Expression of Beef- Versus Dairy-Type in Crossbred Beef × Dairy Cattle Does Not Impact Shape, Eating Quality, or Color of Strip Loin Steaks

Myosin heavy chain (MyHC) type and muscle fiber size are informative but time-consuming variables of interest for livestock growth, muscle biology, and meat science. The objective of this study was to validate a semiautomated protocol for determining MyHC type and size of muscle fibers. Muscle fibers obtained from the longissimus and semitendinosus of fed beef carcasses were embedded and frozen within 45 min of harvest. Immunohistochemistry was used to distinguish MyHC type I, IIA, and IIX proteins, dystrophin, and nuclei in transverse sections of frozen muscle samples. Stained muscle cross sections were imaged and analyzed using two workflows: 1) Nikon workflow which used Nikon Eclipse inverted microscope and NIS Elements software and 2) Cytation5 workflow consisting of Agilent BioTek Cytation5 imaging reader and Gen5 software. With the Cytation5 workflow, approximately 6 times more muscle fibers were evaluated compared to the Nikon workflow within both the longissimus (P < 0.01; 768 vs. 129 fibers evaluated) and semitendinosus (P < 0.01; 593 vs. 96 fibers evaluated). Combined imaging and analysis took approximately 1 h per sample with the Nikon workflow and 10 min with the Cytation5 workflow. When muscle fibers were evaluated by the objective thresholds of the Cytation5 workflow, a greater proportion of fibers were classified as glycolytic MyHC types, regardless of muscle (P < 0.01). Overall mean myofiber cross-sectional area was 14% smaller (P < 0.01; 3,248 vs. 3,780) when determined by Cytation5 workflow than when determined by Nikon workflow. Regardless, Pearson correlation of mean muscle fiber cross-sectional areas determined by Nikon and Cytation5 workflows was 0.73 (P < 0.01). In both workflows cross-sectional area of MyHC type I fibers was the smallest and area of MyHC type IIX fibers was the largest. These results validated the Cytation5 workflow as an efficient and biologically relevant tool to expedite data capture of muscle fiber characteristics while using objective thresholds for muscle fiber classification.

Semi-automated technique for bovine skeletal muscle fiber cross-sectional area and myosin heavy chain determination

Fuerniss

Johnson

2023

Beef embryos in dairy cows: feedlot performance, mechanistic responses, and carcass characteristics of straightbred Holstein calves and Angus-sired calves from Holstein, Jersey, or crossbred beef dams

Fuerniss

Wesley

Bowman

et al. 2023

Improved reproductive management has allowed dairy cow pregnancies to be optimized for beef production. The objective of this sire-controlled study was to test the feedlot performance of straightbred beef calves raised on a calf ranch and to compare finishing growth performance, carcass characteristics, and mechanistic responses relative to beef × dairy crossbreds and straightbred beef cattle raised in a traditional beef cow/calf system. Tested treatment groups included straightbred beef steers and heifers reared on range (A×B; n = 14), straightbred beef steers and heifers born to Holstein (H ET; n = 15) and Jersey dams (J ET; n = 16), Angus × Holstein crossbreds (A×H; n = 15), and Angus × Jersey crossbreds (A×J; n = 16). The finishing trial began when cattle weighed 301 ± 32.0 kg and concluded after 195 ± 1.4 d. Individual intake was recorded from d 28 until shipment for slaughter. All cattle were weighed every 28 days; serum was collected from a subset of steers every 56 days. Cattle of straightbred beef genetics (A×B, H ET and J ET) and A×H were similar in final shrunk BW, dry matter intake (DMI), and carcass weight (P > 0.05 for each variable). Compared with A×J cattle, J ET were 42 days younger at slaughter with 42 kg more carcass weight (P < 0.05 for both variables). No difference was observed in longissimus muscle area between all treatments (P = 0.40). Fat thickness was greatest for straightbred beef cattle, least for A×J cattle, and intermediate for A×H cattle (P < 0.05). When adjusted for percentage of adjusted final body weight, feed efficiency was greater for straightbred beef cattle compared with beef × dairy crossbred cattle (P = 0.04). A treatment × day interaction was observed for circulating insulin-like growth factor I (IGF-I; P < 0.01); 112 d after being implanted, beef × dairy crossbred cattle had greater circulating IGF-I concentration than cattle of straightbred beef genetics (P < 0.05). Straightbred beef calves born to Jersey cows had more efficient feedlot and carcass performance than A×J crossbreds. Calves of straightbred beef genetics raised traditionally or in a calf ranch performed similarly in the feedlot.

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

Fuerniss,

Young,

Hall

et al. 2023

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 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.