Location: Dairy Forage Research
Project Number: 5090-12210-001-18-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Jan 1, 2016
End Date: Dec 31, 2019
To investigate the relationship between pasture input variables and growth of dairy heifers. We hypothesize that improving pasture productivity and nutritive value will improve heifer growth and success of breeding. The cost of rearing heifers is second only to feed costs on a dairy farm, and efficient rearing of heifers intended as replacement animals in the lactating herd is critical to profitability. The specific objective of the ARS investigator will be to determine the influence of management input on 1) pasture annual net primary productivity and forage nutritive value; 2) soil chemical and biological properties; 3) weight gain, physical characteristics, and reproductive efficiency of grazing heifers; and 4) economics of the rearing process.
A 12-hectare (ha) pasture having a history of continuous stocking will be subdivided into four equal areas to compare two pasture management practices typically utilized by producers (two replicates). In the spring of 2016, soil potassium and phosphorus fertility of all areas will be assessed and corrected as needed. Weed population and diversity will be determined in each replicate. The treatments will be 1) introduction and maintenance of improved grass and legume species, and 2) limited nitrogen fertilizer application. Improved grass and legume species (Treatment 1) will be sown in early spring of 2016 after weeds are eliminated by herbicide. Nitrogen will be applied (Treatment 2) when legumes from Treatment 1 have been established. A cohort of 40, six-month old Jersey dairy heifers purchased by the cooperator for this research will be weighed and body condition scored on three consecutive days prior to the initiation of grazing. Groups of equivalent total body weight will rotationally graze 0.4-ha paddocks within each treatment. Cattle will graze pastures throughout the season (late April to early October) when sward height reaches 25-30 cm and will be removed when residual sward height reaches 10 cm. Pre- and post-grazing sward dry matter yield will be measured by rising plate meter; forage produced in excess of animal demand will be harvested and conserved. Nutritive value (protein, cell wall, digestibility) will be measured on all forage, grazed or harvested. At the end of the grazing season, heifers will be scored and weighed as before, and success of breeding confirmed by a veterinarian. Carbon and nitrogen mineralization of soil samples collected at the beginning and end of the grazing season will be measured. Cost of all inputs will be measured. Data from each management system will be compared.