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 Genetic Parameters for Different Measures of Feed Efficiency and Their Relationship to Production Traits in Three Purebred Pigs

Life ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 830
Author(s):  
Kier Gumangan Santiago ◽  
Bryan Irvine Lopez ◽  
Sung-Hoon Kim ◽  
Dong-Hui Lee ◽  
Young-Gyu Cho ◽  
...  
Keyword(s):  
Genetic Correlation ◽  
Feed Intake ◽  
Feed Efficiency ◽  
Genetic Parameters ◽  
Daily Weight Gain ◽  
Phenotypic Variance ◽  
Production Traits ◽  
Feed Conversion ◽  
Muscle Area ◽  
Initial Testing

Residual feed intake (RFI) gained attention as a potential alternative to the feed conversion ratio (FCR). Thus, this study aimed to estimate genetic parameters for different feed efficiency (FE) traits (FCR, RFI1 to RFI5) and their genetic correlation to on-test daily weight gain (ADG), backfat (BFT), loin muscle area (LMA), lean percentage (LP), and total feed intake (FI) for 603 Male Duroc (DD), 295 Landrace (LL), and 341 Yorkshire (YY). The common spatial pen effect was also estimated in these traits. Five RFI measures were estimated by regressing daily feed intake on initial testing age (ITA), initial testing weight (IBW), and ADG for RFI1; other models were the same as RFI1 except for additional BFT for RFI2; LMA for RFI3; BFT and LMA for RFI4; BFT, LMA, and average metabolic body weight (AMBW) instead of IBW for RFI5. Genetic parameters estimated using two animal models and the REML method showed moderate heritability for FCR in all breeds (0.22 and 0.28 for DD, 0.31 and 0.39 for LL, 0.17 and 0.22 for YY), low heritability for the majority of RFI measures in DD (0.15 to 0.23) and YY (0.14 to 0.20) and moderate heritability for all RFI measures in LL (0.31 to 0.34). Pen variance explained 7% to 22% for FE and 0% to 9% for production traits’ phenotypic variance. The genetic correlation revealed that selection against less complex RFI1 in DD and LL and RFI2 in YY would bring the most advantageous reduction to FI (0.71 for DD, 0.49 for LL, 0.43 YY) without affecting ADG in all breeds (0.06 for DD, −0.11 for LL, 0.05 for YY), decrease in BFT, and increase in LP in DD (0.51 in BFT, −0.77 in LP) and LL (0.45 in BFT, −0.83 in LP). Therefore, inclusion of these breed-specific RFI measures in the future selection criteria would help improve feed efficiency in the swine industry.

scholarly journals PSVIII-38 Late-Breaking Abstract: Estimating genetic parameters of feed efficiency traits in American mink

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 347-347
Author(s):  
Pourya Davoudi ◽  
Duy Ngoc Do ◽  
Guoyu Hu ◽  
Siavash Salek Ardestani ◽  
Younes Miar
Keyword(s):  
Body Weight ◽  
Genetic Correlation ◽  
Feed Intake ◽  
Feed Efficiency ◽  
Fixed Effects ◽  
Genetic Parameters ◽  
American Mink ◽  
Genetic Correlations ◽  
Final Body Weight ◽  
Selection For

Abstract Feed cost is the major input cost in the mink industry and thus improvement of feed efficiency through selection for high feed efficient mink is necessary for the mink farmers. The objective of this study was to estimate the heritability, phenotypic and genetic correlations for different feed efficiency measures, including final body weight (FBW), daily feed intake (DFI), average daily gain (ADG), feed conversion ratio (FCR) and residual feed intake (RFI). For this purpose, 1,088 American mink from the Canadian Center for Fur Animal Research at Dalhousie Faculty of Agriculture were recorded for daily feed intake and body weight from August 1 to November 14 in 2018 and 2019. The univariate models were used to test the significance of sex, birth year and color as fixed effects, and dam as a random effect. Genetic parameters were estimated via bivariate models using ASReml-R version 4. Estimates of heritabilities (±SE) were 0.41±0.10, 0.37±0.11, 0.33±0.14, 0.24±0.09 and 0.22±0.09 for FBW, DFI, ADG, FCR and RFI, respectively. The genetic correlation (±SE) was moderate to high between FCR and RFI (0.68±0.15) and between FCR and ADG (-0.86±0.06). In addition, RFI had low non-significant (P > 0.05) genetic correlations with ADG (0.04 ± 0.26) and BW (0.16 ± 0.24) but significant (P < 0.05) high genetic correlation with DFI (0.74 ± 0.11) indicating that selection for lower RFI will reduce feed intake without adverse effects on the animal size and growth rate. The results suggested that RFI can be implemented in genetic/genomic selection programs to reduce feed intake in the mink production system.

scholarly journals Response of growing rabbits to graded levels of fermented and unfermented pineapple peel

2021 ◽  
Vol 38 (1) ◽  
pp. 86-98
Author(s):  
O.A. Adeyemi ◽  
A.O. Ajado ◽  
A.O. Okubanjo ◽  
O.O. Eniolorunda
Keyword(s):  
Feed Intake ◽  
Feed Efficiency ◽  
Control Diet ◽  
Daily Weight Gain ◽  
Trial Period ◽  
Feed Conversion ◽  
Feed Cost ◽  
Pineapple Peel ◽  
Inclusion Level ◽  
Retail Cuts

Forty growing rabbits were allocated equally to five groups in a 2 x 3 factorial layout and caged individually for a 56-day trial period in hutches. They were used to compare the effects of two processing methods (unfermented and fermented) and three dietary replacement levels of Pineapple peel meal (PPM) at 0%, 12.5% and 25% of maize on weight for weight basis. Parameters evaluated during the trial period included: growth rate, feed intake, feed conversion ratio and feed cost. Results show that average daily weight gain (ADG) reduced (P<0.05) as dietary inclusion level of PPM increased, although rabbits fed PPM at 12.5% dietary inclusion level compared favourably (P>0.05) with those fed the control diet (0%). However, ADG of rabbits fed fermented PPM was statistically higher (P<0.05) than that recorded for rabbits fed unfermented PPM. No significant (P>0.05) difference was observed in daily feed intake of rabbits as a result of dietary inclusion level or processing type of PPM. Better (P<0.05) feed efficiency was recorded in rabbits fed PPM at 12.5% dietary inclusion level than those fed at 25%. Fermentation enhanced the nutritional value of feedstuff and also improved feed efficiency. Total feed cost reduced (P<0.05) by 21.39% when PPM was included in the diet at 25%. However, production result was not comparable with the control. But feeding fermented PPM at 12.5% inclusion level resulted in the best (P<0.05) economy of production. Processing type or dietary inclusion level of PPM had no significant (P>0.05) effect on dressing-out percentage of experimental animals. There were neither significant (P>0.05) effects of processing type nor dietary inclusion level on retail cuts of the rabbits fed the different experimental diets. In all feeding rabbits with diets containing fermented PPM up to 12.5% replacement level for maize optimum performance.

Genetic parameters for growth and feed efficiency in weaner versus yearling Charolais bulls

2001 ◽  
Vol 52 (4) ◽  
pp. 471 ◽  
Author(s):  
P. F. Arthur ◽  
G. Renand ◽  
D. Krauss
Keyword(s):  
Feed Intake ◽  
Feed Efficiency ◽  
Genetic Correlations ◽  
Residual Feed Intake ◽  
Conversion Ratio ◽  
Feed Conversion Ratio ◽  
Progeny Test ◽  
Parameter Estimates ◽  
Feed Conversion ◽  
Total N

Data on young Charolais bulls were used to evaluate the effect of age of dam, and provide genetic parameter estimates for growth and feed efficiency traits in weaners compared with yearlings. Records on 510 performance test bulls born from 1985 to 1989 and 792 progeny test bulls born from 1988 to 1997 were used, plus available pedigree information (total n = 5493). After weaning (approximately 225 days of age), progeny test bulls were housed in barns and tested until 15 months for all bulls and 19 months of age for half of the bulls. From the records, the test period was artificially partitioned into a weaner and a yearling test. Both tests were for 140 days, with the weaner test commencing at approximately 274 days of age (6–8 weeks after weaning), and the yearling test commencing at approximately 430 days of age. For each test (weaner or yearling), average daily gain, daily feed intake, feed conversion ratio (feed intake per unit weight gain), and residual feed intake (feed intake net of the expected requirements for growth and maintenance) were calculated. Liveweights at 12 and 18 months of age were also studied. Age of dam effect was significant (P < 0.05) for weight at 12 and 18 months of age, and for all weaner traits except residual feed intake. All the traits studied were moderately heritable (0.20–0.46) except for feed conversion ratio in yearlings (0.10). Genetic correlations for the same traits measured in weaners and later in yearlings were less than unity (0.42–0.95), with the 3 highest correlations obtained for weight (0.950.03), feed intake (0.900.07), and residual feed intake (0.750.12). Therefore, for genetic improvement purposes, traits measured in weaners should be considered different from those measured in yearlings, except for weight and feed intake. However, the medium to very high genetic correlations between weaner and yearling tests for most of the traits studied indicate that selection based on weaners will have a positive correlated response in yearlings and vice versa.

Residual feed intake and body composition in young growing cattle

2003 ◽  
Vol 83 (2) ◽  
pp. 189-204 ◽  
Author(s):  
J. A. Basarab ◽  
M. A. Price ◽  
J. L. Aalhus ◽  
E. K. Okine ◽  
W. M. Snelling ◽  
...  
Keyword(s):  
Body Composition ◽  
Chemical Composition ◽  
Body Fat ◽  
Feed Intake ◽  
Accretion Rate ◽  
Average Daily Gain ◽  
Residual Feed Intake ◽  
Body Water ◽  
Backfat Thickness ◽  
Marbling Score

Crossbred steers (n = 176), 7–8 mo of age and from the five BeefBooster strains (M1, M2, M3, M4 and TX), were used to determine the relationships between residual feed intake (RFI) and growth rate, body composition and heat production (HP), and to quantify differences in RFI independent of differences in body composition. Animals with different RFI levels were also characterized for growth, carcass and body compositional traits. Steers from each genetic strain were selected at random and serially slaughtered on 5 pre-selected days of the finishing period. Steers grew at 1.52 (SD = 0.22) kg d-1 and had dry matter intake (DMI) of 8.5 (SD = 1.0) kg d-1 during the last 71 to 183 d before slaughter. Metabolic mid-point weight, average daily gain (ADG), gain in empty body fat and gain in empty body water accounted for 67.9, 8.6, 3.9 and 1.1%, respectively, of the variation in actual feed intake. Similarly, metabolic mid-point weight (68.5%), ADG (8.2%), gain in ultrasound backfat thickness (1.8%), gain in ultrasound marbling score (1.1%) and year (1.3%) accounted for 80.9% of the variation in actual feed intake. Residual feed intake adjusted for differences in estimated composition of gain (estimated gain in empty body fat and water; RFIII) ranged from -2.06 kg d-1 to +1.61 kg d-1 (SD = 0.60 kg d-1). Residual feed intake adjusted for live animal measures of body composition (gain in ultrasound backfat thickness and marbling score; RFIIII) ranged from -2.11 kg d-1 to +1.88 kg d-1 (SD = 0.62 kg d-1). Low RFIIII animals (efficient) had 6.0% lower metabolizable energy intake (MEI), retained 9.3% less energy and had 4.5% lower HP than medium RFIIII animals (P < 0.01). Low RFIIII animals also had 10.2% lower MEI, retained 12.0% less energy and produced 9.3% less heat than high RFIIII animals (P < 0.01). Liver (P <0.01), small and large intestine (P = 0.09) and stomach and intestine (P < 0.01) weights were less in low and medium RFIIII steers compared to high RFIIII steers. There was a trend for low RFIIII steers to have less dissectible carcass fat (P = 0.08), intermuscular fat (P = 0.06), body cavity fat in the butt and loin (P = 0.01), faster accretion rate of empty body water (P = 0.04) and a slower accretion rate of empty body fat (P < 0.01) than medium and high RFIIII steers. A portion of the greater MEI by high RFIIII steer was accounted for by differences in the chemical composition of gain. However, a greater proportion was due to a disproportionate increase in the energy required for maintenance and heat increment of feeding in high RFIIII steers. An attempt should be made to adjust RFI for changes in the chemical composition of gain, possibly by the inclusion of ultrasound backfat thickness and marbling score into the equation for determining RFI. Key words: Cattle, feed efficiency, residual feed intake, remote sensing, GrowSafe System

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.

The importance of body composition in explaining variation in feed conversion efficiency and residual feed intake between meat sheep at two different ages

2006 ◽  
Vol 2006 ◽  
pp. 153-153
Author(s):  
S A Knott ◽  
L J Cummins ◽  
B J Leury ◽  
F R Dunshea
Keyword(s):  
Body Composition ◽  
Feed Intake ◽  
Residual Feed Intake ◽  
Feed Conversion ◽  
Lean Tissue ◽  
Tissue Mass ◽  
Physiological Factors ◽  
The Difference ◽  
The Relationship ◽  
Meat Sheep

Residual feed intake (RFI) is a measure of feed efficiency calculated as the difference between an animal’s actual intake and its expected intake based on its liveweight and growth rate over a specified period of time (Richardson, Herd et al. 2002). The efficiency with which an animal utilises energy during growth, is dependent on a number of physiological factors including body composition and the relative proportions of lean tissue mass (LTM) and fat tissue mass (FTM), due to differences in the energy cost of depositing and maintaining these tissues. Protein or lean tissue is continually degraded and resynthesised and thus the rate at which this occurs may contribute to the variation in energy required by an animal for maintenance and growth (Archer, Richardson et al. 1999). The objective of this work was to determine the relationship between feed conversion ratio (FCR, kg feed:kg gain) and residual feed intake (RFI) with body composition in rams at six months of age (6mo), and then again in the same rams at thirteen months of age (13mo).

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.

scholarly journals Evaluation of animal performance, feed intake, and economic losses in sheep experimentally infected with Trypanosoma vivax

2017 ◽  
Vol 38 (3) ◽  
pp. 1323 ◽  
Author(s):  
Parmênedes Dias de Brito ◽  
Telma De Sousa Lima ◽  
Andréia Freitas de Oliveira ◽  
Débora Andrea Evangelista Façanha ◽  
Carlos Iberê Alves Freitas ◽  
...  
Keyword(s):  
Weight Gain ◽  
Feed Intake ◽  
Feed Efficiency ◽  
Efficiency Index ◽  
Infected Group ◽  
Daily Weight Gain ◽  
Economic Losses ◽  
Animal Performance ◽  
Trypanosoma Vivax ◽  
Feed Conversion

Trypanosoma vivax is a protozoan originating from the African continent, which, although it has not yet been able to complete its biological cycle in South America, due to the absence of the tsetse fly, can still cause death in ruminants. The objective of this study was to verify the effects of T. vivax on the measurements and indices in sheep that characterize animal performance, as well as on economic losses in meat animals. Twenty intact adult male sheep were used for this study, all of approximately the same ages and weights, reared in confinement, and subjected to the same management and diet, which was balanced and supplemented with adequate minerals. The animals were divided into two groups: the control group (CG) and the infected group (IG), which was inoculated intravenously with 1.3 x 105 trypomastigotes of T. vivax. Feed intake was verified daily, whereas the feed conversion (FC), feed efficiency index (FEI), and weight gain were obtained weekly. Total weight gain (TWG) was determined after 70 days post-infection. The economic loss was calculated by subtracting the value obtained (IG) from the expected value (CG), and the difference was expressed as a percentage. A randomized block design was used to isolate the effect of the initial weight. The means were compared by the Student “t” test at 5%. Of the 10 infected animals, one died from the parasitism, yielding a rate much lower than that observed in natural outbreaks. The groups presented similar feed intakes throughout the experimental period; however, the TWG of the infected group was significantly lower (50.7%) than that of the CG. Similarly, the daily weight gain (DWG), feed conversion (FC), and feed efficiency index (FEI) of the IG were significantly lower than those of the CG. In addition, the worst rates of FC and FEI coincided with parasitemia peaks and recurrences, probably due to immunological demand and tissue repair. The abdominal circumference of the infected animals was statistically lower than that of the CG, which may be directly related to fat mobilization, in addition to the possible negative effect on the digestive capacity. The economic losses due to weight alone were 24.07% and could reach 31.66% of the herd value due to animal death. Infection with T. vivax negatively affected animal performance indices, even when the animals were well nourished. Trypanosoma vivax in sheep destined for slaughter caused economic losses of 31.66% due to the decrease in performance and the death rate in the infected group.

Residual feed intake adjusted for backfat thickness and feeding frequency is independent of fertility in beef heifers

2011 ◽  
Vol 91 (4) ◽  
pp. 573-584 ◽  
Author(s):  
J. A. Basarab ◽  
M. G. Colazo ◽  
D. J. Ambrose ◽  
S. Novak ◽  
D. McCartney ◽  
...  
Keyword(s):  
Feed Intake ◽  
Feeding Activity ◽  
Residual Feed Intake ◽  
Backfat Thickness ◽  
Feed Conversion ◽  
Beef Heifers ◽  
Feeding Frequency ◽  
Calving Rate ◽  
Age At Puberty ◽  
Relationship Of

Basarab, J. A., Colazo, M. G., Ambrose, D. J., Novak, S., McCartney, D. and Baron, V. S. 2011. Residual feed intake adjusted for backfat thickness and feeding frequency is independent of fertility in beef heifers. Can. J. Anim. Sci. 91: 573–584. This study examined the effects of residual feed intake (RFI), RFI adjusted for off-test backfat thickness (RFIfat) and RFI adjusted for off-test backfat thickness and feeding event frequency (RFIfat & activity) on heifer fertility and productivity. Beef heifers (n=190) were monitored for individual daily feed intake and feeding event activity over 108–112 d using the GrowSafe System® and assessed for age at puberty based on plasma progesterone concentration. Individual animal daily feed intake, feeding event activity and off-test backfat thickness were then used to calculate RFI, RFIfat and RFIfat & activity and group heifers as either negative ([−], RFI<0.0) or positive ([+], RFI≥0.0) for RFI. Heifers averaged 298 kg (SD=34) in body weight, were 276 days of age (SD=19) at the start of test, grew at 0.90 kg d−1 (SD=0.21), consumed 7.62 kg DM head−1 d−1 (SD=0.84) and had a feed conversion ratio of 8.93 (SD=2.43). Age (351 d, SD=43) and weight (367.3 kg, SD=45.0) at puberty were similar between [−] and [+] RFI heifers, but age at puberty was delayed in [−] RFIfat (P=0.04) and RFIfat & activity (P=0.08) heifers compared with [+] RFIfat and RFIfat & activity heifers. Efficient or [−] RFI heifer exhibited a lower pregnancy (76.84 vs. 86.32%, P=0.09) and calving rate (72.63 vs. 84.21%, P=0.05) compared with [+] RFI heifers. These differences were partially removed in [−] RFIfat and completely removed in [−] RFIfat & activity compared with their [+] RFI counterparts (pregnancy rate, 80.85 vs. 82.29%, P=0.80; calving rate, 75.53 vs. 81.25%, P=0.34). No differences were observed between efficient and inefficient heifers in calving difficulty, average calving date, age at first calving, calf birth weight, calf pre-weaning ADG, calf weaning weight and heifer productivity. However, [+] RFI heifers exhibited a 1.9-fold higher calf death loss compared with [−] RFI heifers (11.11% vs. 5.71%, P=0.24). This difference was more pronounced in [+] RFIfat and [+] RFIfat & activity heifers, which exhibited 2.2-fold (11.84% vs. 5.33%, P=0.15) and 3.0-fold (12.66% vs. 4.17%, P=0.06) higher calf death loss compared with [−] RFI heifers. There was no relationship of RFI adjusted for backfat thickness and feeding activity on fertility traits indicating that backfat thickness and feeding activity may be associated with feed intake and should be considered when selecting heifers for improved feed efficiency.

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