In situ ruminal degradation kinetics of grass-legume mix baleage isoflavones in dairy cows fed diets with different forage:concentrate ratios.

Isoflavones are a class of phytoestrogens shown to have positive and negative effects on animal and human health. Red clover (RC) is a major source of isoflavones for dairy cows. We aimed to evaluate the in situ ruminal degradation kinetics of isoflavones from grass-legume (GR-LG) baleage composed of a mix of orchardgrass, white clover, and RC in lactating dairy cows fed diets with different forage:concentrate (F:C) ratios. Four ruminally cannulated multiparous Holstein cows averaging (mean ± SD) 214 ± 38.7 DIM, 741 ± 83.2 kg of BW, 23.1 ± 2.68 kg/d of DMI, and 35.7 ± 5.41 kg/d of milk yield in the beginning of the experiment were used in a crossover design study with 2 periods of 16 d each (14 d for diet adaptation and 2 d for sample incubation and collection). Cows were fed 2 experimental diets (DM basis): (1) low-forage (LF; 50:50 F:C ratio; 24.9% starch and 28.1% ash-free NDF), and (2) high-forage (HF; 70:30 F:C ratio; 20.8% starch and 33.4% ash-free NDF). Approximately 7 g of lyophilized and ground GR-LG baleage samples were weighed in triplicate nylon bags; sequentially incubated in the rumen of each cow in reverse order for 0 (not incubated in the rumen), 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, and 20 h; and simultaneously removed. The effective degradability (ED) of isoflavones in the rumen was calculated using the equation ED = a + b × [Kd /(Kd + Kp )], where a is the soluble fraction (%), b is the potentially degradable fraction (%), Kd is the rate of degradation of fraction b (%/h), and Kp is the ruminal passage rate (%/h; 4.59 and 4.73 for HF and LF, respectively). The ruminal degradation of isoflavones was fit to the model p = a + b × 1 - e - K d × t , where p is the proportion (%) of isoflavones disappeared at time t, and a, b, and Kd are as specified in the previous equation. The ED of total (93.3% vs. 92.5%) and individual isoflavones was greater in the HF diet than the LF diet. However, fractions a (52.7%), b (46.6%), and Kd (30.4%/h) of total isoflavones were not affected by diets. Except for the ruminal disappearance (p) of genistein, which was greater in cows fed HF (85.5%) than those fed LF (81.1%), that of total isoflavones (87.1%), formononetin (87.4%), daidzein (80.6%), and biochanin A (86.5%) was not affected by treatments. In summary, our results showed that the ED of isoflavones from GR-LG baleage was greater when feeding HF compared with LF, but treatment differences were small and potentially not biologically meaningful.