Digestibility of Canola Meal Protein For Ruminant Utilisation

Crushing of canola seed yields valuable commodities including high-value meal traded worldwide as a protein source. Due to its amino acid profile and high digestibility, canola meal is supplemented into dairy cattle feed to optimise milk protein synthesis and lactation output. This research primarily investigated factors impacting the degradability of canola meal protein as a protein source for ruminant use.

Initial studies identified three in vitro SGP procedures as effective alternatives to the 16 h ruminal fluid reference procedure to estimate rumen undegradable protein (RUP) in oilseed meals. A modification of the Krishnamoorthy et al. (1983) procedure by air-drying of RUP residues overnight then combustion of the entire filter paper avoids time expenditure, and N-loss attributed to subsampling, and may be used for routine estimation of RUP in canola meal and soybean meal without the requirement for ruminal fluid.

This research included a benchmark quantitative survey of general and digestibility characteristics of protein (for ruminants) in Australian produced oilseed (i.e. canola, soybean, cottonseed, and flaxseed) meals. Ruminal protein digestibility differed between oilseed types and oil-extraction techniques. Research outcomes highlight opportunity to improve the quality of Australian oilseed meals by refining oil-extraction technique conditions. Monitoring of ruminal protein digestibility of oilseed meals may benefit future feed formulation for improved dairy cattle utilisation.

To understand origins of the variability of protein digestibility for ruminant nutrition in expelled canola meal, variation during production and attributed to factors including subplot, geographical location, cultivar, seed breeder and herbicide tolerance traits was examined. Crude protein content in canola meal consistently varied between cultivars and necessitates analysis to determine if this is related to differences in mechanisms of N metabolism among cultivars. Outcomes imply digestible fibre-associated protein is contributing to differences in protein degradability between cultivars. The degree of moist heat pressure (MHP)-induced in vitro RUP formation in expeller meals was found to differ between cultivars, and in the conversion of rapidly degradable to intermediately degradable protein. Induced changes of canola meal by dry-heat and MHP treatment may impact the supply of proteins and AAs and subsequently the yield and composition (protein and lipid) of milk produced by dairy cows. To the author’s best knowledge, the first reports of the microscopic structure of cold-press, expeller and moist heat pressure treatment canola meals are presented.

Research findings may benefit meal producers by furthering knowledge of the: general nutritional and ruminal digestibility characteristics of canola meal; factors contributing to RUP levels in canola meal; and, effects of barrel dry-heat temperature and MHP treatment on (i) Maillard reaction product formation in canola meal, (ii) ruminal digestibility, molecular and microscopic structural characteristics of canola meal, and, (iii) microscopic characteristics of canola meal that favour resistance to enzymatic degradation. These advancements will enhance ration formulations and the predictions of animal performance, and assist production of canola meal with improved protein value for ruminants.