Effect of extrusion-cooking temperature on the nutritive value of lupin seeds in fattening lambs

Twelve Polish-Merino lambs, divided into two groups of 6, were fattened from 18 to 39 kg body weight on diets containing 14% crude protein and 11% crude fibre in dry matter; 25% of crude protein was from untreated lupin seeds or a mixture of lupin extruded at 160°C with barley (1:1). Daily body weight gains of lambs fed extruded lupin seeds were higher (P<0.5) than those of lambs led the untreated lupine-barley mixture (234 vs 186 g). Feed efficiency was 5.0 kg dry matter and 729 g crude protein in lambs fed the untreated lupine-barley mixture and 4.2 kg dry matter and 597 g crude protein in animals receiving the extruded mixture. Effective protein degradability of untreated lupin was 0.85, untreated barley 0.75 or untreated lupin-barley mixture 0.80, whereas that of extruded at 130,140, 150 or 160°C lupin-barley mixtures gradually decreased from 0.70 to 0.67. The respective effective protein degradability values for barley extruded at 135 or 155°C were 0.72 and 0.60. The coefficient of intestinal protein digestion of untreated lupine was 0.59, of barley, 0.83, and of the lupin-barley mixture, 0.71, whereas for extruded lupin-barley mixtures, it only slightly increased with temperature from 0.92 to 0.94, while for extruded barley from 0.91 to 0.92. Substitution of unprocessed lupin seeds with extruded seeds decreased protein degradation in the rumen, increased protein intestinal digestibility and effectiveness of fattening lambs. Increasing the extrusion temperature to over 130°C did not significantly improve degradability in the rumen or intestinal digestibility of protein.


INTRODUCTION
Lupin seed protein is rapidly degraded in the rumen, which is why it is poorly utilized.One of the ways of limiting its degradation is extrusion.An additional benefit from extruding feeds containing easily digested protein, aside from limiting the extent of its degradation in the rumen, is the resulting rise in true ileal protein digestibility (Cros et al., 1991;Kibelolaud et al., 1993).
The objective of this experiment was to examine the influence of extrusioncooking temperature on the effective degradability and ileal digestibility of rumen undegraded yellow lupine seeds and to see if extruding lupin seeds improves protein utilization by growing lambs.

MATERIAL AND METHODS
Twelve Polish Merino male lambs about 85 days old and weighing about 18 kg were divided into two groups of six animals each.The ration, containing 14% crude protein (CP) and 11% crude fibre in dry matter (DM), provided: meadow hay, 10; whole barley grain, 66; dried sugar beet pulp, 14%.In the control group (RL) the ration was supplemented (about 25% CP of the ration) with untreated yellow lupin cv.Juno, in the experimental group (EL), with lupin extrudate (extruder INSTA-PRO 600).
The extrudates used to study the effect of extrusion temperature on the effectiveness of protein degradation in the rumen (deg) and the ileal digestibility of rumen undegraded protein (dsi) were prepared from barley meal (50%) and lupin cv.Juno meal (50%>) at extrusion temperatures of 130, 140, 150 and 160°C.Lambs were fed the extrudate that was characterized by the lowest rumen protein degradability and highest ileal digestibility, prepared at a temperature of 160°C.The feed was given twice daily, normalizing the daily DM ration according to body weight (BW) of the lambs using the following equation: DM, = (41.9x BW,t -217.6)x 0.0011 Both groups received the same mineral-vitamin supplement of Polfamiks O and Mikrofos.The animals were housed individually on sawdust and had free access to water and salt blocks.
Rumen protein degradation was determined according to Mehrez and Orskov (1977).Effective rumen protein degradation at k was computed according to Orskov and McDonald (1979).Ileal protein digestibility of rumen-undegraded protein was determined according to Hvelplund et al. (1992) by the mobile nylon bag method (mesh size 42 |um).Analysis of feeds was carried out using AOAC (1990) methods.Daily body weight gain, DM and CP utilization over 100 days of fattening were determined.

RESULTS AND DISCUSSION
An increase in the extrusion temperature of a lupin-barley mixture caused a slight decline in the effective degradation of protein in the rumen and a non-significant increase in the intestinal digestibility of rumen undegraded protein (Table 1).Extrusion of the lupin-barley mixture decreased effective rumen protein degradation (to 0.67) in comparison with raw lupin seeds (0.85) and barley grain (0.75) or raw lupin-barley mixture.These results are similar to those of Cros et al. (1991) and Kibelolaud et al. (1993), who found a decline in rumen protein degradation after extrusion of white lupin at temperatures ranging from 110 to 195°C.An increase in extrusion temperature improved intestinal digestibility of extrudate protein and of PDIN 10 to 32%, and PDIE 57 to 194% (Cros et al., 1991).
Extrusion lowered the amount of protein degraded in the rumen by about 13-17%) of the amount degraded from the unextruded mixture (216 vs 180-188 g/ kg DM).In our experiment, the amount of protein digested in the small intestine after extrusion rose over twofold from 38 to 76-85 g/kg DM.We also observed a 15-18%) rise in the PDIN value in the extruded mixture in comparison with the value computed for the mixture not subjected to this process; PDIE rose 37-45%).
Increasing the temperature of barley extrusion from 135 to 155°C decreased amount of protein degraded in the rumen by 4 and 20%), respectively, and increased amount of rumen undegraded protein digested in small intestine by 25 and 80%, respectively, in relation to the respective value for untreated barley (Table 2).Table 3 presents the nutritive value of DM rations determined for the period of 100 days of fattening.At a similar crude protein content (143-145 g in DM) in the rations, the amount of protein digested in the small intestine was 11% higher when ration EL was fed than RL, similarly, the PDIN content in the ration for group EL lambs was about 15% higher than for the control lambs.Body weight gains in the experimental group lambs were about 25% higher than in the control group (Table 4).Feed utilization was better by 16 (DM) to 18% (CP) in the group receiving the extrudate than in the control group.Sanson (1992) obtained similar results when feeding soyabean meal extrudate.

CONCLUSIONS
Increasing the temperature of extrusion of yellow lupin seeds and barley grain decreases rumen protein degradation and markedly increases the amount protein undegraded in rumen and protein digested in small intestine.
Replacing lupin seeds with their extrudate increases the growth rate of lambs and leads to better feed utilization.

TABLE 4
Fattening performance of lambs and feed efficiency