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Journal of Animal Science - Animal Nutrition

Effects of timing and duration of test period and diet type on intake and feed efficiency of Charolais-sired cattle1

 

This article in JAS

  1. Vol. 94 No. 11, p. 4748-4758
    unlockOPEN ACCESS
     
    Received: May 13, 2016
    Accepted: Sept 09, 2016
    Published: October 27, 2016


    3 Corresponding author(s): dshike@illinois.edu
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doi:10.2527/jas.2016-0633
  1. C. J. Cassady*,
  2. T. L. Felix*22,
  3. J. E. Beever*,
  4. D. W. Shike 3* and
  5.  
  1. * Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, 61801
     The names and affiliation of scientists working with the National Program for Genetic Improvement of Feed Efficiency in Beef Cattle are listed at http://www.beefefficiency.org/about.html

Abstract

Objectives of this experiment were to: 1) determine appropriate test length, timing, and repeatability of DMI, ADG, and efficiency over different biological time points; 2) determine the efficacy of using decoupled performance and intake data to generate accurate feed efficiency measures; and 3) determine the relationship between forage-and grain-feed efficiency measures. Over 2 yr, Charolais crossbred heifers (n = 308) and steers (n = 320) were fed for two 70 d periods and DMI, ADG, and 12th rib fat thickness were recorded. Steers were fed grain-based diets during the growing and finishing periods to determine the effects of test period and timing on DMI and feed efficiency. Heifers were fed forage during the growing period and grain during the finishing period to test the effect of diet type on measures of DMI and feed efficiency. For each 70 d test period, individual DMI was recorded using the GrowSafe (Airdrie, AB) system. Residual feed intake (RFI) was calculated for each test period. Total feeding period ADG (FP_ADG) was calculated for steers by regressing all weights taken from feedlot arrival to final BW, which was calculated by dividing HCW by a standard dressing percentage (63%). Dry matter intake and RFI were correlated (r = 0.56; P < 0.01, and 0.63; P < 0.01, respectively) for the growing and finishing periods of grain-fed steers. Average daily gain was not repeatable (r = 0.11; P = 0.06) across both test periods for steers. However, growing and finishing ADG were correlated (r = 0.58; P < 0.01, and r = 0.69; P < 0.01, respectively) to FP_ADG. To assess the potential of shortening the intake test, DMI was analyzed in 7 d increments for grain-fed steers during the growing and finishing periods. Regardless of test length, from 7 to 70 d, DMI was strongly correlated (r ≥ 0.87; P < 0.01) to total DMI during the growing period. Heifer forage DMI was correlated (r = 0.58; P < 0.01) to grain DMI; subsequently, forage and grain RFI were moderately correlated (r = 0.40; P < 0.01). This study suggests that DMI is repeatable across varying stages of maturity in cattle, and accurate feed efficiency measures can be obtained in either the growing or finishing period. The relationship of forage and grain DMI and efficiency in heifers suggests that measures of DMI and feed efficiency in heifers are relevant, regardless of diet fed. Intake evaluation periods can be shortened with minimal effects on the accuracy of predicting individual animal DMI.



INTRODUCTION

In beef production systems, individual feed consumption represents the greatest financial burden (Miller et al., 2001). However, a majority of the intake evaluations performed in beef cattle have been conducted in cattle fed grain-based diets rather than those grazing forages. Furthermore, regulation of feed intake is driven largely by diet type; thus, there may be limitations of using feedlot intake information in heifer development systems. For example, intake of grain-based, high-energy feeds is controlled metabolically or chemostatically (NRC, 1996), whereas when poor-quality, roughage-based diets are fed, intestinal capacity, “gut-fill,” limits intake (Mertens, 1994). In addition, Durunna et al. (2011, 2012) discovered that feed efficiency reranking occurs in cattle fed different diet types at different biological stages. Therefore, the regulation of feed intake of these different diet types may influence their efficiency of feed utilization, and some calves may be more efficient on different diet types.

Finding new, cost-effective ways to accurately measure and utilize intake and efficiency information is critical for the improvement of beef production efficiency. We hypothesize that intake evaluations can be shortened with minimal effects on accuracy, feed efficiency can be measured at different stages of maturity, and accurate feed efficiency measures can be obtained using decoupled performance and intake data. However, because intake of forage and grain are regulated by different mechanisms, we hypothesize that measures of intake and feed efficiency will not be repeatable across diet type. This experiment has three objectives: 1) determine appropriate test length, timing, and repeatability of DMI, ADG, and efficiency over different biological time points; 2) determine the efficacy of using decoupled performance and intake data to generate accurate feed efficiency measures; and 3) determine the relationship between forage- and grain-fed efficiency measures.


MATERIALS AND METHODS

Cattle were managed according to the guidelines recommended in the Guide for the Care and Use of Agriculture Animals in Agriculture Research and Teaching (FASS, 2010). All experimental procedures with animals were approved by the University of Illinois Institutional Animal Care and Use Committee.

Management and Diets

A 2-yr study was conducted using 628 Charolais × SimAngus heifers (yr 1: n = 132; yr 2: n = 176) and steers (yr 1: n = 145; yr 2: n = 175). All calves were born at the Dixon Springs Agricultural Center (Simpson, IL) and early weaned at 85 ± 18 d of age. Calves were backgrounded for 96 ± 13 d on mixed pastures of endophyte infected fescue (Festuca arundinacea), red clover (Trifolium pretense), and orchard grass (Dactylis glomerata), and a complete creep feed was offered free choice. Calves were then shipped 350 km to the University of Illinois Beef Cattle and Sheep Field Laboratory (Urbana, IL) via commercial trucking at 180 ± 29 d of age. All calves were vaccinated with Bovi-Shield Gold FP5 L5 HB (Pfizer). In yr 1, calves were vaccinated with One Shot Ultra 7 (Pfizer), and Pulmo-Guard MpB (Boehringer Ingelheim Pharmaceuticals Inc.). In yr 2, calves were vaccinated with Covexin 8 (Schering-Plough Animal Health Corp., Omaha, NE), and an autogenous Moxella bovis (Schering-Plough Animal Health Corp.). Steers were implanted with a Component TE-IS with Tylan implant (120 mg trenbolone acetate, 24 mg estradiol, 29 mg tylosin; Elanco) and heifers were implanted with a Component TE-IH with Tylan implant (80 mg trenbolone acetate, 8 mg estradiol, 29 mg tylosin; Elanco) 24 wk after weaning (age = 253 ± 18 d). Steers and heifers were re-implanted during the finishing period; approximately 11 wk after the first implant. Steers received a Component TE-S with Tylan implant (80 mg trenbolone acetate, 16 mg estradiol USP, 29 mg tylosin; Elanco) and heifers received a Component TE-H implant (140 mg trenbolone acetate, 14 mg estradiol USP, 29 mg tylosin; Elanco).

Two separate postweaning intake and performance evaluations were conducted on Charolais X SimAngus calves (n = 628; initial BW = 238 ± 46 kg, age = 211 ± 32 d). The 2 performance and intake tests represent the 2 major biological periods in the feedlot: growing and finishing. Upon arrival at the feedlot and prior to the growing period, steers were transitioned over 3 wk to a grain-based growing diet, and heifers were fed a forage-base diet (Table 1). After completion of the 70 d growing period, heifers were transitioned over 3 wk from the forage-based diet to the grain-based diet. All cattle were fed the common, grain-based diet (Table 2) for the 70 d finishing period.


View Full Table | Close Full ViewTable 1.

Composition of growing diets, %DM

 
Year 1
Year 2
Item Forage Grain Forage Grain
High-moisture corn 20 30
Dry rolled corn 30 20
Distillers grains with solubles 15 15
Corn husklage 25
Corn silage 47.5 47.5 25
Alfalfa haylage 47.5 47.5
Low calcium supplement1 5 5
Medium calcium supplement2 10
High calcium supplement3 10
Analyzed values
NDF, % 44.6 25.0 48.7 24.6
ADF, % 28.4 8.6 33.4 10.9
Fat, % 3.0 4.6 3.5 3.6
CP, % 15.0 16.3 13.2 13.5
1Contains 85.94% ground corn, 10% limestone, 2% dairy trace mineral salt (Trace mineral salt contains: 8.5% Ca [as CaCO3], 5% Mg [as MgO and MgSO4], 7.6% K [as KCl2], 6.7% Cl [as KCl2], 10% S [as S8, prilled], 0.5% Cu [as CuSO4 and Availa-4; Zinpro Performance Minerals; Zinpro Corp, Eden Prairie, MN]), 2% Fe [as FeSO4], 3% Mn [as MnSO4 and Availa-4], 3% Zn [as ZnSO4 and Availa-4], 278 mg/kg Co [as Availa-4], 250 mg/kg I [as Ca(IO3)2], 150 Se [Na2SeO3], 2,205 KIU/kg VitA [as retinyl acetate], 662.5 KIU/kg VitD [as cholecalciferol], 22,047.5 IU/kg VitE [as DL-α-tocopheryl acetate], and less than 1% CP, fat, crude fiber, salt), 0.34% Rumensin (198 mg monensin/kg DM; Elanco Animal Health, Greenfield, IN), 0.22% Tylan (88 mg tylosin/kg DM; Elanco Animal Health), and 1.5% fat.
2Contains 73.87% ground corn, 6.6% urea, 17.5% limestone, 1% dairy trace mineral salt, 0.17% Rumensin (Elanco), 0.11% Tylosin (Elanco), and 0.75% fat.
3Contains 57.97% ground corn, 25% limestone, 15% urea, 1% dairy trace mineral salt, 0.17% Rumensin (Elanco), 0.11% Tylosin (Elanco), and 0.75% fat.

View Full Table | Close Full ViewTable 2.

Composition of finishing diets, %DM

 
Item Year 1 Year 2
High-moisture corn 20 30
Dry rolled corn 30 20
Distillers grains with solubles 15 15
Corn husklage 25
Corn silage 25
Medium calcium supplement1 10
High calcium supplement2 10
Analyzed values
NDF, % 23.2 22.8
ADF, % 8.5 9.2
Fat, % 4.1 3.1
CP, % 17.0 13.0
1Contains 73.87% ground corn, 6.6% urea, 17.5% limestone, 1% dairy trace mineral salt (Trace mineral salt contains: 8.5% Ca [as CaCO3], 5% Mg [as MgO and MgSO4], 7.6% K [as KCl2], 6.7% Cl [as KCl2], 10% S [as S8, prilled], 0.5% Cu [as CuSO4 and Availa-4; Zinpro], 2% Fe [as FeSO4], 3% Mn [as MnSO4 and Availa-4], 3% Zn [as ZnSO4 and Availa-4], 278 mg/kg Co [as Availa-4], 250 mg/kg I [as Ca(IO3)2], 150 Se [Na2SeO3], 2205 KIU/kg VitA [as retinyl acetate], 662.5 KIU/kg VitD [as cholecalciferol], 22,047.5 IU/kg VitE [as DL-α-tocopheryl acetate], and less than 1% CP, fat, crude fiber, salt), 0.17% Rumensin (Elanco Animal Health, Greenfield, IN), 0.11% Tylosin (Elanco), and 0.75% fat.
2Contains 57.97% ground corn, 25% limestone, 15% urea, 1% dairy trace mineral salt, 0.17% Rumensin (Elanco), 0.11% Tylosin (Elanco), and 0.75% fat.

Feed Sampling and Analysis

Individual feed ingredients were sampled every 2 wk from the initiation of the growing period until the end of the finishing period. Feed ingredient samples were dried at 55°C for 3 d, ground using a Wiley mill (1-mm screen; Arthur H. Thomas, Philadelphia, PA), and composited at the end of both evaluation periods. Ingredients were analyzed for NDF and ADF (using Ankom Technology method 5 and 6, respectively; Ankom200 Fiber Analyzer, Ankom Technology), CP (Leco TruMac, LECO Corporation, St. Joseph, MI), fat (ether extract, Ankom method 2; Ankom Technology), and ash (600°C for 2 h; Thermolyte muffle oven Model F30420C; Thermo Scientific, Waltham, MA). Feed ingredient analyses were used to construct diet nutrient analyses.

Growing/Finishing Intake and Performance Data Collection

Upon arrival, cattle were stratified by sire (n = 30) and allotted to pens equipped with a GrowSafe automated feeding system (Model 4000E; GrowSafe Systems Ltd., Alberta, Canada) so individual intakes could be recorded. Individual feed intakes were audited daily by trained personnel. Daily individual feed intake data were considered acceptable if both 85% of the feed supplied to the bunk and 90% of the corresponding feed disappearance assigned to each individual electronic ID was accounted for. Data were discarded for the affected pens not meeting these criteria. For each performance and intake test (growing and finishing) a minimum of 70 d were required each year to calculate individual animal ADG and DMI. This complies with Beef Improvement Federation (BIF) recommendations for performance data and intake collection (BIF, 2010). At the conclusion of the 70 d finishing period test, individual feed intakes were no longer recorded using the GrowSafe system, as cattle were bunk fed for 60 ± 30 d until slaughter.

Performance data collection remained the same for both years during both the growing and finishing performance tests. Initial and final BW for each test was the average of 2 consecutive d BW measurements prior to morning feeding but feed was not withheld. All cattle were weighed every 2 wk. Individual animal ADG was calculated by regressing each individual weight of all time points during both the growing and finishing evaluation period. Individual midtest metabolic BW (MW) was determined by the linear regression coefficients for each animal for the growing and finishing evaluation period.

At the conclusion of each test period, 12th rib fat thickness was measured via ultrasound to account for the variation in residual feed intake and residual BW gain measures due to body composition. Ultrasound measurements were taken by trained personnel using an Aloka 500SV (Wallingford, CT) B-110 mode instrument equipped with a 3.5-Mhz general purpose transducer array. Twelfth rib fat thickness measurements were taken in transverse orientation between the 12th and 13th ribs approximately 10 cm distal from the midline. Images were analyzed using CPEC imaging software (Cattle Performance Enhancement Company LLC., Oakley, KS).

Total Intake Period Performance and Intake Data Collection

Individual feed intakes were recorded during the growing, transition, and finishing periods of this experiment for steers fed grain throughout the study; therefore, the combination of recorded individual DMI during these periods was identified as the 161-d total intake period DMI (161DMI). Initial and final BW represented the average of 2 consecutive d BW measurements during the growing and finishing periods, respectively. Individual animal ADG was calculated by regressing all weights taken over the course of the growing, transition, and finishing periods and was identified as 161ADG. One hundred sixty-one d total intake period midtest metabolic BW (161MMW) was calculated using the ADG regression coefficients.

Total Feeding Period Performance Data Collection

For steers fed the grain-based diet during both test periods, performance was evaluated for the duration of time on feed from feedlot arrival to slaughter. This method was used to determine total feeding period BW gain. Initial BW represented the BW of calves at arrival at the feedlot (age = 180 ± 29 d). Individual final BW was calculated by dividing HCW by a standard dressing percentage of 63%. Two total feeding period performance measures were calculated to test the relationship between traditional and regressed measurements of performance during an animal’s time on feed. Total feeding period ADG (FPADG) was calculated by the difference between initial and final BW, divided by the number of days between feedlot arrival and harvest. Regressed individual feeding period ADG (R_FPADG) was determined via regression of all weights taken from feedlot arrival to adjusted final BW.

Test Duration for DMI

To test the effects of intake evaluation period timing and duration, individual animal DMI during the growing and finishing periods was divided into 10 sections in each period. Sections of intake during the growing period included: the final 7 d of intake (70_63DMI), the final 14 d of intake (70_56DMI), the final 21 d of intake (70_49DMI), the final 28 d of intake (70_42DMI), the final 35 d of intake (70_35DMI), the final 42 d of intake (70_28DMI), the final 49 d of intake (70_21DMI), the final 56 d of intake (70_14DMI), the final 63 d of intake (70_7DMI), and the final 70 d of intake (70_0 DMI).

Individual animal DMI was also divided into 10 sections during the finishing period. Sections of intake during the finishing period were the initial 7 d of intake (0_7DMI), the initial 14 d of intake (0_14DMI), the initial 21 d of intake (0_21DMI), the initial 28 d of intake (0_28DMI), the initial 35 d of intake (0_35DMI), the initial 42 d of intake (0_42DMI), the initial 49 d of intake (0_49DMI), the initial 56 d of intake (0_56DMI), the initial 63 d of intake (0_63DMI), and the initial 70 d of intake (0_70DMI).

Calculation of Feed Efficiency

Feed efficiency traits were determined for all cattle during the growing and finishing periods. Feed conversion ratio (FCR) represented the ratio of individual animal feed:gain and was calculated by dividing individual average daily DMI by regressed ADG. Contemporary groups were assigned for each individual animal according to year born and sex. Individual animal residual feed intake (RFI) and residual BW gain (RG) were calculated for both growing and finishing periods. Residual feed intake was calculated using the PROC MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) and was assumed to represent the residuals of a multiple regression model regressing DMI on MW, ADG, and 12th rib fat thickness using pen as a random effect. Likewise, RG was calculated using the PROC MIXED procedure of SAS and was assumed to represent the residuals of a multiple regression model regressing ADG on DMI, MMW, and BF using pen as a random effect.

One hundred sixty-one d measures of feed efficiency were calculated for all steers fed grain during both periods. Feed conversion ratio for the 161-d total intake period (161FCR) represented the ratio of individual animal feed:gain and was calculated by dividing individual average 161DMI by 161ADG. Residual feed intake for the 161-d total intake period (161RFI) values were determined using the PROC MIXED procedure of SAS; and was assumed to represent the residuals of a multiple regression equation regressing 161DMI on 161ADG, 161MMW, and BF from the finishing period, using pen as a fixed effect. Similarly, 161-d total intake period residual BW gain (161RG) were calculated using the PROC MIXED procedure of SAS; and was assumed to represent the residuals of a multiple regression equation regressing 161ADG on 161DMI, 161MMW, and BF from the finishing period, using pen as a random effect.

RFI Calculation Using Decoupled Intake and Performance

Retallick and Weaber (2015) claimed that accurate measures of RFI can be used when shortened test period DMI is regressed on midtest metabolic BW and ADG from weaning and yearling performance records. To test the concept of a decoupled RFI in this experiment, 35 d of recorded intake were evaluated along with FPADG as the measurement of individual animal BW gain, and midtest BW was calculated by the average of calves’ initial and final BW, raised to the 0.75 power. The 35 d of recorded intake evaluated in this measure of feed efficiency represented the first and final 35 d of each feeding period. Residual feed intake represented the residuals of a multiple regression equation regressing 35 d of recorded DMI on FPADG, feeding period midtest metabolic weight, and carcass BF using pen as a random effect.

Statistical Analysis

The descriptive statistics for all variables were calculated using the PROC UNIVARIATE procedure in SAS. Individual animal served as the experimental unit. Simple correlations were calculated for ADG, DMI, and efficiency for the growing, finishing, 160-d total intake period, and total feeding periods using the PROC CORR procedure of SAS. Pearson correlations were used to test the number of days required for accurate DMI estimates using the PROC CORR procedure of SAS. All rho values were considered significant when P ≤ 0.05. Correlations were considered strong when rho values were greater than or equal to 0.70; moderate when rho values were between 0.30 and 0.69; and weak when less than 0.29.


RESULTS

Descriptive statistics of postweaning performance and efficiency in steer calves during the growing and finishing periods are presented in Table 3. A moderate, positive relationship (r = 0.56; P < 0.05) existed between grain DMI during the growing and finishing period (Table 4). During the growing period, steer ADG was correlated (P < 0.05) to RG and FCR at 0.71 and -0.31, respectively. However, growing period ADG was not correlated to ADG during the finishing period (r = 0.11; P = 0.06). Relationships existed between measures of feed efficiency during the growing period. Steers with more desirable RFI values also had more desirable RG (r = -0.42; P < 0.05) and FCR (r = 0.59; P < 0.05) values during the growing period. There was a strong correlation between RG and FCR during the growing period (r = -0.76; P < 0.05). Relationships between feed efficiency measures during the growing and finishing periods existed. Growing period RFI was moderately correlated (r = 0.63; P < 0.05) to finishing period RFI. Although RG during the growing period was correlated (r = 0.24; P < 0.05) to RG in the finishing period, the relationship was much weaker compared to RFI. Calculated FCR during the growing and finishing periods were also moderately correlated (r = 0.41; P < 0.05). Similar to the growing period, a positive relationship existed (P < 0.05) during the finishing period between DMI and ADG and RFI at 0.49 and 0.66, respectively. Even though a positive relationship existed (r = 0.22; P < 0.05) between finishing period DMI and FCR; the relationship between these 2 variables was weaker in the finishing period than it was in the growing period. A strong, positive correlation was observed between finishing period ADG and finishing period RG (r = 0.77; P < 0.05). A strong correlation existed between finishing period ADG and FCR (r = -0.72; P < 0.05). Similar to the growing period, relationships existed between measures of feed efficiency during the finishing period. A moderate relationship existed between finishing period RFI and RG (r = -0.51; P < 0.05) and FCR (r = 0.49; P < 0.05). Likewise, finishing period RG was also strongly correlated (r = -0.84; P < 0.05) to FCR.


View Full Table | Close Full ViewTable 3.

Raw mean postweaning performance, efficiency, and SD of all steers fed grain during the growing and finishing periods

 
Item Mean SD Minimum Maximum
Year 1
n = 145
Growing ADG, kg 1.68 0.27 0.58 2.23
Growing DMI, kg 7.04 1.09 3.80 9.55
Growing residual feed intake, kg 0.00 0.51 -1.53 1.48
Growing residual BW gain, kg 0.00 0.18 -0.70 0.49
Growing feed conversion ratio, kg1 4.21 0.61 2.66 7.67
Growing G:F 0.24 0.03 0.13 0.38
Finishing ADG, kg 1.78 0.25 0.81 2.31
Finishing DMI, kg 9.74 1.01 7.13 13.05
Finishing residual feed intake, kg 0.00 0.65 -1.96 2.66
Finishing residual BW gain, kg 0.00 0.19 -0.53 0.49
Finishing feed conversion ratio1 5.58 0.89 3.81 9.77
Finishing G:F 0.18 0.03 0.10 0.26
Year 2
n = 175
Growing ADG, kg 1.84 0.21 1.12 2.43
Growing DMI, kg 8.03 1.06 2.87 10.46
Growing residual feed intake, kg 0.00 0.61 -1.72 1.45
Growing residual BW gain, kg 0.00 0.15 -0.38 0.39
Growing feed conversion ratio, kg1 4.40 0.54 2.57 5.71
Growing G:F 0.23 0.03 0.18 0.39
Finishing ADG, kg 1.79 0.24 0.98 2.39
Finishing DMI, kg 9.90 1.03 6.08 12.31
Finishing residual feed intake, kg 0.00 0.67 -2.08 1.45
Finishing residual BW gain, kg 0.00 0.18 -0.66 0.50
Finishing feed conversion rato1 5.61 0.71 3.96 8.88
Finishing G:F 0.18 0.02 0.11 0.25
1Expressed as feed:gain

View Full Table | Close Full ViewTable 4.

Simple phenotypic correlations between postweaning traits for steers fed grain1

 
Item Growing DMI Growing ADG Growing RFI2 Growing
RG3
Growing FCR4 Finishing
DMI
Finishing
ADG
Finishing
RFI2
Finishing
RG3
Finishing
FCR4
Growing DMI 1 0.64 0.49 0.00 0.51 0.56 -0.02 0.27 -0.30 0.44
Growing ADG 1 0.00 0.71 -0.31 0.29 0.11 -0.04 -0.04 0.11
Growing RFI2 1 -0.42 0.59 0.38 -0.06 0.63 -0.39 0.34
Growing RG3 1 -0.76 -0.04 0.19 -0.28 0.24 -0.22
Growing FCR4 1 0.38 -0.13 0.37 -0.30 0.41
Finishing DMI 1 0.49 0.66 0.00 0.22
Finishing ADG 1 0.00 0.77 -0.72
Finishing RFI2 1 -0.51 0.49
Finishing RG3 1 -0.84
Finishing FCR4 1
1|R| values in bold are significant (P < 0.05).
2Residual feed intake.
3Residual BW gain.
4Feed conversion ratio expressed as feed:gain.

There were moderate, positive relationships among ADG across the measured time points (Table 5). Growing ADG was correlated (P < 0.05) to 161ADG, R_FPADG, and FPADG at 0.57, 0.58, and 0.58, respectively. Stronger linear relationships existed (P < 0.05) among finishing period ADG and 161ADG, R_FPADG, and FPADG at 0.76, 0.69, and 0.58, respectively. Regressed ADG during the 161 d intake period was correlated to R_FPADG (r = 0.96; P < 0.05) and FPADG (r = 0.81; P < 0.05). Regressed, total feeding period ADG was strongly correlated (P < 0.05) to FPADG at 0.85.


View Full Table | Close Full ViewTable 5.

Simple phenotypic correlations between measurements of ADG during different feeding periods and biological timepoints1

 
Item Growing Finishing 161ADG2 R_FPADG3 FPADG4
Growing 1 0.11 0.57 0.58 0.58
Finishing 1 0.76 0.69 0.58
161ADG2 1 0.96 0.81
R_FPADG3 1 0.85
FPADG4 1
1|R| values in bold are significant (P < 0.05).
2161 d intake period.
3Total feeding period (regressed ADG).
4Total feeding period

The linear relationships between feed efficiency measured in steers during different evaluation periods are presented in Table 6. Strong linear correlations exist (P < 0.05) among growing period RFI and 161RFI at 0.89. Growing period RG was moderately correlated (P < 0.05) to 161RG at 0.59. Likewise, growing period FCR was strongly correlated to 161FCR (r = 0.77; P < 0.05). Similar results were observed when comparing the relationship between measures of feed efficiency during the finishing period and 161d intake period. Finishing RFI values were strongly correlated (P < 0.05) to 161RFI at 0.86. A strong linear relationship existed between growing period RG and 161RG (r = 0.72 0.61; P < 0.05). Finishing period FCR was strongly correlated to 161FCR (r = 0.75; P < 0.05).


View Full Table | Close Full ViewTable 6.

Simple phenotypic correlations between measures of feed efficiency for grain-fed steers in the growing period, finishing period, intake evaluation period, and total feeding period1

 
Item Growing RFI2 Growing RG3 Growing FCR4 Finishing RFI2 Finishing RG3 Finishing FCR4
161RFI5 0.89 -0.31 0.48 0.86 -0.47 0.41
161RG6 -0.34 0.59 -0.53 -0.20 0.72 -0.58
161FCR7 0.61 -0.46 0.77 0.51 -0.64 0.75
1|R| values in bold are significant (P < 0.05).
2Residual feed intake.
3Residual BW gain.
4Feed conversion ratio expressed as feed:gain.
5161 d intake period residual feed intake.
6161 d intake period residual BW gain.
7161 d intake period feed conversion ratio expressed as feed:gain.

Relationships between different durations of mean DMI observations in grain-fed steers from the end of the growing period are presented in Table 7. Rho values between the number of recorded d of DMI and total growing period DMI increased linearly when a greater number of days were incorporated into the intake evaluation. Specifically, total growing period mean DMI was strongly correlated (P < 0.05) at 0.95 when 35 d of intake were recorded. However, the final 14 d of recorded intake during the growing period was moderately correlated to total DMI during the finishing period (r = 0.62; P < 0.05). Rho values between the number of recorded d of DMI in the growing period and total finishing period DMI decreased linearly as daily increments of recorded DMI from the final 14 d of the growing period increased. The final 7 d of recorded intake during the growing period was strongly correlated to 161DMI (r = 0.86; P < 0.05). Increasing daily increments of recorded DMI from the ending of the growing period resulted in a linear increase in the relationship between growing period DMI and 161DMI. Similar results were noticed when comparing mean DMI observations from the beginning of the finishing period (Table 8). Rho values between the number of recorded d of DMI and total finishing period DMI increased linearly when a greater number of days were incorporated into the intake evaluation; and total finishing period DMI was also strongly correlated (P < 0.05) at 0.93 when 35 d of intake were recorded. The initial 14 d of recorded DMI were moderately correlated (r = 0.60; P < 0.05) to growing period DMI. Rho values between the number of recorded d of DMI in the finishing period and total growing period DMI decreased quadratically as daily increments of recorded DMI from the initial 14 d of the finishing period increased.


View Full Table | Close Full ViewTable 7.

Simple phenotypic correlations during different durations of mean DMI observations from the end of the 70d growing period in grain fed steers1

 
Item 70–63DMI 70–56DMI 70–49DMI 70–42DMI 70–35DMI 70–28DMI 70–21DMI 70–14DMI 70–7DMI 70–0DMI FDMI2 161DMI3
70–63DMI 1 0.97 0.95 0.94 0.93 0.92 0.91 0.90 0.89 0.88 0.58 0.86
70–56DMI 1 0.99 0.97 0.95 0.91 0.91 0.89 0.88 0.87 0.62 0.87
70–49DMI 1 0.99 0.97 0.93 0.93 0.91 0.91 0.89 0.62 0.88
70–42DMI 1 0.98 0.96 0.95 0.94 0.93 0.92 0.61 0.89
70–35DMI 1 0.99 0.98 0.97 0.96 0.95 0.61 0.90
70–28DMI 1 0.99 0.98 0.97 0.97 0.58 0.89
70–21DMI 1 0.99 0.99 0.98 0.56 0.89
70–14DMI 1 1 0.99 0.56 0.90
70–7DMI 1 1 0.56 0.90
70–0DMI 1 0.56 0.90
FDMI2 1 0.85
161DMI3 1
1|R| values in bold are significant (P < 0.05).
2Finishing period DMI (d91–161DMI).
3161 d intake period total DMI (d0–161DMI).

View Full Table | Close Full ViewTable 8.

Simple linear phenotypic correlations during different durations of mean DMI observations from the beginning of the 70 d finishing phase in grain fed steers1

 
Item 0–7DMI 0–14DMI 0–21DMI 0–28DMI 0–35DMI 0–42DMI 0–49DMI 0–56DMI 0–63DMI 0–70DMI GDMI2 161DMI3
0–7DMI 1 0.96 0.92 0.89 0.88 0.87 0.85 0.84 0.82 0.80 0.62 0.81
0–14DMI 1 0.94 0.91 0.89 0.89 0.87 0.85 0.83 0.81 0.60 0.79
0–21DMI 1 0.98 0.97 0.95 0.93 0.92 0.90 0.88 0.56 0.80
0–28DMI 1 0.99 0.97 0.95 0.95 0.93 0.91 0.53 0.79
0–35DMI 1 0.98 0.97 0.96 0.95 0.93 0.52 0.80
0–42DMI 1 0.99 0.98 0.97 0.96 0.57 0.84
0–49DMI 1 1 0.99 0.98 0.57 0.85
0–56DMI 1 1 0.99 0.56 0.85
0–63DMI 1 1 0.56 0.85
0–70DMI 1 0.56 0.85
GDMI2 1 0.9
161DMI3 1
1|R| values in bold are significant (P < 0.05).
2Growing period DMI.
3161 d intake period total DMI.

The correlations between decoupled measures of RFI and 70 d test period (growing and finishing) RFI are presented in Table 9. A moderate correlation existed between growing RFI values and RFI values using decoupled DMI and ADG measurements (0.46 ≤ r ≤ 0.71; P < 0.05). A positive, yet weak correlation existed (P < 0.05) between finishing period RFI and RFI when the first 35 d of DMI during the growing period were used to predict total feeding period DMI at 0.28. However, correlations were moderate to strong (0.62 ≤ r ≤ 0.85; P < 0.05) when comparing finishing period RFI to total feeding period RFI when all other 35 d sections of DMI were used to predict total feeding period DMI.


View Full Table | Close Full ViewTable 9.

Simple phenotypic correlations between measures of feed efficiency for grain fed steers during the growing, finishing, and total feeding period using decoupled DMI and ADG variables in the predicted DMI model in the total feeding period1

 
Item Growing RFI2 Finishing RFI2
0–35RFI3 0.70 0.28
36–70RFI4 0.54 0.62
90–125RFI5 0.56 0.85
126–161RFI6 0.46 0.79
1|R| values in bold are significant (P < 0.05).
2Residual feed intake.
3Total feeding period residual feed intake when predicted total feeding period DMI is a linear function of the first 35 d of recorded DMI during the growing period, FPADG and mid-test metabolic BW, and carcass BF.
4Total feeding period residual feed intake when predicted total feeding period DMI is a linear function of the final 35 d of recorded DMI during the growing period, FPADG and mid-test metabolic BW, and carcass BF.
5Total feeding period residual feed intake when predicted total feeding period DMI is a linear function of the first 35 d of recorded DMI during the finishing period, FPADG and mid-test metabolic BW, and carcass BF.
6Total feeding period residual feed intake when predicted total feeding period DMI is a linear function of the final 35 d of recorded DMI during the finishing period, FPADG and mid-test metabolic BW, and carcass BF.

The descriptive statistics of postweaning performance and efficiency in heifer calves on different diet types are presented in Table 10. When heifers were fed forage during the growing period, ADG, RFI, and FCR were correlated to forage DMI (P < 0.05) at 0.25, 0.69, and 0.24, respectively (Table 11). Likewise, heifer ADG during the growing period was correlated (P < 0.05) to RG and FCR at 0.53 and -0.72, respectively. A moderate, linear relationship suggests that as forage RFI improved, forage RG (r = -0.29; P < 0.05) and forage FCR (r = 0.39; P < 0.05) improved. Improvements in forage RG resulted in reduced forage FCR during the growing period (r = -0.53; P < 0.05). A positive correlation (r = 0.58; P < 0.05) between heifer forage DMI and grain DMI suggests heifers with greater forage DMI also had greater grain DMI. Subsequently, forage and grain RFI values were moderately correlated (r = 0.40; P < 0.05). A negative, linear correlation of -0.30 (P < 0.05) existed between ADG on forage and ADG on grain. There was a negative correlation (r = -0.16; P < 0.05) between forage and grain FCR. No significant correlation (P = 0.08) existed between forage RG and grain RG.


View Full Table | Close Full ViewTable 10.

Raw mean postweaning performance, efficiency, and SD of all heifers on study during the growing and finishing periods

 
Item Mean SD Min Max
Year 1
n = 132
Forage ADG, kg 0.97 0.20 0.41 1.74
Forage DMI, kg 5.81 0.89 3.33 7.96
Forage residual feed intake, kg 0.00 0.41 -1.07 1.41
Forage residual BW gain, kg 0.00 0.13 -0.33 0.38
Forage feed conversion ratio1 6.11 1.04 4.52 10.01
Forage G:F 0.17 0.02 0.10 0.22
Grain ADG, kg 1.70 0.24 1.16 2.52
Grain DMI, kg 9.20 0.95 6.26 12.20
Grain residual feed intake, kg 0.00 0.62 -1.66 1.70
Grain residual BW gain, kg 0.00 0.20 -0.61 0.48
Grain feed conversion ratio1 5.53 0.95 3.85 9.07
Grain G:F 0.19 0.03 0.11 0.26
Year 2
n = 176
Forage ADG, kg 0.64 0.16 0.17 1.04
Forage DMI, kg 6.30 1.25 3.65 14.73
Forage residual feed intake, kg 0.00 0.96 -2.18 6.89
Forage residual BW gain, kg 0.00 0.12 -0.36 0.24
Forage feed conversion ratio1 10.44 3.72 6.50 40.30
Forage G:F 0.10 0.02 0.02 0.15
Grain ADG, kg 1.84 0.25 0.93 2.58
Grain DMI, kg 9.44 1.12 5.95 12.55
Grain residual feed intake, kg 0.00 0.72 -3.13 2.26
Grain residual BW gain, kg 0.00 0.21 -0.57 0.70
Grain feed conversion ratio1 5.20 0.71 3.46 7.33
Grain G:F 0.20 0.03 0.14 0.29
1Expressed as feed:gain.

View Full Table | Close Full ViewTable 11.

Simple linear phenotypic correlations between postweaning traits in heifers fed different diets1

 
Item Forage DMI Forage ADG Forage RFI2 Forage RG3 Forage FCR4 Grain DMI Grain ADG Grain RFI2 Grain RG3 Grain FCR4
Forage DMI 1 0.25 0.69 0.00 0.24 0.58 -0.01 0.24 -0.26 0.43
Forage ADG 1 0.00 0.53 -0.72 0.16 -0.30 -0.03 -0.17 0.42
Forage RFI2 1 -0.29 0.39 0.25 0.00 0.40 -0.17 0.17
Forage RG3 1 -0.53 -0.08 -0.11 -0.15 -0.10 0.05
Forage FCR4 1 0.14 0.27 0.17 0.06 -0.16
Grain DMI 1 0.36 0.65 0.00 0.38
Grain ADG 1 0.00 0.82 -0.70
Grain RFI2 1 -0.36 0.46
Grain RG3 1 -0.79
Grain FCR4 1
1|R| values in bold are significant (P < 0.05).
2Residual feed intake.
3Residual BW gain.
4Feed conversion ratio expressed as feed:gain.

DISCUSSION

The majority of performance and intake records have been obtained in growing animals when fed high-grain, energy-dense diets. However, regulation of feed intake may be influenced by diet type and stage of physiological maturity in cattle (Illius and Jessop, 1996), and feed efficiency can be influenced by diet type (Durunna et al., 2011). Therefore, this study was designed to investigate the effects of test period duration and timing, as well as diet type on measures of feed efficiency. The results of this study confirm that growing and finishing steers that eat more will gain more, which is well documented (Schwartzkopf-Genswein et al., 2002; Kelly et al., 2010; Durunna et al., 2011;). The moderate, negative correlations between steer ADG and FCR during the growing and finishing period agree with previous literature (Nkrumah et al., 2007) and suggest that accelerated growth rates play a vital role in determining feed efficiency in young, growing animals. This association is not surprising, since FCR is a function of ADG and DMI. However, increases in grain DMI resulted in less desirable RFI and FCR, which is consistent with Nkumrah et al. (2007). It was not surprising that a linear association did not exist between RFI and ADG during either feeding period because RFI is independent of growth traits (Koch et al., 1963; Arthur and Herd, 2008; Black et al., 2013). Associations of feed efficiency in growing animals are well documented (Arthur et al., 2001a,b) A strong linear relationship existed between RG and FCR during both feeding periods. This was expected, as evidence of the moderate to strong linear relationship of ADG to RG and FCR during the growing and finishing periods, respectively.

The moderate association between DMI in the growing and finishing periods suggests that intake evaluations can be repeatable across varying growth stages. In this study, cattle that consumed more feed earlier in life also had greater DMI at a later stage of maturity. The moderate association of DMI during the growing and finishing periods of this experiment reflects the results of Kelly et al. (2010), who reported a correlation of 0.61 between DMI when heifers were fed a 70:30 pelleted concentrate:corn silage diet during consecutive feeding periods. However, ADG was not repeatable in steers between the growing and finishing periods in our trial. Although this was a surprise, because DMI was repeatable and related to ADG in both periods, this phenomenon was also observed by Kelly et al. (2010); who also reported the same correlation of 0.11 and suggested that cattle ADG may re-rank compared to their contemporaries. The fact that ADG was not repeatable may be attributed to the possibility of compensatory gain during the growing period of some cattle. A moderate, positive association between RFI values calculated in the growing and finishing periods, suggested that RFI is repeatable when evaluated at different biological time points. Considering the fact that DMI explains a majority of the variation in RFI, the repeatability of RFI was not surprising, because DMI was moderately related in both test periods. This positive association mirrors the findings of Kelly et al. (2010) and suggests that more efficient cattle, based on RFI during the growing period, will also be more efficient in the finishing period. There has been limited work evaluating the repeatability of RG across the growing and finishing periods. This study observed a weak, positive correlation between growing RG and finishing RG. This weak association may be attributed to the fact that ADG was not repeatable across the 2 evaluation periods. The moderate linear relationship between FCR between growing and finishing periods suggest that FCR is repeatable, and cattle that have more desirable FCR during the growing period will also be more efficient in the finishing period based on FCR. This relationship was also observed by Kelly et al. (2010).

The fact that ADG was not repeatable was not expected. However, there were moderate associations between growing and finishing ADG when compared to R_FPADG and FPADG. This suggests that regardless of timing of the evaluation of postweaning gain, both periods can serve as similar proxies in determining the performance of a growing animal during its entire time spent on feed. The stronger correlation between 161ADG and R_FPADG and FPADG suggests that longer periods of performance evaluation may result in more accurate determinations of ADG over an animal’s entire lifespan. The strong, positive correlation between R_FPADG and FPADG suggests that cattle performance may be accurately predicted by dividing the difference of an animal’s final BW and feedlot arrival weight by the number of days on feed. This is important, because FPADG is a measure of performance that is widely accepted within the industry. When FPADG is calculated by dividing the difference between adjusted HCW and feedlot arrival BW by the number of d on feed, FPADG can be an effective proxy for individual ADG over the lifespan of calves, which is supported by Retallick (2015).

Guidelines have been established for uniform performance testing practices (BIF, 2010). Historically, the minimum days required was due to the number of days on test needed to accurately measure ADG. In fact, an early study claimed that 112 d were needed to accurately measure ADG (Brown et al., 1991). In later years, Archer et al. (1997) found that the accuracy of recorded DMI and ADG may not be improved with evaluation periods that were longer than 70 d. In this study, the strong, positive relationship between 161RFI and RFI during both 70 d test periods suggests that factors other than ADG contributed to the variation in RFI, because ADG was not repeatable across test periods.

Similarly, the moderate to strong correlations between 161RG and RG in both 70 d suggests that both evaluation periods are accurate measures of RG. This data set showed strong linear associations between 161FCR and FCR during both feeding periods, and since ADG was not repeatable across test periods, suggests that DMI accounts for more of the variation in FCR, and accurate FCR information can be obtained using test periods of 10 wk.

This study suggests that it is feasible to obtain accurate measures of feed efficiency for the duration of a calf’s lifespan by using the difference of feedlot arrival BW and adjusted HCW divided by number of d on test, combined with a 35 d test of DMI. Therefore, the capacity of cattle to be tested annually depends on the number of days needed to obtain accurate individual DMI information, and shorter test periods equate to more cattle being tested annually. During the growing period, one wk of recorded DMI was strongly correlated to test period DMI at 0.88. As the number of recorded d of DMI increased, the association between number of d of recorded DMI and overall period DMI increased. Due to a strong correlation of 0.95, this experiment suggests that only 35 d of recorded intake are sufficient for predicting 70d test period DMI. However, when DMI intake is recorded for those 35 d makes a difference. Recorded DMI during the end of the growing period was a more accurate predictor of DMI during the finishing period, and recorded DMI at the beginning of the finishing period was a more accurate predictor of DMI during the growing period. This study shows that to accurately predict DMI across different time points in life, not only is it important to record a sufficient amount of d, but the proximity of the different test periods being compared is an important factor to consider as well.

Minimal work has been done investigating the idea of decoupling performance and intake information when determining the feed efficiency of a feedlot steer during its entire time on feed. Interest in this concept is due to the fact that accurate measures of DMI and ADG require substantially different durations, and performance and intake evaluation tests are costly (Archer et al., 1999). Total beef production efficiency can be improved when a greater number of animals are tested annually; therefore, more cost-effective ways to test growing animals are needed. In our trial, comparisons were made between RFI values using short-duration intake test periods (35 d) with FPADG, and RFI measures calculated by the standards set forth by the BIF. Moderate association between these measures of RFI using decoupled DMI and ADG and 70 d test period RFI suggests that there is a possibility that these alternative measurements of RFI may have efficacy to the industry.

Durunna et al. (2011) claimed that diet type affects measures of feed efficiency when cattle are fed a grower and finishing diet in their respective growing and finishing periods. The repeatability of DMI and feed efficiency in grain-fed steers in this study suggests that comparison of intake and efficiency can be conducted at differing biological time points. The fact that forage DMI and grain DMI were related in this study is encouraging. This suggests that intake information derived from the feedlot may be adequate in predicting forage intake in developing heifers. This is a novel, yet important finding, because the majority of intake information is derived through feedlot or bull development evaluations.

A negative, relationship between ADG when forage- and grain-based diets were fed to heifers, suggested that heifers that performed poorly when fed forage actually performed better on grain. This finding confirms the theory of compensatory gain when cattle fed forages are grain-fed during the finishing period. The compensatory gain affect likely masked the ability to detect association between RG values among heifers between periods. Similarly, a weak, negative correlation existed between FCR values on forage compared to FCR values compared to grain. Since the relationship of grain DMI and ADG for heifers were similar (r = 0.43 and 0.42, respectively), the compensatory gain effect influenced the negative correlation of -0.16. This relationship is weak, and may not be biologically relevant when trying to compare FCR between cattle on different diet types.

Regulation of feed intake may differ when cattle are fed differing diet types, and DMI is related to energy content of the feed delivered (NRC, 1996) or physical fill. Since DMI plays a vital role in feed efficiency, mechanisms of intake regulation for divergent diet types may confound the accuracy of comparing RFI of cattle when fed grain or forage. Minimal research has been conducted comparing RFI values when cattle are fed differing diet types. The correlation between forage and grain DMI was 0.58. This linear relationship of DMI closely parallels the relationship of DMI during the growing and finishing period of grain-fed steers (0.56), and in this study, suggests mechanisms of intake regulation on these diet types may not differ. The moderate, positive correlation between RFI values derived from forage- and grain-based diets suggested that young, growing cattle that were more efficient when fed high-quality forage were also more efficient when fed grain. This is an important discovery, as most feed intake and subsequent efficiency tests are done in feedlot-like test stations. However, further investigations need to be considered when evaluating the effects of diet type on intake and efficiency, especially when extremely low-quality forages are fed.

In conclusion, DMI is repeatable within different test periods. This suggests that accurate intake information can be obtained during either the growing or finishing periods. Additionally, the positive relationship between DMI of different diet types suggests that intake information on grain-based diets can predict high-quality forage intake. Cattle can be accurately tested for efficiency by shortening postweaning DMI evaluation tests and using simpler calculations of ADG; thus, allowing for a greater number of cattle to be tested annually, leading to more rapid improvements in feed efficiency within the beef industry.

 

References

Footnotes


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