Greater Ribeye Area Research Articles

PSXIII-20 Impact of Aspergillus oryzae fermentation-derived prebiotic-like additive combined with monensin on feedlot performance in finishing steers

Abstract The aim of this study was to investigate the effects of supplementing a prebiotic-like action additive product derived from the fermentation of Aspergillus oryzae (AM; 2 g Amaferm/d) in combination with monensin throughout the entire feedlot period. The primary objective was to evaluate the impact of this dietary intervention on feedlot performance, focusing on parameters such as feed intake, feed-to-gain ratio, body weight (BW), average daily gain (ADG), and carcass quality. Steers (n = 1,200), aged approximately 18 mo with an initial BW of 307.8 ± 17 kg, were randomly assigned to 8 pens (150 steers per pen) and each pen was randomly assigned to two treatments: a control diet with monensin (M; monensin supplemented at 33 mg/kg DM) and a treatment diet with the addition of AM (M+AM; monensin supplemented at 33 mg/kg DM and 2 g Amaferm/d). The feedlot period comprised three steps, with daily feed delivery adjustments using a feed bunk management system. A multilevel model using the PROC MIXED procedure of SAS with pen as experimental unit, was employed to evaluate feed intake, feed to gain ratio, BW and ADG for each period, also including effects on carcass quality and growth measured by ultrasound (random sample of 45 animals per pen; 30% of each pen). No significant differences were observed in feed intake across the three diet steps (P > 0.10). During the adaptation period, steers fed AM had greater ADG (+0.168 kg/d; P = 0.003) and increased BW at d 20 (+5.5 kg; P < 0.001). Although ADG during the finishing phase was similar for both treatments, a trend was observed for greater BW at d 108 (+4.6 kg; P = 0.095) when supplemented with AM. The inclusion of AM showed no impact on feed-to-gain ratio for the entire period (P = 0.589). In the finishing period, a positive effect on ribeye area (REA) growth rate (+0.54 cm2/mo; P = 0.016) and a trend towards greater back fat deposition rate (+0.11 mm/mo; P = 0.069) were observed with AM supplementation. At the end of the finishing period, a trend towards greater REA (+1.39 cm2; P = 0.101) was noted with no differences in back fat. Overall, this study demonstrates that the addition of AM throughout the feedlot period positively influenced the productive response during the adaptation period, leading to improvements in carcass growth during the finishing period.

358 The effect of increasing dietary limestone concentration on growth performance, gas flux, and carcass characteristics in finishing beef cattle

Abstract Reducing methane (CH4) emissions from beef cattle is desirable as CH4 is a greenhouse gas that represents an energetic loss from the production system. Limestone is commonly fed to cattle as a source of calcium but may also act as a rumen buffer and decrease CH4 emissions by limiting hydrogen availability for methanogenesis. The objective of this experiment was to determine if diet limestone concentration influences growth performance, gas flux, and carcass characteristics in finishing beef cattle. Yearling steers [n = 16; initial body weight (BW) 619 ± 34 kg] were stratified by BW and randomly assigned to 1 of 2 isocaloric and isonitrogenous dietary treatments in a completely randomized design where limestone was included at 1.3% (1X) or 2.6% (2X) of diet dry matter (DM). Finishing diets were formulated to contain 0.43 or 0.96% DM as Ca and were fed ad libitum using automated cattle feeders (SmartFeed Pro; C-Lock Inc.; Rapid City, SD) in a single pen for the final 37 d of finishing. Body weights were measured on d -1, 0, 36, and 37. An automated head chamber system (GreenFeed; C-Lock Inc.) was used to measure gas flux. Analysis of variance was conducted using JMP Pro 17 to determine the fixed effect of treatment with individual animal as the experimental unit. Statistical significance was defined as P ≤ 0.05 with a tendency defined as 0.05 < P ≤ 0.10. Increasing the dietary limestone concentration from 1.3 to 2.6% of DM did not influence DM intake, but numerically increased final shrunk BW (P = 0.68) and hot carcass weight (P = 0.75) and increased average daily gain (ADG; P = 0.02) and gain to feed ratio (G:F) by approximately 12%. Cattle fed the 2X diet tended to have 6.5% greater ribeye area (P = 0.09), but similar USDA yield grade, backfat thickness, and dressing percentage (P ≥ 0.34) when compared with cattle fed the 1X diet. Daily CO2 and CH4 emissions, daily O2 consumption, CH4 yield, and respiratory quotient were unaffected by treatment (P ≥ 0.47). The improvement in ADG resulted in a tendency for CH4 emission intensity to be decreased by 9.1% (P = 0.09) when the concentration of limestone was 2.6% of dietary DM. While increasing dietary limestone concentration from 1.3 to 2.6% of diet DM did not influence absolute daily CH4 emissions, it increased ADG through an improvement in feed efficiency, which translated to a tendency for a reduction in CH4 emission intensity. These preliminary data suggest that there may be a benefit to feeding limestone or calcium at levels greater than currently recommended by the NASEM (2016). Future research should focus on determining optimum dietary limestone or calcium levels for finishing cattle.

The importance of developmental programming in the beef industry

The beef industry relies on multiple focused segments (e.g., cow-calf, stocker/feeder, and meat packing) to supply the world with beef. Thus, the potential impact of developmental programming on the beef industry needs to be evaluated with regards to the different production traits that drive profitability within each segment. For example, when nutrient restriction of dams occurred early in gestation embryo survival was decreased and the ovarian reserve of heifer progeny was negatively affected. Restriction during mid- to late gestation negatively impacted first service conception rates and pregnancy success of daughters. Even non-nutrient stress has been reported to impact transgenerational embryo development through the male progeny. Primary and secondary muscle fibers form during months two to eight (Days 60–240) of gestation. Therefore, external stimuli (nutrition or environmental) during this window have the potential to decrease the postnatal number of muscle fibers; which has an irreversible impact on animal growth and performance. Nutrient restriction during the last third of gestation resulted in decreased weaning weights, and in some instances decreased dry mater intake, hot carcass weight, and marbling scores. Protein supplementation during late gestation; however, increased weaning weight and ADG to weaning, but progeny of dams restricted in protein in late gestation had greater ribeye area. The importance of developmental programming is recognized; however, its precise application depends on comprehension of its integrated effects across the multiple-focused segments of the beef industry.

Meat Quality and Muscle Tissue Proteome of Crossbred Bulls Finished under Feedlot Using Wet Distiller Grains By-Product

Wet distiller grains (WDG) are a corn by-product rich in protein and fiber that can be used in feedlot diets. This study evaluated F1 Angus-Nellore bulls fed on a control diet vs. WDG (n = 25/treatment). After a period of 129 days on these feeds, the animals were slaughtered and Longissimus thoracis samples were collected for both a meat quality evaluation and gel-based proteomic analyses. A greater ribeye area (99.47 cm²) and higher carcass weight (333.6 kg) (p < 0.05) were observed in the WDG-finished cattle compared to the control (80.7 cm²; 306.3 kg). Furthermore, there were differences (p < 0.05) in the intramuscular fat between the WDG and control animals (IMF = 2.77 vs. 4.19%), which led to a significant decrease (p < 0.05) in saturated fatty acids (FA). However, no differences (p > 0.10) were observed in terms of tenderness, evaluated using Warner–Bratzler shear force (WBSF). The proteomic and bioinformatic analyses revealed substantial changes in the biological processes, molecular functions, and cellular components of the WDG-finished cattle compared to the control. Proteins related to a myriad of interconnected pathways, such as contractile and structural pathways, energy metabolism, oxidative stress and cell redox homeostasis, and transport and signaling. In this experiment, the use of WDG supplementation influenced the protein expression of several proteins, some of which are known biomarkers of beef quality (tenderness and color), as well as the protein–protein interactions that can act as the origins of increases in muscle growth and reductions in IMF deposition. However, despite the effects on the proteome, the tenderness, evaluated by WBSF, and fatty acid profile were not compromised by WDG supplementation.

Evaluation of the association between plasma glucose-dependent insulinotropic polypeptide, respiratory quotient, and intramuscular fat deposition in feedlot cattle fed different levels of dry matter intake.

The objectives of this trial were to evaluate the association between different levels of dry matter intake (DMI) on gas exchange, plasma glucose-dependent insulinotropic polypeptide (GIP) concentration, and intramuscular (IM) fat deposition. We used 60 individually fed backgrounded Angus × SimAngus-crossbred steers (n = 30) in a randomized complete block design. Steers (paired by body weight [BW] and gain to feed ratio [G:F]) were randomly allocated to one of the following treatments: ad libitum intake (AI) or restricted intake (RI; the same diet fed at 85% of the AI) of a finishing diet. The diet contained 61% cracked corn, 9% corn silage, 15% distillers’ dried grains with solubles, 5% soyhulls, and 10% of a protein-mineral-vitamin premix. Measurements of CO2 emission and consumption of O2, and respiratory quotient (RQ) were taken using the GreenFeed system (n = 15/treatment). Plasma and gas samples were collected 10 d before slaughter, 1 h before and 2 h after feeding. Plasma glucose, non-esterified fatty acids, GIP, and insulin concentration and gasses (O2, CO2, and RQ) were analyzed using the MIXED procedure of SAS evaluating the fixed effect of treatment, time (repeated measurement) and their interaction, and the random effect of the block. Final BW and carcass characteristics were analyzed with a similar model, without the time statement and its interaction. Compared with RI, AI steers had greater (P < 0.01) DMI and average daily gain (ADG). Steers on AI had greater final BW (P = 0.02), tended to have a greater ribeye area (P = 0.09), and had lower plasma GIP concentration (P = 0.04). There was no treatment effect (P ≥ 0.11) on G:F, subcutaneous backfat (BF), and IM fat, O2 consumption, CO2 emission, and RQ. Plasma glucose concentration of AI steers was greater before and after feeding than RI (P < 0.05). In conclusion, feeding steers ad libitum increased DMI, ADG, and plasma glucose and GIP concentration but does not affect G:F, BF, IM fat, CO2 emission, and O2 consumption. Plasma GIP concentration and RQ are not associated with IM fat deposition.

Description of the main attributes (origin, gender, age, body condition, and slaughter weight) at slaughter house arrival and their impact on carcass characteristics from cull Quarter Horse

In order to describe the effects of origin (Mexico and United States of America), sex, age at slaughter (AS, 4categories), body condition score (BCS, 5 categories) and slaughter weight (SW, 4 categories) on carcass characteristics of culled quarter horses, data from 235 horses sacrificed in the same slaughter facility within a 150 days period wereanalyzed. Overall, 74.5% were from the US, 80% were &lt; 15 years of age and had BCS ≤ 4, and sex proportion was similar(51.5% female vs 48.5% males). Horses from USA had heavierSW (27%), leg circumference (4%), carcass weight (4.2%) and carcass yield (2.9%). Sex did not affect any characteristics evaluated. Horses from 3 to 8 years had greater rib eye area(REA) and backfat thickness. Except for leg length, as BCS and SW improved, all carcass characteristics linearly increased as BCS and SW increased. It is concluded that origin, sex, and age, explained very little on the carcass characteristics. The slaughter weight mainly explained changes in linear measures,carcass weight, and compact index, while BCS mainly explained carcass yield and REA.

133 Effect of terminal sire breed on grazing performance, parasitism and market grade of crossbred lambs

Abstract Improvements in growth and carcass conformation through terminal sire crossbreeding systems may improve lamb value in a pasture-based system. Therefore, the aim of this study was to compare the effects of different terminal sires on parasitism, growth, composition, and marketability of grazing lambs. Suffolk (SU; n = 2) and Texel (TX; n = 2) sires were mated to commercial ewes at the WVU Organic Farm. April-born lambs were managed on pasture as one group until weaning in midJune, then were separated into 3 replicates per sire breed. Lambs were rotationally grazed for 93 d with paddock movement every 10 d. Lambs were supplemented at a rate of 2% of bodyweight with a 16% CP corn-soybean meal supplement. Weights were collected at weaning and then weekly for the duration of the study. Fecal egg counts (FEC) and FAMACHA scores were collected biweekly. Lambs were de-wormed when FAMACHA score was ≥ 3. Ultrasound measures of rib eye area (REA) were obtained at study conclusion and lambs were marketed at a graded auction. Sire breed did not impact weaning weight or growth rate throughout the test. Fecal egg count was slightly higher in TX vs. SU-sired lambs (257 vs 191 eggs/g; P &lt; 0.05). FAMACHA scores were lower in TX vs. SU-sired lambs (1.58 vs. 1.96; P &lt; 0.0001). Fewer deworming treatments were necessary in TX-sired lambs at 10% (4/39) whereas as SU-sired lambs required 55% (22/40) (P &lt; 0.0001). TX-sired lambs had greater REA (11.57 vs 9.42 cm2; P &lt; 0.0001) and graded better at the saleyard. Grading was set to a 6 pt scale with higher equating to higher sale price. Lambs sired by TX rams graded 5.2 and SU-sired lambs graded 3.6 (P &lt; 0.0001). These data demonstrate that Texel-sired lambs required fewer dewormer treatments and were compositionally more desirable when marketed

Gender status effect on carcass and meat quality traits of feedlot Angus×Nellore cattle.

The study evaluated the effect of gender status on carcass and meat quality of feedlot Angus×Nellore cattle. A total of 176 cattle, 20 months old, were confined for 190-days and assigned to four treatments: bulls, immunocastrated, steers, and heifers. Bulls had greater rib eye area and HCW (p=0.0001). Heifers had increased fat thickness (p=0.0001). Steers and heifers had higher marbling scores (p=0.0001). There was interaction between gender and aging time for Warner-Bratzler Shear Force (p=0.0002), L* (p=0.0118), and b* (p=0.0113) values of beef. The sensory panel results showed that beef from bulls had the lowest consumer overall acceptance (p=0.0278). Especially, regardless tenderness, steers and immunocastrated beef were considered tender, independent of aging time. Beef produced by heifers, steers, and immunocastrated is considered to be of higher quality than bulls. Thus, it is may be an interesting alternative to produce high-quality beef than bulls, to attend the consumer demand for high-quality products. Additionally, the low fatty acids n6 levels and low n6:n3 ratio, high levels of CLA, MUFAs, and oleic acid suggests that the heifer meat is favorable for human health.

639 Effect of trace mineral supplementation with or without hormone implants on growth and carcass characteristics of steers

To determine the effects of trace mineral (TM) supplementation and hormone implant strategy on growth and carcass characteristics of cattle, 72 Angus-cross steers (388 ± 17 kg) were blocked by BW (6 steers per pen) to a 2 × 3 factorial. Steers were either implanted (d 0 with Component TE-IS, reimplanted d 56 with Component TE-200; IMP) or not (NoIMP). Within implant treatments cattle received no supplemental TM (CON), TM supplemented at 2016 NRC recommendations of 10 Cu, 30 Zn, 20 Mn, 0.10 Se, 0.15 Co, and 0.50 I (mg/kg; NRC), or TM supplemented at feedlot consultant recommendations of 20 Cu, 100 Zn, 50 Mn, 0.30 Se, 0.20 Co, and 0.50 I (mg/kg; IND). Blood samples were collected on d -7, 70 and 124. Steers received a finishing diet for 124 d in GrowSafe bunks and were harvested on d 125. Data were analyzed in SAS as a 2 × 3 factorial with the fixed effect of block, and steer as experimental unit (n = 12 per combination). Day -7 glucose concentrations were used as a covariate in analysis. There was a tendency (P = 0.06) for an IMP × TM for d 124 plasma glucose with NoIMP/NRC being greater than NoIMP/IND and all other treatments intermediate. There were no IMP × TM for final BW, overall ADG, DMI, G:F, dressing percent, backfat, marbling score, or KPH (P ≥ 0.17). Overall ADG tended (P = 0.07) to be and HCW was (P = 0.03) affected by TM, where IND was greater than CON (HCW: 373, 378, and 388 kg for CON, NRC, and IND, respectively). Overall DMI was increased by TM (P < 0.0001) with NRC and IND being greater than CON. Steers receiving implants had greater (P < 0.0001) final BW (559 and 617 kg for NoIMP and IMP, respectively), overall ADG (1.35 and 1.83 kg for NoIMP and IMP, respectively), DMI, G:F, and HCW (359 and 400 kg for NoIMP and IMP, respectively) than NoIMP. There was an IMP × TM (P = 0.02) for ribeye area (REA) with IMP/CON having greater REA than IMP/IND, with IMP/NRC being intermediate; NoIMP had smaller REA, regardless of TM supplementation. There was an IMP × TM (P = 0.02) for YG where NoIMP/IND was greater than IMP/CON with all other treatments intermediate. These data indicate NRC TM recommendations might not be adequate for finishing beef steers, irrespective of hormone implant administration.

Differences between sexes, muscles and aging times on the quality of meat from Wagyu × Angus cattle finished in feedlot

Our objectives were to assess quality parameters and chemical composition, and to evaluate the effects of sex, muscle and aging time on the quality of meats from Wagyu × Angus cross cattle reared under tropical conditions. Analyses were performed on the longissimus thoracis, semitendinosus and triceps brachii muscles obtained from chilled carcasses of a total of 30, 24-month-old, male (immunocastrated) and female animals (15 each sex). An effect of sex (P ≤ 0.05) was observed for subcutaneous fat thickness, marbling score, and ribeye area. The longissimus thoracis muscle from males was less (P &lt; 0.0001) marbled than that from females, but males had greater subcutaneous fat thickness (P = 0.0001) and greater ribeye area (P = 0.0411) compared with females. No effect of sex (P ≥ 0.05) was observed for fat colour measures. An interaction effect of sex and muscle (P &lt; 0.03) was detected for cooking loss, yellow intensity (b*), ash, and fat. Main effect of sex was not observed (P &gt; 0.07) only for the ultimate pH and water-holding capacity. Greater shear force and moisture values were observed (P &lt; 0.01) in meat from males than that from females, but a greater value of luminance (L*), red intensity (a*), chroma (C), hue (Ho), dry matter and protein was observed (P &lt; 0.001) in meat from females than that from males. Main effect of muscle was not observed only for water-holding capacity (P = 0.13). Ultimate pH and shear force values were lesser (P &lt; 0.001) in the longissimus thoracis muscle compared with other muscles. The triceps brachii muscle had the least (P ≤ 0.001) L* and Ho values among muscles, whereas the semitendinosus muscle had the greatest values of a* and C (P &lt; 0.001). The semitendinosus muscle presented the greatest (P &lt; 0.01) protein content compared with other muscles, although not differing in moisture and dry matter content from the triceps brachii muscle. An interaction effect of sex × aging time was observed for ultimate pH (P = 0.0110), meat colour parameters (except for Ho; P ≤ 0.01), and fat L* (P = 0.0025). Greater cooking loss, shear force, and fat a* values were observed (P &lt; 0.01) in meat from males than that from females, but greater values of meat Ho, fat a* and Ho, dry matter, and protein were observed (P ≤ 0.03) in meat from females than that from males. Meat aging of longissimus thoracis reduced shear force. Based on these findings, we recommend that meat from Wagyu × Angus cross cattle should be aged during 7 days because, although differences between 7 and 14 days were observed in either aging times, meat subjected to this process is considered as very tender, based on shear force values. In addition, aging in a shorter period of time can reflect on costs by reducing particularly those related with energy, due to less refrigeration time.

Carcass merit and meat quality in Suffolk lambs, Katahdin lambs, and meat-goat kids finished on a grass–legume pasture with and without supplementation

The experiment evaluated traditional U.S. sheep (Suffolk), hair sheep (Katahdin), and meat goat (Boer crossbred; Goat) carcass and meat quality parameters when finished on pasture with and without supplemental whole cottonseed (Gossypium hirsutum L.). Supplemented animals had greater ribeye area (P<0.01), body wall thickness (P<0.001), and lean quality score (P<0.05) than unsupplemented animals. Whole cottonseed increased fatty acids (FA) 18:1 trans-10, 18:1 trans-12, 18:2, and Omega6:Omega3 ratio and decreased FA 18:1 trans-11, 18:3, and Omega3 in longissimus muscle (LM). Katahdin LM had greater (P<0.001) intramuscular fat compared to Suffolk and Goat. Goat LM had less (P<0.001) FA 14:0, 18:0, 18:1 t11, 18:3, 20:3n−6, and saturated FA when compared to Suffolk or Katahdin. Carcass weights from pasture-finished sheep and goats would be acceptable for most ethnic markets in the USA. Omega6:Omega3 ratios in chevon and lamb were within the guidelines for meats that can improve human diets and health.

Candidate SNPs for carcass and meat traits in Nelore animals and in their crosses with Bos taurus

The objective of this work was to evaluate the effects of single-nucleotide polymorphisms (SNPs) in the genes IGF1 (AF_017143.1:g.198C&gt;T), MSTN (AF_320998.1:g.433C&gt;A), MYOD1 (NC_007313:g.1274A&gt;G) and MYF5 (NC_007303:g.1911A&gt;G) on carcass and meat traits in Nelore (Bos indicus) and Nelore x B. taurus. A total of 300 animals were genotyped and phenotyped for rib eye area (REA), backfat thickness (BT), intramuscular fat (IF), shear force (SF) and myofibrillar fragmentation index (MFI). The effects of allele substitution for each SNP were estimated by regression of the evaluated phenotypes on the number of copies of a particular allele using the general linear model. The polymorphism at IGF1 was non-informative in Nelore animals. In crossbred animals, the IGF1 C allele was associated with greater REA. However, this relation was not significant after Bonferroni correction for multiple testing. The A allele of the MSTN polymorphism was absent in Nelore cattle and was only found in two crossbred animals. The polymorphisms of MYOD1 and MYF5 were little informative in Nelore animals with G allele frequency of 0.097 and A allele frequency of 0.031, respectively. These markers show no association with the analyzed traits in the total sample of evaluated animals.

Callipyge gene effects on lamb growth, carcass traits, muscle weights and meat characteristics

Normal (N, n=11) and heavy muscled (HM, n=9) lambs were produced from Polypay dams and Dorset sires heterozygous for the Callipyge (CLPG) gene to study the effects of the gene on live body weights, carcass and meat parameters. Lambs were grown as a single group on a high energy diet to a target slaughter weight of 57 kg. Live body weights were recorded monthly from birth to pre-slaughter. At slaughter, kidney and pelvic fat were recorded and two muscles, biceps femoris-caudal (BFC) and semitendinosus (ST), were removed, weighed, and used for other studies. Carcasses were sectioned between the 12th and 13th vertebrae for determination of ribeye area (REA) and fat depth over the loin and lower rib. Two additional muscles, biceps femoris-major (BFM) and semimembranosus (SM), and four loin chops cut 2.5 cm thick were removed from each carcass, sealed in Cryovac wrap, and frozen for later cooking. HM lambs had greater REA (23.0 vs. 13.6 cm 2; P<0.01), less fat ( P<0.01 for all measures), and greater weight of all dissected muscles (all P<0.01 except BFC for which P=0.13). Chops were cooked by grilling and the leg muscles were individually wrapped in aluminum foil and roasted whole, all to an internal temperature of 70 °C. HM carcasses produced higher Warner–Bratzler shear values for longissimus muscle (4.7 vs. 2.2 kg, P<0.01), but no significant differences were detected for BFM (2.6 vs. 2.5 kg) or SM (4.9 vs. 4.5 kg). The two genotypes did not differ in either percent cooking loss or percent moisture in the cooked meat from any of the three muscles.

Effects of immunization against GnRH, Melengestrol Acetate, and a trenbolene acetate/estradiol implant on growth and carcass characteristics of beef heifers

A 2 × 3 factorial experiment was conducted to determine the effects of an implant (trenbolene acetate/estradiol or no implant) and method of estrus suppression (immunization against GnRH, melengestrol acetate, or no suppression) on growth performance and carcass characteristics of heifers fed for slaughter. At the start of a 21 -d feed adaption phase, crossbred beef heifers (n = 144, 390 ± 2.8 kg) were given their first dose of an anti-GnRH vaccine or started on melengestrol acetate (MGA). Thereafter, heifers were fed a high-concentrate diet (78% barley grain) for 84 d (Days 0 to 83), received implants on Day 0, a second vaccination on Day 21, and were slaughtered on Days 84 or 85. Implanting increased average daily gain (1.72 vs 1.50 kg/d, P<0.01), feed efficiency (6.02 vs 6.75 kg dry matter intake/kg gain, P< 0.01), preslaughter weight (532 vs 513 kg, P < 0.01), carcass weight (301 vs 289 kg, P < 0.01), and ribeye area (88.6 vs 85.9 cm 2, P < 0.05), but had no affect (P > 0.05) on dry matter intake, grade fat thickness. marbling score, or lean yield. Compared to heifers fed MGA, those immunized against GnRH had a greater ribeye area (90.0 vs 84.6 cm 2) and lean yield (63 vs 61%), and had thinner grade fat (7.5 vs 8.6 mm; P < 0.05 for each). Furthermore, immunized heifers had lower (P < 0.001) plasma progesterone concentrations than control heifers on Days 42, 63 and 83. Heifers fed MGA had less estrus mounting activity (P < 0.05) and lower plasma progesterone concentrations (P < 0.001) than the remaining heifers. Method of estrus suppression did not affect (P > 0.05) preslaughter weight, average daily gain, dry matter intake, feed efficiency, carcass weight, or marbling score. In conclusion, implanting significantly increased growth performance and preslaughter and carcass weights. Compared to heifers fed MGA, immunization against GnRH significantly increased ribeye area and lean yield, and reduced grade fat thickness.

SEX AND YEAR EFFECTS ON CARCASS CHARACTERISTICS OF THREE-WAY CROSS BEEF CATTLE REARED AT TWO LOCATIONS

From 1973 to 1978, 3673 steers and heifers sired by Charolais (C), Simmental (S), Limousin (L) or Chianina (Chi) were born to first-cross dams under farm (Brandon, Man.) and range (Manyberries, Alta.) conditions. Dam crosses included the Hereford × Angus (HA) and crosses sired by C, S or L sires and out of H, A or Shorthorn (N) dams. All calves entered the feedlot at approximately 206 days of age. Brandon calves, fed at that location were brought to full feed (100% grain concentrate) by 220 days of age. Manyberries calves, fed at Lacombe, received a ration of cereal silage and grain concentrate with the silage component reducing from 70% to 30% over a period of 5 mo. The minimum slaughter age was 13.5 mo at both locations but age alone (13.5 and 15 mo) was the slaughter criterion at Brandon whereas Lacombe employed the dual criteria of liveweight and degree of finish. These location differences in feeding and slaughter criteria resulted in greater slaughter weights (278 vs. 265 kg), greater rib fat (1.61 and 1.09 cm) and a higher percentage of kidney fat (2.09 vs. 1.75%) for the Brandon animals. They were also reflected in the sex differences for age at slaughter (sexes equal at Brandon; heifers &gt; steers at Lacombe) and degree of finish (sexes equal in rib fat at Lacombe; steers &gt; heifers at Brandon). Heifers at Brandon had a larger percentage of hide (P &lt; 0.0001) and lower dressing percentage (P &lt; 0.0001) than steers. Percentage of head, front feet and hind feet were also less for heifers than steers at this location. Rib eye was greater for steers but heifers had greater rib eye area per unit weight (P &lt; 0.0001) and a higher percentage of kidney fat (P &lt; 0.0001). The sex ranking for percentage chuck, shank and flank was steers &gt; heifers (P &lt; 0.0001) and the reverse for percentages of rib, long loin and the combined cuts of rib, round and long loin (P &lt; 0.0001). For percentages of lean in the long loin, rib and chuck the ranking was steers &gt; heifers (P &lt; 0.0001) with heifers &gt; steers for percentage lean of round (P &lt; 0.0001). Heifers relative to steers had significantly (P = 0.0001) lower percentages of bone in the round, rib and chuck and greater (P = 0.0001) lean to bone ratios for the combined trait of long loin and round. The sex differences observed at Lacombe for these traits were in good agreement with Brandon although sex by location interaction was not tested. Year differences were large but year-by-sex interactions were non-existent for virtually all carcass traits evaluated at both locations (P ≤ 0.05). Sire-by-sex and dam-by-sex interactions were also absent. Key words: Beef cattle, crossbreeding, carcass characteristics, year effects, sex effects