Merino lambs need fat and muscle to survive

Jim Watts

All of the 40 SRS Merino studbreeders in Australia use breeding values for body fat and muscle to select rams that will improve lamb survival and the overall fitness of the flock, and the flocks of ram buying clients.

We are indebted to researchers, Mark Ferguson and Andrew Thompson, as well as SRS Merino studbreeders, Mark and Vicki Murphy from the SRS Karbullah Poll Merino Stud, Queensland, who jointly discovered that more lambs survive when sired by rams with high breeding values for fat cover and eye muscle depth.

The Table below are the results of the 2008 lambing of Mark and Vicki Murphy’s SRS Merino flock.  About 20 % more lambs survived through to weaning at 5 months of age when sired by rams with high breeding values for fat and muscle.

The Karbullah flock is located in south western Queensland, a challenging environment for sheep where quantity and quality of pasture feed can be limiting, and  Haemonchus contortus (Barber’s Pole worm) infections can be severe.

The rams A to F all have high genetic levels of fat and muscle to pass onto their lambs. Fat and muscle are the body sources of energy and protein respectively for the newborn lambs to survive in cold, wet weather and when the ewe’s milk supply is restricted.

Take the example of ram A. Its fat breeding value of 0.9 mm indicates, that compared to all of the rams tested in Australia, its fat cover is 0.9 mm genetically greater. Whilst 0.9 mm extra fat may not sound much, it is, and can account for 20% extra lambs surviving (compared to a ram with zero for fat) in a drought.

Sire Fat cover breeding value Eye muscle breeding value Number of lambs born % lambs weaned
High fat and muscle sires:
A 0.9 1.6 41 100
B 0.7 1.6 41 97
C 0.9 1.6 40 97
D 1.0 2.0 72 96
E 1.2 0.8 64 95
F 0.9 0.7 54 85
Low fat and muscle sires:
G 0.1 – 0.8 35 88
  • 0.8
  • 1.0
73 79
I 0.4 0.0 46 79
  • 0.9
-1.9 57 77