Monitoring mammary gland development in preweaning dairy heifers using ultrasound imaging.

Existing literature on the long-term effects of nutritional manipulation on milk production is incomplete and inconsistent as animals are typically culled before lactation. In addition, longitudinal studies are rarely conducted due to high costs and constraints related to tissue sampling; therefore, additional research is necessary to better understand the effect of early nutrition and growth on subsequent growth and milk production. Thirty Holstein heifer calves were pair-fed high (H; 27% CP and 20% fat) or low (L; 22% CP and 15%) milk replacers. Mammary gland ultrasound images and BW were collected twice weekly, and blood samples weekly, for the first 8 wk of life. Calves fed H had higher ADG and mammary gland growth through 8 wk of life. Calves from the H group also had larger fat pads at 8 wk of age. Glucose and insulin concentrations were increased in H calves compared with L calves, whereas nonesterified fatty acid concentrations were not different between treatments. Our results suggest that ultrasound is a practical, noninvasive tool to monitor udder development preweaning, although additional research is necessary to improve image analysis techniques to analyze tissue composition. Our preliminary work provides data suggesting that the use of mammary gland ultrasound could provide a method of longitudinal analysis of the effects of preweaning nutrition on milk production.