S.A. Gunter

Animal performance and economic comparison of novel and toxic endophyte tall fescues to cool-season annuals.

Increased costs of annual establishment of small grain pasture associated with fuel, machinery, and labor are eroding the profitability of stocker cattle enterprises. Interest has therefore increased in development of cool-season perennial grasses that are persistent and high quality. This study occurred on 24 ha (divided into thirty 0.81-ha paddocks) located at the University of Arkansas Division of Agriculture Livestock and Forestry Branch Station, near Batesville. Two tall fescue (Festuca arundinacea Schreb.) cultivars infected with novel endophytes (NE), Jesup infected with AR542 endophyte (Jesup AR542), and HiMag infected with Number 11 endophyte (HM11) were established in September 2002. Jesup AR542 and HM11 were compared with endemic endophyte Kentucky 31 (KY-31) tall fescue; wheat (Triticum aestivum L.) and cereal rye (WR, Secale cereale L.) planted in September 2003, 2004, and 2005; and annual ryegrass [RG, Lolium perenne L. ssp. multiflorum (Lam.) Husnot] planted in September 2004 and 2005. Each year, 3 steers (3.7 steers/ha) were placed on each pasture for fall and winter grazing, and 5 steers (6.2 steers/ha) were placed on each pasture for spring grazing. Animal performance is presented by year in the presence of a year x treatment interaction (P < 0.01). Body weight gain per hectare of steers grazing NE tall fescue was greater (P < 0.01) than those of KY-31 and WR during 2003 to 2004, whereas in 2004 to 2005, BW gain per hectare of steers grazing NE and RG did not differ (P < or = 0.29) and was greater (P < 0.01) than that of WR, which was greater (P < 0.01) than that of KY-31. During 2005 to 2006, BW gain per hectare was greater (P < 0.01) for steers grazing RG than those of NE and WR, which did not differ (P > or = 0.14). Body weight gain per hectare was least (P < 0.01) for steers grazing KY-31. Average net return of NE tall fescue was greater (P < 0.01) than KY-31, but profitability of NE did not consistently differ from cool-season annuals. Across the 3-yr study, NE tall fescue produced net returns per hectare of

Effects of on-arrival versus delayed modified live virus vaccination on health, performance, and serum infectious bovine rhinotracheitis titers of newly received beef calves

219; this level of profitability would require 4 yr for a new planting of NE tall fescue to break even. Novel endophyte tall fescues offer potential benefits related to decreased risk of stand establishment of annual forage crops, longer growing season, and acceptable animal performance.

Matching plant and animal processes to alter nutrient supply in strip-grazed cattle: Timing of herbage and fasting allocation1

Stress commonly associated with weaning, marketing, and shipment of feeder cattle can temporarily compromise immune function, thereby reducing the effective response to vaccination intended to control bovine respiratory disease (BRD). Two vaccination timing treatments were used to evaluate the effect of timing of a multivalent modified live virus (MLV) BRD vaccine on health, performance, and infectious bovine rhinotracheitis (IBR) antibody titers of newly received stocker cattle. Crossbred bull and steer calves (n = 528) were weighed (197 +/- 2.4 kg) and randomly assigned to MLV vaccination treatment: 1) MLV vaccination upon arrival (AMLV), or 2) delayed (14 d) MLV vaccination (DMLV). All cattle were processed similarly according to routine procedures, with the exception of the initial MLV vaccination timing. Subsequently, BW were recorded on d 14, 28, and 42. Blood samples were collected on d 0, 14, 28, and 42 to determine serum IBR titers, and comparisons were made between treatments on a receiving-day basis and an equivalent postvaccination day basis. Daily BW gains were greater (P < or = 0.05) for DMLV calves from d 0 to 14 (1.16 vs. 0.88 +/- 0.22 kg/d) and from d 0 to 42 (0.75 vs. 0.65 +/- 0.09 kg/d). Days to first treatment, total treatment cost, percentage death loss, and pasture ADG after the 42-d receiving period did not differ (P > or = 0.15). Morbidity rates for BRD were high for both AMLV and DMLV (71.5 and 63.5%, respectively) and did not differ (P = 0.12). Positive IBR titer seroconversion was greater (P < or = 0.03) for DMLV calves on d 42 of the study, and for the 28- and 42-d equivalent postvaccination basis. Delaying vaccination by 14 d may increase ADG during the receiving period compared with AMLV, and seroconversion to IBR was greater in DMLV calves, indicating a possible improvement in acquired immune response when MLV vaccination is delayed.

REVIEW: The Interaction of Diurnal Grazing Pattern, Ruminal Metabolism, Nutrient Supply, and Management in Cattle

This work aimed to assess the impact of timing of herbage allocation and fasting on patterns of ingestive behavior, herbage intake, ruminal fermentation, nutrient flow to the duodenum, and site and extent of digestion. Treatments were daily herbage allocation in the afternoon (1500 h, AHA), morning (0800 h, MHA), AHA after 20 h of fasting (AHAF), and MHA after 20 h of fasting (MHAF). Four ruminally and duodenally fistulated heifers (279 +/- 99 kg of BW) individually strip-grazed wheat pastures in a Latin-square design. Eating, rumination, and idling behavior were recorded every 2 min, and bite and eating step rates were measured hourly while the heifers were grazing (11 h MHA and AHA; 4 h MHAF and AHAF). Ruminal DM pools were measured 4 times daily (0800, 1200, 1500, and 1900 h) to estimate daily herbage DMI and its pattern. Ruminal fluid was sampled at these same times and also at 2300 h. Duodenal digesta was sampled over 2 d to determine the site of herbage digestibility. Treatments did not affect daily herbage DMI (16.5 g/ kg of BW, SE = 0.0025; P > 0.05). However, they altered the eating pattern; the evening grazing bout of AHA and AHAF was greater (P < 0.05) and more intense (P < 0.05 for bite mass and rate, eating step, and intake rates). Ruminal nonglucogenic:glucogenic VFA ratio and pH were lower (P < 0.05) for AHA and AHAF during the evening. The flow of OM, N, microbial protein, and nonmicrobial OM to the duodenum did not vary (P > 0.05) among MHA, MHAF, and AHAF; however, it averaged 970, 40, 300, and 540 g/d, respectively, greater (P < 0.05) for AHA. Total tract digestibility did not differ (P > 0.05) for MHA, AHA, and AHAF, but was lower for MHAF (P < 0.05). Apparent ruminal digestion did not differ (P > 0.05) within fasted and nonfasted treatments; however, it was greater (P < 0.05) for fasted than nonfasted treatments. True OM ruminally digested did not differ (P > 0.05) among MHA, MHAF, and AHAF, but was greater (P < 0.05) for AHA. The results demonstrate the strong link between ingestion and digestion patterns, and its impact on nutrient supply. At the same amount of resource allocation, nutrient supply to grazing cattle can be modified through strategic grazing management.

Effect of herbage depletion on short-term foraging dynamics and diet quality of steers grazing wheat pastures.

ABSTRACT Daily herbage intake depends on factors governing the initiation and cessation of successive grazing bouts. Ruminal fill is one such factor, regulating grazing bout-eating behavior. Under grazing conditions, nutrient supply varies among grazing bouts, not only in amount, but also in balance. Also, there is evidence suggesting differential energy expenditures in herbage harvesting and ingestive mastication among grazing bouts. The animal internal state plays an important role in shaping grazing pattern, although demands of ruminal microflora may be at times more important. It may well be that perception of ruminal conditions most likely dominates the short-term intake rate during a complete grazing bout, whereas on a larger spatiotemporal scale, the animal may operate within a framework of daily level of energy demand. Simultaneously, cattle might be dealing with pasture progressive defoliation as the grazing event progresses. This leads to selective behaviors and herbage intake rate reductions. From this work emerges that integrating different ingestive and digestive behaviors across foraging spatio-temporal scales would provide greater comprehension of factors driving the diurnal grazing patterns of cattle, helping in the design of better grazing methods.

Review: Behavior and daily grazing patterns of cattle

Two complementary experiments were completed to assess short-term foraging dynamics, diet quality, and ruminal degradation kinetics of herbage consumed by steers with 3 levels of herbage depletion. Experiment 1 was a behavioral study in which 2 ruminally cannulated steers were allocated to grazing scenarios simulating 3 levels of herbage depletion. These treatments included an ungrazed sward (control), as well as medium and high levels of herbage depletion. Grazing scenarios were sampled for sward surface height and amount of green leaf and stem before being grazed. Foraging dynamics were determined through measurements of bite rate, bite depth, eating step rate, eating distance, potential area consumed while grazing, and bites and intake per eating step. Also, quality of potential herbage consumed was estimated from hand-plucked herbage. In Exp. 2, ruminal degradation kinetics of DM for samples of herbage consumed (masticate) by steers during Exp. 1 were assessed in situ using 5 ruminally cannulated steers. The immediately soluble, degraded, and undegraded DM fractions were determined. The DM disappearance rate and lag times were determined from a nonlinear regression model, and the effective degradability of DM was calculated. Herbage depletion resulted in increased eating steps/minute, as well as the potential area harvested while grazing (P < 0.05) and reduced herbage intake/eating step (P < 0.05). Neither the herbage potentially consumed nor the ruminal degradation kinetics was affected by extent of depletion (P > 0.05). Under these experimental conditions, steers adapted their foraging dynamic and were able to sustain diet quality in the short term. These results imply that behavioral adaptations would make diet quality less sensitive to certain levels of herbage depletion.

Effect of wheat forage maturity and preservation method on forage chemical composition and performance of growing calves fed mixed diets

Abstract Grazing ruminants consume their food in discrete grazing events. The frequency and distribution of these events depend on the current physiological state of the animal and its environment. Within a small spatio-temporal scale, foraging decisions such as when to begin, which frequency, and how to distribute the grazing events may determine how cattle allocate time to meet their nutritional needs. The longest and most intense grazing events occur normally at dusk; this intake pattern serves to maximize daily energy intake, provide a steady release of nutrients, and maintain satiety over the night. Although ruminants may have a high motivation to seek food at dawn, this grazing event normally is of lesser intensity and duration than the dusk grazing event. Because of the timing of these grazing events, ruminants seem to be crepuscular animals, and light provides an environmental cue as to when to seek food. Certainly, the preference for twilight grazing plays a role in shaping the daily grazing pattern, yet it remains to be explained if this preference also reflects temporal variation in the underlying physiology. On the other hand, modern husbandry could not have eliminated any evolved anti-predator strategy legated by their ancestors. Voluntary feed intake ultimately abuts on animal psychology. Clearly, there are major gaps in our knowledge because there are virtually no published data relating the last question to domestic ruminants.

Effects of Feeding Supplemental Organic or Inorganic Selenium to Cow-Calf Pairs on Selenium Status and Immune Responses of Weaned Beef Calves1

Three 2.4-ha wheat (Triticum aestivum L.) fields were used to test the effects of maturity at harvest (boot vs. dough) and preservation method (hay vs. silage) on forage yield, chemical composition, and animal performance when fed in mixed diets. Forages were incorporated into 4 diets in a 2 x 2 factorial arrangement of treatments with hominy feed, soybean hulls, and cottonseed meal as the primary concentrate ingredients. In Exp. 1 diets contained 20% wheat forage (DM basis) and were fed to 96 beef calves (n = 48 steers and 48 heifers; initial BW 229 +/- 6.0 kg) in 12 mixed-sex pens. In Exp. 2 diets contained 40% wheat forage (DM basis) and were fed to beef steers (n = 48; initial BW 198 +/- 6.8 kg) in 12 pens. These diets were also individually fed to 32 calves (Exp. 1, n = 16, BW = 187 +/- 9.4 kg; Exp. 2, n = 16 calves, BW = 160 +/- 8.2 kg) to determine DM and NDF digestibility and gastrointestinal tract passage kinetics. Advanced maturity increased (P < 0.01) DM yield, decreased (P < 0.01) CP concentrations, and tended (P = 0.10) to increase nonfiber carbohydrate concentrations, but did not affect (P >or= 0.22) NDF, ADF, or TDN concentrations. Maturity at harvest, preservation method, or their interaction did not affect (P >or= 0.15) ADG when wheat forage was fed as 20 or 40% of the diet. When calves were fed the 40% wheat forage diets, maturity at harvest did not affect (P >or= 0.27) DMI or G:F. Calves fed 40% hay diets consumed more (P = 0.04) feed DM as a percentage of BW than calves fed silage diets, but tended (P = 0.09) to be less efficient. With 20 or 40% wheat forage diets, there were no differences (P >or= 0.13) in passage rate, ruminal retention time, or fecal output due to maturity or preservation method. Digestibility of DM tended (P = 0.07) to be greater for silage than hay diets when fed in 20% wheat forage diets. Dry matter and NDF digestibility of 40% boot-stage wheat forage diets were greater (P < 0.01) than diets containing forage harvested in dough stage. Forty percent hay diets also tended (P = 0.07) to have greater DM digestibility, and NDF digestibility was greater (P < 0.01) compared with silage diets. Although differences in performance were not noted in the present experiments, increased maturity at harvest and preservation as silage can cause differences in DMI and digestibility of DM and NDF in diets containing 40% wheat forage.

Development of Replacement Heifers Using Programmed Feeding1

In current marketing channels, calves are purchased with little indication of nutritional status on which a fully functional immune system is dependant. Adequate immune function in recently weaned calves is required for development of disease resistance. At weaning, 18 spring-born steer calves (BW = 200 ± 5.2 kg) were randomly selected from six groups of 20 cows to test the effects ofSe supplementation and source of Se fed pre-weaning on Se status and immune function of calves after weaning. Mineral supplements supplying no Se, 26 ppm of Se from sodium selenite, or 26 ppm of Se from Se-yeast were fed in a free-choice mineral supplement. After weaning, calves were fed bermudagrass (Cynodon dactylon [L.] Pers.) hay and 1.40 kg of supplement daily. Selenium status and immune characteristics of calves 22 d after weaning were tested by analysis of whole blood Se, glutathione peroxidase (GTH-Px) activity, lymphocyte proliferation, macrophage phagocytosis, and interferon-γ (IFN) production. In vivo cell-mediated immunity was tested by skin-swelling response to an intradermal phytohemagglutinin (PHA) injection. Whole blood Se concentrations and GTH-Px activities (54.7 ppm and 40.2 Eu/gHb, respectively) suggested Se deficiency of control calves. Supplementation with Se increased (P<0.01) whole blood Se concentration and GTH-Px. Seleniumyeast increased (P<0.01) whole blood Se concentration and macrophage phagocytosis compared with sodium selenite. In vivo cell-mediated immune response tended (P=0.12) to increase with Se supplementation. Supplementation of cow herds with Se before weaning increases Se status of weaned calves in areas where Se deficiency may be a problem.

Effects of Diet Fed During Backgrounding in Drylot on Ruminal Function of Cattle During Adaptation to Pasture1

This experiment was conducted to determine the effects of diet and pattern of gain on reproductive performance. On November 24, 80 spring-born Angus- and Brangus-sired heifers (BW = 230 ± 23 kg) were allotted by breed and BW to one of four treatments (two replicates per treatment). Heifers were program-fed to gain 0.68 kg/d until April 14 (134 d, MODERATE ), grazed wheat (cv. Hickory, Triticum aestivum L.) and ryegrass (cv. Marshall, Lolium multiflorum Lam.) interseeded into bermudagrass pasture ( GRAZED ), or were program-fed to gain 0.23 kg/d until February 4 (71 d) and then program-fed to gain 0.91 kg/ d (63 d, SLOW-FAST ) or grazed wheat and ryegrass pastures ( SLOW-GRAZED ). On February 4, MODERATE heifers were heavier (P 0.70) among treatments. Pregnancy rate tended to be less (P=0.16), conception date was later (P SUN ) tended to be greater (P=0.14) for GRAZED and SLOW-GRAZED heifers than for MODERATE and SLOW-FAST heifers. Program feeding can be a valuable tool for developing replacement heifers as long as BW goals pre-breeding are reached. Grazing heifers on cool-season annuals during breeding may impair reproduction as a result of the high forage N concentrations, causing reduced fertility.