Effects of Yucca schidigera Extract Inclusion in Holstein Calves' Diets on Performance, Metabolism, and Rumen Volatile Fatty Acid Profile

In the diet of calves, the search for additives that aid in their development is essential due to the impact that these can generate throughout their lives, resulting in a relationship with their longevity and the maintenance of the herd. Yuca schidigera has been used in ruminant diets, impacting health and performance; however, there are few reports on its intake by dairy cattle in the rearing phase. Therefore, this study's objective was to evaluate whether adding Yucca schidigera to the diet of calves in the rearing phase can benefit health, productive performance, and feed efficiency. The study was conducted over 60 days, with 24 calves divided into two groups: G1 had no added Yucca schidigera and G2 had 188 mg of Yucca schidigera added per kg of dry matter intake. Data and samples were collected at 30-day intervals. No treatment effect was observed in body weight, weight gain, daily weight gain, or feed intake (p > 0.05); however, the calves in G2 showed 26.3% lower feed efficiency than those in G1. Using the concentrate consumption of the calves, the amount of Yucca schidigera ingested was calculated, i.e., 555 mg/calf/day. The total leukocyte count was significantly lower in the calves in G2 compared to G1 on the 60th day. No effect from the treatment or treatment x day interaction was observed for the hematologic variables: erythrocytes, hemoglobin, hematocrit, lymphocytes, granulocytes, monocytes, and platelets. The activities of the enzyme's gamma glutamyl transferase and aspartate aminotransferase were higher in the animals in group G2. There was no effect from the treatment on albumin, globulin, total protein, C-reactive protein, glucose, cholesterol, urea, or amylase. There was a treatment x day interaction for levels of reactive oxygen species, lipid peroxidation, and glutathione S-transferase, which were higher in the blood of calves in group G2 compared to the control. The activity of myeloperoxidase, superoxide dismutase, and catalase did not differ between groups. Tumor necrosis factor and interleukins (IL-1 and IL-6) in the serum of calves that consumed Yucca schidigera were higher on day 60 compared to the control. A higher concentration of short-chain fatty acids in the ruminal fluid was observed in animals in group G2 compared to G1, primarily due to the higher levels of acetic acid. The amounts of propionate and butyrate were lower in the ruminal fluid of calves in group G2. These results allow us to conclude that the consumption of Yucca schidigera at a dose of 555 mg/animal/day interferes with calves' metabolism and negatively affects feed efficiency.