Location: Forage and Range Research
Project Number: 2080-21000-018-048-A
Project Type: Cooperative Agreement
Start Date: Aug 1, 2021
End Date: Dec 31, 2024
Determine the influence of dairy breed on heifer growth and nutrient leaching when grazing either grass-monoculture or grass/birdsfoot trefoil mixed pastures.
This experiment will be conducted at the Utah State University Intermountain Pasture Research Farm located near Lewiston, UT, USA. The proposed study will be arranged as a 4 × 2 factorial with four levels of dairy breed and two levels of pasture-type [i.e., grass monoculture (MONO) and grass-BFT mixture (MIXED)]. For each of grazing season four pre-pubertal dairy heifers of four dairy breeds (Holstein, Jersey, Holstein/Jersey crossbreds, and ProCross crossbreds) will graze the pastures. Rotational stocking will be used with a stocking period of 3.5 days per paddock, followed by a rest period of 31.5 days, such that the entire rotation cycle is 35 days. There will be three rotation cycles each year for a total of 105 grazing days (15 May to late August each year). In addition, three feedlot replicates of three heifers per breed will be fed a TMR formulated for an ADG target of 0.8 kg/day, and feed offered and refused each day weighed to calculate TMR DMI. SubObjective 1: Determine the influence of dairy breed on livestock growth. All heifers will be weighed, body condition scored, and have blood samples drawn at the initiation of grazing, and at the end of every 35 day grazing cycle thereafter. Blood work will entail an assay for insulin-like growth factor 1 (IGF1; produced mainly by liver and is the primary mediator of GH production and release). Blood will be collected from the coccygeal vein into heparinized vacutainer tubes and stored on ice until processed. Blood samples will be analyzed for IGF-I in duplicate following manufacturer-recommended procedures. SubObjective 2: Determine the influence of dairy breed on nutrient leaching. Soil water (leachate) nitrogen will be monitored by means of 90-cm suction-cup lysimeters (below the root zone). Leachate will be collected every week during the growing season. The leachate will be analyzed for nitrate-nitrite concentration using QuickChem Method 10-107-04-1-C . Leachate concentration and volume will be used to determine total leachate N. Composite soil samples will be analyzed for available nitrogen (NO3-N). Nutrient cycling and N-use efficiency will be evaluated by studying the relationships between herbage N intake with N loss in leachate and the soil and fecal, urine urea, and blood urea N. SubObjective 3: Objective 3. Ascertain the influence of dairy breed on the economic sustainability of pasture-based heifer development: Partial budgeting techniques will be used to determine the cost differences from each heifer development program. Costs associated with procuring and feeding the different breeds of heifers will be determined. These costs will be subdivided for each of the breeds according to pasture-type (MONO or MIXED) and TMR-fed. The partial budgets will be used to quantify the impact of heifer performance, under each pasture-type and TMR, on the economic value of the four breeds.