Body, carcass, and steak dimensions of straightbred Holstein calves and Angus-sired calves from Holstein, Jersey, and crossbred beef dams

Abstract

Beef genetics are used with increasing frequency on commercial dairies. Although use of beef genetics improves calf value, variability has been reported in beef × dairy calf phenotype for traits related to muscularity and carcass composition. The objective of this study was to characterize morphometric and compositional differences between beef, beef × dairy, and dairy-fed cattle. Tested treatment groups included Angus-sired straightbred beef steers and heifers (A × B; n = 45), Angus × Holstein crossbreds (A × H; n = 15), Angus × Jersey crossbreds (A × J; n = 16), and straightbred Holsteins (H, n = 16). Cattle were started on trial at mean BW of 302 ± 29.9 kg and then fed at 196 ± 3.4 d. Morphometric measures were recorded every 28 d during the finishing period, ultrasound measures were recorded every 56 d, and morphometric carcass measures were recorded upon slaughter. Muscle biopsies were collected from the longissimus thoracis of a subset of steers (n = 43) every 56 d. Strip loins were collected from carcasses (n = 78) for further evaluation. Frame size measured as hip height, hip width, and body length was greatest for H cattle (P < 0.05), and A × H cattle had greater hip height than A × J cattle (P < 0.05). Relative to BW as a percentage of mature size, ribeye area of all cattle increased at a decreasing rate (negative quadratic term: P < 0.01), and all ultrasound measures of fat depots increased at an increasing rate (positive quadratic term: P < 0.01). Although no difference was observed in muscle fiber area across the finishing period from the longissimus thoracis (P = 0.80), H cattle had a more oxidative muscle phenotype than A × B cattle (P < 0.05). Additionally, H cattle had the smallest area of longissimus lumborum in the posterior strip loin, greatest length-to-width ratio of longissimus lumborum in the posterior strip loin, and least round circumference relative to round length (P < 0.05). Beef genetics improved muscularity in portions of the carcass distal to the longissimus thoracis.

Holstein genetics were associated with greater mature size, and variation in morphometric measurements demonstrated that differences in muscularity between beef- and dairy-influenced carcasses were more evident at distal locations than near the last rib.

Introduction

Body measurements have been used to describe cattle phenotype related to growth and body composition (Black et al., 1938; Cook et al., 1951; Kohli et al., 1951; Gilbert et al., 1993a, 1993b). Furthermore, Garcia-de-Siles et al. (1977) and Tatum et al. (1986a, 1986b, 1986c) demonstrated that morphometric measurements could differentiate mature size, muscularity, and carcass cutability. As 3D technology continues to develop, opportunity exists to automate morphometric measurements that could distinguish cattle composition and growth potential (Ruchay et al., 2020; Li et al., 2022). This could be particularly valuable for describing carcass composition because carcass composition is not always well-described by traditional measurements, including USDA Yield Grade (Lawrence et al., 2010).

Increased beef × dairy crossbreeding further emphasizes the need to describe carcass composition more precisely (Foraker et al., 2022b; Jaborek et al., 2023). Sex-sorted semen has created a need to manage heifer inventories and, consequently, an opportunity to optimize dairy pregnancies for beef production (Holden and Butler, 2018; Overton and Dhuyvetter, 2020; Machado and Ballou, 2022). In response, sales of beef semen have increased while sales of dairy semen have decreased (Halfman and Sterry, 2019; McWhorter et al., 2020; National Association of Animal Breeders, 2022; Pereira et al., 2022; Lauber et al., 2023). Although resulting beef × dairy calves are more valuable than straightbred dairy calves, beef × dairy calves are less valuable than straightbred beef calves (Cabrera, 2022; McCabe et al., 2022). Recent reviews by Berry (2021); Foraker et al. (2022b); Basiel and Felix (2022); Poock and Beckett (2022), and Jaborek et al. (2023) all mention improving muscularity as a challenge in beef × dairy production systems.

Fat, muscle, and bone are all economically relevant tissues, but muscle and bone are of particular interest because the ratio of muscle to bone is theoretically constant at maturity while fat continues to dilute both muscle and bone with advancing maturity (Haecker, 1920; Berg and Butterfield, 1966, 1976; Simpfendorfer, 1974; Elsley, 1976). Muscle-to-bone ratio has been suggested to be more valuable for assessing cutability than muscularity alone (Abraham et al., 1980). Historically, ribeye area has been used to assess muscularity of beef cattle and carcasses (Stouffer et al., 1961; Hedrick et al., 1962; Davis et al., 1966; Turner et al., 1990; Duello, 1993; Greiner et al., 2003a, 2003b). In most genetic evaluations in the United States, ribeye area is the lone predictor of muscularity (Beef Improvement Federation, 2021). Repeatedly, beef-type cattle have been found to have greater ribeye area than dairy-type cattle or beef × dairy cattle (Bertrand et al., 1983; Riley et al., 1986; Rust and Abney, 2005; Boykin et al., 2017; Eriksson et al., 2020; Frink, 2021; Foraker et al., 2022a). However, Wheeler et al. (2004) reported no difference in ribeye area between Angus- and Holstein-sired calves when compared at a common age, carcass weight, fat thickness, or marbling score. Nour et al. (1981, 1983a) reported similar increases in ribeye area as carcass weight increased for both Holstein and Angus steers. Once confounding factors of age and maturity have been accounted for, minimal difference between ribeye area of beef and dairy cattle may exist.

Still, dairy-influenced cattle have a greater percentage of bone in the carcass than beef-type steers (Branaman et al., 1962; Cole et al., 1964; Nour et al., 1981, 1983b, 1983a; Stiffler et al., 1985; Rezagholivand et al., 2021). Therefore, beef-type cattle have a favorable muscle-to-bone ratio (Berg and Butterfield, 1968; Nour et al., 1981). Muscles other than the longissimus contribute to carcass cutability. At the posterior end of the loin, Branaman et al. (1962) observed greater yield of Porterhouse steaks for beef-type cattle compared to dairy-type cattle. Similarly, Garcia-de-Siles et al. (1977), found muscles of the hypaxial lineage to be more developed in British cattle than in dairy cattle. Specifically, the triceps had greater circumference in beef cattle compared to dairy cattle, and the difference was measurable as forearm circumference on the live animal; Tatum et al. (1986a, 1986b, 1986c) found similar results. In addition, Garcia-de-Siles et al. (1977) observed that beef cattle had greater circumference relative to length of triceps, longissimus, semitendinosus, biceps femoris, and adductor muscles than Holstein cattle while the weight and circumference of the longissimus were poorly related to cutability and edible portion, muscles of hindquarter had greater predictive power (Garcia-de-Siles et al., 1977). In addition, others have identified hindquarter muscling to be more variable within cattle populations and to be more closely associated with muscle-to-bone ratio than ribeye area (Kauffman et al., 1976; Tatum et al., 1986a, 1986c; Rathmann et al., 2009; Howard et al., 2014; Foraker et al., 2022c).

In the studies of Fuerniss et al. (2023a, 2023b), differences were detected in frame size and muscularity of beef and beef × dairy calves, but no difference in ribeye area was detected between beef, beef × dairy, and dairy-fed cattle after being placed in the feedlot at a common weight and being fed for a similar number of days. Therefore, it was hypothesized that beef genetics produced a more moderately sized and muscular phenotype that typical carcass data could not detect. The objective of this experiment was to characterize morphometric and composition differences between the same beef, beef × dairy, and dairy-fed cattle described by Fuerniss et al. (2023a, 2023b).

Materials and Methods

Animal care and use

All cattle were managed according to protocol 19048-05 and SOP022 approved by Texas Tech University Animal Care and Use Committee. The cattle were housed at the Texas Tech University Beef Center ~11 km east of New Deal, TX.

Description of treatments

The objective of this experiment was to characterize morphometric differences between the beef, beef × dairy, and dairy-fed cattle previously described by Fuerniss et al. (2023a, 2023b). A model with genetic control was used where calves with at least half beef genetics were sired by a single Angus bull (G A R Momentum, American Angus Association registration number 17354145). The straightbred beef steers and heifers (A × B; n = 45) included fourteen Angus × commercial beef calves raised with their dam on range, 15 Angus × commercial beef calves gestated by Holstein cows and raised at a calf ranch, and 16 Angus × commercial beef calves gestated by Jersey cows and raised at a calf ranch. The traditional beef calves and the beef calves raised in the dairy system were combined into one group because minimal differences were observed in feedlot and carcass performance for these cattle (Fuerniss et al., 2023a). The beef × dairy cattle evaluated were either Angus × Holstein (A × H; n = 15) or Angus × Jersey (A × J; n = 16) steers and heifers born on commercial dairies and raised at a calf ranch. The proportion of steers and heifers included in each treatment is referenced in Tables 3 and 4. The dairy cattle evaluated were straightbred Holstein steers (H; n = 16) born on commercial dairies and raised at a calf ranch. The genetic composition of each animal was considered its treatment, and individual animal was considered the experimental unit.

Table 3.

Estimated marginal means of body measurements adjusted to a base of all steers at 28% empty body fat

	Treatment*				Heifer adjustment†	SEM2	P Value
	A × B	A × J	A × H	H
N	45	16	15	16
n, steers	26	8	7	16
n, heifers	19	8	8	0
Hip height, cm	124.9d	129.0c	133.6b	142.5a	−3.5	0.94	<0.01
Body length, cm	137.2c	141.3b	141.5b	150.6a	−2.6	1.13	<0.01
Body circumference, cm	225.8b	228.2b	230.6a,b	237.9a	−7.3	2.06	<0.01
Forearm circumference, cm	60.6a	57.5b	59.6a,b	59.6a,b	−3.0	0.84	<0.01
Hip width, cm	42.0c	42.1b,c	43.3b	48.6a	−0.9	0.41	<0.01
Top width, cm	33.9b	33.1b	34.1b	36.0a	−0.8	0.49	<0.01

^*A × B was progeny of Angus bull × commercial Angus-influenced cow; A × J was progeny of Angus bull × Jersey cow; A × H was progeny of Angus bull × Holstein cow; H was straightbred Holstein.

^†The heifer adjustment added to the presented treatment means estimated the magnitude of each dependent variable that would be observed for heifers; this is only applicable to the Angus-sired cattle and not the straightbred Holstein cattle.

^a,

^b,

^cMeans without common superscript differ between treatments by pairwise comparisons with Tukey adjustment (P < 0.05).

Table 4.

Estimated marginal means of carcass measurements adjusted to a base of all steers^*

	Treatment†				Heifer Adjustment‡	SEM	P Value
	A × B	A × J	A × H	H
N	45	14	15	16
n, steers	26	8	7	16
n, heifers	19	6	8	0
Carcass length, cm	119.4a,b	118.2b	119.1a,b	120.3a	0.2	0.46	0.01
Round circumference, cm	127.7c	133.6b	132.2b	138.2a	−0.4	0.74	<0.01
Round length, cm	68.4c	71.7b	71.1b	77.4a	−2.2	0.45	<0.01
Round circumference:round length	1.75a	1.65b	1.68b	1.56c	0.06	0.012	<0.01

^*Model included fat thickness and carcass weight as fixed effects.

^†A × B was progeny of Angus bull × commercial Angus-influenced cow; A × J was progeny of Angus bull × Jersey cow; A × H was progeny of Angus bull × Holstein cow; H was straightbred Holstein.

^‡The heifer adjustment added to the presented treatment means estimated the magnitude of each dependent variable that would be observed for heifers; this is only applicable to the Angus-sired cattle and not the straightbred Holstein cattle.

^a,

^b,

^cMeans without common superscript differ between treatments by pairwise comparisons with Tukey adjustment (P < 0.05)

Cattle management

Calfhood management was described by Fuerniss et al. (2023b). Briefly, the 14 A × B calves that were managed with their dam on rangelands were weaned at an average age of 205 d. All calves raised through calf were separated from their dam at birth housed in individual hutches with free choice water and starter feed and were offered 2.84 L of milk twice per d. Weaning was completed by ~65 d of age, and calves were transported to the Texas Tech University Beef Center at ~235 d of age.

Finishing cattle management was described by Fuerniss et al. (2023a). Cattle were started on trial at mean BW of 302 ± 29.9 kg and then fed at 196 ± 3.4 d. On trial day 0, cattle were implanted in the right ear with Synovex One Feedlot (200 mg trenbolone acetate and 28 mg estradiol benzoate; Zoetis, ­Parsippany, NJ). From days 0 to 27, cattle were fed on a pen level in concrete feed bunks while transitioning from the grower diet to the final fishing diet. On day 28, measurement of individual finishing diet intake began with SmartFeed bunks (C-Lock, Rapid City, SD). The finishing diet was composed of steam-flaked corn, Sweet Bran, dry rolled corn, alfalfa hay, cotton burrs, supplement, and yellow grease and included 1.48 ± 0.039. Mcal of net energy for gain based on chemical analysis.

Body measurements

Throughout the finishing period, body weight was measured using a platform scale to the nearest 0.45 kg at days 0, 28, 56, 84, 112, 140, 168, and at shipment for slaughter which occurred at 196 ± 3.4 d. Cattle were weighed at 0600 h without feed or water restriction except for the final body weight for which cattle were held without feed for 12 h and weighed at 0400 h. A 4% shrink was applied to all weights. Morphometric measurements were obtained at each sampling using similar methods to those described by Tatum et al. (1986b). Measurements were recorded to the nearest mm and included the following:

1. Forearm circumference: circumference of the left forelimb measured using flexible tape immediately distal to the lateral epicondyle of the humerus.

2. Body circumference: circumference of the body measured using flexible tape immediately anterior to the navel.

3. Top width: distance measured using caliper between the most lateral tissues at the first lumbar vertebra.

4. Hip width: distance measured using caliper between the lateral surfaces of the tuber coxae.

5. Hip height: distance measured using caliper-type device from a point on the dorsal midline between the tuber coxae to the chute floor while the animal was standing with natural posture.

6. Body length: distance measured using caliper-type device parallel to animal’s back between lateral tuberosity of the humorous and the ischiatic tuberosity.

In addition to body weight and morphometric measurements, B-mode ultrasound was used to assess composition characteristics. After BW and measurements were recorded on days 0, 56, 112, and 168, all cattle were scanned to estimate longissimus muscle area, subcutaneous 12th rib fat thickness, subcutaneous rump fat thickness, and intramuscular fat percentage. Images were taken with an Aloka 500V real-time ultrasound machine (Corometrics Medical Systems, Wallingford, CT) with a 17.2 cm, 3.5-MHz linear transducer. Magnification was set to 1.5, overall gain was set to 90, near gain was set to −25, and far gain was set to 2.1. Five images were collected for intramuscular fat, two images were collected for 12th rib fat and longissimus muscle area, and two images were collected for rump fat. All measurements were collected following recommendations of the Ultrasound Guidelines Council (Hays and Meadows, 2012).

Muscle biopsy

Subsets of steers from each treatment were selected for repeated longissimus thoracis biopsy to assess cellular-level muscle growth. On day 0, steers with SBW closest to 305 kg (mean SBW = 309 kg, SD = 28.3 kg) were identified for biopsy on days 0, 56, 112, and 168 of the trial. In total, 43 steers were intensively studied (A × B, n = 21; A × J, n = 7; A × H, n = 7; H, n = 8). The first biopsy was collected on the right side of the animal at the posterior edge of the 10th rib, and the second biopsy was collected at a symmetrical position on the left side of the animal. The third biopsy was collected on the right side of the animal at the posterior edge of the 11th rib, and the final biopsy occurred at a symmetrical position on the left side of the animal. Longissimus thoracis muscle tissue was collected using a 6-mm Bergstrom biopsy needle as described by Dunn et al. (2003); Smith et al. (2019), and Wellmann et al. (2021). Sections of muscle tissue with parallel muscle fibers were identified and aligned in optimum cutting temperature media (VWR International, Radnor, PA) on a 1 × 1.5 cm piece of 0.64 cm-thick cork. Muscle tissue was covered in optimum cutting temperature media and rapidly frozen in 2-methylbutane that was cooled by dry ice. Frozen samples were wrapped in foil, placed in a Whirl-Pak bag (Nasco, Fort Atkinson, WI), and transported in dry ice. Muscle biopsy samples were stored at −80 °C until all biopsies were completed.

Immunohistochemistry

Muscle fiber cross-sectional area and myosin heavy chain type were determined as described by Fuerniss and Johnson (2023). Embedded samples were equilibrated to −20 °C overnight before 10 μm-thick cross-sections were cut using a Leica CM1950 cryostat (Leica Biosystems, Buffalo Grove, IL) with the chamber temperature at −21 °C. Three cross-sections of muscle were placed on positively charged glass slides (Superfrost Plus, VWR International). Muscle cross-sections were immunohistochemically stained similar to previously published methods (Gonzalez et al., 2007; Paulk et al., 2014; Hergenreder et al., 2016; Scheffler et al., 2018). Cross sections were fixed in 4% paraformaldehyde phosphate-buffered saline (PBS, pH 7.4) for 10 min at room temperature. After fixation, slides were washed three times for five min each in PBS. Blocking solution consisting of 0.2% Triton-100×, 2% bovine serum albumin, and 5% horse serum in PBS was applied to slides, incubated for 30 min at room temperature, and then removed. Primary antibodies (Table 1) were diluted in blocking solution, applied to cross sections, and incubated for 1 h at room temperature. Since myosin heavy chain (MyHC) type IIB fibers are not present in bovine skeletal muscle (Maccatrozzo et al., 2004), only MyHC type I, IIA, and IIX were considered. Primary antibody solution was removed, and slides were washed 3 times for 5 min each in PBS. Without exposure to light, secondary antibodies (Table 2) were diluted in blocking solution, applied to cross sections, and incubated for 30 min at room temperature. Secondary antibody solution was removed, and slides were washed 3 times for five min each in PBS. ProLong Gold Antifade Mountant with DAPI (Life Technologies, Carlsbad, CA) was applied to cross-sections before covering with thin glass coverslips (VWR International) and incubating for 24 h at 4 °C in the dark. Coverslips were sealed after 24 h of incubation in preparation for imaging.

Table 1.

Primary antibodies

Antibody	Target antigen	Isotype	Host	Source	Dilution
BA-D5	MyHC type I (MYH7 gene)	IgG2b	Mouse	DSHB1	1:100
BF-35	All MyHC except type IIX (MYH2 gene)	IgG1	Mouse	DSHB*	1:75
PA137587	Dystrophin (DMD gene)	IgG	Rabbit	Invitrogen†	1:100

^*Developmental Studies Hybridoma Bank, Iowa City, IA.

^†Invitrogen, Carlsbad, CA.

Table 2.

Secondary antibodies

Antibody	Reactivity	Target isotype	Conjugate	Host	Source*	Dilution
A-21143	Mouse	IgG2B	Alexa-Fluor 546	Goat	Invitrogen	1:1000
A-21126	Mouse	IgG1	Alexa-Fluor 633	Goat	Invitrogen	1:1000
A-11008	Rabbit	IgG	Alexa-Fluor 488	Goat	Invitrogen	1:1000

^*Invitrogen, Carlsbad, CA.

Slides were imaged using BioTek Cytation5 with Gen5 software (Agilent, Santa Clara, CA). The center region of the slide (~1.18 cm by 1.96 cm) was imaged using brightfield microscopy and 40 × working magnification. From the image, two regions of interest were defined on a single muscle cross-section. Each region of interest was ~1,000 μm × 1,000 μm. Then, the 40 × working magnification was used to capture fluorescent images. The image was autofocused using the GFP channel; images were captured with filters optimized for GFP, Texas Red, TRITC, and DAPI. Then, a data reduction step was used to recognize muscle fibers based on GFP fluorescence of dystrophin staining. Muscle fibers were defined as the absence of GFP fluorescence.

Within each fiber, average fluorescent intensities of TRITC and Texas Red were used to classify each fiber’s MyHC type by objective standards. Type I fibers were defined as having mean Texas Red fluorescent intensity greater than or equal to 21,000 and mean TRITC fluorescent intensity greater than or equal to 7,500. Type IIA fibers were defined as having mean Texas Red fluorescent intensity greater than or equal to 21,000 and mean TRITC fluorescent intensity less than 7,500. Type IIX fibers were defined as the absence of intracellular staining as mean Texas Red fluorescent intensity less than 21,000 and mean TRITC fluorescent intensity less than 7,500. After classification, fiber counts and areas were aggregated across both regions of interest for each sample. Overall mean fiber cross-sectional area and the proportion of cross-sectional area occupied by each MyHC type were calculated. To summarize the MyHC type distribution as a single number, an oxidative index score was calculated with a possible range from 0 to 1. Oxidative index was defined as the area occupied by MyHC type I muscle fibers plus half of the area occupied by MyHC type IIA muscle fibers divided relative to the total muscle area evaluated.

Carcass evaluation

On the scheduled day of slaughter, cattle were weighed at ~0400 h before being transported 161 km to a commercial beef processing plant. Traditional carcass evaluation was completed as described by Fuerniss et al. (2023a); briefly, marbling score, carcass weight, ribeye area, subcutaneous fat thickness, percentage of kidney, pelvic, and heart fat were recorded. From the carcass data, adjusted final body weight (AFBW) was calculated using the equation of Guiroy et al. (2001) to estimate the shrunk BW when empty body fat was 28%. For some analyses, dependent variables were regressed against cattle chemical maturity approximated by live weight as a percentage of AFBW.

In addition to traditional carcass evaluation, morphometric measurements were recorded from carcass sides ~18 h after slaughter. Carcass measurements were recorded on each side of the carcass and included the following:

1. Carcass length: distance from the aitch bone to the articulation of the first rib and spine measured with a metal tape measure.

2. Round length: distance from the aitch bone to the calcaneal tuberosity measured with a caliper.

3. Round circumference: circumference of the round measured at the aitch bone perpendicular to the long axis of the carcass measured using flexible tape measure.

Strip loin dimensionality

When carcasses were fabricated, the boneless strip loin (Institutional Meat Purchase Specifications Item No. 180; NAMP, 2010) was collected from the right side of carcasses (N = 78). Striploins were vacuum packaged and stored at 4 °C at the Gordon W. Davis Meat Laboratory (Lubbock, TX). At 7 d postmortem, each strip loin was fabricated into 2.54-cm-thick steaks. After the anterior surface of the strip loin was squared perpendicular to the long axis of the strip loin, steaks were cut from anterior to posterior. Each steak was imaged using a DLSR camera (Model D7100, Nikon Corp., Thailand) equipped with a fixed-zoom lens (Model DXSWMVREDIF, Nikon Corp., Thailand) that was attached to a tripod directly above each steak. A ruler was placed adjacent to each steak at a height of ~2.54 cm in each image. The longissimus lumborum of each steak was measured in duplicate for area, medial to lateral length, and width at 25%, 50%, 75%, and 87.5% of the steak length from medial to lateral using Image J (version 2.0.0, National Institute of Health, Bethesda, MD) as described by Frink (2021).

Statistical analysis

All statistical analyses were performed in R version 4.3.1 (R Core Team, 2023). Functions from the dplyr package (Wickham et al., 2022) and plyr package (Wickham, 2011) were used for all data merging and calculations. Assumptions underlying statistical tests (normality, homoscedasticity, and freedom from outliers) were tested using functions of the rstatix package (Kassambara, 2021). When data failed to meet the assumption of normality, log transformation was used. Linear models were fit using the base lm function, and mixed models were fit using the lme4 package of R (Bates et al., 2015).

To account for unbalanced proportions of each sex within treatment, all means were presented on a steer base and an adjustment was given for heifers when data were presented in tabular form. The heifer adjustment added to the estimated marginal mean for steers is equivalent to the estimated marginal mean for heifers. The heifer adjustment value was calculated as the difference in estimated marginal means of heifers and steers for each dependent variable across the treatments that included both steers and heifers; therefore, the heifer adjustment should not be applied to estimate means for Holstein heifers. No heifer adjustment was used for dependent variables related to muscle fiber type and muscle fiber size because muscle biopsies were collected from only steers.

Body morphometric measurements and ultrasound measurements were analyzed as a completely randomized design with repeated measures. Independent variables were regressed against shrunk body weight or shrunk body weight as a percentage of mature size (AFBW). Each model included fixed effects of treatment (breed type) and body weight. The interaction of treatment and weight was included by forward selection; additionally, polynomial terms for weight were included by forward selection. In addition to the repeated measures analysis, body measurements adjusted to 28% empty body fat were analyzed by one-way ANOVA appropriate for a completely randomized design. The effects of treatment on carcass measurements were evaluated by one-way ANOVA appropriate for a completely randomized design. In addition to the main effect of treatment, linear effects of side weight and 12th rib fat thickness were included in the model for carcass measurements.

For analysis of muscle fiber size and MyHC type, A × H and A × J cattle were pooled into a single group (Angus × Dairy; A × D). Both variables were analyzed as a completely randomized design with repeated measures. Mean muscle fiber cross-sectional area was evaluated with a linear model that included fixed effects of experiment day, treatment, and the interaction of experiment day with treatment. Oxidative index was evaluated by logistic regression with a model that included fixed effects of experiment day, treatment, and the interaction of experiment day with treatment.

Dimensions of striploin steaks were analyzed as a completely randomized design with repeated measures. Dimensions were regressed against the location of the steak within the strip loin from anterior to posterior. Fixed effects in each model included sex, treatment, steak location, and the interaction of treatment and steak location. Polynomial terms were included for steak location by forward selection. Additionally, dimensions of the most anterior and most posterior steaks of the strip loin were evaluated by one-way ANOVA appropriate for a completely randomized design.

Independent variables were evaluated by analysis of variance (ANOVA) with Kenward-Roger approximation of denominator degrees of freedom. Pairwise comparisons were protected by ANOVA significance, and Tukey adjustment was used for multiple comparisons. Treatment means were presented as estimated marginal means calculated using the emmeans package of R (Lenth, 2022). Standard errors ­presented in tabular form ­represent the largest standard error of the treatment means. Statistical significance was evaluated compared with α of 0.05. When 0.05 ≤ P < 0.10, tendencies were considered. Exact P values were referenced when main effects and interactions were presented whereas the P-value relative to the alpha was ­referenced for pairwise comparisons. Visualizations were built in R using ggplot2 (Wickham, 2016), cowplot (Wilke, 2020) and ggpubr packages (Kassambara, 2020).

Results

Morphometric live measurements

Relative to body weight, H cattle had the greatest hip height across the finishing period (P < 0.05; Figure 1). When body weight was between 70% and 115% of mature size, straightbred beef cattle had lesser hip height than H cattle by ~15 cm. While A × H and A × J cattle had similar height when BW was 300 kg (P > 0.05), A × H cattle were taller than A × J cattle once BW reached 500 kg (P < 0.05). Beef cattle had lesser hip height than dairy-influenced cattle (P < 0.05). Similar patterns were observed for body length where H cattle were longer than A × B cattle (P < 0.05). When adjusted for the percentage of mature size, body length of A × H and A × J was less than that of H cattle (P < 0.05) and greater than that of A × B cattle (P < 0.05).

Figure 1.

Skeletal measurements of N = 92 steers and heifers regressed against weight (W) either as body weight or body weight as a percentage of adjusted final body weight calculated using the equation of Guiroy et al. (2001). Shaded region represents 95% CI; treatments (T) without overlapping shading are different (P < 0.05). Regressions included n = 45 Angus-sired beef cattle (A × B), n = 14 Angus × Jersey cattle (A × J), n = 15 Angus × Holstein cattle (A × H), and n = 16 straightbred Holstein steers (H).

Minimal differences were detected in body circumference relative to weight, especially at heavier weights (Figure 2). At 300 kg, A × J and A × H cattle had greater (P < 0.05) body circumference than all other cattle types (P > 0.05). Relative to mature size, H cattle had the greatest body circumference once BW was greater than 100% of AFBW (P < 0.05). Forearm circumference was greatest for A × B cattle and least for H cattle when BW was greater than 400 kg (P < 0.05). When expressed relative to AFBW, forearm circumference of A × J cattle was less than that of A × B cattle (P < 0.05).

Figure 2.

Body circumference measurements of N = 92 steers and heifers regressed against weight (W) either as body weight or body weight as a percentage of adjusted final body weight calculated using the equation of Guiroy et al. (2001). Shaded region represents 95% CI; treatments (T) without overlapping shading are different (P < 0.05). Regressions included n = 45 Angus-sired beef cattle (A × B), n = 14 Angus × Jersey cattle (A × J), n = 15 Angus × Holstein cattle (A × H), and n = 16 straightbred Holstein steers (H).

No difference in hip width was detected for Angus-sired cattle when BW was greater than 300 kg (P > 0.05; Figure 3). However, hip-width of H cattle was greater than that of all other treatment groups at all percentages of mature size between 70% and 115% and at all BW greater than 300 kg (P < 0.05). Consequently, H cattle had lesser top width relative to hip width when compared to Angus-sired cattle across all BW and proportions of AFBW tested (P < 0.05).

Figure 3.

Body width measurements of N = 92 steers and heifers regressed against weight (W) either as body weight or body weight as a percentage of adjusted final body weight calculated using the equation of Guiroy et al. (2001). Shaded region represents 95% CI; treatments (T) without overlapping shading are different (P < 0.05). Regressions included n = 45 Angus-sired beef cattle (A × B), n = 14 Angus × Jersey cattle (A × J), n = 15 Angus × Holstein cattle (A × H), and n = 16 straightbred Holstein steers (H).

When measurements were adjusted to 28% empty body fat (when body weight was 100% of AFBW), H cattle were larger framed than Angus-influenced cattle (Table 3). Hip height, body length, hip width, and top width were greatest for H cattle (P < 0.05). Even though A × H cattle had greater hip height than A × J cattle (P < 0.05), A × H and A × J cattle were similar in body length (P > 0.05). Forearm circumference of A × B cattle was greater than that of A × J (P < 0.05) while that of A × H and H cattle was intermediate.

Composition changes during finishing period

As BW increased as a percentage of AFBW and cattle approached maturity, rate of muscle accretion decreased, and rate of fat accretion increased (Figure 4). When ribeye area was regressed against BW as a percentage of AFBW, the coefficient of the quadratic term was negative (P < 0.01). In contrast, quadratic terms for intramuscular fat and subcutaneous 12th rib fat thicknesses and rump fat thicknesses were positive (P < 0.01). The second-order coefficient for the model of intramuscular fat (0.00054 ± 0.000065; P < 0.01) was greater than the coefficients for 12th rib fat thickness (0.000082 ± 0.000019; P < 0.01) and rump fat thicknesses (0.00011 ± 0.000015; P < 0.01). Treatment differences were detected for all traits measured by ultrasound (P ≤ 0.05). Rump fat and 12th rib fat thickness were greater for A × B than A × J cattle (P < 0.05), and H cattle had the least intramuscular fat (P < 0.05).

Figure 4.

Body composition measured by ultrasound of N = 92 steers and heifers regressed against weight (W) either as body weight or body weight as a percentage of adjusted final body weight calculated using the equation of Guiroy et al. (2001). Shaded region represents 95% CI; treatments (T) without overlapping shading are different (P < 0.05). Regressions included n = 45 Angus-sired beef cattle (A × B), n = 14 Angus × Jersey cattle (A × J), n = 15 Angus × Holstein cattle (A × H), and n = 16 straightbred Holstein steers (H).

Like ultrasound ribeye area patterns relative to increasing maturity, mean muscle fiber area increased from experiment days 0 to 112 and was not statistically different between days 112 and 168 (P > 0.05; Figure 5). When no interaction was observed between treatment and experiment day, mean muscle fiber cross-sectional area was not different within MyHC type I, within MyHC type IIA, or across all muscle fibers (P ≥ 0.55). Cross-sectional area of MyHC type IIA fibers was greater for H cattle than all other cattle at experiment days 56 and 112 (P < 0.05); however, no differences between treatments were observed at experiment days 0 or 168 (P > 0.05). Relative abundance of MyHC types was summarized as oxidative index. On day 0, H cattle had greater oxidative index than Angus-sired cattle (P < 0.05; Figure 6). Although oxidative index scores decreased from days 0 to 56, oxidative index scores increased from days 56 to 168. At day 168, A × B cattle had lesser oxidative index scores than H cattle, and beef × dairy crossbred cattle had intermediate scores (P < 0.05).

Figure 5.

Muscle fiber cross-sectional area from a subset of N = 43 steers by myosin heavy chain (MyHC) type. Points without common letters were different (P < 0.05); squares represent pairwise comparisons between experiment days (D), and circles represent pairwise comparisons of treatment (T) within experiment day. Means included n = 21 Angus-sired beef steers (A × B), n = 14 Angus × Holstein or Jersey steers (A × D), and n = 8 Holstein steers (H).

Figure 6.

Muscle oxidative index was calculated as all the proportion of cross-sectional area occupied by myosin heavy chain type I muscle fibers added to half of the proportion of cross-sectional area occupied by myosin heavy chain type IIA muscle fibers. Means included n = 21 Angus-sired beef steers (A × B), n = 14 beef × dairy steers (A × D; Angus × Holstein or Angus × Jersey), and n = 8 dairy steers (H; straightbred Holstein). Means without common letters were different within experiment day (P < 0.05).

Carcass and steak dimensionality

Holstein carcasses had the greatest round length (P < 0.05; Table 4). Carcasses from A × J cattle were shorter than H carcasses (P < 0.05) and numerically shorter than A × B and A × H carcasses. However, length was least for A × B rounds (P < 0.05) and no difference was observed between length of A × H and A × J rounds (P > 0.05). Straightbred beef rounds had the greatest ratio of circumference to length, A × H and A × J had intermediate ratio, and H had the least round circumference relative to length (P < 0.05).

Similar changes in longissimus lumborum steak dimensions were observed from anterior to posterior locations of the strip loin across all treatments (Figure 7). A linear decrease in longissimus lumborum area was observed from anterior to posterior (P < 0.01). The interaction (P < 0.01) between treatment and location of steak in the strip loin. The interaction demonstrated that longissimus area of H steaks decreased more rapidly from anterior to posterior compared to A × B or A × J steaks (slope coefficients of −0.21 vs. −0.13 and −0.12; largest SE = 0.019; P < 0.05). A quadratic increase in medial to lateral length was observed (P < 0.01). Similarly, quadratic or cubic decreases in longissimus lumborum width toward the posterior 75% of the strip loin were observed (P < 0.01). In the most posterior end of the strip loin, H cattle had the least width at 25% and 50% of steak length (P < 0.05). Consequently, the ratio of length to width increased toward the posterior end of the strip loin. In the posterior half of the strip loin, steaks from H cattle had the greatest length-to-width ratio of the longissimus lumborum (P < 0.05).

Figure 7.

Measures of steaks from the longissimus lumborum from N = 78 strip loins from steers and heifers regressed against steak location (P) as a percentage from anterior (0%) to posterior (100%). Treatments (T) included n = 44 Angus-sired beef cattle (A × B), n = 13 Angus × Jersey cattle (A × J), n = 13 Angus × Holstein cattle (A × H), and n = 8 straightbred Holstein steers (H). Shaded region represents 95% CI.

Discussion

Mature size

Historically, body measurements have been used to describe cattle phenotype related to growth and composition (Black et al., 1938; Cook et al., 1951; Kohli et al., 1951; Gilbert et al., 1993a, 1993b). Compared to Angus or Hereford cattle, Holstein genetics are expected to have greater mature skeletal size (Kidwell and McCormick, 1956; Nour et al., 1981; Thonney et al., 1981; Thonney, 1987; Perry et al., 1991). This was observed in the current study when hip height and body length were measured. Even half-blood dairy animals had greater hip height and body length than beef-type cattle at a constant body weight. Regardless, the significant negative quadratic term for both body length and hip height indicated that skeletal growth was plateauing as cattle reached heavier weights at the end of the finishing period. Once slaughtered, Holstein-influenced carcasses had greater length, particularly of the round than beef-type carcasses. Linear skeletal growth was observed to be greater for Holstein-influenced cattle and carcasses.

Muscularity

Like linear skeletal measurements, muscle growth reached a plateau at the end of the feeding period. Both forearm circumference and ribeye area were best modeled with a negative quadratic term; measurements increased rapidly at light weights and when BW was a lesser percentage of AFBW. Forearm circumference has been highly related to carcass cutability and edible portion (Garcia-de-Siles et al., 1977; Tatum et al., 1986b, 1986c, 1986a), but ribeye area remains the only objective measure of muscularity used to evaluate beef carcasses or for genetic improvement. Both measures assess muscularity and are related to protein accretion. Owens et al. (1995) reported that protein accretion relative to empty BW was linear up to an empty BW of 520 kg. The cattle in the current study were fed past an empty BW of 520 kg (Fuerniss et al., 2023a); the observation that muscularity increased at a decreasing rate indicated that an upper limit of body protein mass exists as previously reported (Haecker, 1920; Simpfendorfer, 1974; NASEM, 2016).

No difference in ribeye area at time of slaughter was detected by Fuerniss et al. (2023a) between the same carcasses used in this study. In the data presented in this paper, this was confirmed on a cellular level. Longuissimus thoracis muscle fiber cross-sectional area increased to experiment day 112 (like ribeye area observations), but no effect of treatment on muscle fiber cross-sectional area was observed. However, at more distal locations, differences in muscularity were observed. Regressions for area of the longissimus lumborum identified an interaction where longissimus area decreased more rapidly from anterior to posterior for Holstein cattle than other breed types. Similarly, Foraker et al. (2022c) identified greater variation in area of strip loin steaks in the posterior end of the strip loin than in the anterior end of the strip loin. The cattle described by Foraker et al. (2022c) were grouped by visual assessment of muscularity, largely based on conformation of the hindquarter, suggesting that differences were detectable in hindquarter muscularity even though the differences were not detected between the 12th and 13th ribs. In the present study, straightbred beef cattle had greater forearm circumference relative to BW or BW as a percentage of AFBW than calves with half dairy genetics. This was also true for these same cattle during calfhood as reported by Fuerniss et al. (2023b). This study and the work of Foraker et al. 2022 suggest that differences in both objective and subjectively evaluated muscularity of the forequarter and hindquarter can exist even among cattle with similar ribeye area.

Similarly, carcass measurements from this study identified differences in round conformation. Round circumference as a ratio to round length was greatest for beef carcasses, intermediate for beef × dairy carcasses, and least for Holstein carcasses. Round length was indicative of length of the long bones of the pelvic limb—namely the femur and tibia. Round circumference was indicative of the cross-sectional area of muscle fat and bone of the round. The model used to analyze the ratio of round circumference to round length included effects of carcass side weight and fat thickness. Remaining biological variation is likely caused by differences in bone and muscle; however, this assumes constant relationships between 12th rib fat thickness and total ­carcass fat (including intermuscular fat) and between carcass weight and bone weight. Others have found the ratio of muscle to bone to be greater for beef-type cattle compared to dairy-type cattle (Berg and Butterfield, 1968; Nour et al., 1981, 1983b). In many instances, muscle-to-bone ratio has been more highly associated with red meat yield than ribeye area (Kauffman et al., 1976; Tatum et al., 1986b, 1986a; Rathmann et al., 2009; Howard et al., 2014; Foraker et al., 2022c). When comparing the beef-type cattle, dairy-type cattle, and beef × dairy cattle in this study, measurement of ribeye area did not detect differences in muscularity that might have existed if evaluated as muscle-to-bone ratio. Animal-to-animal variation was subjectively observed in the cattle measured in this study and was reported in populations of beef × dairy crossbred cattle by Foraker et al. (2022c). Opportunity exists to use objective measurement of hindquarter (or forequarter) muscularity to improve prediction of red meat yield.

Although differences in ribeye area and cross-sectional area of muscle fibers near the last rib were not detected, differences in the distribution of MyHC were detected. Oxidative index values were calculated to describe the muscle fiber size of each MyHC type and the proportion of each MyHC type of a muscle sample simultaneously. Oxidative index values were minimal at day 56 (the first sampling after a steroidal implant was administered). Similarly, Smith et al. (2019) found that proportion of MyHC type IIX fibers was increased 28 d after a steroidal implant was administered, but the difference was minimized with extended days on feed. Across all the treatments in this study, oxidative index increased from days 56 to 168. Longitudinal increases in oxidative index were consistent with increases in ultrasound intramuscular fat. This was consistent with oxidative muscle fibers being associated with greater lipid and mitochondria content (Klont et al., 1998; Picard et al., 2020), but a causal link cannot be determined from the results of this study.

At all timepoints, the calculated oxidative index of H muscle biopsies was greater than that of A × B muscle biopsies. Holstein cattle were expected to have a more ­oxidative ­muscle phenotype because Holstein genetics have been associated with greater abundance of oxidative muscle fibers and smaller glycolytic muscle fibers compared to beef-type cattle (Ashmore, 1974; Spindler et al., 1980; Wegner et al., 2000; Picard et al., 2020; Frink, 2021). Within beef × dairy crossbred cattle, Foraker et al. (2022c) found no difference in MyHC type or muscle fiber size between cattle divergent in frame size and muscling; therefore, MyHC distribution seems to be more related to breed type than to muscularity. This is particularly intriguing when beef and dairy breeds are crossed because the effect of divergent mitochondrial lineages and potential interaction with genomic markers of muscle fiber phenotypes are unknown (Giles et al., 1980; Birky, 1995; Mishra et al., 2015; Mishra and Chan, 2016). Regardless, the greater final oxidative index values for Holstein cattle agreed with the findings of Galyean et al. (2023) who found that marbling score increased more rapidly in Holstein steers than in beef steers or beef heifers with incremental increases in days on feed.

Fatness

Fatness increased quadratically as expected based on previous reports (Simpfendorfer, 1974; Owens et al., 1995; NASEM, 2016). Increased rate of fat accretion occurred at similar timepoints that rate of muscle accretion declined. Another indicator of fattening observed in this study was the ratio of top width to hip width. Regardless of treatment, cattle had greater top-width-to-hip-width ratio as BW and fatness increased. As cattle fatten, width at the 13th rib is increased more than width at the tuber coxae because cattle fatten from anterior to posterior on the dorsal surface (Luitingh, 1962; Berg and Butterfield, 1976). Thus, a greater ratio of top width to hip width could be used as a simple indicator for live cattle of progression of fattening and, therefore, chemical composition. Since these measurements can be captured from above, these measurements could be practically collected in modern commercial cattle handling systems.

Steak appearance

When comparing beef, beef × dairy, and dairy steaks under retail conditions, some have reported that variation in steak shape made merchandising steaks from different breed types alongside one another difficult (Schaefer, 2005; Foraker et al., 2022c). In this study, strip loin steaks from Holstein carcasses had greater length-to-width ratio than steaks from all other breed types, particularly when steaks were cut from the posterior end of the strip loin nearest the hip. Uniquely, Holstein cattle also had the greatest hip width; the skeleton and its anchoring of muscle attachments could change the dimensionality of beef cuts. Similar to the results of this study, Frink (2021) found that steaks from beef-type and beef × dairy cattle were wider than steaks from dairy-type carcasses. However, research is limited to define consumer preference for steak dimensions. Thonney et al. (1991) found that retail meat managers could not identify ribeye steaks from Holstein and Simmental × Angus cattle with accuracy greater than random chance. However, more variation in steak dimensions likely exists between posterior strip loin steaks as compared to ribeye steaks. Holstein strip loin steaks were longer and narrower, but the economic implications of steak dimensionality remain unquantified. Furthermore, differences in steak dimensionality and longissimus area in the posterior end of the strip loin would not have been identified by ribeye area alone because ribeye area was not different between these cattle. This disparity warrants the use of other objective measurements to better describe muscularity of beef carcasses.

Summary

Morphometric measurements confirmed differences in mature size of beef-type cattle, dairy-type cattle, and beef × dairy cattle where Holstein influence was associated with greater skeletal growth. With advancing maturity, the rate of muscle accretion decreased quadratically while the rate of fat accretion increased quadratically. Although muscularity across all cattle types was similar in the longissimus near the last rib, morphometric differences were observed in the posterior end of the strip loin, the forearm, and round. Dairy-influenced cattle had more oxidative muscle phenotype. Beef genetics improved muscularity in portions of the carcass distal to the longissimus thoracis, and, therefore, differences in muscularity were not able to be detected with ribeye area alone.

Glossary

Abbreviations

AFBW

adjusted final body weight

MyHC

myosin heavy chain

SBW

shrunk body weight

Conflict of Interest Statement

All authors declare no conflict of interest.