Causal factors affecting variation in live weight gain in north Australian beef herds

Sarah Streeter, Nigel Perkins, Trisha Cowley and Neil MacDonald - Meat & Livestock Australia

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

This research article looks at the causal factors affecting variation in live weight gain in north Australian beef herds. Interesting to note that weight and hip height at weaning appeared to be associated with dry season ADG.

What is the problem?

The remainder of this report relates to the prospective study completed over a two to three year period on commercial properties covering multiple regions of the NT. The study investigated genetic, conformation, early management, behavioral and disease factors.

What did the research involve?

●Site Descriptions

• Location
-A total of eleven herds were enlisted in the study, running on properties located across seven regions of the NT and owned by both private and company enterprises.

• Paddock and pasture descriptions
-Information includes total area, area within a 5 km radius of watering points and land system breakdown within respective grazing radii.

• Rainfall
-Rainfall data was summarised for all properties and included seasonal conditions for both the year prior to the animals being weaned and inducted into the study and the observation year.

● Animal descriptions and measures

● Experimental animals
-Eleven study groups of steers on different commercial cattle properties were inducted at weaning and observed in one of three 12-month periods: 2008/09 (n=1); 2009/10 (n=5); and 2010/11 (n=5), with the first year corresponding to the weaning year for the group. Animals were selected at random from a larger mob at weaning and inducted into the study.

• Timing of observations
-Experimental animals were yarded on four occasions for observation over the 12-month study period: Obs1, Obs2, Obs3 and Obs4.

• Mob-level measures
-This included information about the property the animals were located in (PIC), animal breed (BREED) and year of birth (YEAR), age structure of the Dam herd (DAM_AGE), vaccination schedule (VACC), health treatments schedule (TRT), supplementation strategy used (SUPPLEMENT) and method of supplementation delivery.

• Animal measures
-All observations and measurements recorded for individual animals over the 12-month study period are detailed in Table 18. Where data were measured on multiple occasions, the trait code is followed by a numerical prefix that can be mapped to the observation (e.g. LWT1, LWT2).

• Flight speed
-The method of measuring flight speed was an adaptation of the method outlined by Radunz (1992).

What were the key findings?

● Multivariable analyses using ADG measures as outcomes
-This section describes the results from a set of multivariable analyses that aimed to utilize all available data from multiple properties in analyses to explore factors that might explain variance in live weight gain.

● Descriptive analyses for live weight and ADG
-The following tables show simple descriptive summaries (mean, standard deviation, minimum and maximum and count) for each observation period.

● Repeatability of bodyweight measures
-There was interest in collecting repeated measures of live weight on a sample of animals in order to assess the repeatability of weighing systems.

● Impact of day and time on live weight measures
-There was interest in the possible effects of the time period animals may have spent in the yards before they were weighed, particularly since there was some variation in how long animals had spent in the yards between properties and also between observations at the same property.

● Hip height
-In those properties enrolled in the 2009-2010 year, hip height was measured initially at Obs2.

● Differential growth – height vs weight
-Animals within each property were classified as less than or up to the median weaning weight or greater than the median weaning weight for that property.

-The highest dry season increase in hip height was seen in the shorter animals at weaning compared to animals that were taller at weaning.

● Flight speed
– Flight speed was recorded on 4 observation periods but inspection of the data indicated that there were few animals with a flight speed measure recorded on all four occasions.

-The mean flight speed reduced over time. Flight speed is measured in meters per second, meaning that smaller numbers indicate that an animal is moving at a lower speed.

● Body condition score (BCS)
-There was a close association between BCS and live weight at each measuring occasion with increasing BCS associated with increasing live weight.

-Regression analyses were run using ADG measures as outcomes and BCS as a categorical predictor. Models also included a fixed effect coding for a year of enrolment and a random effect coding for the property.

Final comment

The contemporary study incorporated activities looking at repeatability and accuracy of weighing systems and management of animals around the time of weighing in response to concerns over variability in weighing platforms and management of cattle as they were yarded and handled around weighing.

2014 - Australia - Sarah Streeter, Nigel Perkins, Trisha Cowley and Neil MacDonald - Meat & Livestock Australia
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