Chemical composition, in vitro gas production, and nutrient degradability of carob leaves as a sustainable feed for ruminants in Tunisia and Palestine

Soha Ghzayel ¹ Hajer Ammar ^1* Halima Zoabi ¹ Bassam Abuazez ¹ Ahmed E. Kholif ² Moyòsore J. Adegbeye ³ Rym Ben Abdallah ⁴ Mario De Haro-Martí ⁵ Secundino Lopez ⁶ Mireille Chahine ^7*

• ¹ Ecole Supérieure d'Agriculture du Kef, Kef, Tunisia
• ² North Carolina Agricultural and Technical State University, Greensboro, United States
• ³ Department of Animal Production and Health, Faculty of Agriculture, University of Africa, Bayelsa State, Toru-Orua, Bayelsa, Nigeria
• ⁴ National Institute of Applied Science and Technology, Tunis, Tunisia
• ⁵ Gooding County Extension, University of Idaho, 203 Lucy Lane, Gooding, ID 83330, USA., Gooding, United States
• ⁶ Department of Animal Production, University of León, Leon, Spain
• ⁷ Department of Animal, Veterinary and Food Sciences, College of Agricultural and Life Sciences, University of Idaho, Moscow, Idaho, United States

Carob leaves may be a potential roughage source for ruminants in arid areas. The nutritive value of this feedstuff may be considerably enhanced by the application of solid-phase chemical treatments. This study aimed to evaluate the nutritive value of carob leaves collected from Tunisia and Palestine untreated or treated with urea or sodium hydroxide (NaOH), or supplemented with polyethylene glycol (PEG) on chemical composition and in vitro ruminal fermentation. Carob leaf samples were collected from either Palestine or Tunisia, and were used either untreated (control) or treated with urea, NaOH at 4% or PEG at 100 mg/g (dry matter (DM) basis), and analyzed for chemical composition. Carob leaves were incubated in vitro in diluted rumen fluid fermentation for 48 h, measuring fermentation gases (methane (CH4), and carbon dioxide (CO2)), DM degradability and fermentation kinetics. Results showed a significant country×treatment interaction for most measured parameters, indicating that treatment effects are constrained by the origin of the leaves. Palestine untreated carob leaves had higher (P<0.001) crude fat, crude protein (CP) and neutral detergent fiber (NDF), but less nonstructural carbohydrate (NSC), acid detergent fiber (ADF) and acid detergent lignin than Tunisia leaves. Tunisia carob leaves had higher concentration (P<0.01) of flavonoids and tannins than leaves from Palestine. Of the three treatments tested, the addition of PEG increased (P<0.01) the gas production during the incubation in diluted rumen fluid of carob leaves and this effect was greater with leaves from Palestine than with those from Tunisia. The other treatments had less noticeable effects, which were different when applied to the leaves from one or another country, given the significance of the interaction country × treatment detected for most of the variables studied. PEG, NaOH and urea treatments of carob leaves can be applied to enhance the ruminal fermentation and energy value of this feedstuff. However, the effects of these treatments are highly dependent on the parent material, and seem to be more effective when applied to a low digestible material.