Método de Neill para cálculo de socavación en pilares

The aim of the current study was to provide the industry with information regarding the differences between sheep and goats regarding the intake and digestible parameters of high-fibre (HF) and low- fibre (LF) diets. Following the evaluation described in the study, both similarities and differences in the degradable characteristics of sheep and goats in regards to soybean meal (SBM) and sunflower meal (SFM) oilcake was studied. Differences within the same species were also observed. The protein sources evaluated are both commonly used in South African high-production ruminant diets (dairy), though the feed dictionaries of popular dynamic models and programmes generally lack data regarding their use in small ruminants, such as sheep and goats.

Regarding the utilisation of LF or HF diets, no difference was found between goats or sheep in respect of nutrient digestibility, although differences were observed regarding the intake of the nutrients concerned. The sheep were found to consume more neutral detergent fibre (NDF) than did the goats. The higher NDF intake for sheep can be explained in respect of the results obtained by Isac et al. (1994) and Lu et al. (1990), who found an increased outflow rate from the rumen in goats compared with that in sheep. Goats, in contrast, showed a higher intake of crude protein (CP) than did sheep, with the former perhaps digesting the CP of the HF better than they did that of the NDF (Gihad & El- Bedawy, 1980; Reid et al., 1990). In terms of the intake parameters analysed, no significant difference was observed within species for total digestible nutrients and nitrogen retention.

The effective degradability and disappearance of NDF with the LF diet showed better degradation in the case of the sheep than it did with the goats. No difference was observed in respect of the HF diet regarding degradability and disappearance parameters between species, during the in sacco trial. However, Reid et al. (1990) and Gihad and El-Bedawy (1980) showed that digestibility differences between goats and sheep were significantly in favour of the goats. The goats, in contrast, were found to digest the SBM more efficiently than did the sheep, due to the higher degradability of CP in the case of the SBM diet than in the case of the SFM diet. Within species, the sheep showed significant results for effective degradability of the CP contained in the SFM diet.

In terms of the effective degradability of the dry matter (DM) contained in the SFM, the in sacco results differed from the in vitro results observed. The sheep studied showed higher effective DM digestion in

sacco of the SFM than did the goats. During the in vitro trial, no significant difference was found to

have occurred between the sheep and the goats in terms of DM digestibility in respect of both the HF and LF diets. When observing the (a) and (b) values, during the in sacco trial, the SBM showed higher degradation values. However, the rate of degradation ([c] value) was found to be higher for SFM than it was for SBM in both species studied. The in vitro method indicated similar results, in terms of which it was observed that the SBM was effectively more degradable than was the SFM in the case of both the sheep and the goats. The extent of actual DM disappearance after 8h incubation

was used to compare the methods in the case of both SFM and SBM. After comparison, the two sets of data were analysed to highlight the differences which were found between the two diets in both experiments. The 8h DM disappearance values for the SBM, as well as for the SFM, were higher in

vitro, which indicated, in the case of the current study, that the in vitro method overestimated the

degradation which occurred in most cases. In keeping with such a finding, Griffiths (2004) and Broderick et al. (1988) also found higher DMD values using the in vitro method than that did when using the in sacco method. The lower effective degradability results which were found with use of the

in sacco method might be related to the lower incubation values at 8h, which were found in

comparison with use of the in vitro method. More research is necessary to explain such an observation. In the case of additional investigation confirming such a phenomenon, use of such a method might provide a cost-effective alternative to use of the more traditional in sacco method.

The in vitro true digestibility parameters were evaluated between sheep and goats in respect of both SFM and SBM. Though no significant difference was observed between species, goats and sheep showed higher digestibility for the SBM diet than they did for the SFM diet. The in vitro experiment clearly showed that digestion differences between SBM and SFM exist. The DMD parameter for SBM in the in vitro (97.74%) trial correlates with that which was obtained in the in sacco (99.87%) trial results.

On completion of the evaluation, the conclusion can be drawn that sheep and goats do not differ in their digestion parameters when they are compared in terms of different roughages or protein substances. However, within species, differences do occur. SBM and SFM should be protected to minimise rumen degradability in sheep (SBM at 97.74% and SFM at 80.98%) and goats (SBM at 97.68% and SFM at 80.63%), thereby increasing the rumen-undegradable protein (RUP) content of such protein sources.

References

Broderick, G.A., Wallace, R.J., Ørskov, E.R. & Hansen, L., 1988. Comparison of estimates of ruminal protein degradation by in vitro and in situ methods. J. Anim. Sci. 66, 1739-1745.

Gihad, E.A. & El-Bedawy, T.M., 1980. Fibre digestibility by goats and sheep. J. Dairy Sci. 63, 1701-1706.

Griffiths, J.B., 2004. The effect of extrusion on the degradability parameters of various vegetable protein sources. MSc thesis. Stellenbosch University, South Africa.

Isac, M.D., Carcia, M.A., Aguilera, J.F. & Alcaide, E.M., 1994. A comparative study of nutrient digestibility, kinetics of digestion and passage and rumen fermentation pattern in goats and sheep offered medium quality forages at the maintenance level of feeding. Arch. Anim. Nutr. 46, 37-50.

Lu, C.D., Pothchoiba, M.J., Sahlu, T. & Kawas, J.R. 1990. Performance of dairy goats fed soybean meal and bone meal with or without urea during early lactation. J. Dairy Sci. 73, 726-734.

Reid, R.L., Jung, G.A., Cox-Ganser, J.M., Rybeck, B.F. & Townsend, E.C., 1990. Comparative utilization of warm- and cool-season forages by cattle, sheep and goats. J. Anim. Sci. 68, 2986-2994.