Effects of varying inclusion levels of canola meal for grass-fed cattle

Managing variability in pasture quality and quantity and maintaining a consistent supply of cattle that meet specific Meat Standards Australia (MSA) and Pasture-fed Cattle Assurance System (PCAS) requirements throughout the year is a challenge for beef producers supplying to certified grass-fed markets in Australia. Energy and/or protein supplementation is often practiced to overcome livestock nutritional deficits. In recent years canola meal has become readily available throughout south-eastern Australia due to an increase in canola cropping and processing. The overall objective of the research reported in this thesis was to determine the maximum inclusion level of canola meal as a PCAS approved supplement to roughages typical of that normally available during the summer-autumn period in southern New South Wales for grass-fed beef cattle. A combination of pen feeding, meat quality and consumer sensory evaluations, in vivo digestibility, and degradation studies were undertaken to determine the effects of varying inclusion levels of canola meal on animal production, ruminal parameters and nutrient digestibility.

Dry matter intake (DMI) and average daily gain (ADG) were improved when weaner calves fed a basal diet of canola hay were supplemented with 34% canola meal compared with 20% canola meal. Both DMI and ADG decreased when the weaner calves were offered 68% canola meal. Thus, an upper limit to the inclusion level of canola meal for weaner cattle fed roughage diets was established between 47% and 68%. Supplementing canola meal up to 43% in a low-quality roughage ration increased ruminal ammonia (NH3-N) concentrations, while total volatile fatty acid (VFA) concentrations and molar proportions were within normal range for microbial synthesis. Ruminal pH did not decrease below 6.3, indicating canola meal was safe to include at 43% in a basal, low-quality ration for cattle. Meat quality traits and consumer sensory evaluations were not adversely affected when finishing Angus and Angus cross steers were supplemented with either canola meal or a grain-based pellet and offered ad libitum lucerne hay. The overall consumer satisfaction of the meat samples equated to “good everyday quality” and there was no difference between dietary treatments.

Supplementing cattle fed low-quality roughage with up to 47% canola meal had no detrimental effects on apparent nutrient digestibility. In addition, supplementing donor (of ruminal fluid) steers fed a low-quality ration up to 43% canola meal had no negative effects on either the degradation of lucerne hay standard or the degradation of canola meal dietary treatments when using either the in sacco or in vitro ANKOM Daisy™ incubator methods. The relationship between in sacco and in vitro Daisy™ was moderately correlated (R2 = 0.59) indicating the in sacco method as the preferred method (of the two) as it better reflected in vivo apparent digestibility.

Canola meal can be used as an approved PCAS supplement for grass-fed cattle grazing low-quality roughages at levels up to 43% of DMI without any adverse effects on ADG, DMI, feed efficiency, apparent nutrient digestibility, or ruminal parameters. However, there is an upper limit of between 46% and 68% of DMI when supplementing canola meal to cattle fed low-quality rations.