Technical note: Mammary gland ultrasonography to evaluate mammary parenchymal composition in prepubertal heifers

Abstract

Bovine mammary gland development studies are often terminal or involve invasive biopsy procedures. Therefore, noninvasive means of assessing mammary development should be considered as alternative methods in live animals. The objective was to test if mammary ultrasonography can be used as a noninvasive way to estimate mammary parenchyma (PAR) composition in prepubertal dairy heifers with different average daily body weight gains. In the 84 d preceding, the ultrasound exam heifers were maintained in 1 of 3 treatment groups. Individual heifers were fed a high gain (1 kg/d; n = 6), low gain (0.5 kg/d, n = 6), or maintenance (n = 6) treatment diet. To achieve desired body weight gains, heifers were fed differing amounts of the same silage-based diet. Mammary glands of 18 crossbred heifers Holstein:Gyr underwent a single mammary ultrasound exam immediately before heifer slaughter, which took place when heifers weighed 142.0 ± 8.0 kg and were 200 d old. The 4 mammary glands of each heifer were evaluated using a real-time B-mode ultrasound machine equipped with a 6.5-MHz micro-convex transducer. Digital images (8-bit) of glands were obtained and PAR was identified within gland. Average pixel values per unit of PAR area were determined for each gland and analyzed at the level of heifer. Pixel results were interpreted on the basis that lower average pixel values reflect PAR with relatively high amounts of protein as opposed to fat. To help validate that the pixel value within PAR is associated with composition of PAR, pixel findings were compared with histological [number of adipocytes in PAR (Nad) and epithelial area in PAR (Ep)] and biochemical [percent crude protein in PAR (%CP), percent ether extract in PAR (%EE), PAR weight (WPAR), and mammary fat pad weight (WFAT)] composition of PAR in these same heifers. Within PAR, %EE and WFAT were positively correlated with pixel values, whereas %CP, Ep, and Nad were negatively correlated. Parenchyma weight did not correlate with pixel values. Regression analyses (fixed effect log-pixel value; random effect treatment) were used to estimate Nad, Ep, %CP, %EE, WPAR, and WFAT. Sensitivity analysis of regression equations revealed that accuracy of tested equations ranged from 0.77 to 0.93 and precision ranged from 0.56 to 0.82. Concordance correlation coefficients of the equations ranged from 0.41 to 0.76. In conclusion, ultrasonography of PAR can accurately measure and predict PAR composition in prepubertal dairy heifers growing at various rates of gain.

Effect of whole-milk allowance on liveweight gain and growth of parenchyma and fat pads in the mammary glands of dairy heifers at weaning

“…Therefore, there will be less precision using the technique than when the PAR and MFP are dissected from glands and weighed after harvesting. Despite this limitation, other investigators have indicated that gross demarcations between PAR and MFP can be identified using the intensity of pixel brightness [PAR is hypoechoic (black) and MFP is hyperechoic (white)] to aid tracing the outlines of PAR using software (Esselburn et al, 2015;Albino et al, 2017;Furini et al, 2018). For the current study, we reasoned that using software to measure the volume of mammary glands from traced outlines was not necessary because (1) the tracing method also relies on the ability of an observer to interpret where the demarcations are, (2) a single image will usually not capture the entire gland of larger glands and, therefore, superimposed images are required, and finally, (3) the tracing method is very time consuming.…”

“…Ultrasound has increasingly been used in studies on mammary anatomy and milk storage (Bruckmaier and Blum, 1992;Ayadi et al, 2003;Franz et al, 2009), and to monitor the development of mammary glands of replacement heifers to understand what influence diet has on these tissues and to evaluate what influence changes in growth of these tissues have on subsequent lactation (Nishimura et al, 2011;Albino et al, 2015;Esselburn et al, 2015;Albino et al, 2017;Furini et al, 2018). Notably, the technique is noninvasive and has the potential to be objective.…”

Mammary Cistern Size during the Dry Period in Healthy Dairy Cows: A Preliminary Study for an Ultrasonographic Evaluation

“…Ultrasound allows a real-time visualization of various tissues [11] and has been used to evaluate various internal structures of the udder such as the UC [16] and the teat [10,[18][19][20]. Several studies have performed ultrasounds of the UC to demonstrate normal mammary gland features in dairy heifers [11,28] and in lactating cows [16,21,29,30], and other authors have evaluated the non-physiological pattern in a sick mammary gland [31]. To the best of our knowledge, no studies have evaluated the size of the UC in dry cows.…”

Effect of protein supplement level on the productive and reproductive parameters of replacement heifers managed in intensive grazing systems

“…Mammary gland ultrasound images were taken using a micro-convex transducer (Mindray DP2200, Shenzhen, China), operating at a frequency of 6 MHz. Images were taken of each mammary quarter [43].…”