Damara sheep have higher digestible energy intake than Merino sheep when fed low-quality or high-quality feed

The use of animals that are resilient to challenging environments is becoming of increasing importance in animal production systems. Interest in breeds of sheep such as the Damara for sheep meat production is increasing in Australia. Anecdotally this breed outperforms the traditionally grazed Merino in the harsh rangeland environments encountered in the Pastoral Zone of Australia, but little evidence is available to support this claim. A trial was conducted to quantify differences in the efficiency of feed utilisation and growth performance of Damara and Merino sheep under two contrasting dietary regimes. Eighteen castrate males of each breed were offered a ‘low-quality’ diet (L) (7 MJ/kg ME; 8% crude protein, as per manufacturer’s analysis) followed by a ‘high-quality’ diet (H) (11 MJ/kg dry matter and 16% crude protein, as per manufacturer’s analysis). On the L diet, Damaras had similar ad libitum feed intake as Merinos, but the digestibility of feed dry matter and energy was ~10% higher in Damaras than Merinos. Damaras also gained weight (38 g/day) on the L diet, while Merinos lost weight (28 g/day) (P < 0.002). On the H diet the Damaras consumed 14% more feed (P < 0.053) and grew 30% faster than Merinos (P < 0.002), but there was no difference in the apparent dry matter or energy digestibility of the feed. At the conclusion of the trial the Damara carcasses were 22% heavier (28.1 versus 23.1 kg), and had higher dressing percentages (53.2 versus 41.5%) than Merinos, but the proportions of carcass components did not differ. The Damaras achieved higher total digestible energy intakes than the Merinos on both diets. On the low-quality feed this was achieved through higher feed digestibility and on the high-quality feed through greater voluntary feed intake. We speculate that this arises from variation between the breeds in rumen volume, particle flow and the site of digestion, but further studies are required to confirm this contention. The ability of Damara sheep to obtain more nutrients from widely differing feed bases makes them an attractive alternative sheep breed for sheep meat production. Furthermore, the presence of such variation between genotypes offers potential for selective breeding and development of commercial lines of sheep.