Soaked and pasteurised wheat straw was inoculated with five species of Pleurotus fungi (coded P-21, P-30, P-41, P-60 and P-90), packed in polyethylene bags and incubated in a fermentation chamber for 21 days. The chemical composition, in vitro digestibility and in sacco degradability of the treated and untreated straw were estimated using a complete randomised design consisting of six treatments and four replicates. In a feeding trial, in vivo digestibility and voluntary intake were determined in bulls, using a 3×3 change over design. Dietary treatments were: 1) untreated wheat straw (UWS) as control; 2) fungal treated (P-41) wheat straw before mushroom formation (FTWS); 3) spent wheat straw (SPWS) after mushrooms were harvested. Apart from P-90, fungal treatment significantly (p<0.05) increased the crude protein (CP) and reduced the cell wall components of the straw. The in vitro dry mater and organic mater digestibility significantly (p<0.05) increased in the treated straw particularly with the treatments of P-41 and P-60. The in situ degradability and in vivo digestibility of DM and OM were significantly (p<0.05) increased in treated straws with the highest values observed for treatment P-41. The intake of DM, OM and digestible organic mater (DOM) were significantly (p<0.05) increased in cows fed FTWS.

Eight primiparous Holstein cows, in late lactation (255±10 days in milk) and yielding 10.3±1.3 kg/d of 4% fat corrected milk (FCM) were allocated into two groups randomly. Two diets containing 30% wheat straw either untreated (UWS) or treated with Pleurotus ostreatus (FTWS) were offered as total mixed ration (TMR). In vivo digestibility of the diets was determined, using acid insoluble ash as a marker. Daily milk production was recorded and milk samples were collected and analysed. Diet FTWS resulted in significantly (p<0.05) higher dry matter intake (DMI) (12.2±0.86 vs. 10.6±1.3), DM digestibility (58.8 vs. 52.3) and milk yield (9 vs. 7.5 kg). Milk fat contents were 34.2 and 35.6 g/liter that did not differ between cows fed treated or untreated straw. However, the concentrations of lactose, solid non fat, total solids and milk protein for diets UWS and FTWS were 57.3 and 54.9, 98.9 and 93.2, 134.5 and 127.4, 35.7 and 32.3 g/l, respectively, which differed significantly (p<0.05). The average body weights gain (BWG) for UWS and FTWS were 272 and 743 g/d, respectively (p<0.05). The FCM yield per kg of DMI was similar (0.68 and 0.67 liter) for the two groups, but BWG/kgDMI was higher in the FTWS diet.

This study was conducted to investigate the effects of diets that contained different levels of fungal treated wheat straw on the intake, digestibility and performance of lactating cows. Eight primiparous Holstein cows, in late lactation ranging from 170±10 days in milk and yielding 14.3±1.3 kg/d of fat corrected milk (FCM) were allocated into four diets with 0, 10, 20 and 30% fungal (Pleurotus ostreatus coded P-41) treated wheat straw in a 4×4 Latin Square experiment. The daily intake of DM, OM, DOM, CP and TDN were not affected by substitution of alfalfa hay with fungal treated wheat straw. Inclusion of the treated straw at different levels in the diet did not affect the digestibility of nutrients, except for the ADF that was significantly (p<0.05) reduced in the diet contained 30% treated straw. The types of the diet did not significantly affect daily milk and FCM production. The milk composition including fat, protein, lactose, solid non-fat (SNF) and total solid (TS) were not statistically (p>0.05) different among the diets. All cows gained weight, but the inclusion of treated straw to the diet significantly (p<0.05) increased the body weight gain and the highest amount was obtained in the diet containing 20% treated. Inclusion of fungal treated wheat straw up to 30% of the diet of lactating cows supplemented with a protein source such as cottonseed meal had not affected the nutrients intake and lactation performance.

In Iran, the availability of high quality forages is restricted. The use of wheat straw, which is accessible in a huge amount, is limited due to its low nutritional value. Recently, biological method using white-rot fungi to improve the nutritional value of straw have been reported (Zadrazil 1997). However, the data available have been obtained from in vitro works. Additionally, little information is available on the utilization of fungal treated straw fed to dairy cow. Therefore, this experiment was carried out to assess the effect of fungal treated wheat straw on the performance of lactating cows.