G. Scaglia

Dietary Selection by Domestic Grazing Ruminants in Temperate Pastures: Current State of Knowledge, Methodologies, and Future Direction

Abstract Ruminants grazing mixed-species pastures face many choices, including when and where to graze and how much herbage to consume. These choices affect not only the nutritional status of the animal, but also sward composition and nutritive value through selective defoliation. Limited research has been conducted in the area of dietary selection and preference, most of which has been limited to simple model systems often involving a choice between only two herbage species. Although these studies have provided a vital tool to allow understanding of the fundamental principles of foraging behavior, in reality, grazing ruminants are faced with more complex situations. Understanding and managing animal preferences in mixed swards and thereby altering dietary selection can result in greater primary (plant) and secondary (animal) productivity. Key issues to improve this understanding include a better linking of behavioral and nutritional studies, a better understanding of the genetic factors influencing diet selection, and the development of more explicit spatial models of foraging behavior that incorporate multiple scales of decision making. This article, as part of a set of synthesis articles, reviews the current state of knowledge and research methodologies related to diet selection of grazing domestic ruminants with particular reference to improved temperate grazing environments, including how well we understand each part of the complex decision-making process a grazing ruminant faces, the links with primary and secondary productivity, and developments in methodologies. Finally, we identify key areas where knowledge is lacking and further research is urgently required.

Influence of two-stage weaning with subsequent transport on body weight, plasma lipid peroxidation, plasma selenium, and on leukocyte glutathione peroxidase and glutathione reductase activity in beef calves.

An experiment was conducted to assess the effects of two-stage weaning and subsequent transport on oxidative stress markers in calves. Thirty-six crossbred Angus steers (243+/-20.8 kg; 221+/-19.7 days) were allotted to control, fenceline (FL), and nose-clip (NC) weaning groups. Steers were weighed and blood samples were collected on days -7, 0 (pre-transit) and 7 surrounding transport. Leukocytes were analyzed for glutathione peroxidase and glutathione reductase activity, whereas malondialdehyde and Se were measured in plasma. Data were analyzed using PROC MIXED with the Tukey-Kramer adjustment applied post hoc. No treatment effects were detected for blood variables or weights. Glutathione peroxidase activity was not altered by time (P = 0.27). Glutathione reductase activity, Se, and malondialdehyde declined (P<0.001) from day -7 to 7 in all steers. Treatmentxdate interaction was detected for malondialdehyde (P<0.02). Control and FL steers gained weight (P<0.03), whereas NC steers did not gain weight between days -7 and 0 (P = 0.81). All weaning treatment groups gained weight between days 0 and 7 (P<0.05). Results suggest that two-stage weaning has little effect on examined markers of oxidative stress.

Fatty acid metabolism and deposition in subcutaneous adipose tissue of pasture- and feedlot-finished cattle

An experiment was conducted to evaluate the effects of pasture finishing versus feedlot finishing, over time, on fatty acid metabolism in Angus crossbred steers (n = 24). Ruminal fluid, serum, and adipose tissue biopsies were obtained on d 0, 28, 84, and 140. Pasture forages and diet ingredient samples were obtained at 14-d intervals to determine nutritive value and fatty acid composition. The feedlot diet consisted of corn silage, cracked corn grain, soybean meal, and a vitamin and mineral supplement. The pasture-finished steers grazed sequentially on triticale (x Triticosecale rimpaui)/annual ryegrass (Lolium multiflorum), alfalfa (Medicago sativa)/orchardgrass (Dactylis glomerata), and a cool-season grass/legume mixture. The feedlot diet contained an average of 57% of total fatty acids as linoleic acid and 2% as linolenic acid. The pasture forages contained 9% of total fatty acids as linoleic acid and 66% as linolenic acid. Concentrations (% of total fatty acids) of linolenic acid were greater (P < 0.05) in ruminal fluid, serum, and adipose tissue of the pasture-finished steers, compared with the feedlot-finished steers. Concentrations (% of total fatty acids) of cis-9, trans-11 CLA were greater (P < 0.05) in adipose tissue of the pasture-finished steers than feedlot-finished steers. Concentrations of cis-9, trans-11 CLA in adipose tissue declined (P < 0.05) in the feedlot-finished steers from d 0 to 28 to 84. In the pasture-finished steers, concentrations of cis-9, trans-11 CLA in adipose tissue (mg/g of tissue) peaked (P < 0.05) on d 28 and remained elevated (ranged from 9.91 to 12.80 mg/g of tissue) throughout the duration of the study. In the pasture-finished steers, linolenic acid concentrations tended to peak (P = 0.07) on d 28 and remained elevated (ranged from 0.64 to 0.80% of total fatty acids) throughout the study. It appears that only a short time is needed to alter the n-3 and CLA composition of adipose tissue in cattle finished on pasture.

Effects of Alternate Weaning Methods on Behavior, Blood Metabolites, and Performance of Beef Calves1

Beef calves traditionally are weaned by abrupt remote separation from their dams. Alternate weaning strategies have been suggested to reduce stress and improve performance of calves after weaning. Two such strategies were compared with abrupt remote separation weaning in spring-born, Angus-crossbred steers. Cow-calf pairs were allotted to 3 treatments 7 d before (d−7 to 0) weaning: fence-line (FL, calves separated from dams by a fence), nose-clips (NC, placement of antisuckling device on calves which then remained with dams), or control (CTRL, calves remained with dams until d 0). All steers were transported away from their dams on d 0, placed on pasture on d 1, and maintained within weaning-method treatment groups. Behavioral observations were conducted from d−7 to−4 and d 1 to 4. The NC calves spent less time eating, more time idling, more time close to dams, walked less, and had reduced ADG compared with FL or CTRL calves before transport (P < 0.05). The CTRL calves spent less time eating, more time idling, and walked more than FL or NC calves (P < 0.05) after transport. Average daily gain of FL calves was greater than NC calves (P < 0.05). On d 0, NC calves had reduced (P < 0.05) creatine kinase and BUN concentrations and greater nonesterified fatty acid concentration. There were no treatment effects for any blood metabolite detected after transport. Nose-clip weaning did not seem to be a comparable method to FL weaning, whereas FL weaning may be an alternative to traditional weaning.

Performance, carcass, and meat characteristics of beef steers finished on 2 different forages or on a high-concentrate diet

In response to potential changes in consumer demand, the utility of different forage-based systems as finishing programs should be evaluated. Performance and carcass characteristics of yearling steers that grazed monocultures of endophyte-free tall fescue or alfalfa or fed a high-concentrate (feedlot) diet were evaluated. Steers fed a feedlot diet gained more and reached a final endpoint sooner than those grazing tall fescue or alfalfa. Forages were not limiting in terms of mass produced and nutritive value. Despite the greater nutritive value of alfalfa compared with tall fescue, no differences in performance and hence productivity per unit of land were detected. No difference (P > 0.05) in ADG was detected between steers grazing (alfalfa and tall fescue, 0.93 and 0.98 kg, respectively) when compared with those in the feedlot or finished in drylot (1.32 kg). Beef produced on a forage-based diet was leaner and had acceptable organoleptic characteristics. Backfat and ribeye area were greater (P < 0.05) in the carcasses of steers that grazed alfalfa compared with fescue (7.6 vs. 4.0 mm and 66.7 vs. 57.5 cm2, respectively). However, the fat was more yellow (P < 0.05) than the fat of those on tall fescue, indicating a possible effect of the carotenoids that might be present in greater concentration in alfalfa. Forage-fed beef is a niche market that is growing rapidly in the United States. Forage finishing steers on tall fescue or alfalfa is a viable alternative for beef cattle producers interested in meeting the demand for this product.

Classification of Digital Photography for Measuring Productive Ground Cover

Abstract Productive ground cover (PGC) is often used as a measure of sward health and persistence. To measure PGC, a camera stand was constructed to provide diffuse lighting of grass swards for color digital photography; the photographs were classified into productive and nonproductive cover using Mahalanobis distance. The PGC measurement techniques were tested on a grazing experiment that used four forage types: Lakota prairie grass (Bromus catharticus Vahl.), Kentucky 31 endophyte (Neotyphodium coenophialum)-free tall fescue (Lolium arundinaceum [Schreb.] S. J. Darbyshire), Kentucky 31 endophyte-infected tall fescue, and Quantum (novel-endophyte) tall fescue. The accuracy of the PGC maps was assessed using a stratified subsample of 48 images, 12 from each of four productive cover classes (0%–39%, 40%–59%, 60%–79%, and 80%–100%). On each of these 48 images 100 random points were labeled by a single skilled interpreter. The PGC percentages thus derived had an 83.7% agreement with the PGC maps. However, the percentages derived from the PGC maps were not well correlated with the PGC percentages derived from either ocular estimation (r  =  0.22) or a simple digital point quadrat method (r  =  0.47). This experiment highlights the potential for semiautomated classification of ground-based digital photographs for estimating PGC, though further research (including more direct comparison with established field techniques) is warranted.

A study of the level and dynamics of Eimeria populations in naturally infected, grazing beef cattle at various stages of production in the Mid-Atlantic USA.

There is little information available on the species dynamics of eimerian parasites in grazing cattle in the central Appalachian region of the United States. Therefore, the objective of this study was to describe the level of infection and species dynamics of Eimeria spp. in grazing beef cattle of various age groups over the course of a year in the central Appalachian region. Rectal fecal samples were collected from male and female calves (n=72) monthly from May through October 2005, heifers only (n=36) monthly from November 2005 to April 2006, and cows (n=72) in May, July, and September, 2005. Eimeria spp. oocysts were seen in 399 of 414 (96%) fecal samples collected from the calves from May through October. Fecal oocysts counts (FOC) in the calves were lower (P<0.05) in May than all other months and no significant differences were detected from June through September. Eimeria spp. oocysts were detected in 198 of 213 (92%) of fecal samples collected from the 36 replacement heifers monthly from November to April and monthly mean FOC did not differ during this time period. The prevalence of oocyst shedding increased to 100% in calves in September and remained near 100% in the replacement heifers during the sampling period. Eimeria spp. oocysts were also detected in 150 of 200 (75%) samples collected in May, July, and September from the cows and mean FOC did not differ significantly over the sampling period. Eimeria spp. composition was dominated by Eimeria bovis in fecal samples collected from calves, replacement heifers and cows. Mixed Eimeria spp. infections were, however, common in all groups and 13 Eimeria spp. oocysts were identified throughout the sampling period.

Estimation of Forage Intake by Steers Grazing Three Fescue Types and Determination of Alkaloids in Ruminal Fluid and Forage1

Abstract During 2 consecutive grazing seasons, DMI of steers grazing ‘Kentucky-31’endophyte (Neotyphodium coenophialum-infected tall fescue (E+; Festuca arundinacea Shreb.), ‘Kentucky-31’endophyte-free tall fescue (E-), and ‘Quantum’tall fescue infected with endophyte AR542, a non-ergot alkaloid-producing strain (Quantum) was estimated using alkanes as markers. The appearance of ergovaline and lysergic acid amide (LSA) also was quantified in forage and ruminal fluid of steers grazing these forages. Estimates of DMI did not differ(P= 0.88) when based on fecal samples collected at 0800 h, 1700 h, or a composite of the 2 sampling times. Estimation of DMI using hand-plucked samples tended to be greater (P = 0.06) than whole-plant clipped samples. Estimated DMI was greater (P

Grazing Behavior of Beef Steers Consuming Different Tall Fescue Types and Lakota Prairie Grass

The grazing behavior of beef steers was evaluated using behavior data recorders in 4 sampling periods of 5 d each during June to September 2004. Forage treatments were ‘Kentucky-31’ endophyte-infected (K31E+) tall fescue (Festuca arundinacea Schreb.), ‘Quantum’ nil-ergot alkaloid producing endophyte-infected (QNE) tall fescue, and Lakota (LAK) prairie grass (Bromus catharticus Vahl.). There was a weak tendency for steers in LAK to spend more time grazing than steers grazing K31E+ (P = 0.16) and QNE (P = 0.18). Steers grazing K31E+ spent less (P < 0.05) time lying and ruminating and more time standing and idling than steers grazing QNE or LAK. Steers grazing K31E+ had a slower bite rate and took fewer bites and ruminating mastications than steers grazing LAK (P < 0.05). Average daily gain of steers grazing LAK was greater (P = 0.03) than those in K31E+ and tended to be greater (P = 0.07) than QNE. Steers grazing LAK exhibited be

Effects of Delaying Implant and Programmed Rate of Gain on Performance and Carcass Characteristics of Yearling Beef Steers1

Abstract Ninety-six steers (average BW = 335 ± 36 kg) were allotted in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Factors were 1) implant on d 1 or no implant and 2) ad libitum access to feed on d 1 or programmed-fed for a target BW gain of 1.4 kg/d during the first 62 d of the feeding period. On d 63, all steers were implanted with Revalor-S® (Hoechst Roussel Vet, Overland Park, KS) and provided ad libitum access to feed until harvest. From d 63 to 116, ADG and gain efficiency (g gain/kg DMI) for steers programmed-fed to gain slowly were greater (P