Developing a high-throughput walk-over-weighing system for extensive sheep production systems

The profitability of an extensive sheep production system is heavily reliant on the animals' ability to maintain performance in a wide variety of environmental conditions. A resilient animal will have the ability to remain healthy and maintain performance despite the environmental challenges it faces. However, tracking performance in large bands of sheep is encumbered by the ability of a worker to accurately keep track of many animals simultaneously. Furthermore, subtle changes to an animal's condition over time may go unnoticed until performance is severely affected. In Nevada, sheep are grazed in a rangeland environment and monitored by a worker who musters them to an encampment each night, which provides a unique opportunity to routinely collect measurements on individual performance. These measurements can serve both to improve management practices as well as collect trait information for genetic selection in extensive operations.
These funds will be used as part of a wider research effort to explore methods to incorporate precision agriculture for management and genetic improvement in extensive rangeland sheep operations. The objective of this study is to develop a high-throughput and portable walk-over-weighing system that incorporates the use of EIDs for routine weight collection. This system will be used to collect individual daily weight measurements while animals are grazing in a rangeland environment. The objectives of this study are to design and test the ability of this system to:
1) monitor livestock inventory and identify when animals are missing, 2) identify animals that have altered performance, e.g., due to injury or sickness, and 3) gain a better understanding of the genetic basis of resilience in an extensive production system through the integration of pedigree information and lamb-ewe positioning data with the weighing system proposed herein.

Aim 1: Develop a high-throughput walk-over-weighing system for extensive rangeland systems The design of the proposed walk-over-weighing system will need to have three features to provide versatility in its use in this system:
1) the ability to be broken down and transported to other locations,
2) the ability to control the flow of animals through the weighing system while simultaneously providing the throughput to feasibly capture weights on hundreds of animals per day,
3) high enough accuracy to detect fluctuations in body weights. A gated system will be employed to control the flow through the target location where a weighing station will be set up to ensure the animal weights are captured. The proposed system will utilize EID tags to automate weight recording as an individual passes through the gate. Because this system needs to efficiently capture weights as the band of sheep are either leaving or returning to the encampment, being able to efficiently capture weights is instrumental for routine data collection.
Therefore, we will design a multi-gated system with the ability to collect weight data on multiple sheep simultaneously to allow high-throughput collection of weight data. Previous studies using walk-over-weighing systems in intensive production systems in sheep have shown that the accuracy of the measurement is dependent on the ability to control the speed over which the sheep passes over the weigh bars; therefore, we will explore methods to control the flow of animals as they pass through the weighing system. We will first test the system in a controlled environment, where we can test throughput, accuracy and animal behavior of the walk-over-weighing compared to gold-standard methods of weight collection.

Aim 2: Conduct a one-month trial to assess the system as a management tool in a rangeland environment Once an optimal design has been determined, the walk-over-weighting system will be deployed on 180 sheep (~90 ewes and their lambs) from a single band of sheep at the Great Basin Research and Extension Center in Eureka, Nevada for a one-month period to trial the system. A major challenge of extensive production systems while animals are grazing on rangeland is being able to reliably identify when the performance of a flock has been negatively impacted, particularly when the condition of the animal is not severely impacted. Routinely collecting individual weights on animals will provide the ability to identify when an animal's performance has dropped off, which may be related to the overall well-being of the animal. We will identify animals that show a reduction in performance during the trial period and inspect these animals for health or conformation issues that may impact performance to assess the ability of the system to identify lame or sick animals. An additional benefit of the walk-over-weighing system is the ability to track animals and identify when they have gone missing. To demonstrate this, we will record when an animal has gone missing and overlay that with events identified in interviews with workers (e.g., identification of predators in the area being grazed). This will demonstrate the potential of this system to keep livestock inventory.

Aim 3: Develop novel traits for individual performance in a rangeland setting While our proposed system has potential to be used for management purposes, selection of animals that can maintain performance in a range of environments (i.e. resilient animals) can result in improved flock performance and profitability.

The potential to utilize routinely recorded walk-over-weighing data to select for more resilient animals will be assessed by integrating the recorded weight data with pedigree information to obtain estimates of heritability for commonly defined resilience traits developed in intensive production systems. The ability of a ewe to care for her offspring has a major impact on lamb survival pre-weaning. Data collection will take place pre-weaning when lambs are still with their ewes.

Therefore, this system has the potential not only to collect individual weights, but also to determine the proximity of the lamb to its ewe based on timestamps as the animals pass through the gate. Proximity data on both the ewe and the lamb has the potential to assess mothering ability in a rangeland environment, which may have a more favorable impact on lamb survival. With this information, we can explore mothering ability in a rangeland environment as part of our study on traits that indicate resilience. Pre-weaning weights will be assessed as both the trait of the individual as well as a trait in the dam. Expressed as a trait of the dam, this phenotype is indicative of the ability of the ewe to provide the nutrition to sustain her offspring.