Unprocessed whole flaxseed is as effective as dry-rolled flaxseed at increasing α-linolenic acid concentration in milk of dairy cows

Effects of flaxseed processing on the appearance of α-linolenic acid in milk were evaluated using ten primiparous Holstein cows (153 ± 30.7 d in milk) in a crossover design with two 14-d periods. We hypothesized that feeding unprocessed whole flaxseed (WF) is as effective as dry-rolled flaxseed (RF) at increasing α-linolenic acid concentration in milk fat. Experimental diets contained either WF or RF at 100 g kg− 1 of dietary dry matter. Dietary concentrations of neutral detergent fiber, crude protein, and ether extract were 379, 164, and 60 g kg− 1, respectively (dry matter basis). Dry matter intake, milk yield, and concentrations of milk fat, protein, and lactose were not affected by treatments, and averaged 17.5 kg d− 1, 27.5 kg d− 1, 36.0 g kg− 1, 30.0 g kg− 1, 47.3 g kg− 1, respectively. Apparent total tract digestibility of ether extract was lower for WF compared with RF (486 vs. 624 g kg− 1; P < 0.01). Moreover, excretion of α-linolenic acid in feces was greater for WF compared with RF treatment (259 vs. 129 g d− 1; P < 0.001). However, α-linolenic acid concentration in milk was not affected by treatment (8.3 and 8.6 g kg− 1 for WF and RF, respectively), and both treatments had three times as much α-linolenic acid concentration as the period prior to the experiment (2.6 g kg− 1), during which sunflower seed was fed in place of flaxseed. These data indicate that both WF and RF treatments increased the absorption of α-linolenic acid to a similar extent despite the lower digestibility for WF treatment, which can be attributed to reduced lipolysis in the rumen or fatty acid biohydrogenation for WF compared with RF. This speculation is supported by that WF treatment decreased concentration of vaccenic acid, a fatty acid intermediate during biohydrogenation, in milk fat compared with RF (19 vs. 30 g kg− 1; P < 0.01). Dry-rolling of flaxseed does not necessarily improve the absorption of α-linolenic acid probably because processing increases the extent of biohydrogenation in the rumen as well as digestibility. Although some intact whole flaxseed appeared in the feces of cows fed unprocessed flaxseed, the EE content was quite low, indicating that the fats present in flaxseed were available to cattle even in the absence of any visible damage to the seed coat.