Partitioning variances of growth in ultrasound longissimus muscle area measures in Angus bulls and heifers

Estimation of Genetic Parameters for Real-time Ultrasound Measurements for Hanwoo Cows at Different Ages and Pregnancy Status

The purpose of this study was to estimate genetic parameters of ultrasound measurements for longissimus dorsi muscle area (LMA), backfat thickness (BFT), and marbling score (MS) in Hanwoo cows (N = 3,062) at the ages between 18 and 42 months. Data were collected from 100 Hanwoo breeding farms in Gyeongbuk province, Korea, in 2007 and 2008. The cows were classified into four different age groups, i.e. 18 to 22 months (the first pregnancy period), 23 to 27 (the first parturition), 28 to 32 (the second pregnancy), and 33 to 42 (the second parturition), respectively. For each age group, a multi-trait animal model was used to estimate variance components and heritabilities of the three traits. The averages of LMA, BFT, and MS measurements across the cows of all age groups were 50.1 cm², 4.62 mm, and 3.04, respectively and heritability estimates were 0.09, 0.10, and 0.08 for the respective traits. However, when the data were analyzed in different age groups, heritability estimates of LMA and BFT were 0.24 and 0.47, respectively, for the cows of 18 to 22 months of age, and 0.21 for MS in the 28 to 32 months old cows. When the cows of all age groups were used, the estimates of genetic (phenotypic) correlations were 0.43 (0.35), −0.06 (0.34) and 0.21 (0.32) between LMA and BFT, LMA and MS, and BFT and MS, respectively. However, in the cow age group between 28 and 32 (18 and 22) months, the estimates of genetic (phenotypic) correlations were 0.05 (0.29), −0.15 (0.24) and 0.38 (0.24), for the respective pairs of traits. These results suggest that genetic, environmental, and phenotypic variations differ depending on cow age, such that care must be taken when ultrasound measurements are applied to selection of cows for meat quality.

Prediction of carcass composition, ham and foreleg weights, and lean meat yields of Iberian pigs using ultrasound measurements in live animals

The most valuable lean cuts from Iberian pigs are the hams, forelegs, and loins, which yield high quality cured meat products. This study aimed to assess the correlation between body composition measurements taken in vivo by ultrasonography in Iberian pigs and those taken on the carcass, which were then used to develop predictive models to estimate the weight and yield of these cuts. Before slaughter, 241 Iberian pigs were weighed (slaughter BW) and ultrasonically scanned. Ultrasound images were collected at 3 locations: the 10th intercostal space, caudal to the last rib to image the loin muscle, and the rear gluteal region [ultrasound gluteal backfat (u-GBF)]. After slaughter, the weight of the carcass (CW), ham (HW), foreleg (FW), and loin (LW) were determined, and the sum of these lean cuts weights (CLPW) and the corresponding yields were calculated. A portion of loin with the associated bones, backfat, and skin was obtained by cutting the carcass between the 10th and last ribs and was used to measure, at the 10th (10) and last (14) rib locations, the total backfat thickness, the area of the loin muscle (c-LA), and the thickness of the 4 backfat (BF) layers, namely, the outer (c-OBF), middle (c-MBF), outer plus middle (c-OMBF), and the inner (c-IBF). Finally, intramuscular fat percentages (IMF) were obtained from the meat samples. Corresponding measurements from the ultrasound (u) images were similarly taken at the same 2 ribs (u-BF, u-LA, u-OBF, u-MBF, u-OMBF, and u-IBF). The correlation was greatest between u-MBF10 and c-MBF10 (0.84). Most correlations between ultrasound and carcass measurements were lower at the last rib than at 10th rib. The greatest correlation of IMF10 occurred with u-IBF10 (0.40). Ham weight and HL were more correlated with u-BF10 than with u-BF14 whereas FW was more correlated with u-BF14. The u-LA was more correlated with HW, FW, and LW at the last rib than at the 10th rib. Slaughter live weight accounted for 0.84, 0.42, 0.36, and 0.54% of the variation for the prediction of CW, HW, FW, and CLPW, respectively. The u-LA10 and u-LA14 increased the variation explained by the model up to 0.89, 0.48, 0.39, and 0.62% for CW, HW, FW, and CLPW, respectively. Including u-GBF in the models also increased the R(2) values for predicting HW, LW, HY (ham yield), and LY (loin yield). In conclusion, u-LA10, u-LA14, and u-GBF may improve weight of commercial cuts and yield prediction in live Iberian pigs.

Phenotypic and genetic parameters compared during repeated measures of longissimus muscle area and subcutaneous fat thickness in Nelore cattle

Real-time ultrasound is currently used for in vivo carcass evaluation of beef cattle. We estimated heritability and repeatability coefficients for ultrasound-measured carcass traits in Nelore cattle. We measured longissimus muscle area, backfat thickness, and rump fat thickness in male and female animals ranging in age from 10 to 26 months. The variance components were estimated by single-trait analysis using the derivative-free restricted maximum likelihood method, under an animal model. The complete data file included 3077 records of 1172 animals born between 2003 and 2008. Two analyses were performed using a repeatability model: a) all records of longissimus muscle area, backfat thickness, and rump fat thickness of animals aged 10 to 26 months, and b) considering two age periods (11 to 17 and 18 to 24 months). The heritability estimates ranged from 0.33 to 0.46 for longissimus muscle area, from 0.20 to 0.26 for backfat, and from 0.26 to 0.29 for rump fat, demonstrating that direct selection for these traits can provide genetic gain. The repeatability estimates were moderate, ranging from 0.42 to 0.73. The highest repeatability estimates were obtained for longissimus muscle area in both the first (0.70) and second (0.73) analyses. The repeatability estimates suggest that ultrasound measures are precise; higher precision was obtained for longissimus muscle area than for subcutaneous fat thickness. The latter could be obtained during periods of greater feed availability to increase precision.

Genetic parameters for body weight, hip height, and the ratio of weight to hip height from random regression analyses of Brahman feedlot cattle12

The objective of this research was to assess the genetic control of BW, hip height, and the ratio of BW to hip height (n = 5,055) in Brahman cattle through 170 d on feed using covariance function-random regression models. A progeny test of Brahman sires (n = 27) generated records of Brahman steers and heifers (n = 724) over 7 yr. Each year after weaning, calves were assigned to feedlot pens, where they were fed a high-concentrate grain diet. Body weights and hip heights were recorded every 28 d until cattle reached a targeted fatness level. All calves had records through 170 d on feed; subsequent records were excluded. Models included contemporary group (sex-pen-year combinations, n = 63) and age at the beginning of the feeding period as a covariate. The residual error structure was modeled as a random effect, with 2 levels corresponding to two 85-d periods on feed. Information criterion values indicated that linear, random regression coefficients on Legendre polynomials of days on feed were most appropriate to model additive genetic effects for all 3 traits. Cubic (hip height and BW:hip height ratio) or quartic (BW) polynomials best modeled permanent environmental effects. Estimates of heritability across the 170-d feeding period ranged from 0.31 to 0.53 for BW, from 0.37 to 0.53 for hip height, and from 0.23 to 0.6 for BW:hip height ratio. Estimates of the permanent environmental proportion of phenotypic variance ranged from 0.44 to 0.58 for BW, 0.07 to 0.26 for hip height, and 0.30 to 0.48 for BW:hip height ratio. Within-trait estimates of genetic correlation on pairs of days on feed (at 28-d intervals) indicated lower associations of BW:hip height ratio EBV early and late in the feeding period but large positive associations for BW or hip height EBV throughout. Estimates of genetic correlations among the 3 traits indicated almost no association of BW:hip height ratio and hip height EBV. The ratio of BW to hip height in cattle has previously been used as an objective measure of BCS in cows or calves; it may offer a unique assessment of body dimension. Results indicated that there is substantial additive genetic variation for this trait, and it may be possible to use EBV to increase BW without increasing frame score in Brahman cattle.