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

Abstract

AIMS

Firstly, to investigate associations between liveweight and body condition score (BCS) of two-tooth ewes (18-months-old at breeding) at breeding, pregnancy diagnosis (PD) and pre-lambing and the risk of being dry at docking, on commercial New Zealand sheep farms. Secondly, to investigate the association between previous reproductive outcomes as ewe lambs, and risk of being dry at docking as two-tooth ewes.

METHODS

Two-tooth ewes (n=9,006) were enrolled in four cohorts from three commercial sheep farms between 2010–14. Ewes were weighed and BCS assessed immediately pre-breeding, at PD (mid-pregnancy) and pre-lambing. At PD, ewes were identified as either non-pregnant, or having single or multiple fetuses. Palpation and examination of udders at docking was used to classify each ewe as either lactating or dry at docking.

RESULTS

Overall, 437/8,025 (5.4%) of ewes that were diagnosed pregnant at PD were dry at docking. The risk of being dry at docking decreased with increasing pre-lambing conceptus adjusted liveweight (CALW) on all farms (p≤0.002); for 2010-born ewes from Farm A the OR=0.87 (95% CI=0.81–0.92); for Farm B the OR=0.88 (95% CI=0.83–0.92) and for Farm C the OR=0.86 (95% CI=0.79–0.95). The risk of being dry at docking also decreased with increasing CALW gain from PD to pre-lambing for all farms (p≤0.003); for 2010-born ewes from Farm A the OR=0.89 (95% CI=0.84–0.94); for Farm B the OR=0.85 (95% CI=0.81–0.89) and for Farm C the OR=0.88 (95% CI=0.80–0.96). There was no association between BCS at breeding, PD or pre-lambing and the risk of being dry at docking for 2010-born ewes from Farm A, Farm B or Farm C (p>0.05). For 2010-born ewes on Farm A, the risk of being dry at docking was greater for two-tooth ewes that were previously dry at docking as ewe lambs than those that were lactating at docking as ewe lambs (OR=1.7 (95% CI=1.1–2.8); p=0.018), but this difference was not observed for ewes on Farm B or Farm C (p>0.5).

CONCLUSIONS

There were negative associations between ewe CALW pre-lambing, and CALW gain between PD and pre-lambing, and risk of being dry at docking. For all cohorts, heavier ewes and those that gained CALW were less likely to be dry at docking than lighter ewes or those that lost CALW, however these relationships varied between cohorts.

KEY WORDS:

• Ewe
• reproduction
• liveweight
• body condition score
• lamb survival
• dry at docking

Acknowledgements

The authors wish to acknowledge the invaluable assistance of the flock owners and staff, and Geoff Purchas for technical assistance. This research was funded by Beef + Lamb New Zealand, the C. Alma Baker Trust and the Massey University Research Fund.