Performing Department
(N/A)
Non Technical Summary
Dairy youngstock, calves and heifers, are the future of the milking herd and represent a substantial on-farm investment. It is well established that conditions during the rearing period have lifetime consequences. Further, dairy animals contribute to greenhouse gas emissions and compete for land and feed resources. Therefore, the long-term goal of this project is to improve the sustainability of the US dairy industry through an improved understanding of the genetics underlying feed utilization. To accomplish this long-term goal, we will evaluate the genetic influences of dairy heifer feed utilization and growth parameters, compare methane production and energy efficiency between calves, and establish the economic benefits of improved feed efficiency. We expect to show that there is a measurable genetic component underlying feed utilization and methane production in growing dairy youngstock across different ages of the growing phase. Further, we expect that animals having greater feed utilization efficiency will also have reduced costs to producers. This work will contribute to improved farm profitability and improved environmental sustainability of dairy youngstock.
Animal Health Component
80%
Research Effort Categories
Basic
20%
Applied
80%
Developmental
(N/A)
Goals / Objectives
The long-term goal of this project is to improve the sustainability of the US dairy industry through an improved understanding of the genetics underlying feed utilization. To accomplish this long-term goal, we propose the following supporting objectives: 1) Evaluate the genetic influences of dairy heifer feed utilization and growth parameters. 2) Compare postweaning methane production and energy efficiency in between calves with high versus low preweaning feed efficiency. 3) Establish the economic benefits of improved feed efficiency.
Project Methods
Objective 1: Body weight and hip height are recorded upon arrival and on d 56 after arrival at calf rearing facility. All calves have serum total protein measured upon arrival. The standard diet includes a 24/20 milk replacer and 18% crude protein textured calf starter. In addition, calves enrolled will have the following data recorded until 56-d: daily milk replacer intake (offered - refused), daily starter intake (offered - refused), daily fecal scores, all disease treatment, total treatment costs, and bi-weekly body weights. Growth and body traits will be measured on 1500 calves and include arrival weight, 56-d weight, average daily gain through 56-d, arrival hip height, 56-d hip height, hip height gain until 56-d, body mass index upon arrival (bodyweight / hip height), and body mass index at 56-d. A subset of calves (n = 750) will be evaluated for feed efficiency traits with daily intakes recorded. Traits of interest include total dry matter intake, metabolizable energy intake, gain:feed ratio, and the residual values of these traits. All feed intake subset calves will be genomic tested using a commercial testing service for 42k SNP. All phenotypic records will be combined with pedigree data extracted from herd management software utilized by source farms. Analysis: Analyses will be conducted using SAS 9.4 (SAS, 2011), R (R Core Team, 2022), and blupf90 software (Misztal et al., 2018). All models are expected to include farm contemporary effects (herd, year, season of birth) and study effects (trial, treatment). Feed intake traits are also expected to include body weight and average daily gain to account for major energy sinks. Pedigree and genomic data will be included for genetic analyses. We will also evaluate genetic correlations with other traits evaluated by the Council on Dairy Cattle Breeding using sire predicted transmitting abilities.Objective 2:One hundred and forty dairy heifers will be classified at weaning into either high or low feed efficiency groups based on their preweaning gain:feed ratio. Calves will be blocked by age and body weight and assigned to one of 14 pens (n =7 pens per feed efficiency group) in a randomized complete block design with 7 calves/pen. All calves will be fed the same diet formulated to meet the growth requirements of a postweaned heifer, including a textured calf starter and dry alfalfa hay offered ad libitum. Daily consumption of calf starter and hay will be measured by subtracting the amount of refused feed from offered feed. Feed will be offered at 115% of the previous day's intake. Body weights will be measured on individual calves weekly. Gain:feed will be determined using average body weight divided by average feed intake.In addition to determination of gross feed efficiency, energy losses as fecal, urinary, gaseous, and heat energy will be determined to develop a more complete picture of whole-animal energy efficiency. Fecal and urine samples will be collected weekly at 4 equally spaced intervals and analyzed for gross energy using Bomb calorimetry. Two GreenFeed gas measurement systems will be used to measure methane and CO2 production and O2 consumption. Heat production will be estimated using Brouwer, (1965) equation: Heat (kcal/d) = 3.866 * O2 + 1.200 X CO2 - 0.518 * CH4 - 1.431 * N. When combined with total collection of feces, urine, and milk, the complete energy balance of a cow can be calculated including the amount of energy digested, metabolized, expended as gas, produced as heat, used for maintenance, and used for growth. These measurements will allow us to gain a more complete picture of energy partitioning compared to measuring gain to feed alone. Analysis: Models will include the effects of preweaned feed efficiency, treatment nested within trial, and source farm contemporary effects (herd, year, season of birth). Preweaning feed efficiency will have the effect of interest and allow us to determine if animals diverging for feed efficiency also have differing methane production and energy production after weaning.Objective 3: Feed cost will be calculated for each calf as the sum of milk replacer cost and starter cost. We will calculate cost per gain and utilize this trait to determine if high feed efficiency animals have lower cost per gain than low efficiency animals. In addition, treatment costs are calculated for each animal and will allow us to determine the relationship between feed efficiency, growth, and treatment costs.