Utilisation of high- and low-roughage diets by a local and an exotic breed of sheep: intake, growth and digestive efficiency

- We determine intake, digestion and growth between a local and an exotic sheep breed.
- The genetic size-scaling was highlighted for comparisons of biological traits.
- The local sheep breed has a higher capacity to ingest fibre-rich diets.
- No differences were observed between breeds on digestive efficiency.

In the context of sustainable agriculture, there is renewed interest in livestock breeds considered well adapted to harsh environments. Churra da Terra Quente (CTQ), the most important sheep breed raised in the Northeast region of Portugal, are considered to be well adapted to their environment which is characterised by marked fluctuations in feed quality and abundance. However, supporting such a claim is difficult because of large gaps in our knowledge, including the importance of the stage of maturity in influencing the efficiency of using different resources. A study was conducted to determine whether feed intake, digestion and growth differed between CTQ and the Ile-de-France (IF) exotic breed at the same stage of maturity, under two contrasting diets. Twenty female lambs of each of the CTQ and IF breeds, 102±3 and 121±4 days old respectively, with 20.7±1.4 and 33.6±1.1 kg of body weight (BW), corresponding to proportionally 0.45 of estimated mature BW (MBW), were allocated randomly within breed to a high- or a low-roughage diet (hay:concentrate feed proportions of 75:25 and 30:70; HR and LR, respectively) and fed ad libitum. Dry matter intake (DMI) and growth were measured from proportionally 0.45-0.65 of MBW. Then, digestibility was measured in 5 animals per diet and breed. DMI was higher (P<0.001) in the IF breed (1132 vs. 797 g/day), but when scaled by MBW no differences (P>0.1) were observed between breeds. A breed × diet interaction (P<0.01) was observed: on the HR diet, CTQ had higher DMI than IF, the opposite being observed with diet LR (P<0.001). The IF animals grew faster (167 vs. 92 g/day; P<0.001), but needed more time to achieve 0.65 MBW (111 vs. 95 days; P=0.025). However, similar feed efficiency (P=0.880) was found between breeds and the differences in growth and time taken to mature were explained by the MBW of the breeds. Digestibility of organic matter (OM) measured in IF animals was 2.7 and 0.8 percent units higher for diets HR and LR, respectively, but breeds did not differ in neutral detergent fibre or energy digestibility. No differences between breeds were observed in the efficiency of microbial-N flow, rumen pH or in the molar proportions of acetate, propionate or butyrate. However, IF animals had higher rumen ammonia-N (P=0.026) and total volatile fatty acids (P=0.022) concentrations, irrespective of the diet. Data of the current experiment suggest that CTQ has a higher capacity to ingest fibre-rich diets, but not to digest fibre.