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 by 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 samples 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:Kd Kp , where a is the soluble fraction (%), b is the potentially degradable fraction (%), K d 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 ewhere p is the proportion (%) of isoflavones disappeared at time t and a, b, and K d are as specified above.The ED of total (93.3 vs. 92.5%)and individual isoflavones was greater in HF than LF diet.However, fractions a (52.7%), b (46.6%), and K d (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 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 with feeding HF versus LF, but treatment differences were small and potentially not biologically meaningful.