Entire Grazing Period Research Articles

Evaluation of Grazing Options During Summer for Growing Heifers – Year 3

Developing methods to provide high quality forage through most of the year is important for cattle operations. The purpose of this study was to determine forage management options to offset the summer “slump” with fescue. Four grass pasture treatments (10 pastures total; 4 acres each) were used in a completely randomized design and stocked with growing heifers (n = 49; initial wt 461 ± 65 lb). Pasture treatments consisted of novel fescue (FES), crabgrass (CRAB), bermudagrass (BERM), and sorghum-sudan interseeded into novel fescue (SS-FES). Heifers were weighed and they grazed pastures from May to September. Heifers on FES were continuously grazed. All other pastures were rotationally grazed. Sorghum-sudan was interseeded into fescue pastures in May. Average daily gain (ADG) for the entire grazing period was not different between pasture systems. Heifers on BERM and SS-FES had greater gain per acre than those FES pastures, with CRAB being intermediate. This result was primarily based on the increased stocking rates for those pastures. The extreme drought during the summer of 2022 resulted in little to no production of the sorghum-sudan and these pastures had the lowest biomass through the grazing period. Moisture is essential for success of interseeding sorghum-sudan into fescue pastures. Weather patterns impact animal performance as it impacts forage production. The best management practice may involve operations that have a variety of cool and warm-season grasses that producers can use to optimize forage production through varying weather events.

Evaluation of Grazing Options During Summer for Growing Heifers – Year 2

Developing methods to provide high quality forage through most of the year is important for cattle operations. The purpose of this study was to determine forage management options to offset the summer “slump” with fescue. Four grass pasture treatments (10 pastures total; 4 acres each) were used in a completely randomized design and stocked with growing heifers (n = 49; initial wt 473 ± 60 lb). Pasture treatments consisted of novel fescue (FES), crabgrass (CRAB), bermudagrass (BERM), and sorghum-sudan interseeded into novel fescue (SS-FES). Heifers were weighed and grazed pastures from April to September (153 d). Heifers on FES were continuously grazed. All other pastures were rotationally grazed. Sorghum-sudan was interseeded into fescue pastures in May. Average daily gain (ADG) for the entire grazing period was not different between pasture systems. In contrast to the previous year, there were no differences in heifer gain, ADG, or gain per acre for any of the grazing treatments.

PSI-2 Spices in Free-choice Mineral Offer Gain Advantages to Cattle on Tallgrass Native Range and Promise as Fly Control

Abstract This study aims to evaluate effectiveness of two operational management systems for steer gains and fly control. The first strategy evaluated was pasture burn date of March (MAR) or April (APR). The second management strategy was fly control through feeding free-choice mineral with spices (SPICE) or without spices (CON). Eight pastures (n = 281 steers; initial weight 277.7 ± 25.2 kg) were used in a 2 x 2 factorial treatment structure. Steers were weighed individually, randomly assigned to treatment, and grazed for 85 days. Weekly 33% of steers per pasture were photographed and fly numbers counted. ADG was impacted by both burn date and mineral type (P = 0.01). Cattle on the APR-SPICE treatment had a greater ADG than MAR-SPICE and APR-CON with MAR-CON intermediate. Cattle on SPICE gained 4.5 kg (P = 0.12) more than cattle consuming CON mineral. Flies per steer were impacted by burn x mineral x week (P < 0.001). In general, APR-SPICE steers had a greater number of flies weeks 8, 10, and 11 (P < 0.05), corresponding to a time when mineral intake averaged 72% of the formulated intake. The MAR-SPICE steers consumed on average the formulated amount of mineral and through the entire grazing period had lower number of flies than APR-SPICE steers (P < 0.05). The second largest ADG observed with the MAR-CON treatment may be attributed to lower fly numbers as this treatment had one extra week below economic threshold for horn flies. These results are somewhat inconclusive on pasture burn date, but show that the addition of spices to a free-choice complete mineral shows promise as a cost-effective method to increase gains in stocker steers on tallgrass native range. As a fly control method, the spices utilized in this study may be effective if intake is at formulated level.

Tamegrass Forage Options for Growing Heifers During the Summer

Abstract Developing methods to provide high quality forage through a majority of the year is important for cattle operations. The purpose of this study was to determine forage management options to off-set the summer “slump” with fescue. Four grass pasture treatments (10 pastures total; 1.67 ha each) were used in a completely randomized design and stocked with growing heifers (initial wt 190 ± 9.1 kg). Pasture treatments consisted of fescue (FES; n = 2 pastures with 4 head/pasture), crabgrass (CRAB; n = 3 pastures with 4 head/pasture), bermudagrass (BERM; n = 3 pastures with 5 head/pasture), and sorghum-sudan interseeded into fescue (SS-FES; n = 2 pastures with 6 head/pasture from April to July, then 4 head/pasture from July to November). Heifers were weighed in April, May, July, September, and November. Heifers assigned to FES/SS-FES pastures grazed from April to November (213 d) and for CRAB and BERM treatments, May through September (131 d). Heifers on FES grazed continuously, while other grass treatments were rotationally grazed. Heifers remained in treatment pasture through the entire grazing period. Data were analyzed using mixed procedures of SAS with pasture as experimental unit. Average daily gain for the entire grazing period was greater for heifers on SS-FES as compared to all other grass treatments (P = 0.001). Between April and May, FES heifers had greater ADG than SS-FES (P = 0.001); yet, heavier stocking rate in SS-FES resulted in similar BW gain/ha (P = 0.16). May to July ADG and BW gain/ha was greatest for BERM, then CRAB, with FES and SS-FES having the lowest gains (P < 0.001). From July through September, ADG was greater for SS-FES and CRAB as compared to FES, with BERM intermediate (P = 0.03); and BW gain/ha tended to be lower for FES compared to other treatments (P = 0.10). Average daily gain and BW gain/ha were greater for SS-FES than FES (P = 0.001) from late September to November. As a summer grazing option, warm season grass alternatives, either as the sole source of pasture or interseeded into fescue, are better options for gain as compared to fescue alone.

Dual-purpose crops: the potential to increase cattle liveweight gains in winter across southern Australia

Context Dual-purpose wheat (Triticum aestivum L.) and canola (Brassica napus L.) crops have been extensively researched for grazing in Australian farming systems, with a focus on grazing by sheep. In some regions, dual-purpose crops have been grazed by cattle, but there have been reports of animal health problems. Aims This paper sought to collate all known experiments conducted throughout Australia of cattle grazing dual-purpose crops, in order to evaluate grazing management options for cattle on dual-purpose crops that result in high growth rates and good animal health outcomes. Methods There were six experiments. In Expts 1–3, cattle were grazed on wheat crops with and without available mineral supplementation of NaCl and MgO in a 1:1 ratio. In Expt 3, lime was also added to the mineral mix. In Expts 4 and 5, dual-purpose crops were grazed in combination with annual pastures to determine whether strategic use of dual-purpose crops could increase whole farm livestock productivity. In Expt 6, cattle were introduced to dual-purpose canola with different periods of adaptation (0, 4 and 7 days). Liveweight gain was monitored regularly to assess differences between adaptation treatments. Key results Liveweight gain was increased by 0–27% when cattle grazing high quality, dual-purpose wheat were provided with mineral supplement. Cattle had an initial lag in growth rate when introduced to dual-purpose canola for grazing and this was not affected by the adaptation strategy used. Cattle that experienced a shorter adaptation period achieved higher weight gains more quickly. After the lag phase, average daily gain (ADG) was ≥2 kg/head.day, with an ADG over the entire grazing period for all treatments of 1.75 kg/head.day. The effect on the farm system was determined by extending the length of the grazing period on the dual-purpose crops. Grazing periods of shorter duration did not increase overall liveweight gains compared with grazing only pasture, whereas extending the period of dual-purpose crop grazing resulted in increased cattle weights. Conclusions Cattle benefit from the addition of mineral supplements when grazing a dual-purpose wheat crop, with a response similar to that previously demonstrated in sheep. Cattle can safely graze dual-purpose canola and achieve high ADG. Inclusion of dual-purpose crops can improve overall cattle performance in the farming system. Implications The potential area for production of dual-purpose crops within the Australian mixed farming zone is large and there may be insufficient livestock numbers within the zone to utilise the potential forage production. Cattle from other regions could be introduced during autumn and winter to realise this large forage potential during a period that is commonly a feed deficit on grazing-only properties. Estimates suggest that up to two million young cattle could be supported for 60 days, increasing liveweight by 90 kg/head.

PSVI-16 Effects of feeding spices on heifer gains and potential as tick management

Abstract Alternative methods to antibiotics/chemical usage in cattle production has been of interest in recent years and essential oils/spices have been promoted to fill this niche. The purpose of this research was to evaluate effect of feeding spices on heifer gains and as control method for ticks. Eight bromegrass pastures were stocked (March to November) with four heifers per pasture to compare control mineral (CON) to mineral containing spices (SPICE; garlic + proprietary blend of 4 spices). Mineral (113.4 g/hd/d) was blended in dried distillers grains (DDGs) and total blend was supplemented daily at 0.5% of BW. Heifers were weighed on two consecutive days at the start and end of the study and every 28 d. Weekly (1st 10 weeks), ticks were counted and removed from every heifer. Gains evaluated using MIXED (SAS 9.4) as completed randomized design with subsampling where pasture was experimental unit and heifer within pasture as subsample. Ticks/heifer was evaluated similarly using GLIMMIX with binomial distribution. Average daily gain was increased by 0.7 kg/d with the SPICE mineral (P = 0.04) and heifers on SPICE gained 15 kg more over the entire grazing period (P = 0.04) than heifers on CON. The gain advantage for SPICE was observed within the first 28 d (P = 0.05). Overall, these pastures had a low tick population (137 total ticks collected). Even so, there was a tendency (P = 0.09) for a treatment x week interaction, where in weeks 2 and 3, SPICE heifers tended (P = 0.12) to have more ticks/heifer than CON heifers, yet at weeks 8 and 10 SPICE heifers tended (P = 0.07) to have less ticks/heifer than CON. SPICE in a mineral blended with DDGs increase heifer gains and appear, after a minimum of 4 weeks of consumption, to show some repellent effects to ticks.

263 Interaction between stocking and supplementation rates on the performance of steers grazing mixed-grass prairie during winter

Abstract To evaluate the effects of stocking and supplementation rates on steers grazing mixed-grass prairie during winter, 16 pastures (10 to 21 ha each) were selected and treatments were arranged in a 3 x 2 factorial design; the first factor was an stocking rate of 39.4, 33.2, and 29.7 animal-unit-d/ha harvested over 88 d of grazing; the second factor was supplementation at 0.9 or 1.4 kg/d. Steers were fed a 43% CP cottonseed meal-based pellet. Pastures were stocked annually in late January (2009, 2010, and 2011) with British x Continental crossbred beef steers (body weight = 202 ± 6.7 kg; n = 137 steers/yr) at stocking densities described above. Data were analyzed by ANOVA with pasture as the experimental unit and year as a random variable; least-squares means were separated with linear and quadratic contrast. From late-January to mid-March, average daily gain (ADG, kg) did not differ (P = 0.13) among stocking rates, but ADG differed (P = 0.01) between 0.9 and 1.4 kg of supplement/d. From mid-March to late-April and over the entire grazing period, ADG responded to stocking rate and interacted (P < 0.01) with supplementation rate; ADG tended to respond quadratically (P ≤ 0.09) to stocking rate at 0.9 kg/d of supplementation, but with 1.4 kg/d of supplement ADG was not affected (P ≥ 0.18). Body weight gain per hectare tended (P < 0.08) to interact between stocking and supplementation rates. With 0.9 kg/d of supplement the BW gain per hectare increased quadratically (P < 0.01) in response to increasing stocking rate, where supplementation at 1.4 kg/d resulted in BW gain per hectare increasing linearly (P < 0.01). Optimal supplementation rates with high-protein feeds is related to stocking rate. At lower stocking rates, less supplement seems to be most beneficial. At higher stocking rates, more supplement is justified.

Vaccination of calves against Cooperia oncophora with a double-domain activation-associated secreted protein reduces parasite egg output and pasture contamination

With the increasing incidence of anthelmintic resistance worldwide, immunological control of worm infections through vaccination is often put forward as a rational and cost-effective alternative for anthelmintic drugs. In this study we report on the evaluation of a double-domain activation-associated secreted protein purified from the excretory–secretory material of the adult stage of the small intestinal parasite Cooperia oncophora as a vaccine antigen against this parasite. In a first experiment, calves were vaccinated three times i.m. with activation-associated secreted protein and Quil A adjuvant or with adjuvant alone, and subsequently challenged with a trickle infection of 25,000 infective larvae in total over 25days. Vaccinated calves showed a significant reduction of 91% in their cumulative faecal egg counts and a significantly higher number of inhibited L4s present in their intestine compared with control animals. Furthermore, both female and male adult worms were significantly smaller in the vaccinated group than in the control group. In a second experiment, the vaccine antigen was further evaluated under field conditions. Calves were immunised as described above, followed by a natural challenge infection on pasture. Cooperia oncophora faecal egg counts in the vaccinated animals were reduced during the entire grazing period, resulting in a significant reduction in the cumulative faecal egg counts of 58.5%. Numbers of infective C. oncophora larvae were lower on plots grazed by vaccinated calves, with a reduction in mean pasture larval counts of 65% at housing. A significant reduction of 81.6% in total numbers of C. oncophora worms was shown in the vaccinated group compared with the control group. Taken together, the data highlight the protective capacity of the double-domain activation-associated secreted protein and the possibility of controlling C. oncophora infections through vaccination.

A Study on the Transfer of Iron in Soil–Plant–Animal Continuum Under Semi-arid Environmental Conditions in Sargodha, Pakistan

The present investigation on the iron (Fe) transfer from soil to plant and in turn to animal (cows), as a function of sampling periods was conducted at the Livestock Experimental Station Sargodha, Pakistan which falls under semi-arid conditions. Although the iron transfer from soil to forage increased consistently, the forage Fe content decreased progressively with increase in sampling period. Highest Fe transfer from forage to cow blood plasma was observed during October and lowest during January. The transfer of Fe from forage to animal milk was maximum during the months of October and January and minimum during December. The transfer of Fe to plasma and milk was found to be dependent variably on the growth stage of forage in this investigation. Based on the findings of the present study, it is evident that mineral supplementation with higher Fe availability is urgently warranted to the animals particularly during the months of December and January to enhance plasma Fe in the cows being reared at that livestock farm during the entire grazing period. Thus, obligatory supplementation of Fe to the ruminants is highly recommended. Since the processes involved in iron management system in humans, animals, and plants are basically similar, appropriate elemental management must be provided to the living organisms, otherwise deficient or excessive levels of iron may deteriorate the developing cells of the organisms.

Supplementation of stocker steers grazing native Flint Hills pasture with a protein and mineral supplement increases average daily gains (2007)

Supplementation of range cattle with minerals is a common management practice that is used to maximize performance. Flint Hills grasses provide an adequate amount of protein for the diet through the first half of a doublestock grazing period, but declining protein content of native grasses during the latter parts of the grazing season typically cause decreases in forage digestibility and daily gains. The goal of this experiment was to measure differences in performance between steers that were supplemented with a) loose salt for the entire grazing period, b) a stocker mineral supplement for the entire grazing period, or c) a stocker mineral supplement for the first half of the grazing period followed by supplementation with a combination of protein and mineral for the second half of the grazing season.

Determining the Composition of Herbivore Diets in the Trans-Himalayan Rangelands: A Comparison of Field Methods

In late summer, in a semi-arid mountain range in Nepal, we compared 3 field methods for determining the botanical composition of herbivore diets. Data were collected from the same animals belonging to 1 herd of domestic yak (Bos grunniens) and 2 herds of mixed smallstock, consisting of domestic goats (Capra hircus) and sheep (Ovis aries). Bite count, feeding site examination, and microhistological analysis of feces gave different estimates of forage categories and plant species in both animal groups. Because yaks grazed in other vegetation communities when not observed for bite-counts and feeding signs, the results from the latter methods could not be compared directly with that from fecal analysis. In smallstock, feeding site examination gave higher estimates of graminoids and lower estimates of shrubs than the other 2 methods, probably because all feeding signs on shrubs were not detected. Bite-counts and fecal analysis gave comparable results, except that forbs were underestimated by fecal analysis, presumably due to their more complete digestion. Owing to the difficulty in collecting samples that are representative of the entire grazing period and the problem of recording feeding signs correctly, both feeding site examination and bite-counts are unsuitable methods for studying the food habits of free ranging domestic and wild herbivores. Microhistological analysis of feces appears to be the most appropriate method, but correction factors are needed to adjust for differential digestion. The systematic use of photomicrographs improves the speed and accuracy of the fecal analysis.

Determining the Composition of Herbivore Diets in the Trans-Himalayan Rangelands: A Comparison of Field Methods

In late summer, in a semi-arid mountain range in Nepal, we compared 3 field methods for determining the botanical compositionof herbivore diets. Data were collected from the same animals belonging to 1 herd of domestic yak (Bos grunniens) and 2 herds of mixed smallstock, consisting of domestic goats (Capra hircus) and sheep (Ovis aries). Bite count, feeding site examination,and microhistological analysis of feces gave different estimates of forage categories and plant species in both animal groups. Because yaks grazed in other vegetation communities when not observed for bite-counts and feeding signs, the results from the latter methods could not be compared directly with that from fecal analysis. In smallstock, feeding site examination gave higher estimates of graminoids and lower estimates of shrubs than the other 2 methods, probably because all feeding signs on shrubs were not detected. Bite-counts and fecal analysis gave comparable results, except that forbs were underestimated by fecal analysis, presumably due to their more complete digestion. Owing to the difficulty in collecting samples that are representative of the entire grazing period and the problem of recording feeding signs correctly, both feeding site examination and bite-counts are unsuitable methods for studying the food habits of free ranging domestic and wild herbivores. Microhistological analysis of feces appears to be the most appropriate method, but correction factors are needed to adjust for differential digestion. The systematic use of photomicrographs improves the speed and accuracy of the fecal analysis.

Bermudagrass management in the Southern Piedmont USAV: Gastrointestinal parasite control in cattle

Parasite-free pastures would improve cattle health and performance, resulting in possible economic return to producers. Our objective was to determine the effect of a single series of anthelmintic treatment of steers prior to stocking on Coastal bermudagrass pastures, during five consecutive summers, on the parasite burden in cattle. The site for this experiment had been conventionally cropped for several decades, with no exposure to cattle, and would be expected to be relatively free of nematode larvae. The experimental design was a randomized complete block (landscape features) with a split plot arrangement of treatments where main plots were pasture fertilization treatments (mineral, clover plus mineral, and broiler litter) and split plots were low and high forage mass. Anthelmintic treatment included pour-on ivermectin on day −21, albendazole on day −7, and injectable ivermectin 48 h prior to stocking of pastures, with the cattle remaining in drylot during the 48-h period prior to being placed on the experimental paddocks. All steers received only one series of treatments during any given year. Yearling Angus steers (Bos taurus) were managed in a put-and-take grazing system with three “tester” steers assigned to each paddock and “grazer” steers added or removed at 28-day intervals. From 1994 to 1998, steers grazed the paddocks for a 140-day period from mid May until early October each year. Fecal samples for worm egg counts were obtained on day 0 and at 28-day intervals, thereafter. On all sampling days after day 0, samples were obtained only from tester animals. Over the 5-year period, the mean eggs per gram of feces (epg) gradually increased from 0 (following treatment) to a mean of 2.2 (range from 0.7 to 3.0) by the end of the grazing season (the last sampling date) in October. Although the epg were not zero, they were below threshold levels that would allow development of a parasite burden in cattle. In traditional management systems, cattle graze parasite-contaminated pastures; therefore, parasites negatively impact growth and productivity throughout the entire grazing period. Periodic anthelmintic treatments simply give a temporary reprieve from those parasitic infections. Conceptually, using the current grazing system, it should be possible to maintain these pastures in a parasite-free status indefinitely; however, from a drug resistance perspective, it would be most applicable in sod-based rotation systems where cattle graze from two to five years before land is returned to row-crops. By removing the effect of parasites, cattle can grow without the physiological constraints that gastrointestinal parasites place on appetite, digestion, nutrient utilization, and general well being.

Bermudagrass management in the Southern Piedmont USA: V: Gastrointestinal parasite control in cattle

Parasite-free pastures would improve cattle health and performance, resulting in possible economic return to producers. Our objective was to determine the effect of a single series of anthelmintic treatment of steers prior to stocking on Coastal bermudagrass pastures, during five consecutive summers, on the parasite burden in cattle. The site for this experiment had been conventionally cropped for several decades, with no exposure to cattle, and would be expected to be relatively free of nematode larvae. The experimental design was a randomized complete block (landscape features) with a split plot arrangement of treatments where main plots were pasture fertilization treatments (mineral, clover plus mineral, and broiler litter) and split plots were low and high forage mass. Anthelmintic treatment included pour-on ivermectin on day −21, albendazole on day −7, and injectable ivermectin 48 h prior to stocking of pastures, with the cattle remaining in drylot during the 48-h period prior to being placed on the experimental paddocks. All steers received only one series of treatments during any given year. Yearling Angus steers ( Bos taurus) were managed in a put-and-take grazing system with three “tester” steers assigned to each paddock and “grazer” steers added or removed at 28-day intervals. From 1994 to 1998, steers grazed the paddocks for a 140-day period from mid May until early October each year. Fecal samples for worm egg counts were obtained on day 0 and at 28-day intervals, thereafter. On all sampling days after day 0, samples were obtained only from tester animals. Over the 5-year period, the mean eggs per gram of feces (epg) gradually increased from 0 (following treatment) to a mean of 2.2 (range from 0.7 to 3.0) by the end of the grazing season (the last sampling date) in October. Although the epg were not zero, they were below threshold levels that would allow development of a parasite burden in cattle. In traditional management systems, cattle graze parasite-contaminated pastures; therefore, parasites negatively impact growth and productivity throughout the entire grazing period. Periodic anthelmintic treatments simply give a temporary reprieve from those parasitic infections. Conceptually, using the current grazing system, it should be possible to maintain these pastures in a parasite-free status indefinitely; however, from a drug resistance perspective, it would be most applicable in sod-based rotation systems where cattle graze from two to five years before land is returned to row-crops. By removing the effect of parasites, cattle can grow without the physiological constraints that gastrointestinal parasites place on appetite, digestion, nutrient utilization, and general well being.

Grazing Pressure on Beef and Grain Production of Dual‐Purpose Wheat in Argentina

The effects of three different grazing pressures on beef (Bos taurus) and wheat (Triticum aestivum L.) grain production were studied at Pasman (Argentina) during a 3‐yr study. Thirty hectares of the variety ‘Pincen’ wheat were grazed with Angus heifers during 3 yr (1995–1997) until apex differentiation. The different grazing pressures were obtained through different stocking rates, adjusted every 21 d according to forage mass, predicted forage production rate, and an estimated forage allowance of 10, 15 and 20 kg dry matter (DM) heifer−1 d−1 for high, medium, and low pressures, respectively. The three treatments were randomly allocated within a complete block design with two replications. Every 21 d forage samples were clipped and forage mass and plant composition were recorded and in vitro dry matter digestibility (IVDMD), crude protein (CP), and neutral detergent fiber (NDF) were determined. Spike density and grain production were measured at harvest. Average daily gain (ADG) was obtained from 10 heifers per plot, present throughout the entire grazing period. Gain per hectare (GH) was obtained in each plot from the mean ADG and animal days per hectare computed during stocking rate adjustments. During grazing period the levels of CP and IVDMD decreased and NDF content increased, and these trends were more pronounced in 1996 and 1997 because of rust infection. Increased grazing pressure caused increased GH and reduced ADG, forage mass at the end of the grazing period, and grain production. Means of treatments over the years for GH were 283, 225, and 176 kg ha−1, and for grain production were 955, 1150, and 1351 kg ha−1 for high, medium, and low pressures, respectively. The increase in grazing pressure (from low to high treatment) produced an increase of 107 kg ha−1 in beef production and a 396 kg ha−1 reduction in grain production. Taking into account the traditional price of beef with respect to grain in Argentina, this beef gain over grain relation at increased grazing pressure is economically profitable for farmers.

Performance of Steers Supplemented with Zinc During Grazing and Receiving at the Feedlot

Abstract A study was conducted to compare the effects of three supplemental zinc sources on beef steers grazing winter annual pasture and during receiving in a feedlot. In southern Arkansas, 84 steers were weighed (BW = 216 ± 1.5 kg), bled via jugular puncture, and randomly assigned to 12 bermudagrass pastures (0.81 ha each) that had been overseeded with wheat, rye, and annual ryegrass (7 steers per pasture; 116 d of grazing) on January 15; the steers were allowed to graze until May 11. Steers were fed 0.45 kg daily of corn-based supplement containing 103 mg zinc from ZnSO 4 , zinc amino acid complex ( ZnAA ), or zinc polysaccharide ( ZnPOL ) during the entire grazing period. On May 12, steers were shipped to a research feedlot (14 h; 1,016 km; 6.9% BW shrink) in northeast New Mexico. In the feedlot, the same groups of steers were fed a receiving diet (steam-flaked milo) that contained the same zinc sources as fed during the grazing period. Dietary concentrate was increased from 75 to 85% of dietary DM weekly. Data were analyzed as a completely random design; least squares means were separated using contrast. Steer BW on d 28 and 84 of the grazing period were greater (P 4 ; however, ADG over the 116 d of grazing and ending BW did not differ (P>0.28) among zinc sources. In the feedlot, steer BW, ADG, and feed efficiency did not differ (P>0.05) among zinc sources. Serum zinc concentrations did not differ (P>0.05) among zinc sources at any point in time. We conclude that early in the grazing period, ZnAA and ZnPOL improved steer BW compared with ZnSO 4 ; however, no differences were noted among zinc sources later in the grazing period or during receiving in the feedlot.

The effectiveness of a single dose of doramectin pour-on in the control of gastrointestinal nematodes in yearling stocker cattle

Three field studies were conducted to determine the efficacy of a single dose of doramectin pour-on in the control of gastrointestinal nematode infections in yearling stocker calves on pasture. These 140-day studies were carried out between October 1995 and March 1996 in Tennessee (TN), between January and June 1997 in Louisiana (LA), and between May and September 1997 in Wisconsin (WI). Calves with patent nematode infections were equally allocated to treatments (doramectin pour-on, at 500 μg/kg body weight or untreated control) and pastures as randomized complete-block designs (LA and TN studies) or completely at random (WI study). There were six pasture replicates per treatment at each site, with each pasture replicate accommodating six calves at the TN site (36 calves per treatment), five calves at the LA site (30 calves per treatment), and seven calves at the WI site (42 calves per treatment). Fecal samples for nematode egg counts were collected on Day 0, and at 28-day intervals thereafter. Body weights were recorded on Day 0 and at 28-day intervals until study termination. Nematode egg output of the doramectin-treated groups was reduced over the entire grazing period compared to those in the untreated control groups, resulting in average daily weight-gain advantages of 0.055 kg ( p ≤ 0.05) for the TN study, 0.208 kg ( p ≤ 0.05) for the LA study, and 0.116 kg ( p ≤ 0.05) for the WI study.

The effectiveness of a single treatment with doramectin or ivermectin in the control of gastrointestinal nematodes in grazing yearling stocker cattle

Four studies were conducted to a similar experimental design in the U.S. to evaluate the effectiveness of doramectin injectable administered to yearling stocker cattle in the control of gastrointestinal nematodiasis over the subsequent grazing period. Studies were conducted in Wisconsin (WI) and Arkansas (AR) during the summer season. The other two studies were conducted in Georgia (GA) and Mississippi (MS) during the winter/spring season. Doramectin was compared with both ivermectin injectable and ivermectin pour-on in the WI study, with ivermectin injectable alone in the GA study and with ivermectin pour-on alone in the other two studies. At each study site, an area of permanent pasture previously grazed by parasitized animals was subdivided by fencing into equal pasture units each with its own water supply. A treatment designation (non-medicated control, doramectin injectable, ivermectin injectable or ivermectin pour-on) was randomly assigned to each pasture unit. Weaned beef calves with confirmed gastrointestinal nematode infections were randomly allotted to a pasture unit and corresponding treatment group. Each treatment group consisted of three replicates of seven animals per pasture unit (total 21 animals) in the WI study, three replicates of four or six animals per pasture unit (total 16 animals) in the AR study, five replicates of six animals per pasture unit (total 30 animals) in the GA study and three replicates of 12 animals per pasture unit (total 36 animals) in the MS study. Treatments were 1% doramectin injectable solution, 1% ivermectin injectable solution, 0.5% ivermectin pour-on solution or non-medicated controls. The injectables were administered at a dose of 1 ml/50 kg body weight (200 μg doramectin or ivermectin/kg) by subcutaneous injection in the neck. Ivermectin pour-on solution was administered topically at a dose of 1 ml/10 kg body weight (500 μg ivermectin/kg). After receiving their prescribed treatment, animals were placed on their designated pasture unit where they remained for the entire grazing period (84–140 days). Fecal nematode egg counts and body weights were monitored at predetermined intervals throughout each study. Doramectin treatment reduced pretreatment egg counts by between 95 and 100% by 21 days post-treatment. Subsequent rises in egg output from exposure to infective pastures were delayed by two to four weeks resulting in substantial reductions in total egg deposition over the grazing period and, therefore, potential pasture recontamination. Doramectin treatment resulted in substantial average daily weight gain advantages (0.152–0.272 kg) over the grazing season compared to non-medicated controls. Advantages were statistically significant ( P < 0.05) in three of the four studies. There were no significant differences ( P > 0.05) in average daily gain between the doramectin and ivermectin injectable or ivermectin pour-on treated groups.

Winter performance of Hereford cows on fescue prairie and in drylot as influenced by fall grazing

An experiment was conducted to determine the feasibility of winter grazing pregnant Hereford cows on fescue prairie. The experiment was replicated over a 4-yr period (1988–1991, n = 4) and utilized a 2 × 2 factorial design representing fall grazing (September to November) on annual pasture (winter wheat and corn) or fescue prairie; and winter grazing (November to the end of February) on fescue prairie or feeding in a drylot. The cows weighed an average of 519 kg and had an average of 4.4 mm of backfat in late May when summer grazing on fescue prairie began and 7.2 mm of backfat at the beginning of fall grazing. Measurements of cow backfat and cow weights at each feeding change indicated that during the fall grazing period, average daily gain (ADG) was −0.43 kg and change of backfat was −1.0 mm on fescue prairie compared with + 0.12 kg and + 0.9 mm, respectively, on annual forage. Fall grazing of annual forages had no effect on the ADG of cows in winter but resulted in higher backfat after the winter feeding period (5.3 vs. 4.1 mm, P = 0.009). In later winter, cows kept on fescue prairie over the entire grazing period averaged 3.5 mm of backfat, while the cows grazed on annual forages in the fall and wintered in the drylot averaged 5.7 mm. Cows may be kept on fescue prairie in fall and winter. However, feed supplementation is needed to achieve optimal condition at calving. Fall grazing of annual forages may allow cows to maintain their body weight on fescue prairie, minimizing costly feed inputs prior to calving. Key words: Cows, calves, annual forage, backfat, fall grazing

Preliminary results on species selection by animals on sour grassveld

Abstract A study of species selection by cattle under a system of controlled selective grazing using wheel‐point surveys and fistulated animals has demonstrated that both techniques provide valuable information on the preference shown for such species as Andropogon amplectens, Eulalia villosa, Themeda triandra, Trachypogon spicatus, Tristachya hispida and Monocymbium ceresiiforme. The wheel‐point survey, which presents information on the degree of utilization of different species over the entire grazing period, is complemented by the more detailed information obtained by identifying grass species from oesophageal fistula samples obtained at specific times within the grazing period. Preference for species does not appear to be markedly affected by their relative contribution to basal cover, but apparently is subject to seasonal variations.