Relationships between ewe body condition score, production traits and nutrition, on organic sheep farms

Sheep have different nutritional requirements over the production cycle depending, on their life stage. Needs for energy are high at the end of gestation (especially for ewes carrying multiple lambs) and at the beginning of lactation. Ewe body condition score (BCS), production traits and feeding were monitored on three organic sheep farms (Farm A, B and C) during a three year period (2010–2012) throughout the year. On each farm rations were prepared and samples of feeds were analysed to ensure nutritional requirements were met. Each ewe's BCS, on a scale from 1 (emaciated) to 5 (obese), was assessed before mating, at lambing and at weaning. Lambing dates, lamb birth weights and 100-day lamb body weights were recorded. Production data (ewe litter size, lamb birth weight and lamb 100-day weight) were obtained from the Estonian sheep recording database "Pässu". Statistical data analyses was performed to evaluate the influence of the ewe body condition scores on lambing rates, lamb birth weights and lamb 100-day bodyweights. The number of lambs born per ewe was highest (1.78; NS) in ewes whose BCS at mating was 3.0. The most critical time, from the aspect of ewe nutrition, was the gestation period, when mean ewe BCS loss on all three farms was greatest in both the first (–0.39 ± 0.57) and second (–0.20 ± 0.65 points) study years. In the second study year the ewes were fed hay and silage during the last two months of the gestation period on farms A and B, which enabled them to better cover the energy demand, and the BCS change was minimal (farm A –0.04 ± 0.52; farm B –0.04 ± 0.62 points). In the second study year on farm C the ewes were fed only hay in the gestation period, and the BCS loss was –0.61 ± 0.7 point. In the first year the ewes were fed hay and 0.35 kg oats per day and the BCS loss was only –0.35 ± 0.62 points. Maintaining the BCS in the gestation period is important, as lamb birth weights and 100-day weights were related to ewe body condition change during the gestation period; the birth weight of single lambs was significantly different depending on the ewe BCS change during the gestation (p = 0.006). In addition, the 100-day body weights differed in multiple lambs born to ewes whose BCS changed during gestation (p < 0.001). The ewe BCS at lambing was also related to the 100-day body weights of both single (p = 0.004) and multiple lambs (p < 0.004); the 100-day body weights of lambs were greater in those ewes whose body condition was higher at lambing. However, it is also important to avoid large BCS loss during lactation, otherwise ewes cannot restore body energy reserves BCS during the free period by the time of the next mating period. Body condition scoring appears to be a useful tool for monitoring herd nutritional status of organically farmed sheep.