The Penn State Dairy Heifer Diet Formulator
Posted: August 30, 2016
Formulating dairy heifer rations is an often overlooked aspect of farm feeding programs. In addition, most available ration balancing programs were not developed with current heifer growth requirements. Our research team at Penn State has developed and uses a spreadsheet that we call the Penn State Dairy Heifer Diet Formulator (PSU-HDF). The PSU-HDF was originally developed to design and evaluate diets used in heifer research. However, due to the clear need for a ration balancing program focused on heifers it has recently been updated and made available online for anyone to use.
The basis for diet formulation in PSU-HDF is N (nitrogen) intake (g/kg of metabolic body weight) with a target of 1.67 g of N/kg BW0.75. In contrast, NRC emphasizes the intake of crude protein (CP) and its fractions. Furthermore, NRC recommends dairy heifer diets meet certain dry matter intakes (DMI) in addition to meeting metabolizable energy (ME) requirements. Research at Penn State has demonstrated that varying DMI can produce similar average daily gains (ADG) provided the diet precisely meets the ME and N requirements. Therefore, PSU-HDF places more emphasis on meeting N and ME needs and adjusts DMI as necessary. We know from research that there is a cap on maximizing DMI, usually imposed by intake of fibrous feeds, but there is not necessarily a lower limit.
A simple comparison shown in the table below allows us to see how the NRC 2001 model consistently overestimates the nutrient requirements of growing dairy heifers. Using the PSU-HDF model will allow for feeding 15 to 20% less energy, 25% less dry matter, and 0.4 to 1.1 fewer pounds of protein. Our published research studies have shown over and over that these PSU-HDF rations will meet or exceed the desired growth rates for today’s dairy heifers, and allow them to calve at 23 months of age. This spreadsheet will allow nutritionists to formulate diets to meet dairy heifer needs and reduce feed cost by feeding less energy, protein, and dry matter.