Daniel G. Morrical

Grazing Management and Microclimate Effects on Cattle Distribution Relative to a Cool Season Pasture Stream

Abstract Because of concerns about the impact of grazing management on surface water quality, a 3-yr study was conducted to determine grazing management and microclimate impacts on cattle distribution relative to a pasture stream and shade. Three treatments, continuous stocking with unrestricted stream access (CSU), continuous stocking with restricted stream access (CSR), and rotational stocking (RS), were evaluated on six 12.1-ha cool-season grass pastures stocked with 15 fall-calving Angus cows (Bos taurus L.) from mid-May through mid-October of each year. On 2 d · mo−1 from May through September of each year, a trained observer in each pasture recorded cattle position and activity every 10 min from 0600 to 1800 hours. In years 2 and 3, position of one cow per pasture was recorded with a Global Positioning System (GPS) collar at 10-min intervals 24 h · d−1 for 2 wk · mo−1 from May through September. In week 2 of collar deployment in May, July, and September, cattle had access to off-stream water. Ambient temperature, black globe temperature, relative humidity, and wind speed were recorded at 10-min intervals and temperature humidity (THI), black globe temperature humidity (BGTHI), and heat load (HLI) indices were calculated. Based on GPS collars, mean percentage of time cows in CSU pastures were in the stream (1.1%) and streamside zone (10.5%) were greater (P < 0.05) than cows in CSR (0.2% and 1.8%) or RS (0.1% and 1.5%) pastures. Based on GPS collar data, off-stream water did not affect the percentage of time cattle in CSU or CSR pastures spent in the stream. Probabilities that cattle in CSU and CSR pastures were in the stream or riparian zones increased (P < 0.05) as ambient temperature, black globe temperature, THI, BGTHI, and HLI increased. Rotational stocking and restricted stream access were effective strategies to decrease the amount of time cattle spent in or near a pasture stream.

Grazing Management Effects on Sediment, Phosphorus, and Pathogen Loading of Streams in Cool-Season Grass Pastures

Erosion and runoff from pastures may lead to degradation of surface water. A 2‐yr grazing study was conducted to quantify the effects of grazing management on sediment, phosphorus (P), and pathogen loading of streams in cool‐season grass pastures. Six adjoining 12.1‐ha pastures bisected by a stream in central Iowa were divided into three treatments: continuous stocking with unrestricted stream access (CSU), continuous stocking with restricted stream access (CSR), and rotational stocking (RS). Rainfall simulations on stream banks resulted in greater (P < 0.10) proportions of applied precipitation and amounts of sediment and P transported in runoff from bare sites than from vegetated sites across grazing treatments. Similar differences were observed comparing vegetated sites in CSU and RS pastures with vegetated sites in CSR pastures. Bovine enterovirus was shed by an average of 24.3% of cows during the study period and was collected in the runoff of 8.3 and 16.7% of runoff simulations on bare sites in CSU pastures in June and October of 2008, respectively, and from 8.3% of runoff simulations on vegetated sites in CSU pastures in April 2009. Fecal pathogens (bovine coronavirus [BCV], bovine rotavirus group A, and Escherichia coli O157:H7) shed or detected in runoff were almost nonexistent; only BCV was detected in feces of one cow in August of 2008. Erosion of cut‐banks was the greatest contributor of sediment and P loading to the stream; contributions from surface runoff and grazing animals were considerably less and were minimized by grazing management practices that reduced congregation of cattle by pasture streams.

Stocking Rate and Riparian Vegetation Effects on Physical Characteristics of Riparian Zones of Midwestern Pastures

Abstract Grazing at high stocking rates may increase sediment and nutrient loading of pasture streams through transport in precipitation runoff and bank erosion. A 3-yr (2007–2009) grazing study was conducted on 13 cool-season grass pastures to quantify effects of stocking rate and botanical composition on forage sward height, proportions of bare and manure-covered ground, and bank erosion adjacent to streams. Pastures ranged from 2 ha to 107 ha with stream reaches of 306 m to 1 778 m that drained watersheds of 253 ha to 5 660 ha. Bare and manure-covered ground were measured at a 15.2-m distance perpendicular to the stream at 30.5-m intervals at up to 30 locations on each side of the stream by the line transect method in May, July, September, and November of each year. At the midpoint of the 15.2-m line, forage sward height was measured with a falling plate meter (4.8 kg · m−2) and plant species identified. In November 2006, fiberglass pins (1.6 × 76.2 cm) were driven 73.7 cm into the stream bank at 1-m intervals from the streambed to the top of the bank along 10 equidistant transect locations on each side of the stream to measure bank erosion during spring, summer, and fall of each year. Increasing pasture stocking rates increased manure-covered ground and decreased sward height, but did not affect proportions of bare ground. The greatest, intermediate, and least net soil erosion rates occurred during the winter/early spring, late spring/early summer, and late summer/fall seasons. Stocking rates between measurements, expressed as cow-days · m−1 stream, were not related to bank erosion. Increasing stocking rates per unit of stream length will increase manure cover and decrease forage sward height, but not affect proportions of bare ground or bank erosion rates adjacent to pasture streams. Therefore, managing stocking rates may reduce nutrient loading of pasture streams.

Effects of pasture management and off-stream water on temporal/spatial distribution of cattle and stream bank characteristics in cool-season grass pastures

A 2-yr grazing experiment was conducted to assess the effects of grazing management on cattle distribution and pasture and stream bank characteristics. Six 12.1-ha cool-season grass pastures in central Iowa were allotted to 1 of 3 treatments: continuous stocking with unrestricted stream access (CSU), continuous stocking with stream access restricted to 4.9-m-wide stabilized crossings (CSR), or rotational stocking with stream access restricted to a riparian paddock (RP). Pastures were stocked with 15 fall-calving Angus cows (Bos taurus L.) from mid-May to mid-October for 153 d in 2008 and 2009. A global positioning system (GPS) collar recording cow position every 10 min was placed on at least 1 cow per pasture for 2 wk of each month from May through September. Off-stream water was provided to cattle in CSU and CSR treatments during the second of the 2 wk when GPS collars were on the cattle. A black globe temperature relative humidity index (BGTHI) was measured at 10-min intervals to match the time of the GPS measurements. Each month of the grazing season, forage characteristics (sward height, forage mass, and CP, IVDMD, and P concentrations) and bare and fecal-covered ground were measured. Stream bank erosion susceptibility was visually scored in May, August, and October (pre-, mid-, and post-stocking). Cattle in RP and CSR treatments spent less time (P < 0.10) within the stream zone (0 to 3 m from stream center) in June and August and in the streamside zone (0 to 33 m from stream zone) in May through August and May through September, respectively, than cattle in CSU pastures. However, off-stream water had no effect on cattle distribution. Compared with the CSU treatment, the CSR treatment reduced the probability (P < 0.10) that cattle were within the riparian zone (0 to 36 m from stream center) at BGTHI of 50 to 100. Bare ground was greater (P < 0.10) in pastures with the CSU than CSR and RP treatments in the stream and streamside zones in September and October and in July and September. Streams in pastures with the CSU treatment had less stable banks (P < 0.10) mid- and post-stocking than RP or CSR treatments. Results show that time spent by cattle near pasture streams can be reduced by RP or CSR treatments, thereby decreasing risks of sediment and nutrient loading of pasture streams even during periods of increased BGTHI.

Physical Characteristics, Shade Distribution, and Tall Fescue Effects on Cow Temporal/ Spatial Distribution in Midwestern Pastures

Abstract Nonpoint source (NPS) pollution of water resources may occur from congregation of cattle near streams or ponds. Therefore, relationships of physical characteristics, shade distribution, and tall fescue (Festuca arundinacea Schreb.) prevalence in cool-season grass pastures to the temporal/spatial distribution of grazing cattle were evaluated in two studies on beef cow/calf farms. Global positioning system (GPS) collars recorded the location of 2–3 cows per pasture at 10-min intervals for 5–14 d in the spring, summer, and fall annually. Pasture botanical composition was visually assessed annually. In Study 1, cow location was recorded on five pastures ranging in size from 13 ha to 125 ha with 1.9–3.8% of the pasture area in a stream or pond (water source) and 2–30% of the pasture area within 30.5 m of the water source (waterside zone) for 3 yr. Shade covered 27–73% of the pasture area with 3–64% of shade located within waterside zone. In Study 2, cow location was recorded in three pastures with areas of 8 ha, 10 ha, and 15 ha with 17.8%, 43.4%, and 14.7% of the total area and 28%, 73%, and 68% of the total shade in the waterside zone for 1 yr. In Study 1, proportions of cow observations within the waterside zone increased with decreasing pasture area (r2 = 0.61) and increasing proportions of the total pasture area (r2 = 0.37) and shade (r2 = 0.29) within the waterside zone. In Study 2, proportion of cow observations in the waterside zone increased as the proportion of total area (r2 = 0.62) and shade (r2 = 0.42) in the waterside zone increased. Results imply more restrictive measures to minimize the risks of NPS pollution of water resources may be most effective in smaller and narrow pastures. Resumen La contaminación de origen no identificado (NPS) de los recursos hídricos, puede ocurrir debido a la congregación del ganado cerca de los arroyos o estanques. Por lo tanto, las relaciones de las características físicas, distribución de la sombra y la incidencia de Festuca alta (Festuca arundinacea Schreb.) en potreros con gramíneas de crecimiento invernal en la distribución temporal/espacial del pastoreo del ganado se evaluaron en dos estudios en una granja de vaca-becerro. Collares de sistema de posicionamiento global (GPS) registraron la ubicación de 2 a 3 vacas por potrero a intervalos de 10 minutos de 5 a 14 en la primavera, verano y otoño anualmente. La composición botánica de los potreros se evaluó visualmente cada año. En el estudio 1, conducido durante tres años, la ubicación de las vacas se registró en cinco potreros con un rango de 13 a 125 hectáreas de extensión, con 1.9 a 3.8% de la superficie del potrero en arroyos o estanques (fuente de agua) y 2 a 30% de la superficie del potrero dentro de 30.5 m de distancia de la fuente de agua (zona de agua) para 3 años. Los sombreaderos cubrieron de 27 a 37% del área del potrero con 3 a 64% de la sombra ubicada dentro de la zona del agua. En el estudio 2, la ubicación de las vacas se registró en tres potreros con áreas de 8, 10, y 15 hectáreas con 17.8, 43.4 y 14.7% de la superficie total y 28, 73 y 68% de la sombra total en la zona del agua y se evaluó durante un año. En el estudio 1, las proporciones de las observaciones de las vacas dentro de la zona del agua aumentaron con la disminución de la superficie del potrero (r2 = 0.61) y aumentaron las proporciones de la superficie total del potrero (r2 = 0.37) y con la sombra (r2 = 0.29) dentro de la zona del agua. En el estudio 2, aumento la proporción de observaciones de vaca en la zona del agua conforme la proporción de la superficie total (r2 = 0.62) y sombra (r2 = 0.42) en la zona del agua aumentó. Estos resultados sugieren medidas más preventivas para minimizar los riesgos de contaminación de NPS en los recursos hídricos y puede ser más eficaz en potreros más estrechos y pequeños.

Cultural Energy Analysis of Lamb Production in the Feedlot or on Pasture and in the Feedlot

ABSTRACT Data from terminal study conducted to evaluate post-weaning growth and carcass traits of Texel, Suffolk and Columbia sired offspring were used to evaluate cultural energy analysis of lamb production in the feedlot or on pasture and in the feedlot. Study was initiated with exposing 82 whiteface ewes composed of primarily Polypay × Dorset ewes to Texel, Suffolk or Columbia rams for 35-day breeding season. The ewes were wintered outdoors on average quality alfalfa hay fed at a level to meet their NRC (1985) requirements and were not fed any concentrate during late gestation or lactation.

Evaluating Texel-, Suffolk-, and Columbia-Sired Offspring: II. Postweaning Growth and Carcass Traits Under Feedlot and Pasture-Feedlot Finishing Systems1

A terminal sire study was conducted to evaluate postweaning growth and carcass traits of Texel-sired offspring compared with Suffolk- and Columbia-sired offspring. The lambs were weaned at an average age of 70 and 94 d during the 2-yr study, respectively. After weaning, lambs from each sire breed were allocated to one of two finishing programs. Finishing programs were 1) direct to feedlot (FP1) and 2) pasture followed by feedlot (FP2). In the feedlot, lambs were fed ad libitum shelled corn (74.86% TDN and 7.18% CP, as fed) and pelleted protein supplement (43.20% CP) in a ratio of 85:15, respectively. Lambs were harvested at a BW of 58.5 kg (±7.2 kg). The ADG was greatest for Suffolksired offspring, followed by Columbiaand Texel-sired offspring (318, 286, and 262 g, respectively; P<0.01). Mean ADG was greater (P<0.01) for FP1 lambs than for FP2 lambs (333 vs 244 g, respectively). Feed efficiency (FE) in drylot was similar for offspring of each sire breed; however, FE was greater for FP1 than for FP2 (4.4 vs 5.1 kg of DMI/kg of BW gain, respectively; P<0.05). Texel-sired carcasses had greater (P<0.01) longissimus area (LA) than Suffolk- and Columbia-sired carcasses (17.3, 16.1, and 16.1 cm2, respectively). Texel- and Suffolk-crossbred lambs were similar to Columbiacrossbred lambs in backfat (BF) thickness (0.79, 0.61, and 0.70 cm, respectively), although BF thickness was greater (P<0.05) in Texel- than Suffolkcrossbred lambs. Body wall thickness (BWT) was less (P<0.10) in Texel- and Suffolk-sired carcasses than in Columbia-sired carcasses (2.95, 2.99, and 3.21 cm, respectively). Dressing percentage (DP) and quality grades were similar for lambs from the 3 sire breeds. Lambs finished on FP2 had more LA (P=0.05) and less BF (P=0.10) than lambs finished on FP1 (16.4 vs 15.5 cm2 and 0.54 vs 0.64 cm, respectively). The BWT was also less in carcasses of lambs finished on FP2 vs FP1 (2.57 vs 2.85 cm, respectively; P<0.01). The interactions between sire breeds and finishing programs were nonsignificant for all growth and carcass traits except DP. These data indicate that Texel-sired crossbred lambs may have some potential for increasing muscle mass. However, increased lean mass of Texel-crossbred lambs is counterbalanced by lesser postweaning growth rate than Suffolk- and Columbia-sired crossbred lambs. Grazing lambs following weaning and prior to finishing in drylot improved leanness and muscling without influencing quality grade.

Skin Test and Gamma Interferon Enzyme-Linked Immunosorbent Assay Results in Sheep Exposed to Dead Mycobacterium Avium Subspecies Paratuberculosis Organisms

Cell-mediated immunity (CMI) diagnostic tests, such as the gamma interferon enzyme-linked immunosorbent assay (IFN-γ ELISA) and the Johnin skin test, have the potential to detect animals infected with Mycobacterium avium subspecies paratuberculosis (MAP) early in the course of the disease. While these CMI tests tend to be relatively specific in noninfected flocks, in MAP-infected flocks, these tests often identify animals that cannot be confirmed infected by any other reference test, including necropsy and culture. The aim of this study was to determine if antigen exposure by inhalation or oral ingestion of killed MAP organisms would cause a detectable CMI response in sheep. Forty-eight lambs 4 months of age were randomly divided into a control group, an orally exposed group (dosed with 1 × 10 10 autoclaved MAP organisms 3 times), and an inhalation-exposed group (dosed once with 1 × 10 5 dead organisms). Lambs were skin tested and/or bled pre-exposure and 1, 2, 3, 4, and 12 months postexposure. No significant difference was seen with either the oral- or inhalation-exposed groups of lambs versus controls with either the IFN-γ ELISA or the skin test at any time pre- or postexposure. These results suggest that infection/invasion of MAP organisms must occur in order to have a positive skin test or IFN-γ ELISA beyond the false-positive rate. Simple exposure is not enough to elicit a detectable CMI response.

Evaluation of Vitamin E and Selenium Supplementation in Late Gestation on Lamb Survival and Pre-Weaning Growth1

This study was conducted to evaluate vitamin E injection and Se in a mineral supplement in late gestation on lamb survival and pre-weaning growth performance. Ewes were grouped in pens based on their fetal count and BW. The feed provided to ewes in late gestation included alfalfa hay, corn, and protein supplement according to NRC (1985) recommendations. Ewes in late gestation were assigned to a 2 × 2 factorial arrangement of treatments within fetal count (single, twin, and triplet + quad). Treatments were no vitamin E or 900 IU of vitamin E injected i.m. per week and 10 or 90 ppm of Se in a mineral supplement fed ad libitum. Within each pen of ewes (8 to 10 head), approximately one-half of the ewes received injectable E beginning 4 wk before the first expected lambing; the other one-half received no vitamin E. Vitamin E treatments ended at lambing time; however, ewes remained on their respective mineral sources during lactation. Lambs were provided access to creep (16% CP, 83% TDN, and fortified with 35,000 IU of vitamin E, 0.27 g of Se, and 50 g of chlortetracycline/909 kg of creep feed) initiated at an average 10 d of age to weaning. Weekly injection of 900 IU of vitamin E did not affect birth BW (BBW) of lambs. However, 90 ppm of Se fed ad libitum improved BBW of lambs (5.06 vs 4.88 kg, P<0.10) with all of the improvement occurring in lambs born to 6- to 7-yr-old ewes (P<0.01). Vitamin E increased (P<0.05) the pre-weaning performance of lambs from 1- to 2- and 6- to 7-yr-old ewes but did not improve the performance in lambs from 3- to 5-yr-old ewes. Multiple-birth lambs from ewes treated with vitamin E had increased survival in 1 of 2 experimental yr (P<0.05). Survival of single-birth lambs was not effected by vitamin E or Se treatment. These results demonstrate that supplementation of 90 ppm of Se fed ad libitum to ewes during late gestation and throughout lactation improved BBW of lambs from 6- to 7-yr-old ewes, and weekly injection of 900 IU of vitamin E to ewes during late gestation increased the pre-weaning growth of lambs from 1- to 2- and 6- to 7-yr-old ewes and may increase the survival of multiple-birth lambs.

Evaluating Texel-, Suffolk-, and Columbia-Sired Offspring: I. Prolificacy, Survival, and Preweaning Growth Traits Under a Forage-Based Lambing System1

Abstract A terminal sire study was conducted over a 2-yr period to evaluate production traits of Texel-sired offspring compared with Suffolk- and Columbia-sired off-spring in a pasture-lambing system. Polypay x Dorset crossbred ewes were mated to Texel, Suffolk, or Columbia rams for a 35-d breeding season commencing in December of each year. The ewes were wintered outdoors on alfalfa hay (54.5% TDN and 16% CP; as-fed basis) at a level to meet their NRC (1985) requirements. The ewes were not fed any concentrate during late gestation or lactation. A total of 279 lambs were born with an average of 1.7 lambs per ewe. Prolificacy, litter birth, and weaning BW (WBW) were largely unaffected by sire breeds (SB). Birth BW (BBW), WBW, and 60-d adjusted WBW (Adj-WBW) of lambs sired by Texel rams were 5.3, 24.5, and 18.4 kg, respectively, and were comparable with lambs sired by Suffolk rams (5.4, 24.7, and 18.4 kg, respectively) but were greater (P