Genetic and phenotypic relationships of feed intake and measures of efficiency with growth and carcass merit of beef cattle

Feed intake and efficiency of growth are economically important traits of beef cattle. This study determined the relationships of daily DMI, feed:gain ratio [F:G, which is the reciprocal of the efficiency of gain (G:F) and therefore increases as the efficiency of gain decreases and vice versa, residual feed intake (RFI), and partial efficiency of growth (efficiency of ADG, PEG) with growth and carcass merit of beef cattle. Residual feed intake was calculated from phenotypic regression (RFIp) or genetic regression (RFIg) of ADG and metabolic BW on DMI. An F1 half-sib pedigree file containing 28 sires, 321 dams, and 464 progeny produced from crosses between Alberta Hybrid cows and Angus, Charolais, or Alberta Hybrid bulls was used. Families averaged 20 progeny per sire (range = 3 to 56). Performance, ultrasound, and DMI data was available on all progeny, of which 381 had carcass data. Phenotypic and genetic parameters were obtained using SAS and ASREML software, respectively. Differences in RFIp and RFIg, respectively, between the most and least efficient steers (i.e., steers with the lowest PEG) were 5.59 and 6.84 kg of DM/d. Heritabilities for DMI, F:G, PEG, RFIp, and RFIg were 0.54 +/- 0.15, 0.41 +/- 0.15, 0.56 +/- 0.16, 0.21 +/- 0.12, and 0.42 +/- 0.15, respectively. The genetic (r = 0.92) and phenotypic (r = 0.97) correlations between RFIp and RFIg indicated that the 2 indices are very similar. Both indices of RFI were favorably correlated phenotypically (P < 0.001) and genetically with DMI, F:G, and PEG. Residual feed intake was tendentiously genetically correlated with ADG (r = 0.46 +/- 0.45) and metabolic BW (r = 0.27 +/- 0.33), albeit with high SE. Genetically, RFIg was independent of ADG and BW but showed a phenotypic correlation with ADG (r = -0.21; P < 0.05). Daily DMI was correlated genetically (r = 0.28) and phenotypically (r = 0.30) with F:G. Both DMI and F:G were strongly correlated with ADG (r > 0.50), but only DMI had strong genetic (r = 0.87 +/- 0.10) and phenotypic (r = 0.65) correlations with metabolic BW. Generally, the phenotypic and genetic correlations of RFI with carcass merit were not different from zero, except genetic correlations of RFI with ultrasound and carcass LM area and carcass lean yield and phenotypic correlations of RFI with backfat thickness (P < 0.01). Daily DMI had moderate to high phenotypic (P < 0.01) and genetic correlations with all the ultrasound and carcass traits. Depending on how RFI technology is applied, adjustment for body composition in addition to growth may be required to minimize the potential for correlated responses to selection in cattle.     

Effects of growth-promoting agents and season on yearling feedlot heifer performance

Angus x crossbred heifers (270 per trial) were used in an experiment conducted over one 105-d summer and one 104-d winter feeding period. Treatments were identical for each trial and included: 1) control, 2) estrogenic implant (E), 3) trenbolone acetate implant (TBA), 4) E + TBA (ET), 5) melengestrol acetate (MGA) in the feed, and 6) ET + MGA (ETM). Each treatment was replicated in five pens, with nine heifers per pen in each season. Initial weights (mean = 384 kg, SE = 57) were the same for each season. There were no treatment x season interactions for final BW, ADG, G:F, water intake, or carcass characteristics. Heifers receiving a growth-promoting agent were 11.6 kg (SE = 4.08) heavier and gained 0.108 kg/d (SE = 0.04) more (P < 0.05) than control heifers. Heifers receiving ET gained 0.09 kg/d (SE = 0.032) more (P = 0.05) than heifers not receiving ET. Heifers receiving ET (with and without MGA) had greater G:F (P < 0.05) than control, E, and TBA heifers. Carcass weights of ET-treated heifers were greater (P < 0.05) than carcass weights for unimplanted heifers, those fed MGA only, and heifers receiving either E or TBA implants. Marbling scores were increased (P < 0.05) by feeding MGA to ET-treated heifers. Water intake was greater (P < 0.01) in the summer (31 L/d) than in the winter (18 L/ d), with no difference among implant treatments. Heifers fed in the winter had heavier carcasses, less 12th-rib fat, greater marbling scores, larger LM area, and a greater incidence of liver abscesses than heifers finished in the summer (P < 0.01). A treatment x season interaction (P = 0.07) was evident for DMI during the 35-d coldest and hottest portions of the year. Heifers fed MGA and implanted with ET tended (P = 0.07) to have greater DMI in the summer but lesser DMI in the winter. In general, differences among growth-promotant programs were relatively similar over the entire summer and in winter.     

Performance by feedlot steers and heifers: daily gain, mature body weight, dry matter intake, and dietary energetics

Performance, DMI, diet composition, and slaughter data from 9,683 pens of steers and 5,009 pens of heifers that were fed high-concentrate diets for 90 d or more were obtained from 15 feedlots from the western United States and Canada. The data set included pen means for more than 3.1 million cattle fed between 1998 and 2004. Performance measurements assessed included ADG, DMI, dietary NE, shrunk initial weight (SIW), and shrunk final weight. Mature final weight (MFW) for cattle in each pen was estimated based on regression of slaughter weight against SIW and ADG across all pens. Equations were developed to standardize performance projections (ADG, MFW, and break-even values) and analyze feedlot cattle close-outs. Generally, as diet NE concentration increased, DMI was decreased but G:F, dressing percentage, and yield grade all increased. Pens of cattle with greater SIW had greater ADG, DMI, and shrunk final weight but a lower G:F and dressing percentage. Dressing percentage and yield grade were correlated positively. Equations of the NRC relating gain to NE intake explained 85 and 80% of the variation in DMI of steers and heifers, respectively, with mean ratios of predicted to observed DMI (DMIratio) at 1.000 +/- 0.0506 and 0.974 +/- 0.0490. However, a significant (P < 0.001) bias in the NRC estimate of DMI was detected (r(2) = 0.10 and 0.05, for steers and heifers) between the DMIratio and ADG in which DMIratio increased as ADG increased. This was due to inherent confounding of ADG and MFW in the original NE equation of Lofgreen and Garrett. Based on iterative optimization to minimize the difference between expected and observed DMI, revised equations for retained energy (RE, Mcal/kg) were developed for steers and for heifers: RE(steer) = 0.0606 x (LW x 478/MFW(steer))(0.75)ADG(0.905); RE(heifer) = 0.0618 x (LW x 478/MFW(heifer))(0.75)ADG(0.905), where LW = mean shrunk live weight. The revised equations decreased the SD of the DMIratio by 5.4% (from 0.0496 to 0.0469) and eliminated the bias in DMIratio that was related to ADG (r(2) = 0.0006). The similarity between the 2 equations derived for steers and for heifers for estimation of RE from ADG supports the concept that scaling by MFW accounts for energy utilization differences between sexes.     

Genetic relationship between different measures of feed efficiency and its component traits in Japanese Black (Wagyu) bulls

Genetic parameters of average daily gain (ADG), metabolic body weight (MWT), body weight at finish (BWF), daily feed intake (DFI), feed conversion ratio (FCR), and residual feed intake (RFI) were estimated in 740 Japanese Black bulls. RFI was calculated as the difference between actual and expected feed intake predicted by the residual of multiple regression (RFI_phe) and genetic regression (RFI_gen) from the multivariate analysis for DFI, MWT, and ADG. The estimations were made for the test periods of 140 days (77 bulls) and 112 days (663 bulls). The mean for RFI_phe was close to zero and RFI_gen was negative. Most of the traits studied were moderately heritable (ranging from 0.24 to 0.49), except for ADG and FCR (0.20 and 0.15, respectively). The genetic correlations among growth traits (ADG, MWT and BWF) and between DFI and growth traits were high, while the phenotypic correlations between them were moderate to high. The genetic and phenotypic correlations between RFI_phe and RFI_gen were > 0.95 implying that they are regarded as the same trait and the genetic correlations of RFI (RFI_phe and RFI_gen) with FCR and DFI were favorably high. RFI_phe was phenotypically independent of its component traits, MWT (r_p = − 0.01) and ADG (r_p = 0.01). RFI_gen was genetically independent of MWT (r_g = − 0.07), while there was a weak genetic relationship (r_g = 0.18) between RFI_gen and ADG. These results provide evidence that RFI_gen should be included for genetic improvement of feed efficiency in Japanese Black breeding program.     

Growth and slaughter traits of Boer x Spanish, Boer x Angora, and Spanish goats consuming a concentrate-based diet.

The number of Boer crossbred meat goats has been increasing rapidly, although how their growth and slaughter traits compare with those of Spanish goats and influences of maternal genotype have not been thoroughly evaluated. This information would be useful to achieve optimal meat goat production systems and yield of goat products desired by consumers. Therefore, postweaning growth (9 to 24 wk of age) and slaughter traits (212 +/- 5.0 d of age) of Boer x Spanish, Spanish, and Boer x Angora wethers (n = 16, 18, and 18 for growth measures, respectively, and n = 6 per genotype for slaughter traits) consuming a concentrate-based diet were compared. Over the 16-wk performance period, ADG, DMI, and ADG:DMI were greater (P < 0.05) for Boer crossbreds than for Spanish goats (ADG: 154, 117, and 161 g; DMI: 646, 522, and 683 g/d; ADG:DMI: 263, 235, and 261 g/kg for Boer x Spanish, Spanish, and Boer x Angora, respectively). Dressing percentage (46.3, 47.3, and 47.0% of BW; SE = 1.21) and quality grade score (11.17, 9.67, and 11.17 for Boer x Spanish, Spanish, and Boer x Angora, respectively; SE = 0.66 [12 = Choice+; 11 = Choice; 10 = Choice-; 9 = Good+]) were similar among genotypes. Weights of some noncarcass components were greater for Boer crossbreds than for Spanish goats, but relative to empty BW, noncarcass component weights were similar among genotypes. Concentrations of moisture, ash, fat, and protein in carcass and noncarcass components did not differ among genotypes. Contributions to the carcass of different primal cuts were similar among genotypes, and there were few differences in concentrations of separated lean, bone, and fat in primal cuts. In conclusion, when consuming a concentrate-based diet, early postweaning growth rate was similar between Boer x Spanish and Boer x Angora wethers and greater for Boer crossbreds than for Spanish wethers. Slaughter traits were primarily related to differences in final BW.     

Effects of feeding whole cottonseed and cottonseed products on performance and carcass characteristics of finishing beef cattle

Three experiments were conducted to determine the effects of whole cottonseed or cottonseed products on performance and carcass characteristics of beef cattle. In Exp. 1, 120 beef steers (initial BW = 381 +/- 31.7 kg) were fed steam-flaked corn-based finishing diets with 10% (DM basis) basal roughage, and whole cottonseed or individual cottonseed components (cottonseed hulls, meal, and oil). Over the entire feeding period, ADG did not differ (P = 0.95), but DMI increased (P = 0.07) and G:F decreased (P = 0.06) for steers fed the cottonseed diets compared with the control diet. Dressing percent (P = 0.02) and marbling scores (P = 0.02) of carcasses from steers fed the cottonseed diets were less than for steers fed the control diet. In Exp. 2, 150 beef steers (initial BW = 364 +/- 9.9 kg) were used to determine the effects of whole cottonseed or pelleted cottonseed (PCS) on performance and carcass characteristics. Cattle were fed steam-flaked corn-based finishing diets in which whole cottonseed or PCS replaced all of the dietary roughage, supplemental fat, and supplemental natural protein of the control diet. Over the entire feeding period, steers fed the cottonseed diets had lower (P = 0.04) DMI and greater (P < 0.01) G:F than steers fed the control diet. Carcass characteristics did not differ (P = 0.16 to 0.96) among dietary treatments. In Exp. 3, 150 beef heifers (initial BW = 331 +/- 17.1 kg) were used to determine the effects of PCS or delinted, whole cottonseed (DLCS) on performance and carcass characteristics. Heifers were fed rolled corn-based finishing diets in which cottonseed replaced the dietary roughage, supplemental fat, and all or part of the supplemental natural protein of the control diet. Over the entire feeding period, ADG, DMI, and G:F of heifers fed the control diet did not differ (P = 0.19 to 0.80) from those of the cottonseed diets; however, heifers fed the diets containing PCS had greater ADG (P = 0.03) and G:F (P = 0.09) than heifers fed diets containing DLCS. Carcass characteristics of heifers fed the control diet did not differ (P > or = 0.28) from those fed the cottonseed diets. Heifers fed the diets containing PCS had greater (P < or = 0.03) HCW, dressing percent, and LM area than those fed DLCS. Based on our results, whole cottonseed, or products derived from processing whole cottonseed, can replace feedstuffs commonly used in beef cattle finishing diets with no adverse effects on animal performance or carcass characteristics.     

Characterization of feed efficiency traits and relationships with feeding behavior and ultrasound carcass traits in growing bulls

The objectives of this study were to characterize feed efficiency traits and to examine phenotypic correlations between performance and feeding behavior traits, and ultrasound measurements of carcass composition in growing bulls. Individual DMI and feeding behavior traits were measured in Angus bulls (n=341; initial BW=371.1+/-50.8 kg) fed a corn silage-based diet (ME=2.77 Mcal/kg of DM) for 84 d in trials 1 and 2 and for 70 d in trials 3 and 4 by using a GrowSafe feeding system. Meal duration (min/d) and meal frequency (events/d) were calculated for each bull from feeding behavior recorded by the GrowSafe system. Ultrasound measures of carcass 12th-rib fat thickness (BF) and LM area (LMA) were obtained at the start and end of each trial. Residual feed intake (RFIp) was computed from the linear regression of DMI on ADG and midtest BW(0.75) (metabolic BW, MBW), with trial, trial by ADG, and trial by midtest BW(0.75) as random effects (base model). Overall ADG, DMI, and RFIp were 1.44 (SD=0.29), 9.46 (SD=1.31), and 0.00 (SD=0.78) kg/d, respectively. Stepwise regression analysis revealed that inclusion of BW gain in BF and LMA in the base model increased R(2) (0.76 vs. 0.78) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted residual feed intake (RFIc) were moderately correlated with DMI (0.60 and 0.55, respectively) and feed conversion ratio (FCR; 0.49 and 0.45, respectively), and strongly correlated with partial efficiency of growth (PEG; -0.84 and -0.78, respectively), but not with ADG or MBW. Gain in BF was weakly correlated with RFIp (0.30), FCR (-0.15), and PEG (-0.11), but not with RFIc. Gain in LMA was weakly correlated with RFIp (0.17) and FCR (-0.19), but not with PEG or RFIc. The Spearman rank correlation between RFIp and RFIc was high (0.91). Meal duration (0.41), head-down duration (0.38), and meal frequency (0.26) were correlated with RFIp and accounted for 35% of the variation in DMI not explained by MBW, ADG, and ultrasound traits (RFIc). These results suggest that adjusting residual feed intake for carcass composition will facilitate selection to reduce feed intake in cattle without affecting rate or composition of gain.     

Heritabilities and genetic correlations for postweaning growth and feed intake of beef bulls and steers

Data from studies conducted at Miles City, MT and Lethbridge, AB were pooled to evaluate genetic and environmental variation in feed intake (MEI), growth rate (ADG), MEI-to-gain ratio (M/G), final weight (FWT), and fat thickness (FAT). A total of 124 sires with an average of 4.25 progeny each were represented in the data. Restricted maximum likelihood methods were used to estimate within and between paternal half-sib estimates of variance and covariance. Heritabilities and genetic, phenotypic, and environmental correlations with inference to populations at 365 d of age were calculated from the estimates. Heritabilities were as follows: ADG, .38 +/- .16; MEI, .45 +/- .17; M/G, .26 +/- .15; FWT .25 +/- .15; and FAT .52 +/- .17. The genetic correlation of MEI with ADG was large (.73 +/- .13) and antagonistic to genetic improvement of M/G through selection for ADG. Efficient genetic improvement in M/G was found to depend on using either MEI or an indicator of composition of gain as selection criteria in addition to ADG. Selection to improve M/G using an index that included FWT and FAT, in addition to MEI and ADG, resulted in greater predicted response in ADG and lesser predicted response in MEI than the index of ADG and MEI alone.     

Characterization of energetically efficient and inefficient beef cows

Dry matter intake and BW data from 14 mature, nonpregnant, nonlactating Angus cows that were individually fed through two consecutive 70- to 80-d periods (maintenance and ad libitum) were used to predict ADG (ADG = -.512 + .213 DMI - .0017 BW, R2 = .95). This equation then was used to identify feed efficiency types among these cows. Cows were identified as average type (A) if ADG was within one SE of predicted ADG, and as efficient (E) or inefficient types (I) if ADG exceeded one SE above or below, respectively, its predicted ADG. Four, four, and six cows were identified and grouped as I, A, and E types, respectively. During the maintenance period, DM and ME intake and ADG were similar (P greater than .10) across all three efficiency types. But during the ad libitum period, voluntary DM and ME intakes of I cows were greater (P less than .05) than those of A or E cows. Average daily gains of I cows during ad libitum feeding were greater (P less than .10) than those of A cows. Daily ME required for maintenance of I cows was highest, that of A cows was intermediate, and that of E cows was lowest (180.2, 154.6, and 135.1 kcal/kg BW.75, respectively). Inefficient cows tended (P greater than .10) to have less fat and deposited more protein (P less than .05) than A and E cows (137.9 vs 77.2 and 46.2 protein g/d, respectively). Concurrent with higher protein accretion rates, liver weights of I cows were heavier (P less than .05) than those of A and E cows (8.58 vs 7.79 and 7.68 kg, respectively). Inefficient cows were characterized by higher energy requirements for maintenance. Their high protein accretion may partially explain their higher maintenance requirements.     

Effects of divergent selection for serum insulin-like growth factor-I concentration on performance, feed efficiency, and ultrasound measures of carcass composition traits in Angus bulls and heifers

Angus bulls and heifers from lines divergently selected for serum IGF-I concentration were used to evaluate the effects of IGF-I selection line on growth performance and feed efficiency in 2 studies. In study 1, bulls (low line, n = 9; high line, n = 8; initial BW = 367.1 +/- 22.9 kg) and heifers (low line, n = 9; high line, n = 13; initial BW = 286.4 +/- 28.6 kg) were adapted to a roughage-based diet (ME = 1.95 Mcal/kg of DM) for 24 d and fed individually for 77 d by using Calan gate feeders. In study 2, bulls (low line, n = 15; high line, n = 12; initial BW = 297.5 +/- 34.4 kg) and heifers (low line, n = 9; high line, n = 20; initial BW = 256.0 +/- 25.1 kg) were adapted to a grain-based diet (ME = 2.85 Mcal/kg of DM) for 32 d and fed individually for 70 d by using Calan gate feeders. Blood samples were collected at weaning and at the start and end of each study, and serum IGF-I concentration was determined. Residual feed intake (RFI) was calculated, within study, as the residual from the linear regression of DMI on midtest BW(0.75), ADG, sex, sex by midtest BW(0.75) and sex by ADG. In study 1, calves from the low IGF-I selection line had similar initial and final BW and ADG, compared with calves from the high IGF-I selection line. In addition, DMI and feed conversion ratio were similar between IGF-I selection lines; however, calves from the low IGF-I selection line tended (P < 0.10) to have lesser RFI than calves from the high IGF-I selection line (-0.26 vs. 0.24 +/- 0.31 kg/d). In study 2, IGF-I selection line had no influence on performance or feed efficiency traits. However, there was a tendency (P = 0.15) for an IGF-I selection line x sex interaction for RFI. Bulls from the low IGF-I selection line had numerically lesser RFI than those from the high IGF-I selection line, whereas in heifers, the IGF-I selection line had no effect on RFI. In studies 1 and 2, weaning and initial IGF-I concentrations were not correlated with either feed conversion ratio or RFI. However, regression analysis revealed a sex x IGF-I concentration interaction for initial IGF-I concentration in study 1 and weaning IGF-I concentration in study 2 such that the regression coefficient was positive for bulls and negative for heifers. These data suggest that genetic selection for postweaning serum IGF-I concentration had a minimal effect on RFI in beef cattle.     

Effect of duration of performance test on variance component estimates for lamb growth rate

The objective was to determine the effect of periods of adjustment and duration of performance test on estimating genetic variance parameters for ADG. Variance components were estimated from ADG data collected from 1978 to 1984 on a total of 1,047 Targhee ewe and ram lambs at the U.S. Sheep Experiment Station (Dubois, ID). Across all years, lambs averaged 84 +/- 9 d of age and 25 +/- 5.4 kg of weight when placed on test. Lambs were provided ad libitum access to a commercial pellet of barley grain and ground alfalfa for 14 wk. Every 2 wk, ADG was recorded. Overall mean ADG for the entire 14-wk period across all years was 249.3 +/- 56.5 g. Variance components were estimated from a single-trait animal model using REML for cumulative combinations of time on feed in 2-wk intervals from 4 to 14 wk and varying the adjustment period from 2 to 6 wk. The model included fixed effects for year (1978 to 1984), sex of lamb (ewe or ram), and genetic line (selected or control), and two covariates (age and weight at beginning of performance test). As the duration of the performance test increased, phenotypic variances for ADG decreased: 54 and 13 g2 at 4 and 14 wk on test, respectively. Also, estimates of direct heritability increased with extended duration on test: 0.20 +/- 0.06 and 0.35 +/- 0.07 at 4 and 14 wk on test, respectively. Heritability estimates increased little after 8 wk on feed (0.33, 0.33,0.38, and 0.35 for 8, 10, 12, and 14 wk, respectively). Genetic and environmental correlations among durations of the performance test were estimated from two-trait models. All genetic correlations among durations of performance test were greater than 0.88 which suggests that all measures of ADG were genetically similar. However, environmental correlations among duration of performance test ranged from 0.31 to 1.00 with the smaller environmental correlations occurring between 4 to 6 wk with 12 to 14 wk on feed. These results indicate that a period of 8 wk or greater was sufficient to observe differences among animals for ADG due to direct genetic effects under this environment.     

Using ultrasound measurements to predict body composition of yearling bulls

Carcass traits have been successfully used to determine body composition of steers. Body composition, in turn, has been used to predict energy content of ADG to compute feed requirements of individual animals fed in groups. This information is used in the Cornell value discovery system (CVDS) to predict DM required (DMR) for the observed animal performance. In this experiment, the prediction of individual DMR for the observed performance of group-fed yearling bulls was evaluated using energy content of gain, which was based on ultrasound measurements to estimate carcass traits and energy content of ADG. One hundred eighteen spring-born purebred and crossbred bulls (BW = 288 +/- 4.3 kg) were sorted visually into 3 marketing groups based on estimated days to reach USDA low Choice quality grade. The bulls were fed a common high-concentrate diet in 12 slatted-floor pens (9 to 10 head/pen). Ultrasound measurements including back-fat (uBF), rump fat, LM area (uLMA), and intramuscular fat were taken at approximately 1 yr of age. Carcass measurements including HCW, backfat over the 12th to 13th rib (BF), marbling score (MRB), and LM area (LMA) were collected for comparison with ultrasound data for predicting carcass composition. The 9th to 11th-rib section was removed and dissected into soft tissue and bone for determination of chemical composition, which was used to predict carcass fat and empty body fat (EBF). The predicted EBF averaged 23.7 +/- 4.0%. Multiple regression analysis indicated that carcass traits explained 72% of the variation in predicted EBF (EBF = 16.0583 + 5.6352 x BF + 0.01781 x HCW + 1.0486 x MRB - 0.1239 x LMA). Because carcass traits are not available on bulls intended for use as herd sires, another equation using predicted HCW (pHCW) and ultrasound measurements was developed (EBF = 39.9535 x uBF - 0.1384 x uLMA + 0.0867 x pHCW - 0.0897 x uBF x pHCW - 1.3690). This equation accounted for 62% of the variation in EBF. The use of an equation to predict EBF developed with steer composition data overpredicted the EBF predicted in these experiments (28.7 vs. 23.7%, respectively). In a validation study with 37 individually fed bulls, the use of the ultrasound-based equation in the CVDS to predict energy content of gain accounted for 60% of the variation in the observed efficiency of gain, with 1.5% bias, and identified 3 of the 4 most efficient bulls.     

Cattle selected for lower residual feed intake have reduced daily methane production

Seventy-six Angus steers chosen from breeding lines divergently selected for residual feed intake (RFI) were studied to quantify the relationship between RFI and the daily rate of methane production (MPR). A 70-d feeding test using a barley-based ration was conducted in which the voluntary DMI, feeding characteristics, and BW of steers were monitored. The estimated breeding value (EBV) for RFI (RFI(EBV)) for each steer had been calculated from 70-d RFI tests conducted on its parents. Methane production rate (g/d) was measured on each steer using SF(6) as a tracer gas in a series of 10-d measurement periods. Daily DMI of steers was lower during the methane measurement period than when methane was not being measured (11.18 vs. 11.88 kg; P = 0.001). A significant relationship existed between MPR and RFI when RFI (RFI(15d)) was estimated over the 15 d when steers were harnessed for methane collection (MPR = 13.3 x RFI(15d) + 179; r(2) = 0.12; P = 0.01). Animals expressing lower RFI had lower daily MPR. The relationship established between MPR and RFI(15d) was used to calculate a reduction in daily methane emission of 13.38 g accompanied a 1 kg/d reduction in RFI(EBV) in cattle consuming ad libitum a diet of 12.1 MJ of ME/kg. The magnitude of this emission reduction was between that predicted on the basis of intake reduction alone (18 g x d(-1) x kg of DMI(-1)) and that predicted by a model incorporating steer midtest BW and level of intake relative to maintenance (5 g x d(-1) x kg of DMI(-1)). Comparison of data from steers exhibiting the greatest (n = 10) and lowest (n = 10) RFI(15d) showed the low RFI(15d) group to not only have lower MPR (P = 0.017) but also reduced methane cost of growth (by 41.2 g of CH(4)/kg of ADG; P = 0.09). Although the opportunity to abate livestock MPR by selection against RFI seems great, RFI explained only a small proportion of the observed variation in MPR. A genotype x nutrition interaction can be anticipated, and the MPR:RFI(EBV) relationship will need to be defined over a range of diet types to account for this.     

Genetic and phenotypic relationships of feeding behavior and temperament with performance, feed efficiency, ultrasound, and carcass merit of beef cattle

Feeding behavior and temperament may be useful in genetic evaluations either as indicator traits for other economically relevant traits or because the behavior traits may have a direct economic value. We determined the variation in feeding behavior and temperament of beef cattle sired by Angus, Charolais, or Hybrid bulls and evaluated their associations with performance, efficiency, and carcass merit. The behavior traits were daily feeding duration, feeding head down (HD) time, feeding frequency (FF), and flight speed (FS, as a measure of temperament). A pedigree file of 813 animals forming 28 paternal half-sib families with about 20 progeny per sire was used. Performance, feeding behavior, and efficiency records were available on 464 animals of which 381 and 302 had records on carcass merit and flight speed, respectively. Large SE reflect the number of animals used. Direct heritability estimates were 0.28 +/- 0.12 for feeding duration, 0.33 +/- 0.12 for HD, 0.38 +/- 0.13 for FF, and 0.49 +/- 0.18 for FS. Feeding duration had a weak positive genetic (r(g)) correlation with HD (r(g) = 0.25 +/- 0.32) and FS (r(g) = 0.42 +/- 0.26) but a moderate negative genetic correlation with FF (r(g) = -0.40 +/- 0.30). Feeding duration had positive phenotypic (r(p)) and genetic correlations with DMI (r(p) = 0.27; r(g) = 0.56 +/- 0.20) and residual feed intake (RFI; r(p) = 0.49; r(g) = 0.57 +/- 0.28) but was unrelated phenotypically with feed conversion ratio [FCR; which is the reciprocal of the efficiency of growth (G:F)]. Feeding duration was negatively correlated with FCR (r(g) = -0.25 +/- 0.29). Feeding frequency had a moderate to high negative genetic correlation with DMI (r(g) = -0.74 +/- 0.15), FCR (r(g) = -0.52 +/- 0.21), and RFI (r(g) = -0.77 +/- 0.21). Flight speed was negatively correlated phenotypically with DMI (r(p) = -0.35) but was unrelated phenotypically with FCR or RFI. On the other hand, FS had a weak negative genetic correlation with DMI (r(g) = -0.11 +/- 0.26), a moderate genetic correlation with FCR (r(g) = 0.40 +/- 0.26), and a negative genetic correlation with RFI (r(g) = -0.59 +/- 0.45). The results indicate that behavior traits may contribute to the variation in the efficiency of growth of beef cattle, and there are potential correlated responses to selection to improve efficiency. Feeding behavior and temperament may need to be included in the definition of beef cattle breeding goals, and approaches such as the culling of unmanageable cattle and the introduction of correct handling facilities or early life provision of appropriate experiences to improve handling will be useful.     

Genetic parameters for measures of the efficiency of gain of boars and the genetic relationships with its component traits in Duroc pigs

Genetic parameters for the efficiency of gain traits on 380 boars and the genetic relationships with component traits were estimated in 1,642 pigs (380 boars, 868 gilts, and 394 barrows) in 7 generations of a Duroc population. The efficiency of gain traits included the feed conversion ratio (FCR) and residual feed intake (RFI) and their component traits, ADG, metabolic BW (MWT), and daily feed intake (FI). The RFI was calculated as the difference between the actual and expected FI. The expected FI was predicted by the nutritional requirement and by the residual of phenotypic (RFI(phe)) and genetic (RFI(gen)) regressions from the multivariate analysis for FI on MWT and ADG. The means for RFI(phe) and RFI(gen) were close to zero, and the mean for nutritional RFI was negative (-0.11 kg/d). The traits studied were moderately heritable (ranging from 0.27 to 0.53). The genetic and phenotypic correlations between ADG and FI were moderate to high, whereas the genetic correlation between MWT and FI was moderate, and the phenotypic correlation between them was low. The corresponding correlations between RFI(phe) and RFI(gen) were > 0.95, implying that they can be regarded as the same trait. The genetic and phenotypic correlations of FCR with measures of RFI were high but lower than unity. The RFI(phe) was phenotypically independent of its component traits, MWT (r(p) = 0.01) and ADG (r(p) = 0.03). The RFI(gen) was genetically independent of MWT (r(g) = -0.04), whereas there was a weak genetic relationship (r(g) = 0.15) between RFI(gen) and ADG. Residual FI was more heritable than FCR, and the genetic and phenotypic correlations of RFI(phe) and RFI(gen) with FI were positive and stronger than that of FCR with FI. These results provide evidence that RFI(phe) or RFI(gen) should be included in breeding programs for Duroc pigs to make genetic improvement in the efficiency of gain.     

Genetic parameters for six measures of length of productive life and three measures of lifetime production by 6 yr after first calving for Hereford cows

Genetic parameters for length of productive life given the opportunity (LPL/O), measured as days between first calving and disposal conditioned on one of six opportunity groups, L1 through L6 (e.g., L2 is length of productive life in days given the opportunity to live 2 yr after first calving), and lifetime production (LP), measured as the number of calves born (NB), number of calves weaned (NW), and cumulative weaning weight (CW) by 6 yr after first calving, were estimated using records of 1,886 Hereford cows from a selection experiment with three selected lines and a control line. Weaning weights were adjusted to 200 d of age and for sex and age of dam. Estimates of heritability and genetic and environmental correlations were obtained by restricted maximum likelihood with bivariate animal models, with year of birth of cow as a fixed effect and direct genetic and residual as random effects. Genetic trends were estimated by regressing means of estimated breeding values by year of birth and line on birth year. Estimates of heritability (SE) for LPL/O ranged from 0.05 (0.01) to 0.15 (0.03). Estimates of genetic correlations (SE) among LPL/O ranged from 0.74 (0.14) to 1.00 (0.00), and estimates of environmental correlations ranged from 0.67 (0.05) to 0.98 (0.01). Estimates of heritability (SE) for NB, NW, and CW were 0.17 (0.05), 0.21 (0.06), and 0.18 (0.01). Estimates of genetic correlations (SE) among NB, NW, and CW ranged from 0.96 (0.02) to 0.99 (0.01). Estimates of environmental correlations (SE) ranged from 0.93 (0.01) to 0.99 (0.01). Estimates of genetic correlations for L6 with NB, NW, and CW were near 1.00 (0.09). Estimates of environmental correlations (SE) ranged from 0.57 (0.03) to 0.60 (0.03). Estimates of genetic change per year (SE) for L6 were low for all lines and ranged from -3.53 (2.09) to 4.63 (2.11) d/yr. Genetic trends for NB and NW were negligible for all lines. Genetic trends for CW were low and ranged from -2.81 (1.67) to 3.29 (1.76) kg/yr. Differences in genetic trends between selected lines and control were not significant (P > 0.05). Estimates of environmental trends (SE) over all lines were -104.00 (25.48) d/yr, -0.26 (0.02) calves/yr, -0.25 (0.02) calves/yr, and -55.10 (15.63) kg/yr, for L6, NB, NW, and CW, respectively. Selection for LPLIO or LP could be successful in a breeding program, but may be relatively slow due to the low magnitude of heritability and extended generation interval.     

Optimum duration of performance tests for evaluating growing pigs for growth and feed efficiency traits

The optimum duration of test for the measurement of ADG, ADFI, feed:gain ratio [which is the reciprocal of the efficiency of gain (G:F) and therefore increases as the efficiency of gain decrease and vice versa], and residual feed intake was examined in growing pigs. Data from 144 hybrid (mainly Large White x Landrace) pigs involved in a longitudinal (n = 54) and serial slaughter (n = 90) experiment were used. The pigs were housed in individual pens from 70 +/- 1 d of age (mean +/- SD) and fed ad libitum a pelleted commercial diet. Feed intake and BW data on pigs that had a minimum of 10-wk records were partitioned into a 14-d adjustment and a 56-d test period. Phenotypic correlations among weekly measurements were used to examine the repeatability of each trait. Changes in phenotypic residual variance and correlation using shortened (7-, 14-, 21-, 28-, 35-, 42-, and 49-d) tests compared with the full-length 56-d test were used as criteria to assess the optimum test duration. The results of the phenotypic correlations among weekly measurements indicated that ADFI, which was characterized by moderate to high correlations (0.41 to 0.81), was more repeatable than ADG, which was characterized by low correlations (0.00 to 0.43). Mean gut fill (n = 107) was 4.2% of BW but was characterized by large variation among the pigs (SD = 1.8; CV = 42.2%). This variation in gut fill was a major contributor to the low repeatability of the measurement of ADG. These repeatability results indicated that ADG, rather than ADFI, will determine the optimum duration of test for the feed efficiency traits. The results of the shortened relative to the full-length test indicate that for growing pigs under good nutrition and ad libitum feeding, a 28-d test was adequate for the measurement of feed intake, whereas a 35-d test was required to measure ADG, feed:gain ratio, and residual feed intake without compromising the accuracy of measurement.     

Effects of water sulfate concentration on performance, water intake, and carcass characteristics of feedlot steers.

Two hundred forty single-source, cross-bred steers (304 kg) were used to evaluate the effects of various water sulfate concentrations on performance, water intake, and carcass characteristics of feedlot steers. Cattle were stratified by weight and assigned within weight blocks to five water treatments. Averaged over time, actual water sulfate concentrations (+/- SEM) were 136.1 (+/- 6.3), 291.2 (+/- 15.3), 582.6 (+/- 16.9), 1,219.2 (+/- 23.7), and 2,360.4 (+/- 68.2) mg/L, respectively. Weather-related data were recorded. Increasing water sulfate concentration resulted in linear decreases in ADG (P < 0.01) and gain:feed ratio (P < 0.01) and a quadratic effect on water intake (P = 0.02) and tended to quadratically increase then decrease DMI (P = 0.13). Sulfate x period interactions were evident for DMI (P = 0.01), ADG (P < 0.01), and feed efficiency (P < 0.01). Time had quadratic effects on DMI, water intake, ADG, and feed efficiency (P < 0.01 for all models). Increasing water sulfate concentration resulted in linear decreases in final weight, hot carcass weight, and dressing percentage, a linear increase in longissimus muscle area, and a quadratic effect on fat thickness over the 12th rib and predicted yield grade (P < 0.05 for all dependent variables). Mean daily temperature explained 25.7% of the observed variation in water intake. Other factors that explained a significant (P < 0.01) amount of variation in water intake were BW, DMI, water sulfate concentration, barometric pressure, wind speed, and humidity. High water sulfate concentrations had a significant and deleterious effect on performance and carcass characteristics of feedlot steers. Increasing the sulfate concentration in water may have resulted in a functional water restriction early in the trial when ambient temperatures were greatest. However, toward the latter stages of the trial, cattle supplied higher-sulfate water had higher ADG and FE. These improvements later in the trial may represent compensatory gain associated with decreased ambient temperature and water requirements. Averaged over time, a water sulfate concentration of greater than 583 mg/L, equivalent to 0.22% of the diet, decreased feedlot performance.     

Effects of an artificial sweetener on health, performance, and dietary preference of feedlot cattle

Two experiments examined the effects of a saccharin-based artificial sweetener (Sucram) on health, performance, and dietary preference of feedlot cattle. In Exp. 1, 200 steer calves (initial BW = 190.4 +/- 1.47 kg) were fed a 65% concentrate diet supplemented with or without 200 mg of Sucram/kg (DM basis) during a 56-d receiving-growing period. Feeding Sucram did not affect overall (P = 0.19) DMI; however, from d 29 to 56, there was a trend (P = 0.10) for increased DMI with Sucram (5.71 vs. 6.02 kg/d, respectively). From d 0 to 28 and d 0 to 56, there were trends (P = 0.11 and 0.12, respectively) for increased ADG and for increased d-56 BW (P = 0.07) for calves fed Sucram. No differences were detected (P = 0.82) for receiving (REC) period morbidity. During the finishing (FIN) period, 180 steers from the REC period were assigned (9 pens/treatment in a 2 x 2 factorial design) to the following treatments: 1) control REC/control FIN; 2) control REC/Sucram FIN; 3) Sucram REC/control FIN; and 4) Sucram REC/ Sucram FIN. Over the FIN period, ADG tended (P = 0.12) to be greater for Sucram; however, carcass-adjusted ADG did not differ among treatments. Daily DMI was affected by a REC x FIN interaction (P = 0.08), which was the result of greater DMI by cattle in the Sucram REC/Sucram FIN treatment and decreased DMI by cattle in the Sucram REC/control FIN treatment. In general, changes in carcass characteristics were minor. In Exp. 2, 12 steers (initial BW = 395.6 +/- 6.17 kg) were used in a simultaneously replicated 3 x 3 Latin square preference test. Each square consisted of 3 pens, with 2 steers/pen, and 3 time periods. Bunks had dividers at their midpoint, and equal quantities of diet (as-fed basis) were delivered randomly on either side of the divider daily. Treatments were: 1) control; 2) Sucram = basal diet supplemented with 200 mg of Sucram/kg of DM; and 3) choice = control and Sucram on separate sides of the divider. Dietary preference differed on d 1 (P = 0.01) and d 3 (P = 0.02) for control vs. choice and Sucram vs. choice, with the choice group consuming 0.49 and 1.72 kg of DM more of the Sucram diet than the control diet, respectively. This effect, however, was not consistent across days, and average DMI did not differ (P = 0.81) among treatments. Addition of Sucram to the diet of newly received cattle tended to increase receiving period ADG; however, its effects on morbidity, finishing performance, and dietary preference were limited.