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

Abstract

The rates of development of 2 tissues in mammary glands, parenchyma (PAR) and the mammary fat pad (MFP), in response to nutrition in early life might have a major bearing on lifetime milk production. Historical studies reported that feeding greater amounts of dietary nutrients from postweaning to puberty increased growth rates of heifers and stimulated the growth of MFP at the expense of PAR, which might suggest compromised mammary development and future milk production. The current study sought to determine if a higher volume of whole milk (8 vs. 4 L/d) offered to calves would increase rates of growth and development of PAR in mammary glands at weaning (1 to 12 wk). To measure these tissues, we developed 2 simple methods to assess the size of PAR and MFP at the time of screening using ultrasound. We report that calves offered 8 L/d of whole milk had greater rates of growth until weaning (0.86 ± 0.06 vs. 0.81 ± 0.09 kg/d), compared with calves offered 4 L/d. Ultrasonography showed that despite the faster rates of growth in calves offered 8 L/d of milk/d, the ratio of PAR: MFP depth was 40% less at weaning in the front glands (34%) compared with calves offered 4 L of milk/d. Rear glands were less impaired. The ultrasound methods developed here might be useful to monitor the development of mammary glands in response to different nutritional regimens during the preweaning period.

Associations among Mammary Ultrasound Measurements, Milk Yield of Non-Dairy Ewe Lambs and the Growth of Their Single Lambs

“…Image processing was undertaken using ImageJ software [22]. The total depth of mammary gland conservative (MTc) and generous (MTg) were the smallest and the largest likely demarcations of the mammary gland visible on the image, respectively [10,23]. The MTc, MTg, fat pad (FP), parenchyma (PAR) and gland cistern (GC) depth were estimated, in millimetres, at the widest point for each subcompartment using the straight tracer.…”

“…Milk production is a complex biological process primarily determined by the number of secretory cells and their activity [33][34][35][36]. While ultrasound imaging enables the visualisation and assessment of the dimensions of the different tissues in the mammary gland [23,37] and their echo-textural characteristics [2,38], it does not provide information on the number and activities of secretory cells. This may explain the moderate prediction of milk yield using ultrasound measurements in the current experiment and is a limitation to the use of ultrasound as a technique to predict milk yield.…”

Effects of Increased Growth Rates Prior to the First Breeding as Ewe Lambs and Pregnancy Rank on Mammary Glands of Two-Year-Old Ewes

“…A minimum of three images were saved from each udder half. One image per udder half was used for image processing, which had a suitable resolution per udder half and showed the mammary parenchyma, fat pad, gland cistern, and limit between the mammary gland and the abdominal wall [15,21,22]. Udder halves with a palpation score of 4 or 5 at any time point (P119, L29, or L79) were considered "abnormal" [17].…”

“…The ImageJ software [23] was used to process the selected images. The smallest and largest demarcation (abdominal wall) were assessed as the total depth of mammary gland conservative (MTc) and generous (MTg), respectively [22]. The parenchyma (PAR), fat pad (FP), and gland cistern (GC) depths, as well as MTc and MTg, were estimated at the widest point for each compartment using the straight tracer, the skin layer was excluded.…”

“…The present results suggest that there were no carry-over effects of increased growth rates between weaning and breeding at seven months of age on the morphology and dimensions of the internal structures of the mammary gland of two-year-old ewes. Ultrasound imaging, however, enables only the udder dimensions to be visualised [15,22] and echo-textural characteristics [28,29] of the mammary internal structures to be assessed. Further investigations may be warranted to determine the effect of increasing growth rates prior to the first breeding on the cellular development and function of the ewe mammary gland, particularly if greater live weight differences than seen in the present experiment can be achieved.…”