Murray Rogerson



The Effects of Gravity
Grazing mammal figures can be extremely variable, but approximately for every ten-fold increase in adult weight, fecundity halves, conversion rate doubles, metabolism decreases and food fibre consumption percentage increases. A 60kg sheep is capable of 1.3 lambs in 8 months with a 4-1 conversion rate of a grass only diet. A 600kg cow can reproduce 1 calf per year at a conversion rate of 8-1, consuming greater quantities of dry hay with a slower metabolism. A 6000kg elephant produces 1 calf in 5 years with a conversion rate closer to 16-1, very high fibre consumption and very slow metabolism.

It is no accident that the largest adult size occurs in the ocean where water support diminishes the need for internal infrastructure and low water temperature variation dramatically improves conversion rates towards 1-1 for smaller fish.

The march in tractor horsepower stalled suddenly 20 years ago at 500 – 600 hp, because excessive machinery infrastructure weight increased capital cost, fuel usage and compaction dramatically. Without the power of earth rotation, gravity disappears.

The Theories of Size
When the second fleet dropped into Calcutta to pick up 10 Garole ewes from West Bengal with an average adult weight of between 10 and 14kgs and a fecundity of 227% which went on to become the BFec. (Booroola) gene in Australia.
What were they thinking?

When one of Australia’s highest performing ASBV recorded studs entered ewes into the 2016 Elmore sheep trials with an average dam join weight in their final year of 92kgs.
What were they thinking?

When the CSRIO in the previous century decided that a dry sheep equivalent (DSE) was the 7.8 megajoules per day required to maintain a 45kg 2-year-old Merino dry sheep.
What were they thinking?

The Evidence for Optimal Size
Table A below is the weaned wet portion of the complete Stirling Dohne Stud ewe flock showing group NLW averages for 5 weight groups descending in order.

On my website presentation “Accuracy Analysis for Objective Show Judging” I have projected the hypothetical Group 6, where lack of nestling ability combined with low birth weights and climate will possibly plateau NLW.

Table B below are the summarized results for the 4 adult years of the Elmore “Ewes for the Future” 2015-19 trials in descending order of bodyweight plotted against several traits with DSE factored for Dam bodyweight and NLW.

DSE return at 58.6kgs is still rising sharply except for Group 4 which is the Booroola gene effect.

America increased adult size in the 60’s, 40 years before Australia. We both had around 50 to 60 million sheep in 1880. Today we have 65 million whilst America is under 5 million. If low adult size is the sheep population driver, we are on a rocky road but the leading question is, how did the CSIRO come up with the correct answer 70 or 80 years ago?

Acknowledgements – Elmore Field Days “Ewes for the future trails” & CSIRO