Does hogget performance effect the risk of being dry as a two-tooth?

Income for sheep farmers is determined by the number of lambs available for sale at ~3 months of age. The loss of lambs between pregnancy scanning and docking is an issue for farmers in New Zealand as this decreases the final number of lambs available for sale.

Docking or Tailing is when 3 to 6 week old lambs are yarded for ear marking and tail removal. The castration of males also occurs at this time.

The aim of this study was to determine if body condition score (BCS) and live weight (LW) were associated with ewes being dry at docking; and to look at the effect of hogget production on the risk of being dry at docking as a two-tooth.

Lamb survival was not measured in this study, but for a ewe to be identified as dry at docking, it was assumed that most of the losses were lamb deaths after birth.

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Key Points

1. For live weights pre-lambing, heavier ewes were less likely to be dry at docking than lighter ewes.

2. Ewes that decreased live weight between pregnancy diagnosis and pre-lambing had an increased risk of being dry at docking.

3. There was no difference between two-tooths that had or had not been bred as hoggets in the risk of being dry at docking.

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Keywords: #hogget #lambing #reproduction

There were 4 flocks included in this study outlined below indicating the previous production of each flock.

Flock A

• 2010-born ewes

• All bred as hoggets

• Culled if not pregnant as hoggets

Flock B

• 2011-born ewes

• All bred as hoggets

• Culled if not pregnant as hoggets, and not included in study

• Culled if dry at docking as hoggets

Flock C

• 2011-born ewes

• 57% bred as hoggets

• 438 not pregnant as hoggets that were bred again as two-tooths

Flock D

• 2014-born ewes

• All bred as hoggets

• Culled if not pregnant as hoggets

Flock C had more non-pregnant and more single-bearing ewes than the other 3 flocks as shown in graph 1 below. This could be a result of including the previous years hoggets that failed to conceive in this flock, whereas, the other flocks culled the hoggets that failed to conceive.

Culling hoggets that fail to conceive appears to have some benefit in increasing the percentage of multiple-bearing ewes in the flock, however, this should only be done if all hoggets were at adequate live weight, otherwise the reason they did not conceive could be because they had not yet reached puberty, therefore, are likely to have no issues conceiving if given another chance as a two-tooth.

Graph 1. The percentage of two-tooth ewes identified as non-pregnant, single- or multiple-bearing at pregnancy diagnosis.

The graph below shows the percentage of two-tooth ewes that were still lactating at docking. This indicates that the ewe still has at-least one lamb left at foot. A ewe that is dry at docking indicates that her lambs have died between pregnancy scanning and docking. It is likely that majority of these deaths occurred around lambing time.

The multiple-bearing ewes had a greater percentage of ewes still lactating at docking compared with the single-bearing ewes for Flocks A, B and C. There was no difference in percentage of ewes lactating among the birth ranks (single- vs multiple-bearing).

Graph 2. The percentage of single- or multiple-bearing two-tooth ewes that were identified as lactating at docking.

Flock C was the only flock that had two-tooth ewes that were not bred as hoggets. Table 1 below shows that the live weight at breeding was no different from any of the other flocks. The risk of being dry at docking for two-tooths did not differ between ewes that had or had not been bred as hoggets.

Table 1. The average live weight of each flock at breeding, pregnancy diagnosis adjusted for conceptus weight and pre-lambing adjusted for conceptus weight.

The live weights were also similar at breeding between ewes that were dry at docking compared with those that were lactating in all flocks.

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The 3 graphs below show the relationship between the change in live weight adjusted for conceptus weight (kg) between breeding and pre-lambing, and the proportion of ewes dry at docking.

For flock C, as live weight decreases (moving from the centre of the graph to the left side), the proportion of ewes dry at docking increases from around 2% up to 30%.

Two-tooths that increased conceptus adjusted live weight between pregnancy diagnosis and pre-lambing as shown in the graph below were less likely to be dry at docking.

Graph 3. The associations between the estimated proportion of ewes dry at docking and change in live weight (kg) between pregnancy diagnosis and pre-lambing.

Greater BCS was found to have no effect on the risk of being dry at docking, so these results have not been presented here.

The authors concluded that there was a decreased chance of being dry at docking if live weight at pre-lambing was higher and there was an increase in live weight between pregnancy diagnosis and pre-lambing.

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Paper:

Griffiths KJ, Ridler AL, Heuer C, Corner-Thomas RA, & Kenyon PR (2018). Associations between liveweight, body condition score and previous reproductive outcomes, and the risk of ewes bred at 18-months of age being dry at docking. New Zealand Veterinary Journal, 66(6), 290-296.