Response surface analyses of the associative effects of lucerne hay, wheat straw and maize gluten feed on growing lambs

Twenty-seven male lambs were fed nine complete diets based on 40% concentrate and either wheat straw (S), lucerne hay (H), maize gluten feed (G) or their associations. The growth performances and the comparative slaughter technique of lambs were used as the means to study the possible associative effect between S, H and G. The response surface analysis (RSA) model was used to statistically analyse all the growth and slaughter data. expected, the presence of S in the place of H in the ration had a depressing effect on the dry matter intake (P < 0.05), but not on the digestibility of nutrients. Growth rates, feed conversions and protein utilization were consequently worsened (P < 0.05). On the contrary, the presence of G resulted in improving all the lambsʹ performances but dry matter intakes. Particularly remarkable was the association between S and G. When S was present in the ration up to about 12% of the whole diet together with G, all the animalsʹ performance parameters were as good as when S was not present. In fact S could replace up to around 20% of G with no undesirable effect. The same could not be observed when H was associated with G, probably because the lucerne hay was already adequately balanced between energy and nitrogen and its nutritive value could not be significantly exploited by the association with a protein feed as was the case with S. The association of H with S showed a generally negative effect without the presence of G, whereas the digestibility of both energy and crude protein was improved (P < 0.05). onclusion, it is observed that the statistical model represented by the RSA adopted in this work was a very useful and precise means to study the associative effects between ingredients of complete diets. This kind of approach deserves further work to be validated.