Effects of dam size and nutrition during pregnancy on lifetime performance of female offspring

- We examine and model the impacts of dam size and pregnancy nutrition on lifetime impact of ewe offspring.
- Only minor effects of dam size and nutrition on growth and reproductive performance of offspring observed.
- Under the conditions of our study dam size and pregnancy nutrition would not be critical in selecting replacement ewe offspring.

It has previously been shown that both dam size and nutrition in pregnancy can affect individual performance traits of ewe offspring to three years of age. The objective of this study was to determine if dam size and nutrition during pregnancy affected lifetime productivity to six years of age in ewe offspring. In 2005, Romney ewes (G0) were selected as heavy (H; n = 450, mean live weight = 60.8 ± 0.18 kg (s.e)) or light (L; n = 450; mean live weight = 42.5 ± 0.17 kg) based upon live weight at the time of mating, and then randomly allocated to receive pregnancy maintenance (M) or ad libitum (A) pasture feeding treatment from day 21 to 140 of pregnancy; resulting in four treatment groups (HA, HM, LA and LM). Live weight, body condition and reproductive performance data were recorded in the ewe offspring (HA n = 55, HM n = 58, LA n = 42 and LM n = 43) from 2007 to 2011 (580-2298 days of age). In addition live weights of their lambs (grand progeny) to weaning were recorded (n = 1491 in total). Daughter live weights and body condition scores were inconsistently affected by dam size and nutrition over time and at most measurement points no differences (P > 0.05) were found. At 2050 days of age A-daughters had higher proportion that ovulated than M-daughters (P = 0.01) and A-daughters gave birth to more lambs than M-daughters (P = 0.05), but there were no differences (P > 0.05) found in relation to number or weight of lambs weaned. Daughters from H dams had a higher total number of antral follicles (P = 0.018) and total number of follicles (P = 0.05) at 2599 days of age, and greater proportion (P = 0.016) of daughters that were present (survived) in the flock in 2011 compared to daughters from L dams. There were no interactions (P > 0.05) between dam size and nutrition for any parameters of lifetime reproductive performance data collected. This study suggests that dam size and nutrition during pregnancy has a minimal impact on daughter lifetime performance. Therefore under the conditions of the present study farmers do not need to consider dam size and pregnancy nutrition when selecting progeny as replacement ewes.