Chemical Composition and Ruminal Dry Matter and Protein Degradation Parameters of Canola Meal Treated by Microwave Irradiation

In growing ruminants or early lactation dairy cows, production may be limited by a dietary metabolizable protein. In these conditions microbial protein synthesis is not sufficient to meet the animal’s protein requirement. Canola meal (CM), which is an available and good source of protein in ruminant nutrition, especially in Iran. However the protein of CM is highly degradable by rumen microorganisms and on the other hand, anti-nutritional factors, such as phytic acid and glucosinolate in brassica-originated feed, are of concern relative to animal-originated feeds. Glucosinolates are a large group of sulphur-containing secondary plant metabolites and are known to reduce feed intake, induce iodine deficiency and depress fertility in ruminants. Several heat processing methods have been used to enhance nutritive value of oilseed meals, including extrusion, roasting, toasting and Jet-Sploding. Recently, treatment of oilseed meals with microwave irradiation was successful in reducing ruminal degradable protein, anti-nutritional factors and increasing digestible undegradable protein of them. Microwave irradiation is heating faster, processing in less time and higher energy efficiency compared to conventional methods. This research was carried out to evaluate the effects of microwave irradiation (800 W) for 2, 4 and 6 min on dry matter (DM), crude protein (CP) and true protein (TP) ruminal degradability, in vitro CP digestibility, antinutritional factors (glucosinolate and phytic acid), and chemical composition of CM.

The DM of CM was determined and then, sufficient water was added to sample to increase the moisture content of CM to 250 g/kg. Three samples (500 g each) were subjected to microwave irradiation at a power of 800 W for 2, 4 and 6 min. The samples were ground to pass a 2 mm screen for the ruminal in situ study. Degradation kinetics of DM, CP and TP were determined according to in situ procedure. Six grams of untreated or irradiated feed samples were incubated in the rumen of three ruminally fistulated Taleshi bulls for periods of 0, 2, 4, 8, 16, 24 and 48 h. The bulls were fed with a total mixed ration containing 700 g/kg of DM forage (700 g/kg alfalfa hay and 300 g/kg wheat straw on DM basis) and 300 g/kg of DM concentrate. The concentrate consisted of ground barley grain, canola meal, ground canola seed, cotton-seed meal, wheat bran, dicalcium phosphate and a vitamin+mineral premix (530, 130, 160, 40, 120, 10 and 10 g/kg DM, respectively). TP of samples were determined by Bradford,s procedure. Digestibility of rumen undegraded CP was estimated using the three-step in vitro procedure. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was used to monitor protein subfractions and the fate of true proteins of untreated and irradiated feed samples in the rumen.

Microwave irradiation had no effect on improving chemical composition of CM but decreased the total glucosinolate and phytic acid of CM linearly and quadratically. Microwave irradiation for 2, 4 and 6 min decreased the phytic acid content of CM by 13, 30 and 51% respectively, compared to untreated CM. The total glucosinolate contents of CM microwave irradiated for 2, 4 and 6 min decreased by 38.4, 56.0 and 67.1% respectively, compared to untreated samples. Microwave irradiation decreased the washout fraction, degradation rate and effective degradability (ED) of DM, CP and TP and increased potentially degradable fraction of DM, CP and TP of CM. The washout fraction of CP decreased by 15.7 and 39.8% in samples irradiated for 2, 4 and 6 min, respectively. Irradiation for 2, 4 and 6 min decreased ED of CP at a ruminal outflow rate of 0.05 h-1 by 13.6 and 22.7%, respectively. In vitro CP digestibility of CM increased by treating with microwave irradiation up to 4 min. CP digestibility of 2 and 4 min irradiated CM was increased by 6.9 and 10.5%, respectively. Electrophoresis results also indicated that major proteins of CM was Cruciferin (globulin 12S) and Napin (Albumin 2S). Electrophoresis results indicated that in untreated CM, four subunits of Cruciferin and in microwave irradiated CM, four subunits of cruciferin and two subunits of Napin consisted of by-pass proteins.

In this study, microwave irradiation, reduced ruminal degradability of CP and TP, increased in vitro CP digestibility and reduced anti-nutritional factors of CM. Subsequently, in vivo studies are required to investigate effect of feeding irradiated feedstuff on lactation performance of dairy cows