Grazing Phase Research Articles

Influence of fish oil supplementation on growth and immune system characteristics of cattle1

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.

Influence of Betaine on Pasture, Finishing, and Carcass Performance in Steers

Two experiments were conducted to investigate the effects of supplemental betaine on steer performance, fat deposition, and carcass characteristics. In Exp. 1 (grazing phase), 80 steers (317 kg) were fed either 1.0kg of a control supplement (30% CP) or 1.0kg of the control supplement plus 20g of betaine per head per day. Betaine supplementation had no effect on overall gain or fat deposition (P>0.10) but increased ADG (P<0.10) during d 46 to 90 (0.64 vs 0.72 kg; control vs betaine, respectively). The pasture groups remained intact and were moved to the feedlot for 141 d and fed a control diet or the control diet plus 20g of betaine per head per day. Betaine had no overall effect on finishing gain (P>0.10); however, this response was variable by period. Betaine increased final fat thickness and fat thickness change (P<0.10), but did not affect marbling or longissimus area (P>0.10). Supplemental betaine on pasture increased feed intake, final BW, and hot carcass weight (P<0.05) and increased final fat thickness and fat thickness change (P<0.10) during the finishing phase. In Exp. 2, supplemental betaine (40 g/d) was fed to steers (averaging 584 kg) in 11 replications during the last week before harvest. The overall weighted average increase in dressing percentage when betaine was fed was +0.34% (P<0.05). There was no effect (P>0.10) on fat thickness or marbling. Season of year did not affect response.

How are distances between individuals of grazing cows explained by a statistical model?

A statistical model to describe how distances between individuals of grazing cows are explained is discussed in this paper. This model was constructed by the following five effects: (1) behavior of the entire crowd (measured by troop length in this study), (2) repulsive and attractive forces operating directly between two individuals (direct effect), (3) effect of third individual on distance between two given individuals (half-indirect effect), (4) effects of unconnected pairs on the distance between two given individuals (indirect effect), and (5) residual effect which cannot be explained by the above four effects to determine distances between individuals (random/involuntary movement effect). These effects were analyzed using simple and multiple regression equations. Whole data taken every 5 min were divided into two phases: a grazing phase and a resting phase. The distances between two individuals in the grazing phase were much greater than the distances in the resting phase. The temporal variation of distances between two individuals in the grazing phase was much larger than the variation of distances in the resting phase. The order of the contributions of the five effects to the total variation of temporal changes in distances between individuals were: random movement effect>troop length effect∼direct effect>half-indirect effect>indirect effect.

Influence of grazing dormant native range or winter wheat pasture on subsequent finishing cattle performance, carcass characteristics, and ruminal metabolism.

A winter grazing/feedlot performance experiment repeated over 2 yr (Exp. 1) and a metabolism experiment (Exp. 2) were conducted to evaluate effects of grazing dormant native range or irrigated winter wheat pasture on subsequent intake, feedlot performance, carcass characteristics, total-tract digestion of nutrients, and ruminal digesta kinetics in beef cattle. In Exp. 1, 30 (yr 1) or 67 (yr 2) English crossbred steers that had previously grazed native range (n = 38) or winter wheat (n = 59) for approximately 180 d were allotted randomly within previous treatment to feedlot pens (yr 1 native range = three pens [seven steers/pen], winter wheat = two pens [eight steers/pen]; yr 2 native range = three pens [eight steers/pen], winter wheat = four pens [10 or 11 steers/pen]). As expected, winter wheat steers had greater (P < 0.01) ADG while grazing than did native range steers. In contrast, feedlot ADG and gain efficiency were greater (P < 0.02) for native range steers than for winter wheat steers. Hot carcass weight, longissimus muscle area, and marbling score were greater (P < 0.01) for winter wheat steers than for native range steers. In contrast, 12th-rib fat depth (P < 0.64) and yield grade (P < 0.77) did not differ among treatments. In Exp. 2, eight ruminally cannulated steers that had previously grazed winter wheat (n = 4; initial BW = 407 +/- 12 kg) or native range (n = 4; initial BW = 293 +/- 23 kg) were used to determine intake, digesta kinetics, and total-tract digestion while being adapted to a 90% concentrate diet. The adaptation and diets used in Exp. 2 were consistent with those used in Exp. 1 and consisted of 70, 75, 80, and 85% concentrate diets, each fed for 5 d. As was similar for intact steers, restricted growth of cannulated native range steers during the winter grazing phase resulted in greater (P < 0.001) DMI (% of BW) and ADG (P < 0.04) compared with winter wheat steers. In addition, ruminal fill (P < 0.01) and total-tract OM digestibility (P < 0.02) were greater for native range than for winter wheat steers across the adaptation period. Greater digestibility by native range steers early in the finishing period might account for some of the compensatory gain response. Although greater performance was achieved by native range steers in the feedlot, grazing winter wheat before finishing resulted in fewer days on feed, increased hot carcass weight, and improved carcass merit.

Performance of steers supplemented with copper before and during receiving at the feedlot

The effects of supplemental Cu in the diets of beef steers grazing winter-annual pasture and(or) during receiving at a feedlot were examined. On 19 February, 84 steers (average BW = 216 ± 1.5 kg) were weighed and randomly assigned to 12 bermudagrass pastures (0.81 ha each) overseeded with wheat, rye, and annual ryegrass (seven steers/pasture). All steers were fed 0.91 kg daily of a corn-based supplement containing a basal level of Cu (control; 21 mg of Cu d–1) while grazing winter-annual pasture until 16 April. On 16 April, the steers were weighed, bled via jugular venipuncture, and one-half of the steers were supplemented with an additional 1.5 g of Cu proteinate (CuPRO; 150 mg Cu d–1), during the last 29 d of grazing before shipping to a feedlot. On 17 May, the steers were shipped to a research feedlot (14 h transit, 1.016 km). After arrival on 18 May, one-half of the groups of cattle that received each treatment during grazing received 150 mg of Cu from CuPRO daily (2 × 2 factorial) for 42 d. The supplementation of steers grazing pasture with additional Cu from CuPRO during the last 29 d of grazing tended to increase (P = 0.10) ADG and BW on day 29. The BW advantage expressed by CuPRO supplemented steers was not as apparent (P = 0.18 ) upon arrival at the feedlot, but at the conclusion of the receiving period, steers fed CuPRO on pasture were 6.3 kg heavier (P = 0.04). No benefit was noted (P &gt; 0.14) when CuPRO was fed during receiving at the feedlot. During the grazing phase, additional Cu from CuPRO seemed beneficial compared to basal Cu levels. Key words: Beef steers, copper, winter annual, serum

Evaluation of Ralgro® on pasture and subsequent feedlot performance and carcass merit of Mexican crossbred steers (2001)

A pasture/feedlot field study was conducted to evaluate the effects of a single Ralgro implant during the stocker phase on steer grazing performance and subsequent feedlot performance and carcass merit. A total of 2,764 steers of Mexican origin averaging 449 lb were assembled in Texas and shipped to Kansas, where they grazed on three intensively-early-stocked Flint Hills pastures. At initial processing, the steers were individually weighed and randomly assigned to either a non-implanted control group or a Ralgro implant group. Ralgro steers gained more (23 lb; P<0.01) than controls during the 82to 93-day grazing phase. Following the grazing phase, all steers were shipped to a commercial feedlot in southwestern Kansas where steers from each pasture were individually weighed and given a single Component E-S implant. Immediately after processing, steers from each pasture were sorted into either a lightor heavy-weight pen, regardless of pasture implant treatment, resulting in six feedlot pens. Days on feed ranged from 127 to 197. Control steers gained faster (P<0.01) during the feedlot phase; however, Ralgro steers had higher cumulative weight gains across the combined pasture and feedlot phases (P<0.01) and averaged three fewer days on feed (P<0.05). There were no significant differences for marbling, fat thickness, ribeye area, KPH fat, or yield grade. Ralgro steers had lower (P<0.05) quality grades because of a higher incidence (P<0.001) of steers with B and C carcass maturities.

Pasture deworming and (or) subsequent feedlot deworming with fenbendazole. I, Effects on grazing performance, feedlot performance and carcass traits of yearling steers

734 steers, weighing 286 kg, were used during a 118-day grazing period, after which 640 were placed in a feedlot for finishing (average of 121 days, range of 111 to 133 days) to measure the main effects and interactions of 2 pasture deworming treatments (negative control, strategically dewormed with fenbendazole) and 2 feedlot deworming treatments (negative control, dewormed with fenbendazole) on grazing performance, feedlot performance, carcass traits and production economics for yearling steers. Strategic deworming with fenbendazole (FBZ) during the grazing phase increased pasture gain by 22 kg compared with control steers. Feedlot deworming improved performance of steers in all treatments, but it had a much greater effect on performance of pasture control steers. Deworming with FBZ in the feedlot improved daily gain of pasture control steers by 13.4% compared with a 4.2% improvement for steers that had been strategically dewormed on pasture. Similarly, feedlot deworming improved feed/gain ratio by 4.65% for pasture control steers compared with 0.4% improvement for steers that had been strategically dewormed. On a carcass-adjusted basis, feedlot deworming of strategically dewormed steers increased daily gain 6.8%, and feed/gain by 2.9%. Feedlot deworming of pasture control steers increased daily dry matter intake (DDMI) by 7.8% compared with no feedlot deworming, while feedlot deworming increased DDMI by 3.2% in the same comparison for strategically dewormed steers. Carcass traits were affected similarly. Dressing percentage was increased by both strategic deworming on pasture and feedlot deworming with fenbendazole. Feedlot deworming of pasture control steers increased carcass weight by 22 kg, while feedlot deworming of steers that were strategically dewormed on pasture increased carcass weight by 9.5 kg. The percentage of choice carcasses was lower, and the percentage of select carcasses was higher for the pasture control-feedlot control steers compared with the other treatment groups. Strategic deworming during grazing resulted in a net benefit of $33.75 per head. For the complete grazing-finishing system, feedlot deworming of previously non-dewormed steers with FBZ produced a net benefit of $30.61 per head on a carcass-adjusted basis, while feedlot deworming of strategically dewormed steers produced a net benefit of $11.07. Strategic deworming of grazing steers on pasture and yearling steers that were entering the feedlot from summer pasture with FBZ produced clear performance and economic benefits.

Efecto de la carga animal, nivel de abono y suplementación invernal sobre el desempeño a pastoreo de toretes Senepol puros y cruzas

El estudio consistió de una fase de pastoreo y otra fase de pastoreo con suplementación. Cuarenta y ocho toretes Senepol puros y cruzas se asignaron a los siguientes tratamientos: T1: carga animal (CA) de 3.45 anímales por hectárea y 449.1 kg/ha de fertilizante; T2: T1 más supplementación invernal; T3: CA de 1.85 animales por hectárea y 224.5 kg/ha de fertilizante; y T4: T3 más suplementación invernal. La dieta de los animales se suplemento con una mezcla de carnada de pollo, melaza de caña y maíz partido al comienzo del segundo invierno a pastoreo. Durante los primeros 321 días de la fase de pastoreo, el efecto del sistema de manejo de la pastura sobre la ganancia diaria en peso (GDP) y pesos finales no fue significativo (P &gt; 0.05). Sin embargo, los toretes pastando a CA moderadas (T1 y T2) produjeron un total de 218 kg más de ganancia en peso por hectárea (P &lt; 0.05). La suplementación invernal aumentó significativamente (P &lt; 0.05) la GDP; la ganancia en peso por animal y los kilogramos de aumento en peso por hectárea (+0.32 kg/an¡mal/día; +37.1 kg/animal; +104.4 kg/ha de aumento en peso). Los toros en T2 y T4 consumieron diariamente 2.33 y 1.44 kg de materia seca (WIS) de suplemento por animal y mostraron conversiones estimadas de 6.65 y 5.90 kg de MS por kilogramo de ganancia en peso debida al suplemento (P &gt; 0.05), respectivamente. La cantidad de forraje disponible en las pasturas declinó de forma continua y fue significativamente más baja (P &lt; 0.05) al final del estudio. El costo promedio del kilogramo de aumento en peso para ambas fases del estudio (pastoreo y pastoreo con suplementación) fue $0.08/kg más bajo en T2 que en T1. Los animales suplementados y pastando bajo CA de 3.45 animales por hectárea (T2) tuvieron el menor costo por kilogramo de aumento en peso.

Drylot receiving program vs pasture conditioning with Micotil® metaphylaxis for grazing stocker calves (2000)

Three stocker cattle field studies were conducted comparing a traditional 4- to 5-week drylot receiving program with injectable antibiotics administered on a pull-and-treat basis versus a pasture-based conditioning program using an initial metaphylaxis with Micotil® followed by immediately placing cattle on grass. Although daily gains were similar (P=.80) for both receiving programs during the first 28 days, pasture conditioning reduced the number of cattle treated and increased (P<.01) daily gains during the subsequent grazing phase.

Effect of Interseeding Legumes into Endophyte-Infected Tall Fescue Pastures on Forage Production and Steer Performance

Grazing and subsequent finishing performances of steers (Bos taurus) (n=135) that grazed high-endophyte [Neotyphodium coenophialum Glen, Bacon, Price, and Hanlin (formerly Acremonium coenophialum)] tall fescue (Festuca arundinacea Shreb.) pastures interseeded with lespedeza (Lespedeza stipulacea Maxim.), ladino clover (Trifolium repens L.), or red clover (Trifolium pratense L.) were evaluated during 1995, 1996, and 1997. Nine 5-acre established pastures of Kentucky 31' tall fescue with approximately 70% endophyte infection were used in a randomized complete block design containing three replications of each legume treatment. Pastures were seeded with legumes each year in late winter, and steers grazed continuously from early spring to mid-fall. At the end of the grazing phase, steers were finished for slaughter. Legume cover, available forage dry matter, grazing and subsequent feedlot performances of steers, and carcass parameters were measured. Total available forage dry matter was similar among legume treatments. A significant (P 0.05) among legume treatments in 1995 and 1996. In 1997, steers grazing ladino clover pastures gained 36% more (P< 0.01) and 28% more (P < 0.01) than those grazing lespedeza and red clover pastures, respectively. Gains by steers grazing red clover and lespedeza pastures were similar. Legume treatment during the grazing phase had no effects on subsequent finishing performance. Total gains (grazing + finishing) were similar among legume treatments in 1995 and 1996; however, in 1997, steers that grazed ladino clover had higher (P < 0.01) overall gains than those that grazed red clover or lespedeza.

Effect of interseeding legumes into endophyte-infected tall fescue pastures on forage production and steer performance (1999)

A total of 135 steers grazed high-endophyte tall fescue pasture interseeded with either lespedeza, red clover, or ladino clover during 1995, 1996, and 1997. Legume cover, forage dry matter production, grazing steer performance, and subsequent feedlot performance were measured. Legume treatment caused no differences in forage availability. Grazing gains corresponded to the amount of legume coverage present. Results of this study indicate that interseeding high endophyte fescue pastures with ladino clover produced higher stocker gains during the grazing phase than interseeding with lespedeza or red clover. Legume treatment had no effect on subsequent finishing gains.

Effects of implants on daily gains of steers wintered on dormant native tallgrass prairie, subsequent performance, and carcass characteristics.

Fall-weaned crossbred steer calves (n = 300; 184 +/- 2.9 kg) received either no implant (Control) or were implanted with Synovex-C (SC = 10 mg estradiol benzoate + 100 mg progesterone), Synovex-S (SS = 20 mg estradiol benzoate + 200 mg progesterone), or Revalor-G (RG = 8 mg estradiol-17beta + 40 mg trenbolone acetate) to determine the effects of implants on weight gain during winter grazing on dormant tallgrass prairie, subsequent grazing and finishing performance, and carcass characteristics. Steers grazed two dormant tallgrass prairie pastures from October 16, 1996, until March 29, 1997 (164 d), and received 1.36 kg/d of a 25% CP supplement that supplied 100 mg of monensin/steer. Following winter grazing, all steers were implanted with Ralgro (36 mg zeranol) and grazed a common tallgrass prairie pasture until July 17 (110 d). After summer grazing, all steers were implanted with Revalor-S (24 mg estradiol-17beta + 120 mg trenbolone acetate), and winter implant treatment groups were equally allotted to four feedlot pens. Steers were harvested November 17, 1997, after a 123-d finishing period. Daily gains during the winter grazing phase averaged .28, .32, .32, or .35 kg/d, respectively, for Control, SC, SS, or RG steers and were greater (P < .01) for implanted steers than for Controls. Summer daily gains were similar (1.05 +/- .016 kg/d; P > or = .61) for all treatment groups. Feedlot daily gains were also similar (1.67 +/- .034 kg/d; P > or = .21), with implanted steers weighing 14 kg more than Control steers (P = .05) at harvest, despite similar management during summer grazing and feedlot phases. Control steers tended (P = .06) to have lower yield grades. There were no differences (P = .99) in marbling between implanted and nonimplanted steers. Steers implanted during the wintering phase had increased skeletal and overall (P < .01) carcass maturities compared with nonimplanted steers, which resulted in more "B" and "C" maturity carcasses. Because carcass maturity score affects quality grade, the increased maturities of implanted steers resulted in a $9.04 decrease in carcass value/100 kg (P < .01) compared with Controls. The results of this study indicate that growth-promoting implants are efficacious for cattle wintered on dormant native range despite low daily gains. This increased weight is maintained through the summer grazing and feedlot phases; however, the benefit of the increased weight may be offset by decreased carcass quality grade and value due to increased carcass maturity.

Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. III. Runoff, soil erosion and nutrient loss

Runoff and soil erosion were measured in a two-phase experiment for seven consecutive years from 1979 through 1986 on a 44·3 watershed comprising 12 sub-watersheds of 2–4 ha each. These experiments were conducted at Ibadan, Nigeria, which is characterized by two growing seasons per year. The first season lasts from mid-March through mid-July, and the second season from mid-August to early November. Experiments were conducted in two phases comprising different treatments. The six treatments during Phase I (1979–1981), involving different combinations of land clearing and tillage methods, were: (1) manual clearing (MC) with plough-till (PT); (2) MC with no till (NT); (3) shear-blade (SB) clearing with NT; (4) tree-pusher (TP) clearing with PT; (5) TP clearing with NT; (6) traditional clearing and farming (TF). The five farming-system treatments during Phase II (1982–1987) were: (A) alley cropping with Leucaena leucocephala planted on the contour at 4 m intervals, (B) fallowing with mucuna (Mucuna utilis) on severely degraded soils; (C) fallowing with mucuna on moderately degraded soils; (D) ley farming on severely degraded soils; (E) ley farming on moderately degraded soils. The traditional farming treatment of Phase I was discontinued in 1982 at the beginning of Phase II and the land was returned to natural fallowing. Runoff, soil erosion, and nutrient losses in runoff were monitored using a 4·5 feet H-Flume, FW-1 waterstage recorder and Coshocton Wheel sampler. From the mean annual rainfall of 1320 mm, mean annual runoff amounts for the 3-year period from 1979 through 1981 during Phase I were 5·6 mm (0·42 per cent of rainfall) for MC-NT, 5·7 mm (0·43 per cent) for TF, 43·2 mm (3·27 per cent) for SB-NT, 43·5 mm (3·30 per cent) for MC-PT, 68·3 mm (5·17 per cent) for TP-NT, and. 113·1 mm (8·57 per cent) for TP-PT treatments. Runoff losses were consistently more during the first compared with the second growing season. Trends in soil erosion were similar to those of runoff, and annual soil erosion amounts were 0·1 Mg ha−1 for MC-NT, 0·2 Mg ha−1 for TF, 1·5 Mg ha−1 for SB-NT, 3·6 Mg ha−1 for MC-PT, 5·1 Mg ha−1 for TP-NT, and 8·3 Mg ha−1 for TP-PT treatments. Measurements made during Phase II showed that there were no significant differences in runoff or soil erosion among the restorative farming systems adopted. Nutrient concentrations in runoff and nutrient loss were generally high in uncropped treatments, e.g. mucuna fallow during the fallowing phase and ley farming during the grazing phase.

Economic Analysis of Grazing and Subsequent Feeding of Steers from Three Fescue Pasture Alternatives

Cattle grazing tall fescue (Festuca arundinacea Schreb.) infected with the endophytic fungus, Acremonium coenophialum, typically experience toxicity symptoms, resulting in poor animal performance. However, potential exists for compensatory gains during subsequent finishing. This study provides an economic analysis of three grazing alternatives along with subsequent feedlot performance. The pasture alternatives were endophyte-infected »Kentucky 31« tall fescue (IF); IF interseeded with ladino clover (Trifolium repens L., IFL); and endophyte-free »Missouri 96« tall fescue (MO). Three years of agronomic data from pastures and animal performance data from steers (Bos taurus) were collected

Ruminal escape protein supplementation and zeranol implantation effects on performance of steers grazing winter annuals.

Fifty-four crossbred steers (275 kg) were assigned randomly to one of three isoenergetic but not isonitrogenous ruminal escape protein (EP) supplements: high ruminal escape protein (HEP), low ruminal escape protein (LEP), or corn. The supplements contained corn, distillers' dried grains with solubles (DDGS), and fish meal. Supplements were fed at approximately 1.5 kg/d; the HEP and LEP supplements provided .25 and .12 kg more EP per day than corn, respectively. These supplements also supplied .20 and .10 kg more CP per day than corn. Fish meal and DDGS provided 66.7 and 33.3% of the supplemental EP, respectively. One-half of the steers in each supplement treatment were implanted once with 36 mg of zeranol. Steers grazed wheat (Triticum aestivum L.)-annual ryegrass (Lolium multiflorum Lam.) pastures for 73 d (March 1 to May 12). Daily gains (kg/d) increased linearly (P less than .07) as EP increased (HEP, 1.61; LEP, 1.54; corn, 1.47); responses were apparent only during the later periods as forage quality declined. Zeranol implants increased (P less than .02) ADG (kg/d) by 9.7% (1.58 vs 1.44). After grazing, all cattle were fed a finishing ration for 76 d. Pre-feedlot EP level produced a negative linear (P less than .04) response on feedlot ADG (kg/d) (HEP, 1.44; LEP, 1.50; corn, 1.59). Zeranol implantation during the grazing phase did not affect (P greater than .2) performance during the feedlot phase or carcass characteristics other than increased ribeye area (P less than .08). Compensatory feedlot performance negated all weight gain advantages elicited by EP supplementation during the grazing period.(ABSTRACT TRUNCATED AT 250 WORDS)

INJECTABLE COPPER AND ZINC FOR GRAZING YEARLING STEERS

Injectable Cu and Zn were evaluated as mineral supplements using 37 purebred Herefords (Group 1) and 23 Angus-Charolais-North Devon crosses (Group 2). The 60 steers were carried through a 113-d grazing phase. This was followed by a 79-d finishing phase for all steers of Group 1 and seven steers of Group 2. Treatments were combinations of the non-dosing (0Cu, 0Zn) and dosing (+Cu, +Zn) of steers with injectable Cu or Zn at the start of the grazing phase: (1) 0Cu, 0Zn; (2) +Cu, 0Zn; (3) 0Cu, +Zn; and (4) +Cu, +Zn. Injectables were the sole source of supplementary Cu and Zn during grazing and finishing phases. Means (SE) for Cu and Zn, respectively, in forages as milligrams per kilogram dry matter (DM) during the grazing phase were: grasses, 4.4 (0.17), 15.7 (0.46); alfalfa, 6.9 (0.18), 16.5 (1.49); and birdsfoot trefoil 5.0 (0.76), 15.0 (3.41). Injectable Cu did not influence (P &gt; 0.05) body weight during the grazing phase. Body weight responses were lower (P &lt; 0.05) for +Cu steers in the finishing phase, when dietary Cu was low, but steers could not be classified as Cu-deficient based on liver Cu. Liver Cu increased to means greater than 140 mg kg−1 DM in all steers, but was higher (P &lt; 0.05) in +Cu steers during the grazing phase. Serum Cu varied widely during the grazing phase, but was higher (P &lt; 0.05) for +Cu steers only on day 84 of the grazing phase. Neither liver Cu nor serum Cu was influenced (P &gt; 0.05) by injectable Zn. Injectable Zn decreased growth rates in the latter part of the grazing phase but did not affect (P &gt; 0.05) the body weight response during the finishing phase. The concentrations of Zn in liver and serum were not influenced (P &gt; 0.05) by injectable Cu or Zn. Key words: Cattle, grazing, copper, zinc, injectable copper, injectable zinc

Seasonal variations in the trophic structure of phyto-and zooplankton communities in lakes in different trophic states

A number of environmental factors are important in regulating the trophic structure of plankton. Increased nutrient supply results in an explosive development of small algae and herbivorous zooplankton. In the eutrophic lakes (Greifensee, Hallwilersee) several algal community collapses occur each year as a consequence of the grazing habit of the zooplankton, although only the grazing phase in May/June results in a ‘clear water period’. Vertical mixing influences the zooplankton community by reactivating the resting stages of predatory copepods. Predation phases can only be observed in lake Lucerne, where the hypolimnion ist deep and aerobic. Well balanced relationships between the different trophic levels are restricted to the phases with growth limiting conditions.

Copper deficiency: a study of prophylaxis and the interaction with cobalt therapy in lambs on improved hill pastures

ABSTRACTAn experiment was conducted with 84 suckling Scottish Blackface twin lambs on an improved hill pasture with a history of cobalt deficiency and molybdenum/sulphur-induced copper deficiency. The dams of 13 pairs of twins were treated with 90 mg copper at parturition (Cue) and one member of each pair was given a cobalt bullet (Co + ). One member of each of a further 29 pairs was treated periodically with 5 to 15mg copper to maintain plasma copper concentrations &gt;0·6mg/l (Cu+) while their siblings received no supplementary copper (Cu). Fourteen of these pairs also received a cobalt bullet (Co + ). Lambs not treated with cobalt are designated Co−.The Cue treatment increased milk copper concentrations, but only for a short time, and resulted in transitory increases in lamb plasma copper concentrations and rate of live-weight gain. At the end of the grazing phase, at approximately 20 weeks of age, Cu+ lambs had gained 0-28 kg more weight than Cue lambs and 158 kg more than Cue lambs, and had higher liver copper concentrations. Cu+ and Cue lambs had heavier and fatter empty bodies and carcasses than Cu− lambs. The cobalt treatment produced no effects at this stage.Fifty-four of the lambs were housed and given dried grass pellets ad libitum. After 83 days liver copper concentrations were higher in Co− than Co+ lambs, and in Cu+ than in Cu− and Cue lambs. The copper treatments had no effect on rate or efficiency of live-weight gain, but Co− lambs gained weight more quickly and more efficiently than Co+ lambs.

Effect of Protected Lipids on Feedlot Performance and Carcass Characteristics of Short-Fed Steers2

Forty F-1 Brahman × Hereford steers approximately 12 months old were grazed on a winter pasture of wheat, oats and ‘Gulf’ ryegrass for 145 days prior to a 56-day feeding trial. Six of the 40 steers were slaughtered at the end of the grazing phase to obtain slaughter, carcass and palatability data from steers receiving pasture only. The remaining 34 steers wre fed control (C) or protected tallow (PT) diets. The PT diet contained 20.26% protected tallow supplement which provided 8% actual tallow in the diet. Calculated NEg values per animal per day for the two diets using conventional energy values were 6.03 and 5.15 megcal for C and PT, respectively, which projected gains of .98 and .87 kilograms. Actual gains of .92 and 1.10 kg per head per day were 94% of expected for C and 126% of expected for PT. Steers fed either diet for 56 days following the pasture phase had higher dressing percentages (P<.0001), greater amounts of subcutaneous fat, kidney, pelvic and heart (KPH) fat (P<.03) and were more tender (P<.01) than steers slaughtered off pasture. When compared with C, PT steers gained more (P<.02), consumed less (P<.001) feed per kilogram gain, had higher (P<.10) marbling scores and USDA grade, and had greater (P<.10) amounts of fat in the longissimus muscle.

Superphosphate utilization in clover ley farming. II.* Residual effects of pasture topdressing in the cropping phase

A grazing experiment was carried out at the Agricultural Research Institute, Wagga Wagga, over the period 1962-1966. The treatments involved three stocking rates (5, 10 and 15 sheep per ha) and four superphosphate topdressing rates (0, 125, 250 and 375 kg ha-1) with three replications. After the grazing phase three successive crops were grown. Superphosphate was applied with the crops at 0, 63, 125 and 250 kg ha-1. Current and residual effects of this superphosphate were measured. Nitrogen (as urea at 78 kg ha-l) was topdressed on half of each plot. The low stocking rate plots were further tested for response to sulphur. Superphosphate applied to one crop had no residual effect on subsequent crops, regardless of the previous pasture treatment. On the average the yield of the first crop sown without superphosphate increased about 1/3 kg ha-1 for each kilogram of superphosphate per hectare applied annually in the pasture phase, that of the second crop 1 kg and the third crop I-1/3 kg. First crops did not respond to superphosphate applied with the crop, but second crops on plots that were not topdressed in the pasture phase and all third crops did respond to current superphosphate. Yields of third crops receiving superphosphate at 250 kg ha-1 on land that was not topdressed in the pasture phase exceeded those of similar crops on land that had been topdressed in the pasture phase (five out of six comparisons were significant at P = 0.01). A similar effect was found in the second crop in one replicate. The effect of nitrogen varied with the climate. In the drought year of 1967 there was one negative response to nitrogen. In 1968 yields were high and nitrogen decreased yield by increasing lodging. In the following 3 years nitrogen increased yield and the increase was generally greater as the rate of pasture topdressing increased. The stocking rate of the pasture did not affect the yield of the following wheat crops. There was no response to sulphur by the crops. It is suggested that superphosphate can be more efficiently used by omitting pasture topdressing and applying 125 kg ha-I or more with crops. Farmers in the clover ley farming areas could considerably reduce their annual superphosphate requirements. *Part I, Aust. J. Agric. Res., 25: 525 (1974).