New research challenges opinion on mammary development in heifers
Raising dairy heifer replacements cost money. Until they become part of the milking string they are not contributing to the dairy farm’s income. It needs to be realized that raising replacements represent 15-20% of the total cost of producing milk. Reducing these overhead costs has been an impetus to enhance pre-pubertal (up to 8-9 months of age) growth, onset of puberty and lower first calving age. But usually this has been accomplished with adherence to pre-pubertal feeding concerns for optimum udder development.
Recent research at Cornell University by Meyer and Van Amburgh challenged the thinking and opinions established over four decades ago of a direct relationship between pre-pubertal underdeveloped mammary tissue growth and subsequent milk yield. The mammary gland goes through two growth phases whereby the mammary parenchyma tissue (the developing and functional tissue of the udder) DNA increases at a relatively faster rate than the body. The pre-pubertal phase includes mammary duct growth but without secretory alveoli cells. After conception, the second phase occurs under hormonal influence showing a further branching and extension of mammary ducts and the appearance of milk secreting alveoli.
The graph below adapted from Meyer (2005) illustrates the percentage of mammary parenchyma DNA from birth through 2nd calving as a percent of maximum at first calving. Indicated below are: Puberty (A), First Conception (B), First Calving (C), 2 nd Conception (D), Dry Off (E), and 2 nd Calving (F).The pre-pubertal growth phase accounts for only 2% of total parenchyma present at the beginning of 1st lactation. Cornell workers suggested that these small number of cells would have to play a major role to affect milk yield.
A re-evaluation by Van Amburgh of the classic 1960’s research proposed that heifer over-conditioning and calving difficulties at that time may have been overlooked as a primary factor affecting lactation performance, not impairment of udder development per se. Consequently, Cornell research recently investigated the effect of pre-pubertal elevated vs. restricted dietary energy levels. They concluded that heifers on a high plane of nutrition have less parenchyma DNA at puberty as they reach puberty at a younger age. They also found that pre-pubertal mammary development is not directly correlated to first lactation milk yield.
The Bottom-Line: For optimum nutritional management for pre-pubertal heifers, a correctly balanced dietary energy and protein ration that results in good frame growth without over conditioning, plus adequate exercise seems to be important criteria irrespective of udder development during this phase.
More discussion on the above Cornell research and a systematic approach to Calf Nutrition and Management will be presented by Dr. Mike Van Amburgh at the upcoming Professional Dairy Heifer Growers Association (PDHGA) 9th Annual Dairy Calf and Heifer Conference. This conference will be held in conjunction with the Central Plains Dairy Expo at the Sheraton Sioux Falls Convention Center, March 29 through April 1, 2005.
The PDHGA program begins with motivational speaker Jolene Brown presenting “Normal Doesn’t Live Here Anymore.” This will be followed by some excellent paper presentations on a variety of topics including: Managing Pre-weaned Calves for Optimal Health (Dr. Jim Quigley); Where Dairy is Headed (Dr. Roger Cady); Integrating Dairy Cow, Calf and Heifer Behavior into Facility Design and Handling Methods (Dr. Temple Grandin); New Technology for Reproductive and Genetic Solutions (John Metzger), and Cut Costs with Improved Bunk Management (Dr. Robbie Pritchard). There will also be Heifer Management Tips, a Virtual Tour from Dairy and Heifer operations, plus a Dairy Producer–Heifer Grower Panel during the conference.
Throughout the four days there will be a substantial Central Plains Trade Show (over 200 exhibit booths) and also a number of special trade show breakout sessions. Breakout session topics include: Raising Top Quality Heifers, Managing Close-up and Transition Heifers, Selecting Dry Fats for Dairy Cows, Controlling Heel Warts, Vaccination Strategies, Reproduction and BVD Virus, Aspects of Calf Raising, and Improving Silage Quality.
The event will conclude on April 1st with a local bus tour including stops at Boadwine Dairy, Trans Ova Genetics, Dykstra Dairy, and Wielingas Heifer Grower operation. For more information call PDHGA Headquarters at 1-877-434-3377 or e-mail firstname.lastname@example.org. Online registration also can be done at www.pdhga.org.