Evy Tobolski and Elizabeth Plunkett, Graduate Research Associates, Department of Animal Sciences, The Ohio State University
Raising and selecting quality replacements is a necessity for every dairy operation. Selectively breeding for higher milk production has its advantages, but some fail to recognize that genetic merit doesn’t always account for enhanced mammary growth and development, and often, early life nutrition and management can influence the mammary gland more substantially. Advancing technology has led to the exploration of real-time ultrasonography, a non-invasive tool to monitor growth and development across time. The expense associated with raising heifers is worth utilizing developing technology available to explore opportunities to select for more profitable heifers.
Ultrasonography in Heifers
Initial growth and development of the mammary gland begins in utero around day 30 of gestation in dairy cattle. At birth, a rudimentary mammary system is present, consisting of the mammary parenchyma (PAR) and the mammary fat pad (MFP). Epithelial tissue and its surrounding stromal elements make up PAR, which has the capacity to make and secrete milk. The MFP is primarily composed of stromal elements meant for support and structure. Previous research has placed heavy emphasis on studying mammary development in heifers, which requires their timely euthanasia. However, to understand how certain factors that occur during mammary growth and development (e.g., heat stress) impact the secretory capacity of the mammary gland, we must allow these research animals to reach lactation. Studies like these require a tremendous amount of time and money, both of which are limited resources. The use of ultrasound technology, largely used in dairy cows for assessment of the reproductive tract, has now enabled researchers to examine mammary growth and development without the need for early euthanasia, allowing animals to progress into lactation to study their subsequent performance.
A study done by Vang et al. (2024) examined the use of ultrasound technology as a tool to monitor mammary gland growth and development in Holstein heifers, assessing the influence of diet on PAR for the first 8 weeks of life. Thirty Holstein heifer calves were randomly assigned to a pair-fed high protein/fat (27% CP, 20% fat) or low protein/fat (22% CP, 15% fat) milk replacer diet in which calves were fed twice daily one gallon of high protein/fat milk replacer in the high treatment group and 2 quarts of low protein/fat milk replacer in the low treatment group. On day 7, a textured starter (18% CP) was introduced. A Mindray Ultrasound, typically used to determine reproductive status, was used to examine the PAR and MFP areas of all four glands twice weekly from birth through 8 weeks.
Through the use of ultrasonographic imaging, researchers demonstrated that the total PAR area increased in both treatments. However, heifer calves fed the high protein/fat diet had increased growth compared to the low protein/fat diet calves. Mammary PAR area was similar between both treatment groups during the first 2 weeks, but beginning in week 3, the high protein/fat diet calves displayed larger PAR and MFP areas and continued with this dramatic growth through week 8 (Figure 1).
Figure 1. Image of the rear left quarters of paired 8-week-old heifer calves on the low protein/fat treatment (A) and the high protein/fat treatment (B). PAR is outlined in pink and MFP in yellow. The white bar measures 1 cm.
What Do These Results Mean?
From this study, ultrasonographic imaging was successfully used to measure PAR and MFP areas from birth through 8 weeks of age. The results from this study, particularly the finding of increased PAR area of calves fed a high protein/fat milk replacer, demonstrate the effectiveness of ultrasonographic imaging of the mammary gland. This highlights how early dietary choices can influence mammary growth and development. Additionally, this study suggests that features defined through ultrasonographic images of the mammary gland can be a powerful tool to monitor the growth and development of the PAR and MFP in heifers without the need for euthanasia. This can encourage the monitoring of these parameters to extend to lactation and allows researchers to begin making correlations to lactation performance.
The ability to capture mammary growth rates of calves using ultrasonography has the potential to be a worthwhile opportunity for dairy producers to explore. If later lactation performance can be inferred from early use of ultrasonography, producers can begin to select replacement heifers based on yet another parameter. Allowing for early decision making to select for heifers with the highest secretory potential and removal of those that are sub-par. This would also allow you to evaluate the impact of your young stock nutrition and management strategies and enable you to make necessary changes sooner.
Why Should you Start to Care?
With the advancements made in quantifying the growth and development of the mammary gland of heifers, researchers are starting to use this technology to determine treatment options for mastitis. Mastitis, inflammation of the mammary gland, primarily results from an intramammary infection. In a study done by Suzuki et al. (2020), ultrasonographic imaging was used to identify abnormal mammary tissues in cows with clinical mastitis. Further work in this area could lead to the use of ultrasound examinations to predict mastitis outcomes early on and influence treatment decisions. There is a potential economic benefit for producers and the opportunity for early decision-making. While further research is needed to confirm preliminary findings, exploring new advancements in technology that can allow producers to make more informed decisions is critical to the ever-evolving dairy industry.
Sources
Suzuki, N. et al. 2020. Outcome prediction from the first examination in clinical mastitis using ultrasonography in dairy cows.” Animal Science Journal 91:e13452. https://doi.org/10.1111/asj.13452.
Vang, A. et al. 2024. Monitoring mammary gland development in preweaning dairy heifers using ultrasound imaging. Journal of Dairy Science Communications 6:725–28. https://doi.org/10.3168/jdsc.2024-0586.