Hormonal growth implants affect feed efficiency and expression of residual feed intake-associated genes in beef cattle

2014 ◽  
Vol 54 (5) ◽  
pp. 550 ◽  
Author(s):  
W. Al-Husseini ◽  
C. Gondro ◽  
K. Quinn ◽  
L. M. Cafe ◽  
R. M. Herd ◽  
...  
Keyword(s):  
Feed Intake ◽  
Feed Efficiency ◽  
Protein Turnover ◽  
Average Daily Gain ◽  
Residual Feed Intake ◽  
Gene Marker ◽  
Turnover Rates ◽  
Feed Conversion ◽  
Muscle Area ◽  
Eye Muscle

Hormonal growth promotants (HGP) have been used to improve feed conversion ratio (FCR) and growth rates of cattle by modifying protein turnover rates. Residual feed intake (RFI) is correlated with FCR and has been adopted in Australia as a measure of feed efficiency in cattle for the purpose of genetic improvement. Eight genes (AHSG, GHR, GSTM1, INHBA, PCDH19, S100A10, SERPINI2 and SOD3) have been previously reported to be highly associated with RFI and could potentially be used to predict RFI in bulls and steers. In this study, expression levels of these genes in liver tissue of 46 cattle were measured by quantitative real-time PCR. These cattle were part of a larger tenderness gene marker experiment consisting of two breeds (Angus and Brahman); two sexes (steers and heifers) and HGP treatments (implanted vs control). Cattle were measured for growth, feed efficiency, body composition and carcass traits. Results showed the expression of these eight genes was significantly correlated with RFI. However, HGP treatment did not affect RFI or the expression of the RFI-associated genes. HGP treatment increased average daily gain by 20%, improved FCR by 18%, and increased rib eye-muscle area by 7.5%. HGP treatment was effective in improving growth rate, presumably by its known action in the protein turnover mechanism. This mechanism has been hypothesised as one of the regulators of RFI. Lack of effect of HGP treatment on RFI does not support this hypothesis.

Genetic divergence in residual feed intake affects growth, feed efficiency, carcass and meat quality characteristics of Angus steers in a large commercial feedlot

2018 ◽  
Vol 58 (1) ◽  
pp. 164 ◽  
Author(s):  
R. M. Herd ◽  
P. F. Arthur ◽  
C. D. K. Bottema ◽  
A. R. Egarr ◽  
G. H. Geesink ◽  
...  
Keyword(s):  
Meat Quality ◽  
Feed Intake ◽  
Feed Efficiency ◽  
Animal Feed ◽  
Average Daily Gain ◽  
Residual Feed Intake ◽  
Quality Characteristics ◽  
Feed Conversion ◽  
Eye Muscle ◽  
Meat Samples

Growth, feed intake, feed efficiency, and carcass and meat quality characteristics of 136 Angus steers differing in genetic merit for post-weaning residual feed intake (RFIp) were measured over 251 days in a large commercial feedlot. The steers were evaluated in two groups, low (Low-RFI) and high (High-RFI) genetic RFIp, measured by estimated breeding values for RFIp (RFIp-EBV). The difference in RFIp-EBV between the Low- and High-RFI groups was 1.05 kg/day (–0.44 vs 0.61 kg/day; P < 0.05). The Low- and High-RFI steers were similar (P > 0.05) in age (445 vs 444 days) and weight (435 vs 429 kg) at induction, and at the end of the feeding period (705 vs 691 kg). Average daily gain (ADG) over 251 days had a small negative association with variation in RFIp-EBV (P < 0.05), reflecting a 3.6% greater ADG accompanying a difference of 1 kg/day in RFIp-EBV. Pen feed intake and feed conversion by the Low-RFI group were 10.4 kg/day and 9.3 kg/kg, and for the High-RFI group were 11.1 kg/day and 10.4 kg/kg, but without availability of individual animal feed-intake data it was not possible to test for significant differences. Carcass weight and dressing-percentage was similar for the Low- and High-RFI steers. High-RFI steers had a significantly (P < 0.05) greater depth of subcutaneous rib fat at induction and finished with 5 mm more (P < 0.05) fat at the 10/11th ribs on the carcass than the Low-RFI steers. Cross-sectional area of the eye-muscle and three measures of intramuscular or marbling fat did not differ (P > 0.05) between the Low- and High-RFI steers. Shear force was higher (P < 0.05) in meat samples aged for 1 day from the Low-RFI steers, but there was no difference (P > 0.05) from the High-RFI steers after 7 days of ageing. Compression values for meat samples aged for 1 day did not differ between the RFI groups but were higher in meat samples aged for 7 days from the Low-RFI steers. For these Angus steers, genetic superiority in RFI was associated phenotypically with superior weight gain, decreased rib fat depth, slightly less tender meat, and no compromise in marbling fat or other carcass and meat quality traits.

Effects of early weaning on growth, feed efficiency and carcass traits in Shorthorn cattle

2010 ◽  
Vol 50 (4) ◽  
pp. 315 ◽  
Author(s):  
M. L. Wolcott ◽  
H.-U. Graser ◽  
D. J. Johnston
Keyword(s):  
Feed Intake ◽  
Feed Efficiency ◽  
Carcass Traits ◽  
Residual Feed Intake ◽  
Carcass Composition ◽  
Early Weaning ◽  
Feed Conversion ◽  
Muscle Area ◽  
Eye Muscle ◽  
The Impact

This study aimed to examine the impact of early weaning on residual feed intake, and other production and carcass traits, in a group of cattle subjected to early or conventional weaning treatments, but otherwise managed as contemporaries. Shorthorn (n = 140) calves were randomly allocated by sex and sire to early and conventional weaning treatments. Early weaned animals (n = 69) were weaned at an average of 123 days of age and 145 kg liveweight, while conventionally weaned steers and heifers (n = 71) were 259 days old at weaning and 273 kg. Following conventional weaning, animals were managed as contemporaries through backgrounding, and entered feedlot finishing at a mean age of 353 and 408 days for heifers and steers, respectively, for finishing and feed intake testing. At the conclusion of feed intake testing hip height was measured, and animals were ultrasound scanned to assess fat depth, eye muscle area and percent intramuscular fat. Early weaned animals were significantly lighter (P < 0.001) than their conventionally weaned contemporaries, when weighed at conventional weaning. The weight difference observed at conventional weaning of 19.4 kg between treatment groups persisted throughout the experiment, with significant (P < 0.05) differences of 17.1, 15.6 and 15.8 kg at feedlot entry, and the start and end of the feed intake test period, respectively. Weaning treatment also approached significance for daily feed intake (P = 0.06), with early weaned animals tending to eat less than their conventionally weaned contemporaries (daily feed intake = 11.6 and 12.0 kg, respectively). Weaning treat\ment did not significantly affect feed efficiency whether measured as residual feed intake (P = 0.64) or feed conversion ratio (P = 0.27). None of the other traits measured were significantly affected by weaning treatment. These data showed that early weaning, as implemented for this experiment, resulted in animals that were lighter than their conventionally weaned contemporaries through backgrounding and finishing. Weaning treatment did not, however, influence feed efficiency or the post-weaning growth and carcass composition traits measured for this experiment.

The effect of preweaning growth restriction on the feed intake and efficiency of cattle on a grain-based diet before slaughter

2004 ◽  
Vol 44 (5) ◽  
pp. 483 ◽  
Author(s):  
D. W. Hennessy ◽  
P. F. Arthur
Keyword(s):  
Feed Intake ◽  
Growth Rates ◽  
Feed Efficiency ◽  
Average Daily Gain ◽  
Carcass Traits ◽  
Feed Conversion ◽  
Muscle Area ◽  
Eye Muscle ◽  
Efficiency Measures ◽  
Highly Correlated

Records on 78 steers and heifers were used to determine relationships among different measures of growth, feed efficiency and carcass traits, and to evaluate the effects of 2 preweaning growth rates on growth and efficiency in a feedlot. The preweaning growth rates [g/day; 871 (high) or 466 (low)] were imposed on the steers and heifers for 115 days before they were weaned at a mean age of 220 days. They were 'backgrounded' for 7 months on high quality pastures before finishing on grain-based diets in a feedlot for 85 days. The cattle were then slaughtered and carcass measurements recorded. Estimates were made on 10 growth and feed efficiency indices during the feedlot, and 5 carcass traits were assessed at slaughter. Of the indices, the Kleiber ratio which does not require measurement of feed intake (r = 0.98), was highly correlated with relative growth rate (RGR), as was feed conversion ratio (FCR, r = –0.82), which includes feed intake in the calculation. Residual feed intake, calculated using the expected feed intake estimated from the dataset (RFIREG), was correlated (r = 0.62) with RFI calculated from Australian feeding standards (RFISCA), and with FCR (r = 0.45). FCR was not correlated with either carcass rib or hot P8 fat depths but was significantly correlated with carcass weight (0.39), dressing percentage (0.41) and eye muscle area (0.33). RFIREG was not correlated with any of the 5 carcass traits. Whilst the average daily gain in the feedlot was similar between the 2 preweaning groups (1.544 kg/day), the low group was significantly (P<0.05) lighter at feedlot entry (323 v. 376 kg). Daily feed intake was lower (P<0.01) in the low group (10.9 v. 11.8 kg) such that the FCR tended to be lower (P<0.10) relative to the high group. Differences between the preweaning treatment groups were not significant for the other measures of feed efficiency. The results indicate that early life nutritional restriction has some influence on FCR in the feedlot, but little effect on those feed efficiency measures, such as RFI, that account for energy required for both maintenance of liveweight and growth.

scholarly journals PSI-36 Phenotypic Relationship of Feed Efficiency and Fertility in Angus and Red Angus Bulls

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 474-475
Author(s):  
Taylor Lacey ◽  
Stephen Doyle ◽  
Kasey DeAtley
Keyword(s):  
Feed Intake ◽  
Feed Efficiency ◽  
Dry Matter ◽  
Average Daily Gain ◽  
Residual Feed Intake ◽  
Dry Matter Intake ◽  
Feed Conversion ◽  
Chi Square ◽  
Scrotal Circumference ◽  
Red Angus

Abstract Recent advances in measuring feed intake improve selection for efficient beef bulls; however, such selection must not decrease bull fertility. Objectives herein were to determine the phenotypic relationship between feed efficiency and fertility traits in growing Angus (n = 14) and Red Angus (n = 14) bulls. Two feeding trials were conducted at the CSU, Chico University Farm in 2017 (87 d) and 2018 (84 d). Each year, bulls were randomly assigned to 7 x 18 m pens equipped with GrowSafe feed intake units and allowed ad libitum access to water and feed (CP: 15.6%, TDN: 56.22%, NDF: 52%, DM basis). Performance traits included: feed conversion ratio (FCR) and residual feed intake [RFI; measured as the difference between predicted dry matter intake (PDMI) and actual dry matter intake (DMI)], start weight (SWT), end weight (EWT), metabolic mid-weight (MMWT), residual gain and average daily gain (ADG). Breeding soundness exams (BSE) were conducted at 18 mo of age and included traits: scrotal circumference (SC), motility (MT), and morphology (MP). Residual feed intake was calculated by regressing DMI on ADG and MMWT. The RFI group was categorized as low (0.5 SD above the RFI mean), marginal (± 0.5 SD about the RFI mean), and high (0.5 SD above the RFI mean) by year. Data were analyzed using ANOVA, blocking on year-pen and fitting breed and RFI group as independent factors. Tukey pairwise contrasts were run. Motility among breeds and RFI group were analyzed using chi-square. Pearson correlations were calculated between growth, feed efficiency, and BSE measures of SC and MP. There were no differences (P &gt; 0.05) among breeds nor RFI groups for SWT, EWT, MMWT, residual gain, SC, and MT. No interaction was detected between breed and RFI group with exception of MP (P = 0.049); specifically, low RFI Red Angus bulls had poor MP compared to marginal and high RFI groups (66.94 ± 6.87 vs. 87.43 ± 3.77 and 93.74 ± 5.48 %, respectively). Angus bulls were superior to Red Angus bulls in ADG (1.23 ± 0.04 vs. 1.06 ± 0.05 kg/d; P = 0.01), FCR (7.98 ± 0.31 vs. 9.18 ± 0.38; P = 0.04), and RFI (-0.24 ± 0.09 vs. 0.09 ± 0.11 kg DMI/d; P = 0.04). High and marginal RFI groups had greater DMI compared to low RFI group (10.40 ± 0.26 and 9.64 ± 0.18 kg/d vs. 8.31 ± 0.32 kg/d; P &lt; 0.001). There were no significant phenotypic correlations between growth and efficiency measures with SC and MP (P &gt; 0.05). Cumulatively, results indicate that SC and MT were not affected in efficient bulls.

scholarly journals RAPID COMMUNICATION: Residual feed intake in beef cattle is associated with differences in protein turnover and nutrient transporters in ruminal epithelium

2019 ◽  
Vol 97 (5) ◽  
pp. 2181-2187
Author(s):  
Ahmed A Elolimy ◽  
Emad Abdel-Hamied ◽  
Liangyu Hu ◽  
Joshua C McCann ◽  
Daniel W Shike ◽  
...  
Keyword(s):  
Amino Acid ◽  
Beef Cattle ◽  
Protein Degradation ◽  
Insulin Signaling ◽  
Feed Intake ◽  
Feed Efficiency ◽  
Protein Turnover ◽  
Residual Feed Intake ◽  
Ubiquitin Proteasome ◽  
Ruminal Epithelium

Abstract Residual feed intake (RFI) is a widely used measure of feed efficiency in cattle. Although the precise biologic mechanisms associated with improved feed efficiency are not well-known, most-efficient steers (i.e., with low RFI coefficient) downregulate abundance of proteins controlling protein degradation in skeletal muscle. Whether cellular mechanisms controlling protein turnover in ruminal tissue differ by RFI classification is unknown. The aim was to investigate associations between RFI and signaling through the mechanistic target of rapamycin (MTOR) and ubiquitin-proteasome pathways in ruminal epithelium. One hundred and forty-nine Red Angus cattle were allocated to 3 contemporary groups according to sex and herd origin. Animals were offered a finishing diet for 70 d to calculate the RFI coefficient for each. Within each group, the 2 most-efficient (n = 6) and least-efficient animals (n = 6) were selected. Compared with least-efficient animals, the most-efficient animals consumed less feed (P &lt; 0.05; 18.36 vs. 23.39 kg/d DMI). At day 70, plasma samples were collected for insulin concentration analysis. Ruminal epithelium was collected immediately after slaughter to determine abundance and phosphorylation status of 29 proteins associated with MTOR, ubiquitin-proteasome, insulin signaling, and glucose and amino acid transport. Among the proteins involved in cellular protein synthesis, most-efficient animals had lower (P ≤ 0.05) abundance of MTOR, p-MTOR, RPS6KB1, EIF2A, EEF2K, AKT1, and RPS6KB1, whereas MAPK3 tended (P = 0.07) to be lower. In contrast, abundance of p-EEF2K, p-EEF2K:EEF2K, and p-EIF2A:EIF2A in most-efficient animals was greater (P ≤ 0.05). Among proteins catalyzing steps required for protein degradation, the abundance of UBA1, NEDD4, and STUB1 was lower (P ≤ 0.05) and MDM2 tended (P = 0.06) to be lower in most-efficient cattle. Plasma insulin and ruminal epithelium insulin signaling proteins did not differ (P &gt; 0.05) between RFI groups. However, abundance of the insulin-responsive glucose transporter SLC2A4 and the amino acid transporters SLC1A3 and SLC1A5 also was lower (P ≤ 0.05) in most-efficient cattle. Overall, the data indicate that differences in signaling mechanisms controlling protein turnover and nutrient transport in ruminal epithelium are components of feed efficiency in beef cattle.

Daily methane emissions and emission intensity of grazing beef cattle genetically divergent for residual feed intake

2017 ◽  
Vol 57 (4) ◽  
pp. 627 ◽  
Author(s):  
J. I. Velazco ◽  
R. M. Herd ◽  
D. J. Cottle ◽  
R. S. Hegarty
Keyword(s):  
Feed Intake ◽  
Emission Intensity ◽  
Dry Matter ◽  
Average Daily Gain ◽  
Residual Feed Intake ◽  
Conversion Ratio ◽  
Feed Conversion Ratio ◽  
Breeding Value ◽  
Dry Matter Intake ◽  
Feed Conversion

As daily methane production (DMP; g CH4/day) is strongly correlated with dry matter intake (DMI), the breeding of cattle that require less feed to achieve a desired rate of average daily gain (ADG) by selection for a low residual feed intake (RFI) can be expected to reduce DMP and also emission intensity (EI; g CH4/kg ADG). An experiment was conducted to compare DMP and EI of Angus cattle genetically divergent for RFI and 400-day weight (400dWT). In a 6-week grazing study, 64 yearling-age cattle (30 steers, 34 heifers) were grazed on temperate pastures, with heifers and steers grazing separate paddocks. Liveweight (LW) was monitored weekly and DMP of individual cattle was measured by a GreenFeed emission monitoring unit in each paddock. Thirty-nine of the possible 64 animals had emission data recorded for 15 or more days, and only data for these animals were analysed. For these cattle, regression against their mid-parent estimated breeding value (EBV) for post-weaning RFI (RFI-EBV) showed that a lower RFI-EBV was associated with higher LW at the start of experiment. Predicted dry matter intake (pDMI), predicted DMP (pDMP) and measured DMP (mDMP) were all negatively correlated with RFI-EBV (P < 0.05), whereas ADG, EI, predicted CH4 yield (pMY; g CH4/kg DMI) were not correlated with RFI-EBV (P > 0.1). Daily CH4 production was positively correlated with animal LW and ADG (P < 0.05). The associations between ADG and its dependent traits EI and pMY and predicted feed conversion ratio (kg pDMI/kg ADG) were strongly negative (r = –0.82, –0.57 and –0.85, P < 0.001) implying that faster daily growth by cattle was accompanied by lower EI, MY and feed conversion ratio. These results show that cattle genetically divergent for RFI do not necessarily differ in ADG, EI or pMY on pasture and that, if heavier, cattle with lower RFI-EBV can actually have higher DMP while grazing moderate quality pastures.

Genetic parameters and breed differences for feed efficiency, growth, and body composition traits of young beef bulls

2004 ◽  
Vol 84 (2) ◽  
pp. 177-185 ◽  
Author(s):  
F. S. Schenkel ◽  
S. P. Miller ◽  
J. W. Wilton
Keyword(s):  
Body Composition ◽  
Genetic Correlation ◽  
Feed Intake ◽  
Feed Efficiency ◽  
Fixed Effects ◽  
Residual Feed Intake ◽  
Backfat Thickness ◽  
Daily Weight Gain ◽  
Feed Conversion ◽  
Beef Bulls

Genetic associations between feed efficiency, growth, and live ultrasound measured body composition traits were studied in purebred beef bulls of six breeds in Ontario bull test stations from 1991 to 2000. Feed traits included average daily feed intake (FI), feed conversion ratio (FCR), and residual feed intake [feed intake adjusted for production alone (RFIp) or production and backfat thickness (RFIb)]. Growth traits were average daily weight gain (ADG), mid-test metabolic weight (MW), hip height (HH), and scrotal circumference (SC). Body composition traits included ultrasound backfat thickness (BF), longissimus muscle area (LMA), and predicted percentage of intramuscular fat (IFAT). Bulls were measured every 28 d for weight and individual feed intake, and at the end of test for ultrasound body composition traits. Number of records per trait ranged from 2284 (FI) to 13 319 (ADG). Fixed effects of test group, breed and end of test age (within breed), and random effects of animal and herd of origin were modeled using REML bivariate analyses for all traits. Heritability estimates were moderate for all traits (0.30 to 0.55), except for IFAT (0.14). The genetic correlation between RFIp and RFIb was high (0.99) within breeds, but breeds ranked differently with respect to RFIp and RFIb. Genetic correlations of RFIb with ADG and backfat thickness were essentially zero, which indicate that selection on residual feed intake could be implemented to reduce feed intake and improve feed conversion without compromising growth or changing levels of subcutaneous fat. Key words: Central test, genetic correlation, heritability, residual feed intake

scholarly journals Residual feed intake and relationships with performance of Nellore cattle selected for post weaning weight

2011 ◽  
Vol 40 (4) ◽  
pp. 929-937 ◽  
Author(s):  
T. Lucila Sobrinho ◽  
R.H. Branco ◽  
S.F.M. Bonilha ◽  
A.M. Castilhos ◽  
L.A. Figueiredo ◽  
...  
Keyword(s):  
Body Weight ◽  
Standard Deviation ◽  
Feed Intake ◽  
Average Daily Gain ◽  
Residual Feed Intake ◽  
Feed Conversion ◽  
Relative Growth ◽  
Kleiber Ratio ◽  
Nellore Cattle ◽  
Daily Gain

The objective of this work was to evaluate performance, efficiency parameters and phenotypic correlations among measurements of energy efficiency of Nellore cattle selected for post weaning weight and classified according to residual feed intake, calculated by the difference between observed and predicted intake, based on average metabolic body weight and average daily gain. Thus, animals were classified within three groups: high (> mean + 0.5 standard deviation, less efficient); medium (±0.5 standard deviation of the mean); and low (< mean - 0.5 standard deviation, more efficient) residual feed intake. No differences were observed at initial and final body weights, average daily gain and dry matter intake among groups. Animals with low residual feed intake also had greater feed efficiency, feed conversion and partial efficiency of growth and did not differ from the other animals regarding to relative growth rate and Kleiber ratio. Residual feed intake was significantly correlated to feed efficiency (-0.25), feed conversion (0.25), partial efficiency of growth (-0.37) and dry matter intake (0.16) but it did not present significant correlation with body weight (0.04), average daily gain (-0.02), relative growth rate (-0.03) and Kleiber ratio (-0.05). Significant correlations were found between feed conversion and initial body weight (0.34) and average daily gain (-0.46). Partial efficiency of growth presented significant correlation with all other efficiency parameters analyzed. Residual feed intake has high potential in productive efficiency, when compared to the other energy efficiency measurements, being independent of growth and size of the animals.

Effects of antibiotics, dried molasses distillers solubles and zeranol in all-sorghum grain rations fed to steers

1977 ◽  
Vol 17 (85) ◽  
pp. 214 ◽  
Author(s):  
RJW Gartner ◽  
PK O'Rourke
Keyword(s):  
Weight Gain ◽  
Feed Intake ◽  
Conversion Ratio ◽  
Feed Conversion Ratio ◽  
Feed Conversion ◽  
Muscle Area ◽  
Eye Muscle ◽  
Liver Abscesses ◽  
Zinc Bacitracin ◽  
Sorghum Grain

A 23 factorial design was used to examine the effects of the following treatments on the productivity of steers fed in yards on an all-sorghum grain ration : nil vs. 70 mg chlortetracycline head-1 day-1; nil vs. 3 per cent dried molasses distillers solubles; nil vs. 36 mg implant of Zeranol. An additional treatment eompared zinc bacitracin with chlortetracycline. Eighteen groups each of five Hereford steers of a mean initial shrunk liveweight of 273.5 � SE 1.00 kg were used. They were slaughtered at a mean final shrunk liveweight of 399.8 � 2.97 kg. Mean results were: liveweight gain 1 .17 kg day-1, carcase weight gain 0.69 kg day-1, DM feed intake 6.91 kg day-1, feed conversion ratio 6.0. Feeding chlortetracycline resulted in increased carcase weight gain, an improved feed conversion ratio and a reduction in the number of liver abscesses. Regarding productivity, zinc bacitracin was not significantly different from chlortetracycline but it had no effect on reducing liver abscesses. Adding dried molasses distillers solubles caused a decrease in live- and carcase weight gain and an inferior feed conversion ratio. The anabolic implant Zeranol resulted in increased live- and carcase weight gain, increased DM feed intake but no significant differences in feed conversion ratio. The treatments had no effect on eye muscle area or muscle percentage of the carcases. Dried molasses distillers solubles was associated with a lower fat percentage (1 9.5 vs. 20.8 � 0.43; P <0.05). The rationsbsed resulted in an acetic to propionic ratio in ruminal fluid of 0.44 :1. There were no interactions and the usefulness of chlortetracycline and Zeranol and the poorer production using molasses distillers solubles in all-grain diets are discussed.

scholarly journals Meat quality and the calpain system of feedlot steers following a single generation of divergent selection for residual feed intake

2001 ◽  
Vol 41 (7) ◽  
pp. 1013 ◽  
Author(s):  
M. B. McDonagh ◽  
R. M. Herd ◽  
E. C. Richardson ◽  
V. H. Oddy ◽  
J. A. Archer ◽  
...  
Keyword(s):  
Feed Intake ◽  
Shear Force ◽  
High Efficiency ◽  
Subcutaneous Fat ◽  
Residual Feed Intake ◽  
Divergent Selection ◽  
Muscle Area ◽  
Eye Muscle ◽  
Single Generation ◽  
Selection For

Residual feed intake (RFI) is calculated as the difference between an animal’s actual feed intake and its expected feed intake based on its size and growth over a specified test period. Following a single generation of divergent selection for postweaning RFI, Angus steers and Angus × Hereford, Angus×Poll Hereford and Angus × Shorthorn crossbred steers born in 1996 and 1997 were fed in a feedlot. Cohorts of steers were slaughtered at the same age and had attained similar (P&gt;0.05) final liveweights: 467 kg for steers selected for low RFI (high efficiency; HE, n = 91) and 459 kg for steers selected for high RFI (low efficiency; LE, n = 98). The HE and LE steers had similar (P>0.05) carcass weight (247 and 244 kg), dressing percentage (53.1 and 53.2&percnt;) and eye-muscle area (58.9 and 60.3 cm 2 ). The HE steers had slightly less subcutaneous fat over the rib than the LE steers (9.2 v. 10.1 mm, P&lt;0.05), and there was a trend towards less fat over the rump of HE steers (11.5 v. 12.1 mm, P = 0.10). For meat samples taken from the M. longissimus dorsi (LD) there were no differences (P>0.05) between the HE and LE steers in content of intramuscular fat (5.4 and 5.3% fresh weight), marbling scores, meat colour and fat colour. There were also no differences (P>0.05) between HE and LE steers in shear force and compression values for samples of LD aged for 1 day (4.6 and 4.6 kg shear force, 1.45 and 1.44 kg compression), or for 14 days (3.8 and 3.5 kg, 1.36 and 1.32 kg). Myofibril fragmentation index (MFI) measures the breakdown of these structural elements which occurs as an initial step in the process of protein degradation and meat tenderisation. MFI was lower (i.e. less fragmentation; P<0.05) in LD samples from HE steers than from LE steers, both in samples aged for 1 day (67.7 v. 72.5 units) and in samples aged for 14 days (87.8 v. 91.1 units). The rate of decline in MFI between 1 and 14 days post slaughter was similar in the LD samples from both lines of steers. There were no differences (P>0.05) between HE and LE steers in the activity of m-calpain and &micro;-calpain in LD immediately after slaughter (HE steers: 1.9 and 2.3 units, LE steers: 1.8 and 2.1 units). The level of calpastatin in LD from the HE steers was 13% higher than in the LD from the LE steers (5.2 and 4.6 units respectively, P<0.05). Rate of myofibril fragmentation was positively correlated (P<0.01) with the ratios of both m-calpain and µ-calpain to calpastatin, but not (P>0.10) with levels of either calpain or calpastatin. A single generation of divergent selection for RFI produced differences in calpastatin and myofibril fragmentation that may, with on-going selection for low RFI, negatively affect meat tenderness.

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