# Making future udders: Mammary development and perinatal programming of dairy cattle

## TL;DR

Proper care and nutrition during the perinatal period in dairy cows can significantly boost future milk production by promoting early mammary gland development.

## Contribution

The study highlights that mammary gland development in dairy cattle begins much earlier than previously believed, during the perinatal period, and is influenced by environmental and nutritional factors.

## Key findings

- Mammary parenchyma grows 15 to 35 times during the perinatal period, much faster than other tissues.
- Heat stress abatement and improved nutrition in early life enhance mammary development and future milk production.
- Early-life management strategies can program lactational performance in dairy cows.

## Abstract

Summary: The last 2 months before birth and the first 2 months after birth represent a crucial window for organ development, including the mammary gland, in dairy cows. Traditionally, it was thought that allometric mammary growth began after weaning or around puberty. However, recent research indicates that significant early development of the mammary parenchyma occurs during the perinatal period and can influence a cow's future milk production. This early growth is highly sensitive to environmental and nutritional factors. Heat stress abatement and higher nutritional planes in early life increase mammary parenchyma growth and improve future productivity. Proper management during the perinatal period is essential to optimize lifetime milk yield.

Summary: The last 2 months before birth and the first 2 months after birth represent a crucial window for organ development, including the mammary gland, in dairy cows. Traditionally, it was thought that allometric mammary growth began after weaning or around puberty. However, recent research indicates that significant early development of the mammary parenchyma occurs during the perinatal period and can influence a cow's future milk production. This early growth is highly sensitive to environmental and nutritional factors. Heat stress abatement and higher nutritional planes in early life increase mammary parenchyma growth and improve future productivity. Proper management during the perinatal period is essential to optimize lifetime milk yield.

•The perinatal period is a critical window for mammary parenchymal development.•Early-life heat abatement and enhanced milk nutrition promote parenchyma growth.•Environmental and nutritional factors can program future lactational performance.

The perinatal period is a critical window for mammary parenchymal development.

Early-life heat abatement and enhanced milk nutrition promote parenchyma growth.

Environmental and nutritional factors can program future lactational performance.

The perinatal period, described herein as the time spanning the final 2 mo of gestation through 2 mo postnatal, is a critical window of developmental plasticity for many organs in placental mammals, including the mammary gland (MG). In dairy cattle, early-life MG development involves foundational morphogenic events that are highly sensitive to environmental and nutritional factors. Emerging evidence challenges the long-standing belief that substantial MG development begins after weaning and lasts until puberty, showing instead that preweaning mammary parenchymal (mPAR) growth is allometric and its degree of development can influence future lactational capacity. Overall BW typically doubles from birth to 60 d, whereas both whole udder weight and the mammary fat pad increase by ∼2.2 to 3 times over the same period. In contrast, the mPAR exhibits pronounced allometric growth, expanding 15 to 35 times during this time. Early-life management strategies, such as heat abatement to maintain thermal homeostasis and enhanced nutrition through higher milk intake supporting greater average daily gain, further promote mPAR development and can positively influence future lactation performance of dairy cows. These findings underscore the importance of integrating developmental biology into heifer-rearing strategies and emphasize the need for precise environmental and nutritional management during this critical window to support lifelong mammary function and optimize herd performance.