Feedlot Conditions Research Articles

EFFECTS OF BEDDING TYPE AND WITHIN-PEN LOCATION ON FEEDLOT RUNOFF

This two-year study examined the effects of two types of bedding materials (straw and wood chips) and twowithin-pen locations (bedding pack and pen floor) on various feedlot runoff parameters in southern Alberta, Canada, usinga rainfall simulator. Bedding type affected antecedent factors and hydrological parameters differently by year. Bedding packlocations absorbed 23.5% to 32.9% more moisture, had about 8 cm greater manure depths, slopes between 2.1% and 5.1%steeper, and surfaces that were 2.6% to 5.7% rougher than pen floor locations. Pen floor locations had clod bulk densitiesthat were 0.83 Mg m-3 greater than bedding pack locations in 1998. However, the effect of bedding packs on these propertiesdepended on the amount of bedding added, which depended on feedlot conditions. Runoff began sooner from pen floor thanfrom bedding pack locations. Once runoff started, the amount and type of bedding material, length of time since fresh beddingwas added, and within-pen location affected the time for specific runoff volumes. For example, in 1998, 6 L of runoff werecollected about 3 min faster from wood chips than from straw bedding and about 7 min faster from the pen floor than fromthe bedding pack. Runoff coefficients increased during the simulation events and occasionally exceeded rainfall applicationrate depending on whether or not water in depression storage was released. Treatment effects were dependent on year of study,and were inconsistent. Thus, further study is warranted regarding the effects of bedding type on feedlot runoff.

An Assessment of the ARC Metabolizable Energy System to Predict Live Weight Gain of Brown Swiss Cattle Grown under Feedlot Conditions in Turkey

An Assessment of the ARC Metabolizable Energy System to Predict Live Weight Gain of Brown Swiss Cattle Grown under Feedlot Conditions in Turkey

Performance of Botswana composite breed and indigenous breeds under feedlot and grazing conditions

The Botswana Composite Breed (BCB) was developed by Dept. of Agricultural Research to mitigate problems of small herds that could not sustain crossbreeding programs. The breed has 47.5% Sanga, 22.6% Zebu and 29.9% Bos taurus blood. Indigenous Tswana cattle are 40% of the national herd (Masilo and Podisi 2001), indicating an erosion of local genetic material. Tswana cattle are small framed and are prejudiced by the Botswana Meat Commission (BMC) weight-based pricing system in favour of large-framed cattle. Lack of carcass characterization of indigenous cattle contributes to the above situation. The aim of this study was to evaluate performance of BCB and other indigenous breeds under feedlot and grazing conditions in order to promote their attributes.

Spectral Analysis of Feeding and Lying Behavior of Cattle Kept Under Different Feedlot Conditions

This study used spectral analysis in 2 separate experiments to examine feeding and lying behavior of Bos taurus steers under 2 housing treatments: a feedlot yard stocked at 12.0 m2 per head with a dry, firm pen surface (NDF) and a "high density" (HDF) feedlot yard stocked at 6.0 m2 per head with a wet and muddy feedlot pen surface. The study conducted 1 experiment in Autumn, another in Spring. The study measured and analyzed ambient temperatures, relative humidity, and barometric pressure half-hourly onsite, using time series cross-correlations to determine whether steer behavior was associated with them. Both NDF and HDF groups showed similar lying and eating duration. HDF steers exhibited patterns of lying and feeding different from those of NDF steers. Spring observations found a number of correlations with temperature, relative humidity, and barometric pressure. Health and production data showed no differences between treatments. The results indicate that cattle made successful, short-term changes to changed feedlot environmental conditions. However, confirming these findings requires further replication. Spectral analysis was shown to be sensitive enough to detect behavioral differences between treatments and thus has potential animal welfare assessment tool.

Potential of Omani Jebel Akhdar goat for meat production under feedlot conditions

Omani Jebel Akhdar goats fed ad libitum a concentrate diet (16.5% CP) and Rhodesgrass hay (8.8% CP) were reared from birth until slaughter at 11, 18 and 28 kg body weight. Bucks were heavier than does at birth, grew rapidly (144 g/day) and reached predetermined weights earlier than wethers and does. The dressing percentage (DO) at 28 kg body weight were 54, 53 and 55%, respectively, in bucks, wethers and does. Corresponding estimates for carcass weight were 14.1, 13.7 and 13.9 kg, for muscle 64, 62.5 and 61.5%, for bone 15.6, 16.0 and 13.1, and for fat 16.1, 17.7 and 21.3%, respectively. As body weight increased there was a decline in proportions of bone in the carcass and the muscle–fat ratio and an increase in proportions of bone in the carcass and the muscle–fat ratio. Correspondingly, there was an increase in non-carcass organs, i.e. fat and muscle–bone ratio while muscle remained unchanged. Bucks had less fat and more bone and muscles and higher proportions of heads, skin and feet in the empty body weight at 28 kg than does. In conclusions intact males, raised under a feedlot system grew rapidly and had acceptable carcass composition.

Performance of the fat-tailed Barbarine sheep in its environment: adaptive capacity to alternation of underfeeding and re-feeding periods. A review

The Barbarine sheep is characterised by a fat-tail, whose mass varies between 1 and 4 kg. Its management is traditionally based on spring mating. The ability of this fat-tailed ewe to mobilise its body reserves has been demonstrated in lactation and the dry period by experimentally varying the food supply. The severely underfed ewe (200 g oat hay) can survive 161 days and lose 36% of its body weight (BW), with a change of 8.8 kg of dissected adipose tissue (AT) and 3.4 kg of muscle. It reached this stage with an empty BW of 24 kg containing 12% of AT. The fat tail exerts a role as a body reserve mainly through its mass rather than through its ability to be rapidly mobilised. In such situations, plasma NEFA and 3-hydroxybutyrate concentrations are first almost doubled, then decline in permanently underfed ewes, showing the ability of Barbarine ewes to adjust their lipid metabolite concentration in order to limit the toxic effects of high concentrations and therefore prolong survival. By the end of a re-feeding period, Barbarine ewes returned to their initial BW, lipid and protein mass. This breed has a good fertility, which can, however, be depressed in cases of undernutrition. However, if the mating period is extended, the overall reproductive performance is generally satisfactory. Poor nutrition during pregnancy may reduce lamb birth weight and affect subsequent growth, however, in traditional conditions, ewe and lamb mortality rates are surprisingly low in this breed. In normal birth weighted lambs, the post-weaning growth performances of grazing lambs are moderate but in feedlot conditions the conversion rate is rather low and carcass adiposity is high. This review shows that the Barbarine sheep, and specially the ewe, is well adapted to the local conditions mainly because of its high fertility and its ability to deposit and mobilise body reserves.

High molasses diets for feedlot cattle

This experiment investigated the effect of high molasses diets on feed intake, growth rate, carcass traits and meat eating quality of Bos indicus cross cattle under commercial feedlot conditions. Heifers were allocated to 1 of 3 groups and fed feedlot diets containing 1, 29% or 50% molasses on a DM basis. Average daily DM intake for the first 64 days was 23-24 g/kg liveweight for each of the treatment groups. The inclusion of molasses in the diet reduced (P<0.05) average daily gains (ADG) (control, mid and high molasses groups; 2.1 ± 0.04, 1.7 ± 0.05 and 1.3 ± 0.06 kg/d, respectively). The P8 fat depth was lower (P<0.05) for animals fed the high molasses diet (4.2 ± 0.5 mm) than the control and mid molasses groups (6.9 ± 0.5 and 5.8 ± 0.5 mm, respectively). Objective and subjective measures of meat quality were found to be similar between cattle fed a conventional grain-based diet and medium and high molasses diets. The inclusion of molasses at 29 or 50% (DM basis) in feedlot diets could result in acceptable ADG and produce leaner beef without affecting meat quality.

Ultrasonography as a predicting tool for carcass traits of young bulls

Considerable resources have been allocated to support research in the development of non-invasive and non-destructive techniques for carcass composition and quality evaluation. Ultrasonography is a reliable and relatively low-cost technique that can be used. In the present study, real-time ultrasonography was used to predict ribeye area (REA) and subcutaneous fat thickness (FT) in live animals as compared to carcass measurements. Animals used were 115 yearling bull calves (initial body weight, 329 kg), kept under feedlot conditions, of four genetic groups (30, ½ Angus x Nellore; 30, ½ Canchim x Nellore; 30, ½ Simmental x Nellore, and 25 Nellore), and two finishing frame sizes (small and large). Four ultrasonographic measurements were taken every 28 days until slaughter. Predictive precision of ultrasonographic measurements increased as animals approached slaughter, reaching maximum values at the last measurement (R²=0.68 and 0.82 for REA and FT, respectively). FT carcass measurements was influenced by genetic group and live measurements (P &lt; 0.05). Frame size did not influence REA and FT, probably due to small, but distinctive differences among genetic groups.

A dose-response study of melengestrol acetate on feedlot performance and carcass characteristics of beef steers.

The dose response of melengestrol acetate (MGA) on ADG (kg/d) and gain efficiency (gain/DMI, g/kg) was estimated in beef steers fed a finishing diet under commercial feedlot conditions. Melengestrol acetate is not approved for use in steers as a feed additive. The study design was five blocks of four pens (each pen was assigned a dose of MGA) with 166 to 200 steers per pen. Melengestrol acetate was fed to steers at 0 (n = 899, five pens), 0.1 (n = 900, five pens), 0.2 (n = 899, five pens), and 0.4 (n = 900, five pens) mg of MGA/steer daily. Pens within a block were slaughtered on the same day. Blocks 1 through 5 were fed MGA for 123, 122, 116, 124, and 138 d, respectively. The experimental unit was a pen of steers, and blocking was based on source of steers. The ADG was 1.81, 1.85, 1.80, and 1.83 kg/d for steers fed 0, 0.1, 0.2, and 0.4 mg MGA per day, respectively. For ADG, the dose was significant, but neither linear nor quadratic effects were significant. Compared with steers of the control group, ADG was greater for steers fed 0.1 mg MGA (P < 0.01). Feed efficiencies were 170, 173, 171, and 172 g/kg for steers fed 0, 0.1, 0.2, and 0.4 mg MGA/d, respectively; however, no effects of dose (P = 0.19) or linear (P = 0.21) or quadratic (P > 0.60) effects were observed. There was no evidence for either positive or negative effects of MGA on DMI, hot carcass weight, dressing percent, quality grade, yield grade, back fat thickness, marbling score, longissimus muscle area, and incidence of dark cutter carcasses in response to feeding MGA to steers at doses of 0.1, 0.2, and 0.4 mg daily. The incidence of buller behavior (0.43 to 1.11%) was low and did not permit an accurate test of the clinical observations that feeding MGA to steers decreases the occurrence of buller steers. Melengestrol acetate fed to finishing beef steers produced small improvements in growth performance (ADG, 2.2%) at the 0.1 mg MGA dose, but none of the doses examined produced improvement in carcass quality or yield grade measurements.

Effect of dietary protein and energy concentration on the fattening performance of buffalo male calves in southern Iran

During the last decade, development of the buffalo industry has been undertaken in Iran. The prospects for beef production from buffalo management have shown to be successful under local environments. Buffaloes reared under feedlot conditions with suitable diets have the potential to produce high quality carcass (Udeybir and Mandal, 2001). In terms of nutrition, studies are needed for the validation of nutrient requirements (especially protein and energy) for different physiological stages. A system to monitor the nutritional status of buffaloes would be beneficial to reduce losses and maximize efficiency of nutrient utilization. To optimise protein efficiency and reduce nitrogen wastage, diets need to be formulated to provide optimum nitrogen concentration for maximum rumen microbial yield and growth. However, limited work has been reported on nutrient requirements of growing and fattening buffalo calves. The objective of this work was to study the response of Iranian buffalo male calves to the different levels of energy and protein in the diet from 12 to 18 months of age.

Leptin as a predictor of carcass composition in beef cattle.

Our objective was to determine if serum concentrations of leptin could be used to predict carcass composition and merit in feedlot finished cattle. Two different groups of crossbred Bos taurus steers and heifers were managed under feedlot conditions near Miles City, MT. The first group consisted of 88 1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise composite gene combination steers (CGC) harvested at the ConAgra processing facility in Greeley, CO. The second group (Lean Beef Project; LB) consisted of 91 F2 steers and heifers born to Limousin, Hereford, or Piedmontese by CGC F1 cows crossed to F1 bulls of similar breed composition and harvested at a local processing facility in Miles City, MT. Blood samples were collected approximately 24 h before harvest (CGC) or approximately 3 d before and at harvest (LB). No differences in serum concentrations of leptin were detected (P > 0.10) between Hereford, Limousin, or Piedmontese F2 calves nor between LB steers and heifers. Positive correlations (P < 0.01) existed between serum leptin and marbling score (r = 0.35 and 0.50), fat depth measured between the 12th and 13th rib (r = 0.34 and 0.46), kidney, pelvic, and heart fat (KPH) (r = 0.42 and 0.46), and quality grade (r = 0.36 and 0.49) in CGC and LB cattle, respectively. Serum leptin was also positively correlated with calculated yield grade for CGC steers (r = 0. 19; P = 0. 10) and LB cattle (r = 0.52; P < 0.01). Longissimus area was not correlated with serum leptin in CGC steers (r = 0.12; P > 0.10). However, a negative correlation existed between longissimus area and serum leptin in the LB cattle (r = -0.45; P < 0.01). Serum concentrations of leptin were significantly associated with carcass composition (marbling, back fat depth, and KPH fat) and quality grade in both groups of cattle studied and may provide an additional indicator of fat content in feedlot cattle.

Avaliação dos desempenhos produtivo e reprodutivo de um rebanho bubalino no Estado do Ceará

Foram avaliados os desempenhos produtivo e reprodutivo de um rebanho bubalino, localizado no município de Paracuru, litoral oeste do Estado do Ceará. Os animais foram mantidos em sistema intensivo e submetidos a duas ordenhas diárias. Foram analisadas informações de 87 fêmeas da raça Murrah, entre os anos de 1984 e 1998. As análises estatísticas foram efetuadas por meio do procedimento GLM (SAS, 1990), usando um modelo linear misto. As médias observadas para produção total de leite, duração da lactação, produção de leite no pico de lactação, idade ao primeiro parto e intervalo de partos foram: 2130,80+535,60kg, 301,41+49,30dias, 9,78+1,95kg, 1132,69+166,99dias e 430,79+100,44dias, respectivamente. Alta porcentagem de parições das ocorreu no período chuvoso (79,3%) e apenas 20,7%, no período seco. A produção total de leite e a produção no pico de lactação foram influenciadas pelos efeitos do ano e ordem de parto. A duração da lactação foi influenciada pelos efeitos do ano e mês de parto. A idade ao primeiro parto foi influenciada pelo efeito do ano de nascimento da búfala. O intervalo de partos foi influenciado pelo mês do parto anterior, além dos efeitos do mês dentro do ano de parto e mês de nascimento da búfala.

Predicting individual feed requirements of cattle fed in groups.

A published model designed to predict individual feed required for the observed shrunk BW and ADG of growing cattle when fed in groups was modified and evaluated to improve its accuracy. This model is needed to accurately bill feed and compute cost of gain in marketing programs based on individual animal management. Because of its importance in predicting energy required for growth, a database of 401 steers was used to develop an equation to predict percentage of empty-body fat (EBF) from carcass measurements (12th rib fat thickness, hot carcass weight, USDA quality grade, and longissimus muscle area), which accounted for 61% of the variation in EBF with no bias (P > 0.1). When tested with an independent data set of 951 steers, the equation accounted for 51% of the variation with 1% proportional bias. The large variation in the carcass measurements at a particular EBF observed in this study indicates further improvement is limited by the inability of carcass measurements to account for variation in fat distribution in the various carcass components. Because of its importance in setting the target end point, a database of 1,355 steers and heifers was used to determine the relationship between EBF and USDA quality grade. These data indicate growing and finishing cattle reach Select and low-Choice quality grades at an EBF of 26.15 +/- 0.19 and 28.61 +/- 0.20%, respectively (P < 0.05). A data set of 228 steers from different breeds from two serial slaughter studies indicated 14.26 +/- 1.52 kg of empty BW change are required to increase EBF one percentage unit for cattle fed high-energy diets; this adjustment is needed to adjust final shrunk BW to the target EBF end point. The model to predict DM required with modifications developed in this study was evaluated with data from 365 individually fed cattle and it accounted for 74% of the variation in observed DM consumed with no bias (P > 0.1). When the revised model was applied to a commercial feedlot data set containing 12,105 steers and heifers, the total observed DM consumed was predicted with a bias of less than 1%. The model presented in this study accounts for differences known to affect animal requirements (breed type, BW and ADG, and weight at the target EBF end point) and can be used to fairly allocate feed to individuals fed in a group under commercial feedlot conditions.

Genetic correlations for daily gain between ram and ewe lambs fed in feedlot conditions and ram lambs fed in Pinpointer units.

When performance is recorded in automated facilities that measure feed intake of individual lambs that are penned in a group, such as Pinpointer units, a legitimate question is the degree to which daily gain is genetically correlated with daily gain achieved under feedlot conditions. Lambs were from a composite population (1/2 Columbia, 1/4 Suffolk, and 1/4 Hampshire germplasm) and of the F2 or more advanced generations. Data were daily gains of 1,101 rams (PR) fed in Pinpointer units (11 to 17 wk of age) and 2,021 rams (FR) and 3,513 ewes (FE) fed under feedlot conditions (9- or 10-wk period starting at 9 wk of age). The FR and FE lambs were born from 1983 through 1995, whereas the PR lambs were born from 1986 through 1995. Measurements of daily gain in PR, FR, and FE lambs were considered to represent three correlated traits. Unadjusted means were .411, .406, and .326 kg/d for PR, FR, and FE, respectively. Random effects in the model were animal direct genetic, maternal genetic, and maternal permanent environmental. Fixed effects were associated with age of dam (1 to 6 yr), type of rearing (1 to 4), and contemporary group (test date). Variances due to maternal genetic effects with single-trait analyses were near zero, so those effects were eliminated from the three-trait analysis although a random uncorrelated effect due to dam was included in the model. Estimates of heritability were .22, .14, and .23 for PR, FR, and FE, respectively, with fractions of variance due to dam effects ranging from .02 to .05. Estimates of genetic correlations were .86 for PR with FR, .83 for PR with FE, and 1.00 for FR with FE. Estimated phenotypic variances were similar for PR and FR, but one-third less for FE. The similarity of heritability estimates and estimates of genetic correlations all exceeding .83 suggest that daily gain of rams fed in Pinpointer units will reflect genetic expression for daily gain in both ram and ewe lambs fed under feedlot conditions.

Effect of dietary energy level on efficiency of SA Mutton Merino lambs and Boer goat kids under feedlot conditions

Effect of dietary energy level on efficiency of SA Mutton Merino lambs and Boer goat kids under feedlot conditions

THE INFLUENCE OF GENOTYPE ON BEEF PALATABILITY AND COOKING PROPERTIES. AN EVALUATION OF WAGYU F1 CROSSES AND OTHER GENOTYPES UNDER NORTH AMERICAN FEEDLOT CONDITIONS1

ABSTRACT Beef strip loins (100) were evaluated from steers of 10 different genotypes fed under North American feedlot conditions for 150 days. Significant (P&lt;0.05) but small numerical differences were observed in thaw‐drip losses from roasts and cooking losses from steaks. Roast flavor and texture profiles revealed important differences in both individual flavor and texture character notes. However, these differences were of insufficient magnitude to influence the appropriateness balance, and blend of individual character notes. Although differences were not observed (P&gt;0.05) in mean palatability ratings, lower proportions of steaks from Angus were rated tough initially and overall than steaks from any other breed or breed combination. Therefore, incorporation of Wagyu genetics at the F1 level did not improve but was not detrimental to cooking and/or palatability attributes, except in the case of Wagyu x Angus crosses, which were not as acceptable in tenderness as Angus.

Clinical efficacy of enrofloxacin against bovine respiratory disease comparing different treatment regimens

Enrofloxacin is being successfully used for the treatment of respiratory disease of cattle in many countries. The established treatment regimen is a daily injection for 3 to 5 days with a dose range from 2.5 - 5.0 mg/kg. A predominant finding is that a single treatment with an higher dose of 7.5 - 12.5 mg/kg shows excellent clinical efficacy under feedlot conditions. The results of several clinical field trials conducted in the USA and Europe during the last years were used to compare the clinical efficacy of the daily and single treatment regimens. The studies were carried out under varied housing and weather conditions. The results show the equivalency of both treatment regimens. Consequently, the usage of enrofloxacin enables veterinarians to utilize their experience and medical expertise to design either a daily or a single treatment regimen according to the specific infection and management situation.

Direct measurements of methane emissions from grazing and feedlot cattle.

Methane (CH4) emissions from animals represent a significant contribution to anthropogenically produced radiatively active trace gases. Global and national CH4 budgets currently use predictive models based on emission data from laboratory experiments to estimate the magnitude of the animal source. This paper presents a method for measuring CH4 from animals under undisturbed field conditions and examines the performance of common models used to simulate field conditions. A micrometeorological mass difference technique was developed to measure CH4 production by cattle in pasture and feedlot conditions. Measurements were made continuously under field conditions, semiautomatically for several days, and the technique was virtually nonintrusive. The method permits a relatively large number of cattle to be sampled. Limitations include light winds (less than approximately 2 m/s), rapid wind direction changes, and high-precision CH4 gas concentration measurement. Methane production showed a marked periodicity, with greater emissions during periods of rumination as opposed to grazing. When the cattle were grazed on pasture, they produced .23 kg CH4 x animal(-1) x d(-1), which corresponded to the conversion of 7.7 to 8.4% of gross energy into CH4. When the same cattle were fed a highly digestible, high-grain diet, they produced .07 kg CH4 x animal(-1) x d(-1), corresponding to a conversion of only 1.9 to 2.2% of the feed energy to CH4. These measurements clearly document higher CH4 production (about four times) for cattle receiving low-quality, high-fiber diets than for cattle fed high-grain diets. The mass difference method provides a useful tool for "undisturbed" measurements on the influence of feedstuffs and nutritional management practices on CH4 production from animals and for developing improved management practice for enhanced environmental quality.

Performance and digestibilities of beef cattle fed diets supplemented with either soybean meal or roasted soybeans and implanted with Synovex.

Two 160-d feedlot experiments, each consisting of 20 Angus-Hereford steers (216 +/- 5 kg BW, Exp. 1; 258 +/- 5 kg BW, Exp. 2) and 20 Angus-Hereford heifers (208 +/- 5 kg BW, Exp. 1; 236 +/- 5 kg BW, Exp. 2), were used to investigate the effects of supplementing diets with either roasted soybeans (RSB, roasted at 127 degrees C for 10 min) or soybean meal (SBM) and implanting or not implanting with an estrogenic growth promoter (SYN; Synovex-S, 20 mg of estradiol benzoate plus 200 mg of progesterone or Synovex-H, 20 mg of estradiol benzoate plus 200 mg of testosterone) on performance. The cattle were fed a basal diet of 15% orchardgrass silage, 15% corn silage, and 70% corn-based concentrate. Treatments were 1) no SYN and fed a SBM-supplemented diet, 2) no SYN and fed a RSB-supplemented diet, 3) SYN and SBM, and 4) SYN and RSB. Cattle in the SYN groups were reimplanted at 80 d. Four additional Angus-Hereford steers were used in a digestion and nitrogen balance experiment conducted during the first half of Exp. 1. For the total 160-d feedlot experiments, DMI for RSB compared with SBM was lower (P < .01; 8.5 vs 9.2 kg/d, SEM = .07) and ADG/DMI tended to be higher (P < .10; 165 vs 157 g/kg, SEM = 1.3). Final BW of steers fed RSB was similar (P > .10) to that of steers fed SBM (473 vs 478 kg, SEM = 5.6), as was ADG (1.39 vs 1.43 kg/d, SEM = .02). Dry matter intake for SYN-implanted steers was higher (P < .01) than for steers not implanted (9.2 vs 8.5 kg/d). Likewise, final BW (491 vs 460 kg) and ADG (1.49 vs 1.33 kg/d) were higher (P < .01), and ADG/DMI (166 vs 157 g/kg) tended to be higher (P < .10), for SYN-implanted steers than for steers not implanted. During the more rapid muscle growth period (0 to 80 d), DMI for RSB compared with SBM was lower (P < .01; 7.8 vs 8.6 kg/d, SEM = .07) and ADG/DMI was similar (P > .10; 181 vs 172 g/kg, SEM = 1.8). Dry matter intake for SYN-implanted steers was higher (P < .05) than for steers not implanted (8.4 vs 8.0 kg/d), as was ADG/DMI (P < .01, 182 vs 171 g/kg). During this more rapid growth period, the supplement x implant interaction for ADG was significant (P < .05; 1.35, 1.36, 1.59, and 1.44 kg/d for Treatments 1, 2, 3, and 4, respectively, SEM = .04). There were no differences in digestibilities or N balance. The results suggest that there is no improvement in performance under feedlot conditions when RSB replaces SBM in the diet of beef cattle, and, in young cattle, RSB may reduce the response expected by an estrogenic growth promoter.

Releases of Spalangia nigroaenea andMuscidifurax zaraptor (Hymenoptera: Pteromalidae) Increase Rates of Parasitism and Total Mortality of Stable Fly and House Fly (Diptera: Muscidae) Pupae in Illinois Cattle Feedlots

Weekly releases of Spalangia nigroaenea Curtis and Muscidifurax zaraptor Kogan & Legner from May through August of 1991-1993 at small, owner-operated cattle feedlots in Illinois provided weekly emergence of 100-300 parasitoids of each species per feedlot animal. In assessments based on fly and parasitoid emergence from > 47,000 stable fly and house fly puparia collected during the 3-yr period, total stable fly mortality was greater in lots where releases were made (60.7%) than in paired, untreated control lots (51.7%) (P = 0.04; paired t-test); parasitism of stable fly pupae by S. nigroaenea averaged 11.6% where releases were made and 6.4% in paired control lots (P = 0.0016). In lots where releases were made, total mortality of house fly pupae was greater (68.7 versus 56.1%; P = 0.0001); unexplained mortality was greater (55.5 versus 46.1%; P = 0.0018); and parasitism by Muscidifurax spp. was greater (2.4 versus 1.4%; P = 0.07) than in paired control lots. Parasitism, unexplained mortality, and total mortality of both fly species varied significantly from 1991 to 1992 in lots that received the same treatment each year, presumably due primarily to weather. Over the 3-yr period, releasing these species, particularly S. nigroaenea, significantly reduced production of stable fly and house fly adults in cattle feedlots. The potential value of such reductions is likely to vary as a result of feedlot conditions and weather.