes in carcass composition toward a leaner carcass with natural protein (the 25C fed steers) indicate potential benefits from the use of canola meal in barley and potato processing residue-based diets instead of urea as the sole supplemental N source.     

The effectiveness of doramectin pour-on in the control of gastrointestinal nematode infections in cow-calf herds

Two field studies were conducted in the USA to determine the efficacy of a single strategically-timed dose of doramectin pour-on in the control of gastrointestinal nematodosis in beef cow-calf herds and the resultant effects on calf productivity. One study was carried out between May and October 1996 in a spring-calving herd at a site located in Idaho (ID) and the other between January and July 1997 in a fall-calving herd at a site located in Mississippi (MS). In each study, cow-calf pairs were randomly allotted by sex of calf to pastures and one of two treatment groups (doramectin pour-on at the recommended dose rate of 500 microg/kg body weight or untreated control). There were four pasture replicates per treatment at each site. Each pasture contained 12 cow-calf pairs at the ID site and 15 cow-calf pairs at the MS site. Treatment was administered to cows and calves on 21 May 1996 (ID) or 23 January 1997 (MS). Following treatment, cow-calf pairs were assigned to their designated pastures where they remained until the calves were weaned 140 (ID) or 168 (MS) days later. Cow and calf fecal egg counts and calf body weights were recorded on treatment day and then at monthly intervals until study termination. Doramectin treatment reduced nematode egg output in cows and calves over the entire grazing season compared to untreated controls and resulted in calf weight gain improvements of 9.8kg (p=0.295) at the ID site and 17.4kg (p=0.0002) at the MS site.     

Influence of Both Endophyte Infestation in Fescue Pastures and Calf Genotype on Subsequent Feedlot Performance of Steers

Three experiments were conducted to determine the influence of both the concentration of endophytic fungus infestation in tall fescue pastures and calf genotype on the subsequent health and performance of steers in the feedlot. In Exp. 1 and 2, Angus steers grazed fescue pastures in Georgia containing low, moderate, or high endophyte infestations for 182 d (Exp. 1) or 78 d (Exp. 2) with 12 steers per treatment. Steers were transported 1,600 km to Texas in October (Exp. 1) and July (Exp. 2), were fed a 93% concentrate diet during the finishing period, and were harvested at an estimated backfat thickness of 12 mm. In both trials, DMI over the entire feeding period and carcass characteristics were not affected (P>0.05) by endophyte infestation. In both trials, pasture ADG decreased, and feedlot ADG and gain to feed ratio increased as the previous pasture endophyte infestation increased (P<0.05). Serum cholesterol concentrations tended (P<0.10) to decrease with increasing endophyte infestation during the first 14 d in the feedlot. In Exp. 3, Angus and Brahman × British crossbred steers grazed fescue pastures in Georgia containing low, moderate, or high endophyte in each of 2 yr. Six steers of each breed group were on each treatment each year. Steers were transported to Texas in late August of each year, were fed a 93% concentrate finishing diet, and were harvested at an estimated individual backfat thickness of 12 mm. As endophyte infestation increased, serum urea N concentrations and gain to feed ratios increased (P<0.05), whereas pasture ADG, initial BW, transit shrink, serum cholesterol concentrations, final BW, and carcass weights decreased (P<0.05) in Angus steers, but not in Brahman-cross steers. In these studies, the adverse effects of high endophyte infestations in fescue pastures appeared to carry over to the feedlot for ca. 14 d. However, steers from highly infested pastures can compensate for poor pasture performance with improved performance in the feedlot when no adverse health effects occur. Any impact of the endophyte seems to be similar in Brahman-cross and Angus steers.     

Influence of fish oil supplementation on growth and immune system characteristics of cattle

A study was conducted to determine the effects of supplemental fish oil on growth performance and immune system characteristics of beef calves. The grazing phase (78 d) used 48 yearling crossbred steers (231 +/- 22 kg initial BW) grazing 0.45-ha mixed-grass pastures (four per treatment) supplemented with 1.82 kg/d (as-fed basis) of the diets. Diets consisted of 1) corn-based supplement; 2) corn-based supplement with 1.5% (as-fed basis) fish oil; 3) wheat midd-based supplement; and 4) wheat midd-based supplement with 1.5% fish oil. On d 78, all calves were bled by jugular venipuncture, and blastogenic response of peripheral blood lymphocytes to phytohemagglutinin, concanavalin A, and pokeweed mitogen was measured. Fish oil supplementation negatively affected ADG with the corn-based supplement, but it had no effect when added to the wheat midd-based supplement (base-supplement x fish oil interaction; P < 0.03). Isolated lymphocytes from calves fed the corn-based supplement with fish oil had a greater response to stimulation with concanavalin A than did lymphocytes from calves fed the corn-based supplement alone, but there was no effect of fish oil addition to the wheat midd-based supplement (base-supplement x fish oil interaction; P < 0.01). During the growing phase, the 48 steers (352 +/- 32 kg initial BW) from the grazing phase were moved to drylot pens and were stratified by BW and previous dietary treatment (three calves per pen; eight pens per dietary treatment) for a 56-d growing trial. Dietary treatments consisted of 1) control, and 2) the control diet with 3% (as-fed basis) fish oil. Calves supplemented with fish oil had decreased ADG, ADFI, and G:F (P < or = 0.02) compared with controls. Fish oil supplementation during the grazing phase modulated the immune system; however, the decreased growth performance associated with fish oil in both trials may limit its practical use as an immune stimulant.     

Effect of calf weaning age and cow supplementation on cow productivity

Five years of data were collected on 124 Brangus-type cows to evaluate weaning calves at 8.5 or 10.5 mo of age and winter supplementation of the brood cow with 2.25 kg of molasses daily. Cows with calves weaned at 10.5 mg of age gained 14 kg less weight (P less than .01) during the late nursing period than did cows from which calves were earlier weaned. Age of calf at weaning had no effect on cow reproduction, but calves weaned at 10.5 mo were 2 to 3 d younger (P less than .06) and 5.3 kg lighter (P less than .05) at 8.5 mo of age. During the last 2 mo of nursing, calves weaned at 10.5 mo of age gained 37.2 kg and had a 31.9-kg heavier weaning weight than calves weaned at 8.5 mo of age. Molasses supplementation resulted in differences (P less than .01) in cow weight changes. Cows fed molasses had calving percentages 5 to 7 units higher (P less than .30) than cows not fed molasses. Feeding cows molasses for 145 d throughout the calving and breeding season increased calf weaning weight 7.7 (P less than .02) and 11.2 (P less than .03) kg, respectively, at 8.5 and 10.5 mo of age over the nonsupplemented controls.