Animal Sciences Commons^™

Effects Of Sorghum Wet Distillers Grains Plus Solubles In Steam-Flaked Corn–Based Finishing Diets On Steer Performance, Carcass Characteristics, And Digestibility Characteristics, E. K. Buttrey, K. H. Noel, F. T. Mccollum Iii, N. A. Cole, L. O. Tedeschi, James C. Macdonald

Department of Animal Science: Faculty Publications

Two studies were conducted to evaluate the effects of sorghum wet distillers grains (SWDGS) in finishing diets on steer performance, carcass characteristics, and nutrient digestibility. In Exp. 1, 240 steers (initial BW = 379 ± 1 kg) were fed steam-flaked corn–based diets with or without 25% SWDGS and 7.5, 10.0, or 12.5% alfalfa hay. There were no effects of alfalfa hay concentration on BW, DMI, ADG, or G:F (P ≥ 0.16). Including SWDGS reduced (P ≤ 0.05) ADG and G:F. Fat thickness decreased (P = 0.03) and DP tended to decrease (P = 0.09) linearly as level of alfalfa hay …

Effects Of Fat And/Or Methionine Hydroxy Analog Added To A Molasses-Urea-Based Supplement On Ruminal And Postruminal Digestion And Duodenal Flow Of Nutrients In Beef Steers Consuming Low-Quality Lovegrass Hay, R. Lopez, G. D. Bernhard, J. E. Guerra-Liera, S. A. Soto-Navarro, L. A. Balstad, M. K. Petersen, D. V. Dhuyvetter, M. S. Brown, C. R. Krehbiel

Department of Animal Science: Faculty Publications

Five crossbred beef steers (initial BW = 338.6 ± 7.8 kg) fitted with ruminal and duodenal cannulas were used in a 5 × 5 Latin square design experiment to evaluate the effects of methionine hydroxy analog (MHA) and/or yellow grease (fat) added to a molassesurea- based supplement on intake and characteristics of digestion. Steers were fed low-quality hay (long-stem lovegrass Eragrostis curvula: 3.3% CP, 76.8% NDF; DM basis) ad libitum and supplemented with 0.91 kg/d (as fed) of 1 of 4 supplements in a 2 × 2 + 1 factorial arrangement of treatments. Supplemental treatments were 1) control (no supplement, …

Genetic Parameters For Docility, Weaning Weight, Yearling Weight, And Intramuscular Fat Percentage In Hereford Cattle, J. A. Torres-Vázquez, Matthew L. Spangler

Department of Animal Science: Faculty Publications

Cattle behavior, including measures of docility, is important to beef cattle producers not only from a human safety perspective but also due to potential correlations to economically relevant traits. Field data from the American Hereford Association was used to estimate genetic parameters for chute score (CS; n = 25,037), weaning weight (WW; n = 24,908), yearling weight (YW; n = 23,978), and intramuscular fat percentage (IMF; n = 12,566). Single-trait and bivariate animal models were used to estimate heritabilities and genetic correlations. All models included fixed effects of sex and contemporary group, defined as herd–year–season, and direct genetic and residual …

The Effects Of Technology Use In Feedlot Production Systems On Feedlot Performance And Carcass Characteristics, C. L. Maxwell, B. C. Wilson, C. F. O'Neill, B. K. Wilson, C. G. Hixon, C. L. Haviland, A. N. Grimes, M. S. Calvo-Lorenzo, D. L. Vanoverbeke, G. G. Mafi, C. J. Richards, D. L. Step, B. P. Holland, C. R. Krehbiel

Department of Animal Science: Faculty Publications

The objectives of this study were to examine the effects of feedlot production systems with and without the use of a β-adrenergic agonist compared to an all-natural production program on feedlot performance and carcass characteristics. Crossbred beef steers (n = 336; initial BW = 379 ± 8 kg) were randomized to 1 of 3 treatments in a randomized complete block design (RCBD; 14 steers/pen; 8 pens/treatment). Treatments consisted of an all-natural treatment (NAT), a conventional treatment (CONV), and a conventional treatment with a β-agonist (CONV-Z). All treatments were fed the same basal diet with NAT cattle receiving no growth promoting …

Relationships Between Behavioral Measures And Productivity In Growing Beef Cattle, Kelsey Bruno

Theses and Dissertations--Animal and Food Sciences

The relationships between behavioral measures, growth performance, and immunocompetence in receiving beef steers were explored in three experiments. Specifically, exit velocity (EV) and objective chute score (OCS) were examined as temperament measures. In experiment 1, no main effects or interactions with degradable intake protein (DIP) or interactions between temperament measures were observed (P ≥ 0.11); however, high OCS steers had greater intake and gain:feed (P < 0.10) and slow EV steers had higher intake and gain (P < 0.10) than their counterparts. In experiment 2, during week two of social observations, dominance hierarchy rankings were dependent on OCS and EV (P < 0.05); slow EV steers also had increased antibody responses and gain (P < 0.10) and high OCS steers had increased gain (P < 0.10). In experiment 3, subjective chute scores and OCS were positively correlated (P < 0.01) and both EV and OCS treatments changed over time (P < 0.10); intake, vaccine titer response, and gain:feed responses to monensin were dependent on OCS treatment (P < 0.10). The studies suggest that temperament, measured by EV and OCS, affects growth performance and health related measures and is related to social dominance behavior in receiving beef steers.

Feeding Condensed Distillers’ Solubles To Feedlot Finishing Steers And The Effects Of Feed Additives In Adaptation Diets, Marie Elizabeth Harris

Department of Animal Science: Dissertations, Theses, and Student Research

By-products from the dry-milling ethanol process can be used in cattle diets to replace corn. There is a significant interaction between corn processing methods as CCDS concentration increases in the diet. Improvements are observed for SFC in final BW, ADG, and G:F over DRC. An experiment was conducted to determine if greater concentrations of CCDS could be fed in SFC based diets and maintain or improve performance. Performance and carcass characteristics were evaluated with increasing concentrations of CCDS at 0, 9, 18, 27, or 36% in place of SFC in feedlot finishing diets. As CCDS concentration increased, DMI decreased quadratically. …

Beef Cattle Lesson Plans: For Use In The Education Of School-Age Children In The Beef Cattle Industry, Katherine M. Halloran, Cheyenne H. Love

Animal Science

This project was initially created for use at Fort Hope in Arroyo Grande, California. It designs lesson plans created to teach children about the beef cattle industry. The project consists of lesson plans for three age groups: 7-9, 10-12, and 13-15. Each age group will learn various aspects about beef cattle, and lessons will increase in complexity as the children advance age groups. The groups will spend six days in lecture completing worksheets and activities, and on the seventh day, after completion of a review game, the children receive certificates. While the project was created specifically for the Fort Hope …

A Comparison Of The Standard 5-Day Co-Synch With Cidr Protocol And A 14-Day Co-Synch With Cidr Protocol In Primiparous And Multiparous Beef Cattle, Taylor Anne Dericco

Animal Science

No abstract provided.

Uncertainties In Life Cycle Greenhouse Gas Emissions From U.S. Beef Cattle, Quentin M. Dudley, Adam Liska, Andrea K. Watson, Galen E. Erickson

Adam Liska Papers

Beef cattle feedlots are estimated to contribute 26% of U.S. agricultural greenhouse gas (GHG) emissions, and future climate change policy could target reducing these emissions. Life cycle assessment (LCA) of GHG emissions from U.S. grain-fed beef cattle was conducted based on industry statistics and previous studies to identify the main sources of uncertainty in these estimations. Uncertainty associated with GHG emissions from indirect land use change, pasture soil emissions (e.g. soil carbon sequestration), enteric fermentation from cattle on pasture, and methane emissions from feedlot manure, respectively, contributed the most variability to life cycle GHG emissions from beef production. Feeding of …

Qtls Associated With Dry Matter Intake, Metabolic Mid-Test Weight, Growth And Feed Efficiency Have Little Overlap Across 4 Beef Cattle Studies, Mahdi Saatchi, Jonathan E. Beever, Jared E. Decker, Dan B. Faulkner, Harvey C. Freetly, Stephanie L. Hansen, Helen Yampara-Iquise, Kristen A. Johnson, Stephen D. Kachman, Monty S. Kerley, Jaewoo Kim, Daniel D. Loy, Elisa Marques, Holly L. Neibergs, E. John Pollak, Robert D. Schnabel, Christopher M. Seabury, Daniel W. Shike, W. M. Snelling, Matthew L. Spangler, Robert L. Weaber, D. J. Garrick, Jeremy F. Taylor

Department of Animal Science: Faculty Publications

Background: The identification of genetic markers associated with complex traits that are expensive to record such as feed intake or feed efficiency would allow these traits to be included in selection programs. To identify large-effect QTL, we performed a series of genome-wide association studies and functional analyses using 50 K and 770 K SNP genotypes scored in 5,133 animals from 4 independent beef cattle populations (Cycle VII, Angus, Hereford and Simmental × Angus) with phenotypes for average daily gain, dry matter intake, metabolic mid-test body weight and residual feed intake.

Results: A total of 5, 6, 11 and 10 significant …

Effects Of Beef Production System On Animal Performance And Carcass Characteristics, C. L. Maxwell, C. R. Lopez, B. K. Wilson, B. T. Johnson, B. C. Bernhard, C. F. O'Neill, D. L. Vanoverbeke, G. G. Mafi, D. L. Step, C. J. Richards

Department of Animal Science: Faculty Publications

The objective of this study was to evaluate conventional (CONV) and natural (NAT) beef production systems from annual pasture through finishing through grazing. Beef steers (n = 180, initial BW = 250 ± 19 kg) were assigned randomly to 2 treatments in the pasture phase. Steers were implanted with 40 mg of trenbolone acetate (TBA), 8 mg estradiol, and 29 mg tylosin tartrate (CONV), or received no implant (NAT). Steers on the 2 treatments grazed wheat or cereal rye for 109 d. Conventional steers had an 18.5% improvement in ADG (1.22 vs. 1.03 kg/d, P < 0.01) and a heavier final BW (385 vs. 366 kg, P < 0.01) compared with NAT steers. Following the pasture phase, steers (n = 160 steers, 5 steers/pen, 8 pens/treatment) were assigned to a 2 × 2 factorial in the feedlot phase. Production system (NAT vs. CONV) was maintained from the pasture phase, and the second factor was 7 vs. 12% low-quality roughage (DM basis, LOW vs. HIGH). During finishing, CONV steers were given 120 mg of TBA and 24 mg estradiol at processing, fed monensin and tylosin, and fed zilpaterol hydrochloride for the last 20 d of the experiment. There were no program × roughage level interactions (P > 0.07). The CONV steers ate …

Fatty Acid Profile In 4 Types Of Fat Depots In Polish Holstein-Friesian And Limousine × Polish Holstein-Friesian Bulls, Monika Sobczuk-Szul, Zenon Nogalski, Zofia Wielgosz-Groth, Magdalena Mochol, Arkadiusz Rzemieniewski, Paulina Pogorzelska-Przybylek, Cezary Purwin

Turkish Journal of Veterinary & Animal Sciences

The aim of this study was to determine the fatty acid profile in 4 types of fat deposits in Polish Holstein-Friesian (PHF) and Limousine × Polish Holstein-Friesian (LM × PHF) bulls. The experimental materials included samples of intramuscular, intermuscular, subcutaneous, and internal fat collected from the carcasses of 28 PHF bulls and 26 LM × PHF bulls. Determined fatty acids (FAs) were divided into saturated (SFAs) and unsaturated (UFAs) FAs, including monounsaturated (MUFAs) and polyunsaturated (PUFAs) FAs. The UFA/SFA, MUFA/SFA, PUFA/SFA, and PUFA n-6/PUFA n-3 ratios were calculated. Internal fat was characterized by the highest SFA concentrations, and subcutaneous fat …

Impacts Of Feeding Baleage To Beef Calves During The Backgrounding Period, Rachel Morgan Martin

LSU Master's Theses

Two hundred forty beef calves (BW = 217 ± 20.6 kg) were used to evaluate performance, blood metabolites, and rumen development from feeding bermudagrass or ryegrass and rye baleage. Calves were stratified by BW, sex, and breed and assigned to one of 12 paddocks (0.40 ha each) with 4 treatment diets and fed for a 60 d backgrounding period. Diets included: early boot stage bermudagrass hay, (BERH); early boot stage ryegrass and rye baleage (ERRG); late bloom stage ryegrass and rye baleage, (LRRG); and early boot stage bermudagrass baleage, (BERB). Calves on BERH, LRRG, and BERB had free choice access …

Evaluating The Effect Maturity On The Intake And Digestibility Of Switchgrass Hay Consumed By Beef Steers, David H. Davis

Theses and Dissertations--Plant and Soil Sciences

There has been increased interest in utilizing switchgrass (Panicum virgatum) as biomass. There are several challenges to developing this industry, and these have led to the potential use of switchgrass as hay for feeding beef cattle in Kentucky. The effect of increasing maturity on crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and nutritive values of switchgrass hay has been well documented, but few in vivo intake and digestibility trials have been conducted to assess this effect on animal performance when feeding beef cattle. Two in vivo intake and digestibility trials were conducted in 2011 …

Beef Cattle Body Temperature During Climatic Stress: A Genome-Wide Association Study, Jeremy T. Howard, Stephen D. Kachman, Warren M. Snelling, E. John Pollak, Daniel C. Ciobanu, Larry A. Kuehn, Matthew L. Spangler

Department of Animal Science: Faculty Publications

Cattle are reared in diverse environments and collecting phenotypic body temperature (BT) measurements to characterize BT variation across diverse environments is difficult and expensive. To better understand the genetic basis of BT regulation, a genome-wide association study was conducted utilizing crossbred steers and heifers totaling 239 animals of unknown pedigree and breed fraction. During predicted extreme heat and cold stress events, hourly tympanic and vaginal BT devices were placed in steers and heifers, respect i v e l y. I n d i v i dua l s we r e genotyped with t h e BovineSNP50K_v2 assay and data …

Effects Of Maternal Nutrition And Post-Weaning Management In A Late Spring Calving System And Synchronization Of Estrus Using Fixed Time Ai Protocols, John D. Harms

Department of Animal Science: Dissertations, Theses, and Student Research

Three experiments were conducted to determine the impact of development systems, maternal protein supplementation, and estrus synchronization systems on beef cattle. Experiment 1 evaluated the effects of winter supplementation on cow performance and the effects of post-weaning management on progeny. Late spring calving cows grazed dormant range or meadow over winter and received either supplementation or no supplementation. Steer and heifer progeny were weaned and placed on dormant meadow or fed hay ad libitum. One half of the steers were placed in the feedlot at the end of treatment and the other half grazed range over summer. Cow winter treatment …

Beefsd: An Integrated And Intensive Extension Curriculum For Beginning Beef Cattle Producers In South Dakota, K. Olson, Julie Walker, S. Hadrick

Animal Science Faculty Publications

The average age of beef producers in the USis 58 and increasing. A need exists to increase theopportunity and success for the next generation of beefcattle producers. Extension at SDSU and South DakotaFarm Bureau Federation partnered to address this byproviding a 3-year educational program that assistedbeginning beef cow-calf ranchers in South Dakota tobecome economically, ecologically, and sociallysustainable producers. The goal was to present a curriculumthat contributed to future agricultural production, landstewardship, and rural community viability. The learningobjectives were to provide: (1) evaluation of alternativeproduction systems, (2) an integrated understanding of theentire US beef cattle industry, and (3) development ofindividual cattle …

Supplementing Distillers' Grains In A Yearling System As A Forage Replacement Tool With Bunk Or Ground Feeding, And Impact Of Winter Supplementation Level On Finishing Performance And Profit, Kari L. Gillespie

Department of Animal Science: Dissertations, Theses, and Student Research

The benefit of adding weight to cattle prior to entering the finishing phase through a forage-based backgrounding system has become more important with increased corn price. Further, as competition for available forage increases, the value of replacing grazed forage with a supplement such as distillers grains, also increases.

A 2-year beef systems study evaluated optimal supplementation time of distillers grains and summer forage savings with distillers supplementation. High winter level supplementation of distillers grains increased winter ADG, decreased summer ADG, and increased final live weights and HCW compared to cattle supplemented at a low supplement level designed to only meet …

The Effect Of Myostatin Genotype On Body Temperature During Extreme Temperature Events, J. T. Howard, Stephen D. Kachman, Merlyn K. Nielsen, Terry L. Mader, Matthew L. Spangler

Department of Animal Science: Faculty Publications

Extreme heat and cold events can create deleterious physiological changes in cattle as they attempt to cope. The genetic background of animals can influence their response to these events. The objective of the current study was to determine the impact of myostatin genotype (MG) on body temperature during periods of heat and cold stress. Two groups of crossbred steers and heifers of unknown pedigree and breed fraction with varying percentages of Angus, Simmental, and Piedmontese were placed in a feedlot over 2 summers and 2 winters. Before arrival, animals were genotyped for the Piedmontese-derived myostatin mutation (C313Y) to determine their …

Review: Life-Cycle, Total-Industry Genetic Improvement Of Feed Efficiency In Beef Cattle: Blueprint For The Beef Improvement Federation, Merlyn K. Nielsen, M. D. Macneil, J. C. M. Dekkers, D. H. Crews Jr., T. A. Rathje, R. Mark Enns, R. L. Weaber

Department of Animal Science: Faculty Publications

On a life-cycle basis, beef animals are able to consume large amounts of low-cost, low-quality forages relative to higher-cost concentrates compared with pigs and chickens. However, of the 3, beef is still more expensive to produce on a cost–per–edible pound basis. Accordingly, there is need for genetic programs and management changes that will improve efficiency, sustainability, and profitability of beef production. Options include improving reproductive rate, reducing feed used for maintenance, or both, while not reducing output. A goal for improving efficiency of feed utilization is to reduce the amount or proportion of feed used for maintenance. Such reduction is …

Impact Of Direct-Fed Microbials On Nutrient Utilization In Beef Cattle, Nicole Kenney

Theses and Dissertations--Animal and Food Sciences

The impact of lactate producing direct-fed microbial (DFM) on growth performance and rumen fermentation in beef cattle was explored in four studies. Experiment 1 studied the interaction between DFM and degradable intake protein (DIP) supply in receiving cattle. No differences (P≥0.06) in intake, morbidity, or immune response were observed; however, during the first 28 d gain and efficiency responses to DFM were dependent on DIP (DIP×DFM P≤0.05). Experiment 2 showed that in vitro gas production and select endpoint metabolites differed (P≤0.04) with DFM application. Experiment 3 compared lactate producing DFM to a lactate producing/utilizing DFM in finishing cattle. No differences …

The Impact Of Genetic Background On Body Temperature Regulation In Beef Cattle During Periods Of Heat And Cold Stress, Jeremy T. Howard

Department of Animal Science: Dissertations, Theses, and Student Research

Cattle are reared in environments that differ and vary greatly in climate, thus the ability to regulate body temperature across multiple environments is essential. However, inherent differences between animals do exist and can influence their response to extreme temperatures. The objectives of the current study were to model the impact of myostatin genotype (MG) on body temperature during heat and cold stress and conduct a genome-wide association study (GWAS) to better understand the genetic basis of body temperature regulation during extreme temperatures.

Crossbred steers and heifers (n= 239) with varying degrees of Piedmontese influence were fed in four groups over …

Utilization Of Corn Condensed Distillers’ Solubles And Forages In Management Systems For The Cow-Calf Enterprise, Jason M. Warner

Department of Animal Science: Dissertations, Theses, and Student Research

Of the annual expenses necessary to maintain a beef cow, feed and forage are the greatest and most variable. Thus, nutrition programs for cow-calf operations must be developed using economical feedstuffs that optimize cowherd performance. The corn dry-milling industry provides several feedstuffs that are often the most economical sources of energy and protein, but considerations for storage and handling are necessary. Two experiments evaluated an alternative form of storing corn condensed distillers solubles (CCDS) by applying to grass hay windrows before baling. Round bales were treated with either 0 or 20% (Exp. 1); or 0, 16, and 32% (Exp. 2) …

Evaluation Of Internal Markers For Predicting Digestibility And Fecal Output By Cattle Fed Bermudagrass Hays Of Varying Quality, Juvenal Kanani

Graduate Theses and Dissertations

The potential of in situ rumen undegradable dry matter (RUDM), indigestible neutral-detergent fiber (INDF), indigestible acid-detergent fiber (IADF), acid-detergent insoluble ash (ADIA), alkaline-peroxide lignin (APL), and acid-detergent lignin (ADL) to predict digestibility (DMD) and fecal output (FO) by cattle fed bermudagrass [Cynodon dactylon (L.) Pers.] hay-diets categorized by their low (L), medium low (ML), medium high (MH), or high (H) CP concentrations (79, 111, 131, and 164 g/kg DM, respectively) was evaluated. The second objective was to evaluate the effects of time (0600, 1200, 1800, and 2400 h) of fecal sampling on the prediction of FO and DMD. A replicated …

Impact Of Different Handling Styles (Good Vs. Aversive) On Growth Performance, Behavior, And Cortisol Concentrations In Beef Cattle, Joan Bauer

Animal Science Undergraduate Honors Theses

Our objective was to determine effects of aggressive handling on growth performance, behavior, and cortisol concentrations in beef calves. Crossbred calves (313 ± 4.7 kg; n = 54; 24 steers, 30 heifers) from a single herd were stratified by gender, body weight, and initial chute score, then allocated randomly to 1 of 6 pens. Each pen was randomly assigned to 1 of 2 handling treatments (good or adverse) applied on days 7, 35, 63, and 91. The objective of good treatment was to handle the calves quietly and gently to minimize stress. The objective of adverse treatment was to move …

Review: Technical Aspects For The Utilization Of Small Grain Straws As Feed Energy Sources For Ruminants: Emphasis On Beef Cattle, J. Severe, D. R. Zobell

All Current Publications

This publication defines Straw and provide information on straw composition, plant cell wall development, and treatments of straw for feed.

Occurrence Of Hormonal Residues In Feedlot Cattle Waste, Terry L. Mader, Leslie J. Johnson, Shannon L. Bartelt-Hunt, Daniel D. Snow, William Kranz, Charles Shapiro, Simon Van Donk, David P. Shelton, David Tarkalson, T. C. Zhang, Steve Ensley

Department of Animal Science: Faculty Publications

Two identically designed studies were conducted in separate years at the UNL Haskell Agricultural Laboratory using 192 crossbred heifers (96/study). Within a study heifers (initial weight = 386kg) were randomly assigned to 2 groups (3 42.4 m × 14.6 m pens/group/year): 1) treatment (TRT) animals were administered synthetic hormones via subcutaneous implants [d 1, 36 mg zearalonal; d 35, 140 mg trenbolone acetate (TBA) and 14 mg of 17β-estradiol benzoate (Revalor-H)] and fed Melengesterol Acetate (MGA), and 2) control (CON) animals with no synthetic hormone provided. Throughout each study, feedlot pen surface samples were obtained from 4 equally-sized zones (5 …

Use Of A Complete-Feed Diet (Ramp) To Rapidly Transition Cattle To A Finishing Diet, C. J. Schneider, Brandon L. Nuttelman, Dirk Burken, Terry J. Klopfenstein, Galen E. Erickson

Department of Animal Science: Faculty Publications

A study evaluated transitioning cattle from RAMP to a finishing diet with fewer intermediate step diets and days fed during transition. Yearling crossbred steers (n = 390; BW = 341 ± 14 kg) were blocked and stratified by BW, and assigned randomly within strata to 40 feedlot pens, with 9 or 10 steers per pen. Treatments were different grain adaptation programs (27 or 28 d) involving blends of RAMP and finishing diet. A control adaptation program involved decreasing RAMP and increasing a 62.5% corn finishing diet (62.5% high moisture corn (HMC), 25% sweet bran, 7.5% alfalfa hay (AH), and 5% …

Use Of A Complete-Feed Diet (Ramp) In Grain Adaptation Programs Compared To Traditional Grain Adaptation Programs, C. J. Schneider, Brandon L. Nuttelman, Kelsey M. Rolfe Rolfe, William A. Griffin, Terry J. Klopfenstein, Galen E. Erickson

Department of Animal Science: Faculty Publications

A study evaluated using RAMP to adapt cattle to a high grain finishing diet. Yearling crossbred steers (n = 229; BW = 397 ± 28.4 kg) were consecutively weighed over 2 d, stratified by BW, and assigned randomly within strata to 18 feedlot pens, with 12 or 13 steers per pen. Treatments were imposed during grain adaptation (22 d) by decreasing RAMP (100 to 0%) and increasing finishing diet (0 to 100%). RAMP was fed either as a blend in a 1-diet system which was delivered twice daily (RAMP-1RS) or as 2 daily diets where RAMP was delivered in one …

Beef Heifer Retention Decisions, Cody Reed, Dale Zobell

All Current Publications

This publication discusses a number of general factors that are essential to an effective decision regarding whether to retain heifers or not.