Increasing the mammary gland development of heifer calves in the hope of spurring long-term production advantages, has long been a goal for dairy farmers. While there is a broad body of evidence that elevating the level of nutrition after weaning but prior to puberty negatively affects mammary gland development and milk yield, there has been ongoing debate about the effects of elevating the level of nutrition prior to weaning in order to achieve positive effects on the mammary glands. A recent joint study by Virginia Polytechnic Institute and State University and the US Department of Agriculture[i] attempts to shed more light on the subject. They sought to clarify the effects for mammary gland growth of elevating the plane of nutrition before weaning. And, they were particularly keen on discovering the effects that higher levels of pre-weaning nutrition have on the mass of mammary gland parenchyma and on mammary fat pad development.
Thirty-six Holstein heifer calves were separated into two treatments. The control (CON) group was fed 454g of milk replacer (MR) per day containing 20% crude protein (CP) and 20% fat. The accelerated group (ACC) was fed 1.135kg of MR per day at 28% CP and 25% fat. Starter feed was introduced at week 5 and MR was reduced in both treatments to 50% at week eight, to induce weaning. All calves were housed individually with ad libitum access to water. Teats were measured weekly and udders were examined through palpation and visual examination. ACC calves consumed a higher volume of MR pre-weaning per day than CON calves (4.58 litres vs. 3.20 litres).
At weaning, six calves per treatment were killed and their whole mammary glands were removed, weighed and dissected. The ACC calves had longer front (1.3 cm vs. 0.9 cm) and rear (1.2 cm vs. 0.8 cm) teats than CON calves. ACC calves also had heavier whole, untrimmed udders (255g vs. 66g) than the CON calves, with the difference being even more pronounced after the skin was trimmed (198g vs. 38g). Additionally, and more importantly for the researchers, the mammary gland parenchyma and the mammary fat pads of the ACC calves had greater mass than those of the CON calves (10.5g vs. 1.4g and 173g vs. 29g respectively).
The results are strongly aligned with those who have previously found that elevating the pre-weaning plane of nutrition for dairy calves has a strong, positive impact on mammary gland development. While the research team is still looking into the specific molecular and cellular mechanisms which cause these differences, the positive effect of higher pre-weaning nutrition on mammary gland development is clear.