Greater LM Area Research Articles

Evaluation of terminal sire breeds for hair sheep production systems: Forage environment

Terminal sire crossbreeding systems which improve growth performance while maintaining parasite resistance have the potential to enhance the profitability of hair sheep enterprises. Katahdin (KT, n = 5), Suffolk (SU, n = 4), and Texel (TX, n = 5) rams were randomly mated to KT ewes over three years (Y1, Y2, Y3) at the Virginia Tech Southwest Agricultural Research and Extension Center. Post-lambing until weaning (80 d), pairs were managed on fescue pasture. At weaning, lambs (n = 242) were moved to an ungrazed pasture and provided a concentrate pellet daily for a 90 d grazing trial. During this time, body weight (BW), strongylid egg count (FEC), FAMACHA score and packed cell volume (PCV) were collected every 14 d. FAMACHA score ≥ 3 was utilized as the basis for anthelmintic treatment. Post-grazing, lambs were fed to approximately 50 kg BW. Lambs were harvested at the Virginia Tech Meat Center and carcass evaluation performed 1 d post-harvest. Statistical analyses were conducted using SAS with fixed effects of sire breed. No differences existed between sire breeds for adjusted number of lambs born or number of lambs weaned. At weaning, KT-sired lambs had lower BW than terminal sired lambs (P < 0.05). During the grazing trials, lnFEC, FAMACHA and PCV varied over time (P < 0.001) with lower FAMACHA scores for KT-sired lambs than SU- and TX-sired lambs (P < 0.05). Of the terminal sire breeds, TX-sired lambs had a greater FEC at deworming and required a greater number of days before treatment in Y2 (P < 0.05). At harvest, terminal-sired lambs were heavier than KT-sired lambs (P < 0.05) in Y1 while SU-sired lambs had greater BW than TX-sired lambs (P < 0.05) in Y2. Terminal-sired lambs had greater LM area and leg scores than KT-sired lambs (P = 0.05). These results indicate the potential of terminal sires (SU- and TX-sires) to improve lamb growth and carcass merit. Texel-sired lambs had more similar parasite resistance characteristics to KT-sired lambs and may have potential as terminal sires in forage based hair sheep production systems.

PSIII-31 Effects of associative use of additives on performance, carcass characteristics and serum D-lactate in Nellore x Angus young bulls

Abstract The objective was to evaluate the effects of including virginiamycin or bacitracin in diets containing monensin or monensin plus virginiamycin and bacitracin on growth performance and carcass characteristics of feedlot young bulls. Seventy-two young bulls, with an initial average body of 417 ± 38.7kg were allotted in a completely randomized design. The bulls were placed in 18 pens (four animals per pen), with three treatments and six experimental replicates. The diets consisted of 85% concentrate and 15% of corn silage, with 11.4% CP, 75.7% TDN and 18.4% NDF. The treatments were: MON, 25 ppm of monensin in the diet; MONB: monensin plus 8.75 ppm of zinc bacitracin; and MONVM monensin plus 25 ppm of virginiamycin. Feedlot had 109d, with 27d of adaptation and 82d of experimental period. Performance was measured by daily intake records and weighing at the beginning and end of the feedlot. After feedlot, animals were slaughtered to measure carcass traits. Serum D-lactate was collected on day 7 and 43 of the experimental period. There was no significant effect of the additives on performance and most of the carcass traits (Table 1). However, young bulls receiving MONVM tended to have greater LM area. On the other hand, MON diet tended to increase marbling. Finally, there was a tendency for treatment x time interaction (P &amp;lt; 0.08) in the serum concentration of D-lactate. Bulls receiving MON had greater concentration on day 7 (109.5 µmol.µL-1), compared to other groups (66.7 and 89.9 µmol.µL-1 for MONB and MONVM, respectively). There was no effect of additives in the D-lactate content on day 43, being the treatments average 83.5 µmol.µL-1. In conclusion, the use of monensin and their association with virginiamycin or bacitracin did not affect performance but tend to influence carcass traits and serum D-lactate. Funded by Agroceres, Fapemig, CAPES, and CNPq.

Chromium, CLA, and ractopamine for finishing pigs.

This study aimed to evaluate the effects of dietary chromium, CLA, and ractopamine on performance, carcass traits, and pork quality of finishing pigs slaughtered at 115 kg BW. Ninety-six crossbred barrows (initial BW = 70.21 ± 1.98 kg) were randomly assigned to 1 of 6 dietary treatments. There were 8 replicates per treatment (48 pens; 2 pigs/pen). A diet formulated according to the nutritional requirements was used as the control (CON). The other 5 diets were based on the CON and supplemented as follows: 0.4 mg/kg Cr yeast (CrY); 0.5% CLA; 0.4 mg/kg CrY and 0.5% CLA (CrY + CLA); 20 mg/kg ractopamine (RAC); 0.4 mg/kg CrY and 20 mg/kg RAC (CrY + RAC). Lysine levels on diets containing ractopamine were raised by 20% compared to CON to meet the greater requirements of pigs fed ractopamine. Pigs fed RAC and CrY + RAC were fed CON for the first 17 d, and then the respective diets for the last 28 d on trial. Data were analyzed in a model including the fixed effect of treatment (6 levels) and initial BW as a covariate for all characteristics, with the exception of carcass traits, in which final BW was used as a covariate. Least-squares means were separated using Tukey-Kramer's method. Differences were considered when probability values were lower than 0.05. Pigs fed RAC and CrY + RAC had the greatest ( < 0.001) final BW and ADG. Pigs fed CrY + RAC had greater ( < 0.001) G:F than pigs within the other groups, except for those fed RAC. Pigs fed CrY + RAC and RAC had similar G:F, both greater ( < 0.001) than pigs fed CON. Average daily feed intake was similar ( = 0.83) for all diets. Pigs fed CrY + RAC had greater LM area ( = 0.01) and carcass yield ( < 0.02) than pigs fed CON, CrY, CLA, and CrY + CLA. Loin muscle area and carcass yield of pigs fed RAC were not different from pigs fed the others diets. Pigs fed CON diets had greater BF ( = 0.02) than pigs fed CLA diet. Additives did not affect ( > 0.05) pork quality, except for color. No differences ( > 0.05) were observed for carcasses pH and temperature. The values for pigs fed RAC were greater ( = 0.01) than pigs fed other diets. Pigs fed RAC had lower ( < 0.01) values compared to pigs fed other experimental diets. Serum urea nitrogen concentration (SUN) was lower ( = 0.02) in pigs fed CrY + RAC than in pigs fed CON and RAC and similar to pigs fed the other feeding additives. In summary, it was demonstrated that, when combined, CrY and RAC increase LM area and carcass yield, and reduce SUN, suggesting that chromium could improve nutrient utilization by muscle cells in RAC-fed pigs. Additionally, the additives have no major effects on pork quality.

Long-term use of corn coproducts as a source of protein in beef finishing diets and the effects on carcass characteristics and round muscle quality.

A finishing trial was conducted during the late spring and summer of 2 consecutive years to evaluate long-term feeding of corn gluten feed and dried distillers' grains with solubles in finishing rations in the southeastern United States on feedlot performance, carcass characteristics, and meat quality attributes. Each year, 36 steers (yr 1 BW = 396 ± 18 kg; yr 2 BW = 436 ± 23 kg) were assigned to 1 of 3 finishing diets that contained 1) 25% dried corn gluten feed (CGF), 2) 25% dried distillers' grains plus solubles (DDGS), or 3) 10% soybean meal and 15% ground corn (SBM) and evaluated over a 100-d feedlot period. All steers were previously fed their respective diets at 25% of DM in a corn silage-based stockering system for 84 d. During the 100-d feedlot trial, weights were recorded and carcass traits were estimated via ultrasound on d -0, 50, and 100. All steers were subsequently harvested under federal inspection and had carcass data collected for quality and yield traits. At 48 h postmortem, the rectus femoris (RF), vastus lateralis (VL), and semimembranosus (SM) were collected for proximate analysis and aged for 7, 14, and 21 d for Warner-Bratzler shear and sensory analysis. Diet did not affect ( ≥ 0.14) BW, DMI, or ultrasound composition traits; however, DDGS steers had greater ADG ( = 0.05) than SBM steers and had greater ( = 0.04) G:F than CGF or SBM steers. There were no differences in carcass characteristics due to diet except the CGF carcasses had greater LM area and marbling scores ( ≤ 0.05). Protein source did not affect proximate composition, but the RF had greater percent moisture and lower percent protein compared with the VL and SM and greater percent lipid than the SM ( ≤ 0.01). Shear force analysis revealed a diet × aging period interaction ( = 0.04) where DDGS steaks were similar across all aging periods; however, steaks from SBM and CGF carcasses became more tender after 14 and 21 d of aging, respectively. Sensory panel results indicate that DDGS steaks were more tender than CGF and SBM steaks ( = 0.02) and steak tenderness increased, as expected, with aging ( < 0.01). The RF was rated as being more tender ( < 0.01) than the VL and SM, which were similar ( > 0.05). These data show that long-term use of CGF or DDGS at 25% DM will have a minimal impact on animal performance, carcass characteristics, or sensory traits of selected round cuts.

Effects of feeding dry-rolled corn-based diets with and without wet distillers grains with solubles and zilpaterol hydrochloride on performance, carcass characteristics, and heat stress in finishing beef steers.

Zilpaterol hydrochloride (ZH) has been approved for use since 2006; however, there is no research on any interactions between ZH and coproducts. Additionally, there is no published information on the potential effects of ZH on heat stress in feedlot cattle. Therefore, an experiment was conducted to determine the effects of feeding dry-rolled corn (DRC)-based diets with and without wet distillers grains with solubles (WDGS) and ZH on performance, carcass characteristics, and heat stress in feedlot cattle. Four hundred thirty-eight steers were used in a randomized complete block design with a 2 × 2 factorial arrangement of treatments in 16 pens with 26 to 28 steers in each pen. Factors consisted of inclusion of 0 or 30% (on a DM basis) WDGS and inclusion of ZH at 0 or 84 mg/steer daily for 21 d at the end of the finishing period. Therefore, cattle were blocked by BW and randomly assigned to 1 of the resulting 4 treatment combinations: 1) DRC-based diet with 0% WDGS and 84 mg/steer ZH, 2) DRC-based diet with 0% WDGS and no ZH, 3) DRC-based diet with 30% WDGS and 84 mg/steer of ZH, and 4) DRC-based diet with 30% WDGS and no ZH. Final live BW, carcass-adjusted BW, ADG, and G:F were greater for cattle fed ZH than non-ZH-fed cattle (P < 0.01). Additionally, cattle fed ZH consumed 7.4% less DM than cattle not fed ZH (P < 0.01). Cattle fed ZH for 21 d also had a 2.9% greater HCW (P < 0.01), a 1.1% greater dressing percentage (P < 0.01), 7.3% greater LM area (P < 0.01), and an 8.4% improvement in yield grade (P < 0.01) than cattle not fed ZH. For the main effect of WDGS inclusion, ADG was greater for cattle fed 0 vs. 30% WDGS (P = 0.04) and G:F also tended to be greater for cattle fed 0 vs. 30% WDGS (P = 0.07) for the 21-d ZH feeding period. However, when evaluated over the entire experiment, cattle fed 30 vs. 0% WDGS had a greater ADG and G:F (P < 0.01). Furthermore, cattle fed 30 vs. 0% WDGS had a greater dressing percentage and tended to have a greater amount of 12th rib fat (P < 0.07). Heat stress measurements were collected during the time cattle were fed ZH, from May 31 to July 12, 2013. The slopes for change in respiration rate and panting score per day were positive but were not different across dietary treatments (P > 0.71); in addition, the slopes for change in respiration rate and panting score when accounting for environmental conditions were positive but were not different across dietary treatments (P > 0.32).

Effects of dried distillers grains with solubles and crude glycerin on performance, carcass characteristics, and metabolic parameters of early weaned beef calves

ABSTRACT The effects of dried distillers grains with solubles (DDGS) and crude glycerin on performance, carcass, and metabolic parameters in early weaned (EW) beef calves were assessed. Fifty EW Anguscross calves (123 d of age; 170 kg of BW) were blocked by BW and randomly assigned to 1 of 5 dietary treatments: 1) haylage-based control (NEG), 2) corn-based control (POS), 3) 30% DDGS and corn (DDGS+C), 4) 30% DDGS with 15% glycerin replacing corn (15GLY), and 5) 30% DDGS with 30% glycerin replacing corn (30GLY). Diets were fed ad libitum for 160 d. Cattle were commingled on trial d 160 and fed a corn-based finishing diet until slaughter at a common 12th-rib fat depth of 1.0 cm. Final EW phase BW and ADG (P ≤ 0.04) were greater for DDGS+C and 15GLY when compared with 30GLY. Calves fed DDGS+C reached slaughter faster (P = 0.01) when compared with NEG, 15GLY, and 30GLY; however, DDGS+C and POS resulted in lighter slaughter BW and HCW (P ≤ 0.01). Calves fed 15GLY had a greater LM area (P = 0.04) than did POS and DDGS+C, and calves fed 15GLY obtained greater QG (P = 0.05) than did DDGS+C and 30GLY. Calves fed NEG had greater circulating blood glucose and BHBA concentrations (P

Effects of limit feeding corn or dried distillers grains with solubles at 2 intakes during the growing phase on the performance of feedlot cattle1

Energy density in growing diets may affect carcass quality of cattle; however, few reports have described the impact of energy source. The objectives of this research were to determine effects of source [dried distillers grains with solubles (DDGS) vs. corn] and amount (limit-fed to gain 0.9 vs. 1.4 kg of BW/d) of energy during the growing phase on feedlot performance and marbling. Angus-cross steers (144 head) were blocked by BW (average initial BW = 252 ± 36 kg), allotted within each block to 8 pens (6 steers/pen, 24 pens total), and randomly assigned to 1 of 4 feeding systems in a 2 × 2 factorial arrangement of treatments: 1) 65% DDGS fed to gain 0.9 kg of BW/d, 2) 65% DDGS fed to gain 1.4 kg of BW/d, 3) 65% corn fed to gain 0.9 kg of BW/d, and 4) 65% corn fed to gain 1.4 kg of BW/d. Fecal grab samples were collected on d 52 of the growing phase to determine digestibility of DM, ADF, NDF, ether extract (EE), and CP. After the 98-d growing phase, all steers were fed the same finishing diet. Steers were slaughtered by pen when average BW within the pen was 544, 522, and 499 kg for the large, medium, and small BW blocks, respectively. Average daily gain and DMI differed (P<0.01) by design during the growing phase. Compared with the corn-based diets, digestibilities of DM, NDF, and EE were decreased (P<0.02) when DDGS-based diets were fed during the growing phase, whereas the digestibility of N was increased (P<0.01). The ADG was greatest (P=0.02) during the finishing phase for steers fed to gain 0.9 kg of BW/d initially, but source of energy during the growing phase did not affect (P=0.24) finishing phase ADG. Steers fed to gain 0.9 kg of BW/d during the growing phase also had less backfat (P=0.08), decreased USDA yield grades (P=0.03), and greater LM area (P<0.01) than steers fed to gain 1.4 kg of BW/d. There was an interaction between energy source and amount for marbling scores (P=0.02). Steers fed corn-based diets to gain 0.9 kg of BW/d during the growing phase had the most marbling, whereas those fed to gain 0.9 kg of BW/d on DDGS had the least marbling; the remaining feeding systems were intermediate. Overall ADG and DMI were affected (P < 0.06) by both source and amount of energy fed during the growing phase. Feeding the DDGS-based diet to achieve greater ADG during the growing phase increased marbling, whereas feeding the corn-based diet to increase ADG during the growing phase decreased marbling.

Effects of restricting energy during the gilt developmental period on growth and reproduction of lines differing in lean growth rate: Responses in feed intake, growth, and age at puberty1

The overall objective was to compare reproductive performance through 4 parities of gilts developed with ad libitum access to feed or with restriction of energy to 75% of ad libitum intake. Effects on growth and pubertal development are reported. The experiment was a 2 × 2 factorial with 661 gilts. One-half of the gilts (n = 330) were allowed ad libitum access to feed from weaning to breeding at 235 d of age (AL), and 331 littermates were developed with ad libitum access to feed to 123 d of age and then restricted to 75% of ad libitum intake to 235 d of age (Res). Diets for gilts on regimen AL were formulated to meet requirements for growth. All nutrients except energy and selenium were increased in the diet fed to gilts on regimen Res so that nutrient intake per unit of BW was expected to be similar to that of gilts on regimen AL. Sires of all gilts were from an industry maternal line. Dams were either an industry Large White-Landrace cross, or Nebraska selection Line 45, producing gilts denoted as LW/LR and L45X, respectively. Traits were recorded every 2 wk. Recording of feed intake and BW began at 53 d of age, and recording of backfat (BF) and LM area (LMA) began at 123 d of age. Estrus detection began at 140 d of age to determine age at puberty (AP). The G:F ratio from 123 to 235 d of age for gilts on the AL regimen was greater (0.269 vs. 0.257, P < 0.01) than for gilts on the Res regimen; the greatest difference occurred in the first 2-wk period following feed restriction. The LW/LR gilts were heavier, had less BF, and had greater LMA than L45X gilts, but interactions with feeding regimen and period of development existed. Feed restriction reduced BW, BF, LMA, and ratio of BF to BW, but had little effect on ratio of LMA to BW. More L45X gilts than LW/LR gilts (98 vs. 93%, P < 0.01) and more gilts developed on regimen AL than regimen Res (98 vs. 91%, P < 0.01) expressed estrus. Mean age at puberty was 178.6 d for LW/LR and 173.0 d for L45X gilts (P < 0.01) and 174.1 d for regimen AL and 177.5 d for regimen Res (P < 0.05). The Res regimen delayed pubertal development. Subsequently, it will be important to determine effects on reproduction through 4 parities.

Postweaning growth and carcass traits in crossbred cattle from Hereford, Angus, Brangus, Beefmaster, Bonsmara, and Romosinuano maternal grandsires1,2

The objective of this study was to characterize breeds representing diverse biological types for postweaning growth and carcass composition traits in terminal crossbred cattle. Postweaning growth and carcass traits were analyzed on 464 steers and 439 heifers obtained by mating F(1) cows to Charolais and MARC III (1/4 Hereford, 1/4 Angus, 1/4 Pinzgauer, and 1/4 Red Poll) sires. The F(1) cows were obtained from mating Angus and MARC III dams to Hereford, Angus, Beefmaster, Brangus, Bonsmara, and Romosinuano sires. Traits evaluated were postweaning ADG, slaughter weight, HCW, dressing percentage, percentage of carcasses classified as USDA Choice, LM area, marbling score, USDA yield grade, fat thickness, retail product yield (percentage), and retail product weight. Maternal grandsire breed was significant (P < 0.05) for all traits. Animals with Angus grandsires grew faster and had the heaviest carcasses, with the greatest percentage of carcasses classified as USDA Choice and the greatest marbling scores when compared with other grandsire breeds. Animals with Romosinuano and Bonsmara inheritance grew slower, had the lightest weights at slaughter, the lightest carcass weights, the least percentage of carcasses classified as USDA Choice, and the least amount of marbling and fat thickness. Animals with inheritance from these 2 breeds had a more desirable yield grade with the greatest retail product yield. Maternal granddam breed was significant (P < 0.05) for marbling score, USDA yield grade, fat thickness, and retail product yield. Sex class was significant (P < 0.05) for all traits except for retail product yield. Steers grew faster, were heavier, had heavier carcasses, and were leaner than heifers. Heifers had a greater dressing percentage, a greater percentage of carcasses classified as USDA Choice, a greater LM area, and a decreased yield grade when compared with steers. Sire and grandsire breed effects can be optimized by selection and use of appropriate crossbreeding systems.

Effect of Wagyu- versus Angus-sired calves on feedlot performance, carcass characteristics, and tenderness

Wagyu-sired (n = 20) and Angus-sired (n = 19) steers and heifers were used to compare the effects of sire breed on feedlot performance, carcass characteristics, and meat tenderness. Calves were weaned at 138 +/- 5 d of age and individually fed a finishing diet consisting of 65% whole corn, 20% protein/vitamin/mineral supplement, and 15% corn silage on a DM basis. Heifers and steers were slaughtered at 535 and 560 kg of BW, respectively. Carcasses were ribbed between the 12th and 13th (USDA grading system) and the 6th and 7th ribs (Japanese grading system) to measure fat thickness, LM area (LMA), and intramuscular fat (IMF). Two steaks were removed from the 12th rib location and aged for 72 h and 14 d to determine Warner-Bratzler shear force and cooking loss. Sire breed x sex interactions were not significant (P > 0.05). Angus-sired calves had greater (P < 0.05) ADG and DMI than Wagyu. Wagyu-sired calves had improved (P < 0.05) feed efficiency than Angus. Sire breed did not affect (P > 0.20) HCW, 12th-rib fat, or USDA yield grade. Carcasses of Wagyu had greater (P = 0.0001) marbling scores at the 12th rib than those of Angus (770.9 vs. 597.3 +/- 41.01, respectively). Carcasses of Wagyu also had greater (P < 0.02) 12th-rib IMF and 6th-rib IMF than Angus, resulting in a greater proportion of carcasses grading Prime (65.0 vs. 21.1%; P = 0.006). Carcasses from Wagyu tended (P = 0.08) to have greater LMA at the 12th rib, whereas Angus carcasses had greater (P < 0.05) LMA at the 6th rib. Steaks from Angus and Wagyu had similar (P > 0.50) tenderness at aging times of 72 h and 14 d. Cooking loss was greater (P < 0.01) for Angus than Wagyu steaks at 72 h and 14 d. Using Wagyu sires vs. Angus sires on British-based commercial cows combined with early weaning management strategies has the potential to produce a product with greater marbling, but is unlikely to significantly enhance tenderness.

Effects of Ractopamine (Optaflexx) Fed in Combination with Melengestrol Acetate on Feedlot Heifer Performance

Two commercial feedlot experiments were conducted to determine the effects of feeding melengestrol acetate (MGA) or MGA plus ractopamine (MGA+OPT) on the performance and carcass characteristics of finishing heifers. In Nebraska (Exp. 1), 1,807 heifers (337.3 ± 20.0 kg) and in Texas (Exp. 2), 1,964 heifers (331.5 ± 6.1 kg) were fed 0.4 mg of MGA daily. For heifers fed MGA+OPT, 200 mg of ractopamine was fed daily the last 29 (Exp. 2) or 36 d (Exp. 1). Live and carcass-adjusted performance data were collected. On a carcass-adjusted basis, G:F for the entire feeding period was improved (P 0.47) between treatments in Exp. 1. Carcasses from heifers fed MGA+OPT had decreased marbling scores (P = 0.01) and greater LM area (P = 0.01) than carcasses from heifers fed MGA in Exp. 2. In Exp. 1, in which G:F was improved by 8.1%, no effect on QG was observed. In Exp. 2, in which G:F was improved by 27.2%, QG decreased. Based on these results, feeding MGA+OPT increased ADG and improved G:F, with variable effects on carcass characteristics.

Use of recombinant gonadotropin-releasing hormone antigens for immunosterilization of beef heifers1

The objectives of this study were to evaluate the effects of immunization against recombinant GnRH fusion proteins and growth promotants on onset of puberty, feedlot performance, and carcass characteristics of beef heifers. Heifers were immunized against an ovalbumin fusion protein containing 7 GnRH peptides (oGnRH, n = 12), a thioredoxin fusion protein containing 7 GnRH peptides (tGnRH, n = 12), a combination of oGnRH plus tGnRH (otGnRH, n = 12), or a combination of ovalbumin and thioredoxin (control, n = 11). Each heifer received a primary immunization containing 1 mg of protein in 1 mL of adjuvant injected into the mammary gland at wk 0 (mean age = 38 wk) and booster immunizations at wk 6 and 12. Six heifers within each treatment received Synovex H implants at wk -2. Weekly blood samples were collected from wk -2 to 26 for determination of serum progesterone concentrations and GnRH antibody titers. In GnRH-immunized heifers, GnRH antibody titers increased after the first booster injection, peaked after the second booster injection, and remained elevated through the end of the study (P < 0.01). Heifers immunized against oGnRH achieved greater (P < 0.05) GnRH antibody titers than tGnRH heifers but did not differ (P = 0.20) from otGnRH heifers. During the 26-wk study, ovulation was prevented (P < 0.05) in 10 out of 12, 12 out of 12, 11 out of 12, and 0 out of 11 tGnRH, oGnRH, otGnRH, and control heifers, respectively. At slaughter, uterine weights were lighter (P < 0.01) for GnRH-immunized heifers than control heifers. Synovex H-implanted heifers had greater (P < 0.05) ADG from wk -2 to 26, greater LM area, and lesser percentages of KPH, yield grade, and quality grade than nonimplanted heifers, regardless of the immunization treatment. Immunization against GnRH fusion proteins resulted in production of antibodies against GnRH that prevented ovulation in 92% of the heifers without affecting feedlot or carcass performance. Implanting heifers with Synovex H improved ADG, LM area, and yield grade. Improvements in delivery of the oGnRH vaccine may provide a feasible alternative to surgical spaying of heifers.

Responses to 19 generations of litter size selection in the NE Index line. II. Growth and carcass responses estimated in pure line and crossbred litters.

Our objective was to estimate responses in growth and carcass traits in the NE Index line (I) that was selected for 19 generations for increased litter size. Differences between Line I and the randomly selected control line (C) were estimated in pure line litters and in F1 and three-way cross litters produced by mating I and C females with males of unrelated lines. Contrasts of means were used to estimate the genetic difference between I and C and interactions of line differences with mating type. In Exp 1, 694 gilts that were retained for breeding, including 538 I and C and 156 F1 gilts from I and C dams mated with Danbred NA Landrace (L) sires, were evaluated. Direct genetic effects of I and C did not differ for backfat (BF) at 88.2 kg or days to 88.2 kg; however, I pigs had 1.58 cm2 smaller LM area than did C pigs (P < 0.05). Averaged over crosses, F1 gilts had 0.34 cm less BF, 4.29 cm2 greater LM area, and 31 d less to 88.2 kg than did pure line gilts (P < 0.05). In Exp 2, barrows and gilts were individually penned for feed intake recording from 27 to 113 kg and slaughtered. A total of 43 I and C pigs, 77 F1 pigs produced from pure line females mated with either L or Danbred NA 3/4 Duroc, 1/4 Hampshire boars (T), and 76 three-way cross pigs produced from F1 females mated with T boars were used. Direct genetic effects of I and C did not differ for ADFI, ADG, G:F, days to 113 kg, BF, LM area, ultimate pH of the LM, LM Minolta L* score, or percentage of carcass lean. Interactions of line effects with crossing system were significant only for days to 113 kg. Pure line I pigs took 4.58+/-4.00 d more to reach 113 kg than did C pigs, whereas I cross F1 pigs reached 113 kg in 6.70+/-3.95 d less than C cross F1 pigs. Three-way cross and F1 pigs did not differ significantly for most traits, but the average crossbred pig consumed more feed (0.23+/-0.04 kg/d), gained more BW per unit of feed consumed (0.052+/-0.005 kg/kg), grew faster (0.20+/-0.016 kg/d), had less BF (-0.89+/-0.089 cm), greater LM area (5.74+/-0.926 cm2), more lean (6.21+/-0.90%), and higher L* score (5.27+/-1.377) than the average pure line pig did (P < 0.05). Nineteen generations of selection for increased litter size produced few correlated responses in growth and carcass traits, indicating these traits are largely genetically independent of litter size, ovulation rate, and embryonic survival.