Groups Of Steers Research Articles

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.

Effects of surgical or banding castration on stress responses and behaviour of bulls

To compare the effects of surgical and latex banding methods of castration in 14- and 9-month-old bulls. Two randomised, controlled experiments. In Experiment 1, following administration of local anaesthetic, 14-month-old bulls were castrated by either surgical or banding methods, or left entire. Behavioural, plasma cortisol, plasma haptoglobin and bodyweight responses were recorded. A group of steers from the same mob was used as an additional comparison for bodyweight data. In Experiment 2, following administration of local anaesthetic, 9-month-old bulls were castrated by either surgical or banding methods and cortisol, haptoglobin and bodyweight responses were recorded. Entire bulls from the same group were used as an additional comparison for bodyweight data. In Experiment 1, surgical castrates exhibited more leg stamping and tail swishing than banded or entire animals in the hours after castration. Surgical castrates in both experiments also showed an increase in plasma haptoglobin, which resolved after 4 days. Plasma cortisol was generally not affected by castration. Surgical castrates grew more slowly than entire bulls, but faster than banded animals, in the 56 days after treatment. In Experiment 1, after 56 days, the bodyweights of surgical and banded castrates were not different from the bodyweights of the steers. Fourteen-month-old banded cattle developed persistent wounds above the latex band which remained for several weeks after scrotal dehiscence, but this did not occur in the 9-month-old animals. The banding procedure produced fewer acute effects, but a greater suppression of growth than surgical castration and induced prolonged wound formation in the older age group, suggesting that this procedure may not be as suitable for yearling cattle.

The rate of reduction in carotenoid concentration in fat of steers fed a low carotenoid ration, and the role of increasing carcass fatness

Experiments were carried out on steers to determine the effects of different allowances of a low carotenoid ration on fat yellowness and the interval from starting on the ration to significant decreases in fat yellowness. In Expt 1, forty 17–18-month-old steers were fed a ration of maize grain, maize silage, and soybean meal containing 6 mg β-carotene/kg DM, and were slaughtered 0, 28, 42, or 70 days after starting on the ration. Significant decreases in fat yellowness and carotenoid concentration in the fat occurred 70 days after starting on the ration. The exception was subcutaneous fat, which had a significant reduction of carotenoid concentration after only 28 days. Decreases in fat yellowness coincided with and were of a similar magnitude to increases in fat deposits. In Expt 2, 3 groups (n = 13) of 24–26-month-old steers were fed a ration of maize grain and pasture silage, which contained 33 mg β-carotene/kg DM. The ration was fed to steers for 63 days at 1 of 3 allowances with the aim of gaining weight rapidly (FASTGN), gaining weight slowly (SLOWGN), or losing weight (WTLOSS). A fourth group of steers (n = 9) was slaughtered at the beginning of the experiment. The growth rates of the steers over the 63 days were 1.72, 0.71, and –0.03 kg/head.day for FASTGN, SLOWGN, and WTLOSS, respectively. Fat yellowness and carotenoid concentration in the fat depots were lower (P < 0.05) for FASTGN than for WTLOSS and steers slaughtered at the beginning of the experiment, with no differences between the latter 2 groups. The SLOWGN were intermediate with higher fat yellowness or carotenoid concentration in some fat depots than for FASTGN and lower than for WTLOSS in other fat depots. In both experiments there were negative correlations between plasma cholesterol (PChol) concentration and fat yellowness and carotenoid concentration, and positive correlations between these traits and plasma carotenoid concentration (PCar). PCar :PChol ratio was a better predictor of fat yellowness and carotenoid concentration than PCar or PChol concentration alone. The conclusions were that reduction in fat yellowness was largely caused by a dilution of existing fat with whiter fat and the rate of change in fat yellowness depended on the rate of fat deposition. The results suggest that carotenoids do not come out of fat once deposited there but further experiments are required to confirm this suggestion.

Prevalence of Neospora antibodies in beef cattle in New Zealand

dAim:To estimate the prevalence of Neospora infection in a sample of New Zealand beef cattle. dMethods: The prevalence of Neospora caninum infection in New Zealand beef cattle was estimated by collecting blood at slaughter from 499 beef cattle from 40 different farms at 2 slaughter plants in the North Island and 1 in the lower South Island. Sera were tested using an ELISA against Neospora tachyzoite antigen. dResults: The prevalence of seropositive cattle was 2.5% (n=120), 3.6% (n=166) and 2.3% (n=213) at the plants surveyed, the overall prevalence being 2.8%. The serologically positive cattle came from 9 farms, 3 of which had more than 1 positive animal. The highest prevalence recorded amongst animals from 1 farm was 4/13 (31%), in a group of young steers. dConclusion: Neosporosis appears to be present at a lower level in the New Zealand beef cattle population than in the New Zealand dairy cattle population. Nevertheless, from the high seroprevalence evident amongst young cattle on 1 farm, we suggest that Neospora may be a cause of infertility in beef cattle in this country.

Feeding reduces activity of growth hormone-releasing hormone and somatostatin neurons.

Secretion of growth hormone (GH) is synchronized among castrate male cattle (steers) around feeding when access to feed is restricted to a 2-hr period each day. Typically, concentrations of GH increase before and decrease after feeding. Our objectives were to determine whether i) concentrations of GH decrease in blood after start of feeding; ii) activity of immunoreactive growth hormone-releasing hormone (GHRH-ir) neurons decreases in the arcuate nucleus (ARC) after feeding; iii) activity of immunoreactive somatostatin (SS-ir) neurons in the periventricular nucleus (PeVN) and ARC increase after feeding; and iv) GHRH stimulates release of GH to a similar magnitude at 0900 and at 1300 hr, in steers fed between 1000 and 1200 hr. Blood samples were collected at 20-min intervals from 0700 to 1300 hr. Groups of steers were euthanized at 0700, 0900, 1100, and 1300 hr (n = 5 per group). Dual-label immunohistochemistry was performed on free-floating sections of hypothalami using antibodies directed against Fos and Fos-related antigens (Fos/FRA) as a marker of neuronal activity in immunoreactive GHRH and SS neurons. Concentrations of GH were high before and decreased after feeding. The percentage of SS-ir neurons containing Fos/FRA-ir in the PeVN was 50% lower (P<0.01) at 1100 hr and 36% lower (P<0.05) at 1300 hr than at 0900 hr. There was no change in percentage of SS-ir neurons containing Fos/FRA-ir in the ARC. The percentage of GHRH-ir neurons containing Fos/FRA-ir in the ARC was 66% lower (P<0.05) at 1100 hr and 65% lower (P<0.05) at 1300 hr than at 0700 hr. In contrast, the number of GHRH-ir neurons increased from 0700 to 1300 hr. GHRH-induced release of GH was suppressed at 1300 hr compared with 0900 hr. In conclusion, reduced basal and GHRH-induced secretion of GH after feeding was associated with decreased activity of GHRH neurons in the ARC and decreased activity of SS neurons in the PeVN.

Impact of locoweed poisoning on grazing steer weight gains

Emaciation is one of the clinical signs of locoweed poisoning but few studies have documented impacts of locoweed poisoning on weight gains. Stocker steers (British X Continental cross, 200-210 kg) were grazed on locoweed-infested, short-grass prairie in 1996 and 1997 in northeast New Mexico. Each year, half the steers were averted to locoweed to allow them to graze locoweed-infested pastures without eating locoweed. They did not graze locoweed and steadily gained weight (0.50 kg/day in 1996 and 0.71 kg/day in 1997). The other group of steers were allowed to graze locoweed under natural grazing conditions and became intoxicated. Weight gains were not affected for the first 3 weeks, but thereafter the steers lost weight in both years. In 1996, non-averted steers consumed locoweed for a season average of 20% of bites. They were severely intoxicated and did not begin gaining weight for 50 days after they stopped eating locoweed. Steers in the 1997 trial consumed less locoweed (11% of bites) than those in 1996 and they recovered more rapidly. Seasonal weight gains were 21 to 30 kg less for locoed steers than control steers in 1996 and 1997, respectively. Locoweed poisoning will cause weight loss, and severely intoxicated cattle require a lengthy recover period after they cease grazing locoweed before weight gains resume. Stocker cattle should not be placed on locoweed-infested rangelands until green grass is abundant and locoweed begins to mature.

Impact of Locoweed Poisoning on Grazing Steer Weight Gains

Emaciation is one of the clinical signs of locoweed poisoning but few studies have documented impacts of locoweed poisoning on weight gains. Stocker steers (British X Continental cross, 200-210 kg) were grazed on locoweed-infested, short-grass prairie in 1996 and 1997 in northeast New Mexico. Each year, half the steers were averted to locoweed to allow them to graze locoweed-infested pastures without eating locoweed. They did not graze locoweed and steadily gained weight (0.50 kg/day in 1996 and 0.71 kg/day in 1997). The other group of steers were allowed to graze locoweed under natural grazing conditions and became intoxicated. Weight gains were not affected for the first 3 weeks, but thereafter the steers lost weight in both years. In 1996, non-averted steers consumed locoweed for a season average of 20% of bites. They were severely intoxicated and did not begin gaining weight for 50 days after they stopped eating locoweed. Steers in the 1997 trial consumed less locoweed (11% of bites) than those in 1996 and they recovered more rapidly. Seasonal weight gains were 21 to 30 kg less for locoed steers than control steers in 1996 and 1997, respectively. Locoweed poisoning will cause weight loss, and severely intoxicated cattle require a lengthy recover period after they cease grazing locoweed before weight gains resume. Stocker cattle should not be placed on locoweed-infested rangelands until green grass is abundant and locoweed begins to mature. DOI:10.2458/azu_jrm_v53i1_ralphs

Using serial ultrasound measures to generate models of marbling and backfat thickness changes in feedlot cattle.

Serial ultrasound estimates of backfat thickness and marbling score were obtained on two groups of steers fed high-energy rations for averages of 166 and 148 d. These measurements were used to develop mathematical models that described the changes in those two attributes as functions of days on feed. An exponential model best described the increase in backfat thickness, and the rate coefficients were .0117 and .0096 for the two groups (doubling times = 59 and 72 d, respectively). A modified power function was better than either a linear or exponential model for describing the development of marbling. In this model, marbling increased very slowly, approximately one degree every 100 d, in the interval from low Select to low Choice but then increased at faster rates as initial marbling scores became higher. Ultrasound backfat measures could be used to predict days to reach a target carcass backfat level with an average error of 30 d or less when backfat thickness averaged more than 3 mm at evaluation. Projections from measurements taken when cattle were started on feed were not accurate from one group, which averaged only 1.7 mm backfat at that time. Projections of carcass marbling improved as evaluation date neared slaughter date. Projections from the initial evaluation date allowed tentative categorization of candidates for Choice or not Choice but were only 64% accurate. Projections from evaluations made later in the feeding period exceeded 75% accuracy in distinguishing Choice from Select. Only small relationships (r2 = .07 or .16) existed between carcass backfat thickness and marbling score. Results indicate that ultrasound estimates of backfat and marbling made during the feeding period can be used to predict carcass merit at slaughter.

Effects of oral and injected vitamin A (retinol) supplements on liver vitamin A and plasma carotenoid and cholesterol concentrations in cattle

AbstractTwo experiments determined the effects of daily oral supplements of vitamin A (retinol) and injected preparations of vitamin A on liver vitamin A concentration and plasma carotenoid (PC) concentration. Vetade is an oily injectable vitamin A preparation, while Nov-a-Vit is an aqueous injectable vitamin A preparation. Angus crossbred heifers were used in experiment 1 and Angus and Simmental crossbred steers were used in experiment 2. All cattle grazed pasture but were given also 1 kg per head of pellets daily and vitamin A supplements were included in the pellets when required. In experiment 1, one group of heifers was given 1 × 106i.u. vitamin A per head daily for 31 days, while a second group in another part of the paddock was not supplemented with vitamin A. A third group of heifers grazed with this latter group and was injected with 2·5 × 106i.u. vitamin A (Vetade) three times weekly. The oral vitamin A supplement proportionately reduced plasma and liver carotenoid concentrations by 0·49 and 0·41 respectively, while increasing liver vitamin A concentration three-fold. By contrast, the Vetade failed to increase liver vitamin A concentration or to reduce liver and plasma carotenoid concentrations. In experiment 2, two groups of steers were injected twice weekly for 7 weeks with 2 × 106i.u. vitamin A as Nov-A-Vit or as Vetade. A third treatment group, grazing with these steers, received no vitamin A injection, while a fourth group grazing in a separate area of the paddock was supplemented daily with 1 × 106i.u. vitamin A per head in their diet. The injection of Nov-A-Vit and the oral vitamin A supplement decreased PC concentration by a similar amount but the increase in liver vitamin A concentration was larger for steers injected with Nov-A-Vit. Vetade injections failed to increase liver vitamin A concentration and there was no decrease in PC concentration. The plasma cholesterol concentration for the treatment groups varied over the duration of the experiment but could not be related to the vitamin A treatment or to the changes in PC concentration. These results indicate that vitamin A injections can be used to reduce PC concentration provided they increase liver vitamin A concentration.

Effect of interval from castration of bulls to slaughter on carcass characteristics and meat quality

A trial was conducted to see whether reducing the interval from castration to slaughter could produce steer‐like carcasses but retain the weight advantage of bulls. Ninety Angus, Friesian × Hereford, and Friesian × Simmental bulls were allocated to nine groups. Four groups were castrated at 8 months of age (steers), and three groups were castrated on January 17 (Day 0) at 17 months of age (castrates). One group of bulls and one group of steers were slaughtered on Day 5, groups of steers and castrates were slaughtered on Days 62, 111, and 166, and the remaining group of bulls was also slaughtered on Day 166. On Day 0, bulls and steers were 455 ± 6 and 426 ± 5 kg liveweight, respectively. Liveweight gain of castrates was lower than that of steers for 106 days following castration and the carcass weight (CW) advantage of bulls over steers at 17 months of age was lost in castrates slaughtered at Day 62. The rate of change in carcass, meat, and fat characteristics varied with the attribute under consideration. For castrates the proportion of carcasses classified as steer at slaughter on Days 62, 111, and 166 was 20%, 60%, and 73%, respectively. We conclude that the loss of the weight advantage is faster than most other carcass attributes change and there is little opportunity to exploit post‐pubertal castration for economic advantage.

Effect of the polyunsaturated fatty acid composition of beef muscle on the profile of aroma volatiles.

The effect of n-3 polyunsaturated fatty acids (PUFAs) in beef muscle on the composition of the aroma volatiles produced during cooking was measured. The meat was obtained from groups of steers fed different supplementary fats: (i) a palm-oil-based control; (ii) bruised whole linseed, which increased muscle levels of alpha-linolenic (C18:3 n-3) and eicosapentaenoic acid (EPA, C20:5 n-3); (iii) fish oil, which increased EPA and docosahexaenoic acid (C22:6 n-3); (iv) equal quantities of linseed and fish oil. Higher levels of lipid oxidation products were found in the aroma extracts of all of the steaks with increased PUFA content, after cooking. In particular, n-alkanals, 2-alkenals, 1-alkanols, and alkylfurans were increased up to 4-fold. Most of these compounds were derived from the autoxidation of the more abundant mono- and di-unsaturated fatty acids during cooking, and such autoxidation appeared to be promoted by increased levels of PUFAs.

Utilization of bioelectrical impedance to predict carcass composition of Holstein steers at 3, 6, 9, and 12 months of age.

The objective of this experiment was to study the usefulness of bioelectrical impedance analysis (BIA) in determining soft tissue composition (STC) and carcass fat-free mass (CFFM) of Holstein steers at different ages. Growth data and prediction of STC and CFFM were determined for four groups of Holstein steers: 12 of 3 mo, 12 of 6 mo, 15 of 9 mo, and 16 of 12 mo of age. Average weight for animals at 3, 6, 9, and 12 mo were 96.6, 204.7, 354.1, and 465.9 kg, respectively. Average fat content of carcass soft tissue at 3, 6, 9, and 12 mo were 2.6, 9.8, 18.2, and 24.6%, respectively. Average protein content of the carcass soft tissue was 20.7% at 3 mo, 20% at 6 mo, 18.30% at 9 mo, and 16.9% at 12 mo of age. Feed and water were withheld for 20 h before the BIA was applied. Steers were sedated and forced to recumbency in a lateral position on their right sides over a nonconductive surface. Two electrodes were placed on each limb of the right side (metatarsal and metacarpal regions on back and front foot, respectively). Resistance (Rs) and reactance (Xc) were obtained by attaching four terminals to the electrodes. Impedance and other predictors such as Vol1 (L/Rs), Vol2 (L2/(RS2+Xc2).5, Vol3 (geometrical animal volume), L (2 x height + body length), and L2 were calculated from Rs and Xc, and body measurements and were used to generate prediction equations for CFFM and carcass soft tissue composition. Carcass fat-free mass was predicted accurately for all age groups and the pooled data (r2 = .99 at 3 mo, .99 at 6 mo, .97 at 9 mo, .77 at 12 mo, and .98 for the pooled data). Correlation coefficients between impedance readings and CFFM and carcass composition were calculated. Carcass CFFM and kilograms of H2O for the pooled data (across age groups) were both correlated highly to Vol1 (.97), Vol2 (.95), L (.97), and L2 (.97).

Internal Parasitism of Steers Grazing Extensively at Different Stocking Rates

Eighty-four first-year grazing Holstein-Friesian steers were observed through 2 years on 40 ha of reclaimed unfertilized grassland with the objective of investigating the influence of stocking rate (SR) on internal parasitism under extensive grazing conditions. Three groups of steers were grazed each year at low, medium and high SR in separate paddocks (0.53, 1.05 and 1.55 steers/ha). The faecal egg counts of predominantly Cooperia and Ostertagia spp. were influenced by SR in the first year (p < 0.05) with maximum geometric means of 135, 182 and 217 epg in the low, medium and high SR groups, respectively, and part of the second year (p = 0.08) with maximum geometric means of 88, 134 and 195 epg. In the second year, all steers were treated with levamisole by 26 July due to diarrhoea, being particularly severe at high SR and 7 steers were withdrawn from this group at the same time. Serum pepsinogen levels indicated a higher rate of uptake of Ostertagia larvae in higher SR groups in the second season before treatment (p < 0.01). The mean weight gains (+/- s.d.) for the first year were 630 +/- 58, 341 +/- 97 and 300 +/- 151 g/day in the low, medium and high SR groups, respectively, and in the second year the corresponding figures were 565 +/- 109, 357 +/- 135 and 247 +/- 129 g/day. Although the SRs were much lower than commonly found on improved pastures, we conclude that feed on offer was a limiting factor in late season and secondly, that the levels of exposure and uptake of nematodes in steers were affected by SR. The levels of parasitism at the medium and high SR were high enough to have affected production.

Effect of diatomaceous earth as an anthelmintic treatment on internal parasites and feedlot performance of beef steers

AbstractThirty crossbreed steer calves were randomly assigned to one of three feedlot treatment groups to evaluate the effectiveness of diatomaceous earth (DE) as an anthelmintic treatment and its effect on subsequent growth performance. Steers were adapted to a cereal-based diet for 15 days on the farm of origin and given an additional 21 days to adjust to the feedlot diet. Calves had not been dewormed prior to starting the study. On day 0 (2 January 1996) the positive control group of steers (CONV; no. = 11) was given 10 mg/kg of albendazole, a second group began receiving (on day 2) 0·3 kg of diatomaceous earth (DE; no. = 9) mixed daily with their food for 46 days and the negative control group (CTRL, no. = 9) received no anthelmintic treatment. Rectal faecal samples were collected upon arrival at the feedlot and the resulting egg counts showed that all steers were positive for nematodes and coccidia. Faecal samples were collected on days 0, 15, 28 and every 28 days thereafter to determine faecal egg counts. The last sample was taken on the day of slaughter. On day 0, the average count for all calves was over 70 eggs per g faeces (epg) for trichostrongyle type eggs; counts for Nematodirus sp., Strongyloides sp., Trichuris sp. and Capillaria sp. were negligible. CTRL and DE steers had higher parasite levels than CONV steers during the 1st (P &lt; 0·01) and 2nd months (P &lt; 0·05) after treatment. Egg counts for CTRL and DE groups decreased in March and none of the groups differed (P &gt; 0·05) significantly for the remainder of the study. Coccidia levels decreased over time similarly for all groups. Offering 20 g DE per kg food intake for 46 days to beef steers on a high cereal -based diet had no effect (P &gt; 0·05) on body weight, average daily gain, dry-matter intake, food conversion or days on food compared with the untreated control steers. Cumulative food conversion during the first 2 months was better for CONV than for DE and CTRL steers (P &lt; 0·01) but did not differ between the latter two groups (P &gt; 0·05). Cumulative food conversion for the rest of the study remained the same for all groups (P &gt; 0·05). CONV calves required fewer days on food than DE calves (P &lt; 0·05) but about the same number as CTRL calves (P &gt; 0·10). Steers in the DE group required a similar number of days on food (230·22 ± 7·86 days) to reach target end points as CTRL steers (218·75 ± 8·34 days; P &gt; 0·05) but more days than CONV calves (201·64 ± 7·11 days; P &gt; 0·05).

Effect of growth path on the tenderness of the semitendinosus muscle of Brahman-cross steers

The growth paths of 36, nine-month-old Brahman-cross steers were modified to determine the effect of their growth history on tenderness of the semitendinosus (ST) muscle. Steers were assigned to one of three treatment groups. One group of steers (uninterrupted group) was grazed on improved tropical pasture for 257 days and had an average weight gain of 0.6 kg day −1. The other two groups were fed a restricted diet of low-quality grass hay and lost on average ~ 13% of their initial live weight over 100 days. These groups were then regrown for 157 days on either pasture (pasture finished) with the uninterrupted group, or on a grain-based feedlot diet (grain finished). Growth rates of the previously restricted groups during the regrowth phase were indicative of compensatory growth and were significantly different ( p < 0.05) at 0.76 (sem 0.03) kg day −1 and 1.22 (0.05) kg day −1, pasture and grain finished groups, respectively. Growth rates for both restricted groups were significantly different ( p < 0.05) from the uninterrupted group [0.55 (0.02) kg day −1]. At slaughter, the grain finished group had heavier carcases, higher dressing percentages and more fat coverage, than either the uninterrupted or pasture finished groups, the latter being significantly lighter than the uninterrupted group. Tenderness was assessed by shear, compression (C) and adhesion (ADH) measurements. Shear peak force (PF) values of cooked ST samples did not differ significantly between groups. However, PF values of pressure-heat treated ST samples from the grain finished group were significantly less ( p < 0.05) than comparable values from the uninterrupted group suggesting a reduced contribution of connective tissue to toughness. The pasture finished group mean PF value was not significantly different from either the uninterrupted group or grain finished group means. C and ADH values were significantly less ( p < 0.05) in the grain finished group compared to the pasture finished groups values, again indicating a reduced connective tissue contribution to toughness. We conclude that the physical properties of the connective tissue component of the ST muscle may be altered by rapid compensatory growth after a weight loss phase and reduce the connective tissue contribution to toughness which may enhance meat tenderness.

Grazing Management Affects Nutrient Intake by Steers Grazing Tallgrass Prairie

Indicators of nutrient intake were compared for beef steers grazing tallgrass prairie managed with continuous grazing or 8-paddock short-duration grazing. Two replicates of each grazing system were evaluated during the 2 year study. Stocking rates for the grazing systems were similar in both years. Within each treatment replicate, 3 steers fitted with ruminal and duodenal cannulae grazed for the entire grazing season (late April through late September) with larger groups of intact steers. Rest periods for the 8-paddock cells were lengthened as the season progressed and forage accumulation rate slowed. Trials occurred in early June and early August in year 1 and early July and early September in year 2. Flow of organic matter and nitrogen at the duodenum, fecal nitrogen concentration, and fecal output were used as indicators of nutritional status. Chromic oxide was used as a flow marker. Flow of organic matter, total nitrogen, and microbial nitrogen at the duodenum in addition to fecal output were lower (P < 0.04) with short-duration grazing and indicate that forage intake and digestible organic matter intake were depressed in steers on the short-duration grazing treatment. Forage digestible organic matter intake, estimated from microbial protein flow, was 19.3% lower (P < 0.03) on short-duration grazing. Fecal nitrogen concentration was higher (P < 0.03) for steers under continuous grazing. Diet crude protein estimated from fecal nitrogen was 24.4 g kg-1 organic matter higher for continuous grazing. These results suggest that both diet nutrient composition and intake were depressed in steers in the short-duration grazing treatment. These observations partially explain the lower weight gains and higher end-of-season residual standing vegetation noted with short-duration grazing in concurrent grazing trials on these rangelands.

Live animal performance, carcass traits, and meat palatability of calf- and yearling-fed cloned steers.

Two groups of Brangus steers produced by nuclear transplantation cloning were used in parallel studies investigating the impact of calf- and yearling-feeding. The first group (n = 8) were fed as calves (CF; n = 4) or yearlings (YF; n = 4) to a constant age end point of 16 mo. The second group (n = 10) were fed as calves (CF; n = 5) or yearlings (YF; n = 5) to a constant live weight end point (530 kg). When slaughtered at the same age, CF and YF steers did not differ (P > .05) in feedlot ADG, but the CF steers were heavier and had higher dressing percentages, numeric yield grades, and quality grades (P < .05). Top loin steaks from the groups of steers did not differ (P > .05) in palatability traits. When fed to a constant live weight, the YF steers gained more rapidly (P < .05) and had lower (P < .05) numeric yield grades than did CF steers. Again CF steers had higher (P < .05) dressing percentages. There was no difference (P > .05) between the treatments in carcass quality grade or meat palatability characteristics. Thus, when finished to a constant weight end point, YF steers gained more rapidly, with no adverse effects on carcass quality grade or palatability traits; however, CF steers consistently produced higher dressing percentages, largely due to greater external fatness.

Season and Sex Influences on Botanical Composition of Cattle Diets in Southern New Mexico

We conducted a study in southern New Mexico to determine seasonal variation in botanical diet composition of cattle and to compare cow and steer diets. The climate and vegetation is typical of semidesert grassland. Fecal samples were obtained from a group of cows and steers during spring, summer, fall, 1989; winter and summer, 1990. Results showed that cattle diets were highest in grass content during spring (57%), summer (78%), and winter (54%), while fortes comprised the highest proportion of cattle diets during the fall (47%). Shrubs were moderately important during winter (18%). Dropseeds (Sporobolus spp.), black grama (Bouteloua eriopoda [Torr.] Torr.), threeawn species (Aristida spp.), and leatherweed croton (Croton pottsii [Klotzch] Muell. Arg.) were key forage species for cattle. The importance of these species varied with season, availability, physiological stage, and presence of other species. Differences between cow and steer diets varied with season. The relative similarity ranged from 70% (fall) to 90% (summer). The lower fall similarity compared to that in the summer might be related to physiological variation or past differences in grazing experience between cows and steers. For practical purposes, steer diets might generally be used to represent cow diets, but caution should be exercised during periods of low forage quality.

The effect of implants on gain of steers and heifers grazing native grass (1996)

Four trials were con ducted to determine the effect of different implants on steers and heifers grazing native grass pastures for different lengths of time. In addition, two groups of steers were followed through a feeding period to determine if previous implanting had a residual effect on gain. The implanted (Ralgrofi, Ralgrofi Magnum , Synovex Sfi) steers gained faster than the controls; however, no differences in gain occurred among implants. In the finishing group that went on grass at 687 lb, implants had no effect on subsequent feedlot gain. In the second group (on grass at 569 lb and grazing for 80 days), controls gained faster in the feedlot than those that ha d been implanted on grass, resulting in essentially equal weights for all treatments. Among the heifer groups, no differences occurred in pasture gains. Genetic differences in cattle, length o f grazing, and other factors may change implant results.

Daily selection of feeding areas by cattle in homogeneous and heterogeneous environments

Yearling steers were observed in a two-part study to evaluate movement patterns in homogeneous and heterogeneous areas. Previous grazing and fertilization were used to create three heterogeneous patches that varied in forage quality and quantity. Three homogeneous patches were also established. Two groups of steers were released daily from a holding pen and allowed to choose within either the homogeneous area or the heterogeneous area. During the first trial, steers selected patches from a central decision area, and fences divided the patches. During the second trial, division fences were removed. No patch preferences developed in the homogeneous area if data were pooled within a day. However, time spent in patches was not consistent throughout the day. Steers grazed patches nearest to water during midday, but avoided those patches during the morning and evening. Animals developed preferences for the most nutritious patches, as indexed by crude protein concentration, in the heterogeneous area. They avoided a patch with lower forage quality for 21 consecutive days. Cattle tended to return to a particular patch more often in the heterogeneous area, but in both the heterogeneous and homogeneous areas, animals returned to the same patch on consecutive mornings less than 48% of the time. Cattle moved among patches more frequently in the homogeneous area during Trial 2 after fences were dismantled. One or two individuals may have influenced the initial patch selection for the remainder of the group. Uneven grazing distribution patterns associated with cattle grazing heterogeneous environments may occur because they select feeding areas with higher forage quality more frequently than feeding areas with lower forage quality.