Beef Quality Assurance national rancher survey: program participation, best management practices, and motivations for joining future sustainability programs.

Till date, with over 137,000 certified members, the most successful rancher educational program has been the Beef Quality Assurance (BQA) program. The BQA program was established in the mid-1990's to improve animal health and welfare with a primary objective to reduce the incidence of injection site lesions by instructing producers to administer injections in the neck only. The present study investigated the drivers of this success to inform future rancher education programs around agricultural sustainability. An online multistate survey was administered to cattle ranchers in collaboration with state cattlemen's associations to better understand rancher motivations for adopting new practices and to gain insight on current involvement in BQA. In total, the survey consisted of 45 questions and was divided into 3 sections: (1) rancher demographics, (2) BQA participation and current best management practice (BMP) application, and (3) willingness to join new rancher educational programs. Data from 842 respondents are including in this study. Of the survey participants, 70% were currently BQA certified or had been BQA certified at one time, and 30% had never been certified. Ranchers who were BQA certified at any time were less likely to administer injections in areas other than the neck compared to ranchers who were not certified (P < 0.05), demonstrating the effectiveness of the BQA program. More than 80% of survey respondents who joined the BQA program stated they believed the BQA program improved animal health and welfare on their operation (n = 617). Among those who had not joined the BQA program, 40% believed BQA practices did not align with their ranching operation, while 38% had not heard of the BQA program (n = 256). The survey indicated that male ranchers, those with more years ranching, those with a larger percent of income coming from ranching, and ranches with larger total acres grazed were more likely to be BQA certified at any time (P < 0.05). Finally, ranchers who were BQA certified at any time were more likely to state that joining a rancher sustainability program would be beneficial to their operation. In conclusion, not only did the survey provide valuable insight into BQA program adoption but highlighted how BQA pedagogy and program structure may be a suitable framework for creating future rancher sustainability programs.

Mitochondrial abundance and function in muscle from beef steers with divergent residual feed intakes.

The objective of this study was to evaluate the relationship between muscle mitochondrial function and residual feed intake (RFI) in growing beef cattle. A 56-day feeding trial was conducted with 81 Angus × Hereford steers (initial BW = 378 ± 43 kg) from the University of California Sierra Foothills Research Station (Browns Valley, CA, USA). All steers were individually fed the same finishing ration (metabolizable energy = 3.28 Mcal/kg DM). Average daily gain (ADG), DM intake (DMI) and RFI were 1.82 ± 0.27, 8.89 ± 1.06 and 0.00 ± 0.55 kg/day, respectively. After the feeding trial, the steers were categorized into high, medium and low RFI groups. Low RFI steers consumed 13.6% less DM (P < 0.05) and had a 14.1% higher G : F ratio (P < 0.05) than the high RFI group. No differences between RFI groups were found in age, ADG or BW (P > 0.10). The most extreme individuals from the low and high RFI groups were selected to assess mitochondrial function (n = 5 low RFI and n = 6 high RFI). Mitochondrial respiration was measured using an oxygraph (Hansatech Instruments Ltd., Norfolk, UK). State 3 and State 4 respiration rates were similar between both groups (P > 0.10). Respiratory control ratios (RCRs, i.e., State 3 : State 4 oxygen uptakes) declined with animal age and were greater in low RFI steers (4.90) as compared to high RFI steers (4.26) when adjusted for age by analysis of covariance (P = 0.003). Mitochondrial complex II activity levels per gram of muscle were 42% greater in low RFI steers than in high RFI steers (P = 0.004). These data suggest that skeletal muscle mitochondria have greater reserve respiratory capacity and show greater coupling between respiration and phosphorylation in low RFI than in high RFI steers.

Effects of finishing diet sorting and digestibility on performance and feed efficiency in beef steers.

The aim of this study was to test the hypotheses that differences in residual feed intake (RFI) of beef steers are related to diet sorting, diet nutrient composition, energy intake and apparent digestibility. To phenotype steers for RFI, 69 weaned Angus × Hereford steers were fed individually for 56 days. A finishing diet was fed twice daily on an ad libitum basis to maintain approximately 0.5 to 1.0 kg refusals. Diet offered and refused was measured daily, and DM intakes (DMI) were calculated by difference. Body weights were recorded at 14-day intervals following an 18-h solid feed withdrawal. The residual feed intake was determined as the residual of the regression of DMI versus mid-test metabolic BW (BW0.75) and average daily gain (ADG). Particle size distributions of diet and refusals were determined using the Penn State Particle Separator to quantify diet sorting. Sampling of diet, refusals and feces were repeated in four sampling periods which occurred during weeks 2, 4, 6 and 8 of the study. Particle size distributions of refusals and diet were analyzed in weeks 2, 4 and 6, and sampling for chemical analysis of refusals and feces occurred in all four periods. Indigestible neutral detergent fiber (288 h in situ) was used as an internal marker of apparent digestibility. We conclude that preference for the intakes of particles > 19 mm and 4 to 8 mm were negatively correlated to RFI and ADG, respectively. Although steers did sort to consume a different diet composition than offered, diet sorting did not impact intake energy, digestible energy or DM digestibility.

Decision Making Tools: BeefTracker mobile app for tracking and analysis of beef herd pasture use and location.

Beef Tracker is a web-based mapping platform that provides beef cattle ranchers a tool to demonstrate that cattle production fits within sustainable ecosystems and to provide regional data to update beef sustainability lifecycle analysis. After digitizing pastures, herd data (class and number of animals) are input on a mobile device in a graphical pasture interface, stored in the cloud, and linked via the web to a personal computer for inventory tracking and analysis. Pasture use calculated on an animal basis provides quantifiable data regarding carrying capacity and beef production. This data is sought by the National Beef Cattle Association to provide more accurate inputs for beef sustainability lifecycle analyses. This application is a useful way for large, complex ranching operations to have all employees remain informed as to cattle movements and ranch wide improvement projects. Better yet, as users make changes to their operation in BeefTracker, histories are automatically recorded and stored in the cloud. After initial testing by university range scientists and ranchers, we have enhanced the BeefTracker application to improve automation for increased ease of use. The following have been added: ability to access and edit the BeefTracker livestock inventory while disconnected from WiFi and cell service, ability to represent portions of a pasture in BeefTracker as irrigated and nonirrigated, and ability to report animal unit harvest (by pasture) calculated on an annual basis. This will provide quantifiable data regarding carrying capacity and subsequent beef production to provide more accurate data inputs for the beef sustainability lifecycle analysis, enhanced map synchronization, and improved security to allow a single individual to access multiple livestock operations without needing multiple user IDs and passwords.

Growth of total fat and lean and of primal cuts is affected by the sex type.

Knowledge of tissue and cuts growth depending on the sex could be used to improve performance and efficiency. Computed tomography (CT) is a non-invasive technology that enables the study of the body composition of live animals during growth. The aims of the present study were (1) to evaluate variation in the body composition of four sex types (SEX) of pigs (castrated males (CM), immunocastrated males (IM), entire males (EM) and females (FE)) at the live weight of 30, 70, 100 and 120 kg, assessed using CT; (2) to model the growth of the main tissues and cuts; and (3) to predict the mature BW (MBW) of the four SEX and establish the relationships between the growth models and the MBW. There were significant phenotypic differences in the allometric growth of fat and lean among SEX. For the lean tissue, FE and EM showed higher values of the b coefficient than CM and IM (1.07 and 1.07 v. 1.00 and 1.02, respectively) all of them close to unity, indicating a proportional growth rate similar to live weight and that this tissue developed faster in FE and EM than in CM and IM. However, these differences were not related to differences in estimated MBW. There were significant differences in estimated MBW among SEX, being higher in IM and EM than in CM and FE (303 and 247 v. 219 and 216 kg), however, the MBW may have been overestimated, especially for the IM. The poorer accuracy of the MBW estimate for the IM could be due to a maximum live weight of 120 kg in the experiment, or to the fact that this particular SEX presented two clear behaviours, being more similar to EM from birth to the second injection of the vaccine (130 days) and comparable with CM from that point to the final BW.

Predicting fat, lean and the weights of primal cuts for growing pigs of different genotypes and sexes using computed tomography.

The aim of the present study was to find single equations to predict the amounts of fat, lean, and the weights of the primal cuts (ham, loin, belly, and shoulder) as well as ham composition of pigs from 30 to 120 kg BW of different genotypes (GEN; Exp. 1) and sexual conditions (SEX; Exp. 2). Two types of regression equations, taking into account different work situations, were developed: 1) research applications, using computed tomography (CT) parameters, and 2) potential on-farm applications, which could be obtained using easily accessible equipment. Two data sets were used: Exp. 1 included 90 gilts from 3 different GEN: 30 Duroc × (Landrace × Large White), 30 Pietrain × (Landrace × Large White), and 30 Landrace × Large White, and Exp. 2 included 92 Pietrain × (Landrace × Duroc) pigs of different SEX: 24 each of females, entire males, castrated males, and 20 immunocastrated males. Pigs were fully CT scanned in vivo at 30, 70, 100, and 120 kg BW. A subsample of pigs of each GEN ( = 5) or SEX ( = 4) were slaughtered at 30, 70, and 100 kg BW, and all remaining pigs were slaughtered after weighing and scanning at 120 kg BW. For all the slaughtered pigs, the 4 main cuts were fully (GEN) or partially dissected (SEX). CT images were analyzed and used to predict the lean and fat contents as well as the weights of the primal cuts and the composition of the ham. Total amounts of fat and lean for both populations were predicted with high levels of accuracy ( = 0.994 and 0.993, respectively) and proportions of random error for GEN and SEX effects (0.998 and 0.946 for the fat and 0.997 and 0.836 for the lean predictions, respectively). Moreover, the composition of ham (fat, lean, and bone) was very well predicted with high proportions (> 80%) of random error for GEN and SEX effect using CT and potential on-farm predictors.

Vaccination of cattle with chemically modified and unmodified salt-extractable proteins from Brucella abortus.

Beef heifers were vaccinated on Day 0 with either salt-extractable protein (CSP) or chemically modified CSP (dCSP) from Brucella abortus Strain 19 in Freund's complete adjuvant (FCA). Six weeks later, vaccination was repeated, and heifers received either the homologous or heterologous vaccine. Another group of heifers received only FCA and saline. Vaccinations with CSP or dCSP stimulated marked antibody responses to B. abortus, as detected by standard serologic tests, an enzyme-linked immunosorbent assay, or a quantitative fluorometric immunoassay. Twelve percent of the heifers were seropositive by the CARD test 1 year after vaccination. Vaccination stimulated an increased cell-mediated immune response as measured by lymphocyte blast transformation (LBT) to B. abortus antigens. Fifty-six weeks after the initial vaccination, the heifers were challenged intraconjunctivally with 1.9 X 10(7) colony-forming units of B. abortus strain 2308. Sixty to 83% of the heifers aborted in each group and 70-83% of the heifers were culture positive. There were no significant differences (P greater than 0.05) among groups with respect to the number of abortions or the number of culture-positive heifers. Antibody responses increased rapidly within 4 weeks after challenge. Overall, antibody responses were greater for heifers that aborted than for those that did not abort. These differences were significant (P less than 0.05) only as measured by the fluorometric procedure. The LBT responses appeared to be higher for vaccinates than for the control group, but these differences were not significant (P greater than 0.20). There was a significantly lower (P less than 0.05) LBT response to heat-killed B. abortus in those heifers that aborted compared to those that did not.

Sepracell-MN for mononuclear cell separation from cattle: effect on mitogen-and antigen-induced lymphocyte blastogenesis.

Mononuclear leukocytes (MNC) were separated from heparinized and EDTA-treated whole bovine blood by centrifugation after mixing with a commercial colloidal silica preparation (Sepracell-MN (S-MN]. Cell yields and lymphocyte blast transformation (LBT) to pokeweed mitogen (PWM), phytohaemagglutinin (PHA), concanavalin A (Con A), and Brucella abortus antigens were tested against MNC obtained from heparinized whole blood using Ficoll-Hypaque (FH). Separation with S-MN was more rapid and less labor intensive than separation with FH. There was a higher average total yield of MNC but a lower percentage of monocytes in the FH- than in the S-MN-separated MNC. In mitogen-induced LBT assays, MNC responded comparably to each mitogen regardless of the separation technique or anticoagulant used, and a cell concentration effect was demonstrated. In general, FH-separated MNC responded greater to PWM than did S-MN/EDTA separated MNC, but S-MN/heparin separated MNC had the greatest LBT responses to PWM. Overall, S-MN/EDTA separated MNC had the greatest responses to PHA, and responses to Con A were variable among experiments with respect to the separation technique. In antigen-induced LBT assays, two B. abortus antigens were used: a heat-killed strain S1119 (HKA) and a gamma-irradiated strain 19 (gamma BA). The LBT responses of three steers vaccinated with live B. abortus strain 19 were compared with three nonvaccinated steers in three separate experiments. Using HKA, FH separation resulted in an overall greater LBT response for vaccinates than nonvaccinates and a greater differential between responses of vaccinates and nonvaccinates than did S-MN derived MNC regardless of the anticoagulant used. Using gamma BA, FH produced the most responsive MNC in one experiment and S-MN/heparin produced the most responsive MNC in the other. At the highest cell concentration tested, FH-separated MNC had the greatest LBT responses for vaccinated calves, but differences between S-MN- and FH-separated MNC responses were not significantly different (P greater than 0.05). In conclusion, S-MN is a rapid and simple technique for separation of MNC from bovine blood. The technique produces an adequate cell population for mitogen-induced LBT studies; however, FH-separated MNC were generally more responsive in the B. abortus-induced LBT assay.

Estimation of the water requirement for beef production in the United States.

A static model of developed water use for U.S. cattle production was constructed on a spreadsheet. Water use included that consumed directly by various classes of animals, water applied for irrigation of crops that are consumed by the cattle, water applied to irrigated pasture, and water used to process animals at marketing. Government statistics were consulted for numbers of cattle and crop production. The most recent statistics available for numbers of cattle and crops in individual states were used. On January 1, 1992, a total of 33.8 million beef cows and 5.7 million replacement heifers were in U.S. breeding herds, 12 million animals were on feed, and approximately 28 million animals were fed annually. Thus, the U.S. beef cattle herd produced 6.9 billion kg of boneless beef. Beef cattle directly consumed 760 billion L of water per year. Feedlot cattle were fed various grain and roughage sources corresponding to the regions in which they were fed. Feeds produced in a state were preferentially used by cattle in that state with that state's efficiency; any additional feedstuffs required used water at the national efficiency. Irrigation of crop feedstuffs for beef cattle required 12,991 billion L of water. Irrigated pasture for beef cattle production required an additional 11,243 billion L of water. Carcass processing required 79 billion L of water. The model estimates 3,682 L of developed water per kilogram of boneless meat for beef cattle production in the United States. The model was most sensitive to the dressing percentage and percentage of boneless yield in carcasses of feedlot cattle (62 and 66.7, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of ruminant livestock in sustainable agricultural systems.

Ruminants have served and will continue to serve a valuable role in sustainable agricultural systems. They are particularly useful in converting vast renewable resources from rangeland, pasture, and crop residues or other by-products into food edible for humans. With ruminants, land that is too poor or too erodable to cultivate becomes productive. Also, nutrients in by-products are utilized and do not become a waste-disposal problem. The need to maintain ruminants to utilize these humanly inedible foodstuffs and convert them into high-quality foods for human consumption has been a characteristic of advanced societies for several thousand years. Further, ruminant livestock production is entirely consistent with proper agronomy practices in which forages are grown on 25% of arable land to minimize water and soil erosion. Questions have been asked, however, about the use of humanly edible foodstuffs (grains, protein sources, etc.) in ruminant diets. Does their use create a net loss of nutrients for human consumption? What level of their use is necessary or desirable? Does the use of some of these improve the nutrient (e.g. protein) quality or product value? Too often the opponents of animal agriculture evaluate the desirability of animal production on gross calorie or protein intake/output values. However, in many cases the feeds used in animal production are not consumable by humans, and in order to properly evaluate animal production, humanly consumable energy and protein intake should be used for efficiency comparisons. Analysis of the costs/returns of humanly edible energy and protein for a variety of dairy and beef cattle production systems shows that food value is increased with ruminant products, and that net returns of humanly edible nutrients are dependent on the production system used. The efficiency with which ruminants convert humanly edible energy and protein into meat or milk is highly dependent on diet, and hence, on regional production practices. Previous studies suggest that in the United States, dairy production efficiency ranges from 96 to 276% on a humanly consumable protein basis. Beef production efficiency is very dependent on the time spent in the feedlot and digestible energy and protein efficiencies range from 28 to 59% and 52 to 104%, respectively. However, beef production can add to the humanly consumable protein pool depending on the feeding schedule. In addition, the protein resulting from ruminant livestock production is of higher quality with a greater biological value than protein in the substrate feeds. The evidence that ruminant livestock belong in sustainable livestock production systems is convincing.

Beef cattle feed intake and growth: empirical Bayes derivation of the Kalman filter applied to a nonlinear dynamic model.

Feed intake and growth rate of a single group of growing-finishing feedlot beef cattle are difficult to predict. Subsequent performance can be projected more precisely from past performance of a group of cattle. Using an adaptation of the statistical procedure called the empirical Bayes (EB) derivation of the Kalman filter, estimates from any dynamic model (M) can be adjusted based on past performance. The model may be either linear or nonlinear. With this procedure, predictions of intake and body weight gain are periodically updated by multiplying the estimates from M by statistically weighted factors. These factors are derived from the ratio of performance in each period to the performance predicted by M. For comparison to the EB adjustment, weighting of factors by least-squares (LS) adjustment also was tested to predict subsequent feed intake and gain. The test data base consisted of periodic feed intake and gain observations (usually 28 d) for 200 pens of feedlot steers. Bias of prediction was lower for EB than for M or LS for feed intake and (usually) gain. Intake and gain prediction errors averaged for the whole feeding period were .42 kg/d for intake and .14 kg/d for gain by EB, being .84 and .18 kg/d more precise than M and .12 and .33 kg/d more precise than LS predictions. More than two observations were needed before LS produced accurate prediction but after about 80 d, LS and EB estimates converged. Accuracy of both estimates continued to improve as days on feed increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of body weight, frame size and rate of gain on the composition of gain of beef steers.

Energy concentration of gain (EG) is an inherent component in beef cattle feeding systems. The National Research Council (NRC) uses equations based on body weight, rate of gain and cattle type to predict EG and, in turn, to calculate dietary energy requirements. From EG, fat and protein deposition can be calculated directly. A dynamic computer growth model also can be used to estimate EG. In both the NRC and the computer model, EG increases from about 3 to 6 Mcal/kg as body weight increases from 200 to 500 kg if daily gain is 1 kg. Both NRC and the model predict EG of calves to be about .3 Mcal/kg greater than a previous NRC system. In contrast to the NRC, model-predicted EG of yearlings is lower at lighter and greater at heavier body weights. Rate of gain affects estimates of EG more for the dynamic model than for the NRC systems. When predicted EG was compared with observed EG for 46 pens of feedlot steers in comparative slaughter trials, NRC estimates exhibited a narrow range compared with observed values with correlation coefficients of r = .38 and r = .71 (previous NRC). Model estimates of EG were closer (r = .85). The NRC predictions of EG systematically erred with initial body composition, diet metabolizable energy and length of feeding period (P less than .01) and with initial body weight and rate of gain (P less than .05). No systematic errors in model-predicted EG were detected. Enhanced model sensitivity to compensatory growth and rate of gain should reduce both EG and body weight gain prediction errors.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a model to predict forage intake by grazing cattle.

A mathematical model to predict daily DMI and account for effects of energy supplementation on forage intake has been developed in several stages. A previously evaluated dynamic rumen model for sheep was adopted as the fermentation component of the intake model. Intake was adjusted to reach a given level of DM fill, which is the sum of the concentrations of each of the dietary fractions within the rumen. Differential equations described the rate of change of each nutrient fraction. Genetic size scaling rules based on mature body size relationships were used to adjust rate and fill parameters of the intake model from sheep to beef cattle. Nutrient fractions were partitioned into those that flow at the particulate passage rate vs the fluid passage rate. Forty-two data points representing perennial ryegrass, wheat pasture and range grasses were used to parameterize and evaluate the model. The model was relatively sensitive to the coefficient relating DMI to particulate rate of passage, the rate constant for the use of the potentially degraded fiber fraction of the forage, and to the composition constants for the amount of carbohydrate and nitrogen in the microbial mass. Relative insensitivity was observed for starch and protein nutrient use rate constants, for the coefficient relating DMI to fluid passage rate, and for constants relating to the growth of the microbial mass in the rumen. Feed intake of grazing cattle may be predicted by mechanistic models describing various nutrients' contribution to ruminal fill.

Evaluation of a feed intake model for the grazing beef steer.

Responses of a feed intake model for grazing beef cattle to changes in model parameters, forage composition, and supplementation programs with energy and protein were evaluated. Without supplements, the model systematically underpredicted intake of low-quality (low digestibility) forages and subsequent overprediction was observed for high-quality diets. In general, for a reference diet of Italian ryegrass, the model was relatively insensitive to microbial growth parameters, highly sensitive to the microbial carbohydrate composition constant, and moderately sensitive to the microbial N composition constant. Intake prediction was sensitive to changes in the microbial use rate constant for fiber but insensitive to those for protein and starch. Model predictions were highly sensitive to the amount of nondegradable fiber in each of the forages tested. Supplementation effects on forage intake were quantified by supplementing all forage diets with chemical components equivalent to that provided by 1 kg of corn grain or 1 kg of cottonseed meal. Supplementation of the forage diet with the concentrate source resulted in substitution ratios of forage to supplement intake consistent with in vivo results. As forage quality increased, substitution of concentrate for the forage increased. However, the model failed to predict the increased forage intake typically observed with protein supplementation, suggesting that it is insufficient for intake prediction in protein-limiting situations. Nevertheless, the model correctly predicted effects of energy supplementation and forage composition on forage intake, suggesting that different controls must regulate intake responses to supplemental protein.

Compensatory growth and carcass quality in growth-restricted and refed beef steers.

Beef steers were fed in two phases 1) to determine the relative importance of changes in DMI, gastrointestinal tract fill, energy expenditures, and composition of gain in the compensatory growth phenomenon, 2) to compare the effects of growth restriction due to ad libitum consumption of a low-energy (low-concentrate) diet to those of limited intake of a high-energy (high-concentrate) feed, and 3) to examine changes in carcass composition and quality resulting from different types of growth restriction. During the growing phase (237 to 327 kg), steers were fed either a high- (C) of low- (F) concentrate diet. Diet F was available for ad libitum consumption (FA) and diet C was available either for ad libitum consumption (CA) or on a limited basis (CL) to match the live weight gains by the FA group. During the finishing phase (327 to 481 kg), all steers received diet C, either for ad libitum consumption (CA) or restricted (CL) to 70% of the intake by the corresponding CA steers. Backfat thickness was markedly reduced (P < .001) by final feed restriction (7.4 and 6.9 mm for CL-CL and FA-CL respectively), compared with CA-CA (12.6 mm). Backfat also was lower in CL-CA (11.6 mm, P < .10) and FA-CA (9.9 mm, P < .05) than in CA-CA steers. Conversely, marbling scores were similar among groups, except for the FA-CL steers, which had lower marbling scores than FA-CA and CL-CA steers (P < .05). Higher DMI following growth restriction were accompanied by increased rates of live weight (+54 and +27%) and empty body weight (EBW; +57 and +43%) gain for CL-CA and FA-CA steers, respectively, compared with CA-CA steers. Gain:feed (EBW basis) were improved in some restricted/refed groups (+30, +13, and +10%, for Cl-CA, CL-CM respectively CA-CA. Increased DMI played a major role in the compensatory gain response in both CL-CA and FA-CA groups. Maintenance requirement was reduced (-17%) in CL-CA and increased in the FA-CA group (+21%); both changes affected the magnitude of compensatory gain in those animals. In contrast, composition of gain had little or no effect on the compensatory gain response. Programmed feeding can be used to manipulate carcass quality, but low-concentrate feeding during the growing phase may impair overall feedlot performance.

Evaluation of ultrasound for prediction of carcass fat thickness and longissimus muscle area in feedlot steers.

Four hundred fifty-two yearling steers from two experiments were measured for subcutaneous fat thickness and longissimus muscle area between the 12th and 13th ribs using real-time linear array ultrasound equipment. Ultrasonic predictions were compared to corresponding carcass measurements to determine accuracy of ultrasound measurements. In Exp. 1, 74% of the ultrasonic estimates of fat thickness were within 2.54 mm of carcass values (r = .81) and muscle area was predicted within 6.45 cm2 for 47% of all carcasses (r = .43). Although similar correlation coefficients between ultrasonic and carcass fat thickness were obtained in Exp. 2 (r = .82), estimates were more biased; only 62% of ultrasound estimates were within 2.54 mm of carcass measurements. Improvement in longissimus muscle area estimates was noted in Exp. 2, in which 54% of ultrasonic estimates were within 6.45 cm2 of carcass values (r = .63). The extremes for each trait proved most difficult to predict; fat thickness was underestimated on fatter cattle and muscle area was underpredicted on more heavily muscled steers. Ultrasonic measurements of fat thickness are precise and accurate in determining carcass fat thickness, but muscle area estimates are inconsistent and warrant further investigation.

Relationship among weight change, body condition and reproductive performance of range beef cows.

A 5-yr study involving 45 to 78 pregnant Hereford range cows each year evaluated relationships among prepartum nutrition, body condition scores, BW changes and reproductive performance. Four prepartum nutritional treatments were imposed. One group of cows were fed to maintain (M) their November BW until calving in March and April. The other three groups of cows were fed to lose about 5% of their November BW by 8 wk before parturition, then to maintain BW (LM), lose an additional 5% of their BW (LL) or gain 5% of their BW (LG). After calving, all cows were fed to maintain BW. Body condition scores and BW were recorded every 14 d throughout the trial. Linear regression analyses were conducted to examine treatment effects on BW, body condition score and measures of reproductive performance. A discriminant analysis was performed on pregnancy rate and percentage of cows with ovarian luteal activity by 85 d after parturition. The M cows had a greater pregnancy rate (71%) than cows on other treatment groups. The LL cows had a reduced pregnancy rate (42%) compared with LM (51%) and LG (58%) cows. Prepartum nutritional treatment did not affect the days from parturition to conception. Precalving body condition score and November to January BW changes influenced pregnancy rate (P less than .001). A cubic response curve described the relationship between pregnancy rate and precalving body condition score for cows with condition scores of 3 through 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth of Holstein calves from birth to 90 days: the influence of dietary zinc and BLAD status.

The main objective of this study was to describe Holstein neonatal growth and development as influenced by dietary zinc supplementation and the CD18 genotype, both of which may affect immune competence. Holstein calves (n = 421), after being fed colostrum, were brought to a calf facility, randomly assigned to one of four zinc supplementation groups (control at 40 mg Zn/kg DM or the control diet supplemented with an additional 60 mg Zn/kg DM provided as either zinc sulfate, zinc lysine, or zinc methionine), weighed, and measured for morphometric growth parameters. Measurements were repeated at 30, 60, and 90 d. Calves were also genotyped for the presence of the mutant D128G CD18 allele, which, if present in two copies, causes bovine leukocyte adhesion deficiency. Zinc supplementation above 40 mg Zn/kg DM, regardless of the chemical form, did not accelerate growth (P > 0.25). Further, overall calf growth performance was not suppressed or improved (P > 0.4) in calves heterozygous at the CD18 locus relative to calves homozygous for the normal CD18 allele, although genotype negatively affected some morphometric measurements (P < 0.05). Using these data, quadratic models of early growth were generated as a preliminary step to develop growth criteria that will allow producers, veterinarians, and animal scientists to identify poor growth performance early in neonatal life. Such criteria provide the basis for tools to improve economic performance.

Carcass composition in mature Hereford cows: estimation and effect on daily metabolizable energy requirement during winter.

Seventy-two mature, nonpregnant, nonlactating Hereford cows (400 kg) were utilized in a comparative slaughter trial to investigate the effects of carcass composition on the metabolizable energy (ME) required for maintenance in winter. Body condition score (CS), live weight (LW) and weight:height ratio (WTHT) were evaluated and compared as estimators of carcass composition in cows. Cows ranged in LW, CS and WTHT from 275 to 595 kg, 2.0 to 8.0 units and 2.29 to 4.62 kg/cm, respectively. Live weight, CS and WTHT predicted total carcass energy (TMCAL, r2 = .81, .85 and .83), carcass fat (FAT, r2 = .78, .82 and .80), carcass protein (PRO, r2 = .71, .74 and .70) and carcass water (WAT, r2 = .78, .71 and .77) with similar accuracy. When composition was expressed on a per unit weight basis, CS was superior to LW and WTHT as predictors of TMCAL/hot carcass weight, TMCAL/LW and FAT/hot carcass weight (r2 = .82, .60 and .64; .83, .58 and .62; and .82, .64 and .68, respectively). Forty-seven cows were individually fed a complete diet (2.50 Mcal ME/dry matter) in drylot for 114 d in yr 1 and 115 d in yr 2. Daily feed intakes were adjusted each week to maintain constant LW throughout the winter. Data were analyzed by fitting the model: ME intake = k-1 (carcass energy change) + f(CS)LW.75, where k = efficiency of ME use for carcass energy change and f(CS) = function of CS. Year as a class variable and the expression .1028 + .0234(CS) - .0025(CS)2 accounted for 41% of the variation in Mcal ME for maintenance/LW.75. Condition score was more closely related to carcass composition in mature cows than was LW or WTHT and cows in either a thin (CS = 3) condition or a fat (CS = 7) condition required less (4.4% and 8.9%) Mcal ME/LW.75 for maintenance than cows in moderate (CS = 5) condition.

Growth of suckling beef calves in response to parenteral administration of selenium and the effect of dietary protein provided to their dams.

OBJECTIVE: To determine whether parenteral administration of selenium (Se) to calves and the amount of forage and protein provided to their dams affects unadjusted body weight, adjusted 205-day body weight, and average daily gain (ADG) of suckling beef calves. DESIGN: Randomized controlled field trial. ANIMALS: 151 Hereford-Angus crossbred beef calves. PROCEDURE: Newborn calves, randomly assigned to 1 of 3 groups, served as untreated controls (n = 49) or were given Se (0.05 mg/kg [0.023 mg/lb] of body weight, SC) once within 2 days of birth (55) or within 2 days of birth and on days 70, 114, and 149 (47). Until day 149, cow-calf pairs were pastured in fields in which the amount of available forage was high or low and supplemental protein was or was not provided. Calves were weighed on days 1, 70, 149, and 209. On days 160 and 209, blood was obtained from 33 calves for measurements of Se concentration. RESULTS: Mean consumption of supplemental protein was 0.65 kg/dam/d. Between days 1 and 70, calves that received the first of 4 multiple injections of Se had significantly greater ADG than control calves. Average daily gain for calves given only 1 injection was not significantly different from controls. Between days 70 and 149, ADG of calves increased with dietary supplementation of protein to their dams. CLINICAL IMPLICATIONS: Strategic administration of Se to calves and dietary supplementation of protein to their dams may result in greater ADG in suckling beef calves during specific time intervals.