Objective: Increasing feed costs and the shortage of conventional forage resources highlight the utilization of unconventional and readily available feed sources, such as green space tree leaves, as a practical strategy in ruminant nutrition. This study was conducted to evaluate the effects of substituting a portion of dietary forage with different levels of plane tree (Platanus orientalis) leaves on feed intake, productive performance, nutrient digestibility, blood biochemical parameters, and the antioxidant system status in Saanen dairy goats.

Method: The experiment was carried out using 18 multiparous Saanen goats (average milk yield 1.75 ± 0.72 kg/day and lactation days 52.7 ± 13.4) in a completely randomized design with three treatments and six replicates over a period of 56 days (14 days of adaptation and 42 days of the main experimental period). The experimental diets were as follows: 1- control (basal diet without plane leaves), 2- replacement of 20% of forage with plane leaves, and 3- replacement of 40% of forage with plane leaves, all of which were formulated to be isonitrogenous and isocaloric. Throughout the experimental period, dry matter intake and milk yield were recorded daily. Milk samples were collected for composition analysis, blood samples were taken to assess biochemical parameters (glucose, total cholesterol, lipids, and liver enzymes) and oxidative status indicators (total antioxidant capacity and malondialdehyde), and fecal and feed samples were gathered to determine apparent nutrient digestibility. The collected data were analyzed using the MIXED procedure of the SAS software.

Results: Replacing 20% of the dietary forage with plane leaves resulted in a significant increase in dry matter intake, daily milk yield, and 4% fat-corrected milk in Saanen goats compared to both the control group and the 40% replacement group (P < 0.05). Although the percentages of milk fat and total milk solids decreased in goats receiving plane leaves in their diet (P < 0.05), the daily yield (g/day) of protein, fat, non-fat solids, and total milk solids in goats from the 20% replacement group was significantly higher than in the other groups (P < 0.05). Feed conversion ratio and body weight changes were not affected by the experimental treatments. No significant differences were observed among treatments regarding the apparent digestibility of dry matter, crude protein, organic matter, and acid detergent fiber. However, replacing 40% of the conventional dietary forage with plane tree leaves led to a significant decrease in the digestibility of neutral detergent fiber and a significant increase in the digestibility of ether extract (P < 0.05). Regarding blood parameters, triglyceride concentration was higher in the 20% replacement group, while low-density lipoprotein concentration was significantly higher in the 40% replacement group compared to the other treatments (P < 0.05). Liver enzyme activities, including aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase, were not influenced by the dietary treatments. However, serum malondialdehyde concentration in the 40% plane leaf replacement group showed a tendency to decrease (P = 0.086).

Conclusion: In conclusion, the findings of this study indicate that plane tree leaves can serve as an alternative feed source, replacing up to 20% of the conventional forage in the diet of Saanen dairy goats. This level of substitution, while improving feed intake and productive performance, does not exert significant adverse effects on liver health, nutrient digestibility, or the antioxidant status of the animals. Higher substitution levels (40%) may be associated with a reduction in milk fat percentage, possibly due to the presence of secondary compounds. Therefore, the optimal utilization of this feed resource necessitates adherence to an appropriate substitution level.