Study examines feasibility of retaining lambs from hoggets as replacements

// Rearing and Weaning

Should twins born to ewe hoggets and grown out to heavy weights be retained as replacements and mated as ewe lambs?

A Beef + Lamb New Zealand and Massey University research project is seeking to understand the long-term impact of this practice by following the lifetime performance of single and twin ewe lambs born in 2017 from a hogget mating. These lambs were then mated as hoggets.

This project, which will finish early next year, has two objectives. The first is to demonstrate that both single and twin lambs born to hoggets can be bred as ewe lambs and that their lifetime performance will be similar to ewe lambs born to mixed-age ewes. Farmers could also benefit from improved genetic gain generated from a younger ewe flock.

The second is to determine whether ewe lambs grown to heavy pre-mating weights achieve heavier mature weights and what this means for ewe efficiency. 

Led by Professor Hugh Blair, the project follows four treatment groups, all born in 2017 and now run at Massey University’s Keeble Farm near the Manawatu campus.

These groups are: twin lambs born to mixed-age dams and grown to 48kg by their first mating (the fast group), twin lambs born to mixed-age dams and grown to 44kg by mating (the control group), single lambs born to hogget dams and twin-born lambs born to hogget dams.

All the lambs in the trial were identified and weighed at birth and the ‘fast’ group of ewe lambs were supplementary fed to meet the 48kg target mating weight.  All lambs were combined into one mob at eight-months-old for mating at the same time and to the same ram team.

This cycle has been repeated over four years with all lambs weaned in either December or early January, with all groups being farmed as one mob except at lambing.

The variables being measured each year include the number of lambs born and weaned to each group, ewe liveweight and Body Condition Score (BCS) at weaning, percentages of lambs born and weaned, lamb survival to birth, lamb birth weight and lamb weaning weight.  

In his most recent project report, Professor Blair stresses that because this is a lifetime study, data will not be fully analysed until the end of the project in February next year, but initial findings look encouraging, particularly around potential efficiency gains.

As four and a half-year-olds, the ewe’s retained from the hoggets (and themselves mated as hoggets) remained lighter than the control groups, particularly the twins which were about 7kg lighter, but this lack of size doesn’t appear to have hindered reproductive performance.

There were no differences in BCS between the four groups at weaning in December and all groups recorded similar weaning rates (135-147%) and weaning weights (30.48 to 32.2kg).

The report notes that it was encouraging that the ewes born as twins from hoggets weaned a similar proportion of lambs to the control group even with their liveweight handicap.

The project builds on previous research carried out at Massey University which demonstrated that while twin lambs from hoggets were smaller at birth, they produced the same weight of lamb weaned as ewes from mixed-age dams.
This hinted at potential efficiency gains, but unlike this project, those trials did not mate ewe lamb off-spring until they were eighteen-months-old.

How big is too big?

Hogget mating is now a widespread practice for farmers whose farm systems can grow ewe lambs to suitable mating weights and then support them through pregnancy and lactation so they can be successfully mated again as two-tooths.

Specialist forages such as red clover, lucerne and plantain play a role in helping farmers grow out their ewe lambs to achieve mating weights, but sometimes these are in excess of 50kg.

Farmer experience suggest that these animals may grow to excessive mature weights which then erodes their lifetime profitability due to their increased feed consumption.

An important part of this trial is to determine whether there is potentially an optimal pre-mating growth strategy for ewe lambs, so they don’t grow out to be excessively heavy mature ewes while still achieving good hogget breeding performance.

This part of the project will show whether very heavy ewe lambs at breeding have heavier mature weights.  If they do, data will be used to determine what effect this heavier mature weight has on ewe production efficiency.

The results of this project will be released next year.