Effect of ewe prolificacy potential and stocking rate on ewe and lamb performance in a grass-based lamb production system.

The objective of the present study was to investigate the effect of ewe prolificacy potential (PP; predicted number of lambs born per ewe per year) as dictated by sire breed type, stocking rate (SR; ewes per ha), and their interaction on ewe and lamb performance in a temperate grass-based lamb production system. The study was a 2 × 3 factorial design, consisting of 2 differing ewe PP and 3 SR which included 180 medium prolificacy potential (MP- Suffolk-sired crossbred ewes) and 180 high prolificacy potential ewes (HP- Belclare-sired crossbred ewes) allocated to 1 of 3 ( = 60 ewes) SR: low (LSR; 10 ewes per ha), medium (MSR; 12 ewes per ha) or high (HSR: 14 ewes per ha). Each treatment was managed in a 5-paddock rotational grazing system for the duration of the study. Medium prolificacy ewes were consistently heavier ( < 0.001) compared to HP ewes, with HP ewes having a higher BCS at lambing and 6 wk post-lambing (PL; < 0.05). Low SR ewes had a higher BW ( < 0.05) and BCS ( < 0.05) at mating, 6 wk PL, and weaning relative to MSR and HSR ewes which did not differ from each other. Lambs born to MP ewes were heavier at birth and weaning ( < 0.001) and achieved a higher ADG from birth to weaning ( < 0.05). Ewe PP had no effect on lifetime ADG or d to slaughter (DTS) with HP lambs yielding a higher carcass weight ( < 0.001). Low SR and MSR lambs achieved higher ADG from birth to weaning ( < 0.001) and weaning weight ( < 0.001) relative to HSR lambs and did not differ from each other, while post-weaning and lifetime lamb ADG was highest at the LSR, intermediate at the MSR, and lowest at the HSR ( < 0.001). A ewe PP by SR interaction existed for DTS, with MP lambs at the LSR reaching slaughter weight earlier ( < 0.01) relative to HP lambs, while at the MSR and HSR, MP and HP lambs did not differ from each other. High PP ewes produced a higher average born ( < 0.001) and weaned litter size per ewe ( < 0.01), with live weight weaned per ha ( < 0.001) increasing as ewe PP and SR increased. Lambing difficulty, ewe mother ability and lamb viability did not differ by ewe PP or SR. In conclusion, the lack of interaction between ewe PP and SR on many key performance measures in this study demonstrates the potential to increase the live weight of lamb weaned per ha through the use of higher ewe PP and SR levels, with no effect of ewe PP on lifetime lamb performance even as SR increased, with reductions in lamb performance primarily occurring at the HSR.