EFFECT OF CANOLA FAT ON RUMINAL AND TOTAL TRACT DIGESTION, PLASMA HORMONES, AND METABOLITES IN LACTATING DAIRY-COWS

The effects of canola fat on digestion and metabolism were investigated by incorporating 0, 4.5, 9, 13.2, or 17.4% Jet-Sploded(R) canola seed into a diet containing a 60:40 (DM) concentrate:forage ratio. The diets contained 16.5% CP, 30% alfalfa silage, and 10% whole-crop oat silage on a DM basis and were fed for ad libitum consumption as TMR to 10 ruminally cannulated Holstein cows in early lactation. Jet-Sploded(R) canola seed supplementation did not change ruminal pH or NH3 N concentrations, but VFA concentrations declined with increasing level of inclusion. Apparent digestibilities of DM, OM, CP, NDF, and ADF were unaffected by level of inclusion of Jet-Sploded(R) canola seed, but ether extract digestibility declined linearly, which resulted in similar ether extract absorption across the three diets supplemented with canola fat. Based on in sacco data, the percentages of ruminal digestion of OM and CP declined with increasing inclusion of Jet-Sploded(R) canola seed. Plasma glucose and FFA concentrations tended to respond in a quadratic fashion, plasma insulin concentration declined linearly, and plasma glucagon and somatotropin concentrations were unaffected by dietary treatment. The results indicate that a positive productive response may be expected from dietary inclusion of about 5% Jet-Sploded(R) canola seed, but the benefits of increased energy density associated with higher inclusion levels may be offset by reduced availability of energy in the rumen and decreased fat digestibility postruminally. The substantial effects of time postfeeding on ruminal fermentation and on concentrations of plasma hormone and metabolites in animals fed TMR demonstrate that infrequent sampling can result in misleading results and, thus, invalid interpretation of the, influence of dietary fat on these parameters.