Complete Blood Count Analysis on Beef Cattle Exposed to Fescue Toxicity and Rumen-Protected Niacin Supplementation

Abstract

Offspring born to dams genetically tested for resistance to fescue toxicity were separated in groups based on their dams' resistance level (tolerant vs. susceptible). Rumen-protected niacin (RPN) is proposed as a potential alleviator for vasoconstriction produced by fescue toxicity. Complete blood count (CBC) analysis was utilized for detection of significant responses to treatments applied. Our objectives were as follows: (a) to analyze changes in CBC due to fescue toxicity, maternal resistance level, and RPN in growing offspring; and (b) to assess the effects of maternal resistance level when consuming endophyte-infected tall fescue seeds in addition to RPN in offspring performance. Body weight, average daily gain, or health status were not improved by RPN or the genetic test to detect fescue toxicity resistance. Typical signs of alkaloids intoxication and heat stress were noticed in offspring. Particularly, rectal temperature was greater for susceptible control heifers. Results showed that susceptible control offspring presented signs of anemia denoted by low mean corpuscular hemoglobin (MCH) and mean corpuscular volume (MCV). High levels of white blood cells (WBC) and basophils in combination to low neutrophils to lymphocytes ratio were the signs of infection or inflammation detected in the CBC analysis, especially in tolerant niacin steers. Furthermore, offspring of control heifers had a greater percentage of reticulocytes and RDW, denoting signs of anemia.

Keywords: animal performance; beef cattle; complete blood counts; ergovaline; fescue toxicity; fetal programming; genetic test; heat stress; rumen-protected niacin; tolerance index.

Figure 1

Experimental design. Abbreviations: SC: Susceptible, control; SN: Susceptible, niacin; TC: Tolerant, control; TN: Tolerant, niacin; ♀: heifers; ♂: steers, *: stars.

Figure 2

Significant nutritional treatment and sex interactions for hematocrit, hemoglobin, red blood cell distribution width, and white blood cells of Angus × Simmental steers and heifers’ offspring. Hematocrit is represented by the percentage of packed red cells in the blood, hemoglobin (g/dL), red blood cell distribution width (RDW, %), and white blood cells (×10³/uL) results of Angus × Simmental steers (male) and heifers (female) exposed to diets containing rumen-protected niacin (RPN), or without rumen-protected niacin (CTRL), and endophyte-infected tall fescue seeds. Statistically significant differences were declared at p < 0.05 and tendencies at p > 0.05 and <0.1.

Figure 3

Significant genetic treatment and nutritional treatment interactions for mean corpuscular hemoglobin, mean corpuscular volume, neutrophils, and white blood cells of Angus × Simmental steers and heifers offspring. Mean corpuscular hemoglobin (MCH, pg), mean corpuscular volume (fL), neutrophils (×10³/uL), and white blood cells (×10³/uL) concentrations for Angus × Simmental offspring steers (male) and heifers (female) exposed to diets containing rumen-protected niacin (RPN) or without rumen-protected niacin (CTRL), while receiving endophyte-infected tall fescue seeds. Statistically significant differences were declared at p < 0.05 and tendencies at p > 0.05 and <0.1.

Figure 4

Significant interactions between genetic treatment, nutritional treatment and time for reticulocytes, basophils, and neutrophils to lymphocyte ratio for Angus × Simmental steers and heifers’ offspring. Neutrophil to lymphocyte ratio, basophils (×10³/uL) and percentage of reticulocytes results of Angus × Simmental steers (male) and heifers (female) exposed to diets containing rumen-protected niacin (RPN) or without rumen-protected niacin (CTRL), while receiving endophyte-infected tall fescue seeds. Statistically significant differences were declared at p < 0.05 and tendencies at p > 0.05 and <0.1.