Dietary substitution of alfalfa hay with different levels of artichoke (Cynara scolymus L.) silage in sheep: effects on voluntary feed intake, rumen fermentation characteristics, blood metabolites, and nitrogen retention.

This study aimed to investigate how replacing alfalfa hay with varying amounts of artichoke silage (AS) influences voluntary feed intake, ruminal fermentation parameters, blood metabolites, and nitrogen retention in sheep. Accordingly, approximately 400 kg of artichoke forage at the flowering stage was ensiled in 10-liter thick plastic bags for 60 days to evaluate the silage quality characteristics. Eight adult Kurdish rams with an average body weight of 58 ± 2.8 kg were arranged in four treatments according to 4 × 4 Latin square design with four 26-day periods. The first 21 days were for adaptation and the last 5 days were for sample collection. Four isoenergetic and isonitrogenous experimental diets were as follows: (1) diet without any inclusion of AS (AS0), (2) in which 250 g/kg DM of the forage component was replaced with AS (AS250), (3) in which 500 g/kg DM of the forage component was replaced with AS (AS500) and (4) in which 500 g/kg DM of the forage component was replaced with air-exposed AS (silage exposed to air for 3 h prior to feeding; AS500-AE). The digestibility of neutral detergent fiber was significantly reduced in the AS500 and AS500-AE diets (P ≤ 0.05), whereas ruminal pH in these groups was significantly elevated compared to AS0 group (P ≤ 0.05). Conversely, ruminal NH3-N concentration and total ruminal protozoa counts were significantly decreased in sheep fed diets containing AS (P ≤ 0.01). Total volatile fatty acid concentration in rumen fluid was lowest in sheep fed AS500 diet (P ≤ 0.01). Serum cholesterol concentration was significantly decreased in sheep fed AS-containing diets compared to others (P ≤ 0.01). Fecal nitrogen excretion was significantly higher in sheep fed AS-containing diets relative to AS0 (P ≤ 0.01), which corresponded with the lowest retained nitrogen observed in these animals (P ≤ 0.05). Additionally, allantoin and total purine derivatives excreted in urine were significantly lower in sheep fed AS500 and AS500-AE diets compared to AS0 (P ≤ 0.05). Microbial nitrogen and microbial protein production were also significantly reduced in sheep receiving AS500 and AS500-AE diets (P ≤ 0.05). Overall, the findings suggest that although the inclusion of AS in the diet reduced ruminal microbial activity, it did not substantially affect nutrient intake or digestibility.