Phenotypic relationships between maternal energy metabolism and lamb body weight development during lactation for pure- and crossbred sheep populations in low and high input production systems

There is an increasing economic pressure in sheep production. Hence, it is imperative to use all available tools contributing to improvements in lamb survival. In this regard, there is a lack of studies addressing the impact of maternal body condition traits on lamb performances during lactation. Specifically, the focus of the present study was to analyse associations between ewe traits reflecting maternal energy metabolism and lamb body weight (LBW), separately in a low and in a high input production system. The dataset considered 199 Merinoland- (ML) and 45 Rhönsheep (RH) ewes from the high input production system (> 33% concentrates in the ration), as well as 47 Coburger Fuchssheep (CF), 78 RH and eight crossbred (CB) ewes from the low input production system (< 33% concentrates in the ration). The ewe traits were: Body weight (EBW), body condition score (BCS; 1.0 = emaciated to 5.0 = obese), back fat thickness (BFT), back muscle thickness (BMT) and daily weight loss (WL). The lamb traits were: LBW, birth weight (BW), weight at week 3, 6, 9 and 12 and weaning weight (3 W W, 6 W W, 9 W W, 12 W W and WW, respectively), and the corresponding daily gains during these periods. In the high input system (for both breeds ML and RH), a decrease in maternal fat deposits was associated with a continuous gain in LBW. Highest LBW was associated with a moderate ewe BCS of 3.5. The maternal body weight class of ML ewes in the high input system significantly (P < 0.01) influenced BW and WW from all points in time. Lambs from ML ewes with> 100 kg EBW were 1.41 kg heavier at weaning than lambs from ML ewes < 85 kg EBW. Under low input conditions, lambs from dams with BFT > 3 mm had significantly greater 12 W W (2.63 kg, P < 0.01) and 12DG (0.07 kg, P < 0.01), compared to lambs from ewes with lower BFT. Body weights for lambs from ewes with BCS between 1.5 and 2.5 were greater than for lambs from ewes with a BCS of 3.0 or higher. Ewe WL had highly significant (P < 0.001) influence on LBW. Results from the present study indicated different impact of maternal energy metabolism traits on LBW development, depending on the breed and on the production system characteristics. Hence, also from a breeding perspective (i.e., development of sheep breeding goals), breed x production – system characteristics should be taken into consideration.