Supplementing organic zinc enhances growth and blood parameters to preserve ovarian function of Awassi lambs raised in a high summer temperature environment.

The effects of organic zinc supplementation on performance, whole blood parameters, and ovarian function of heat-stressed female Awassi lambs raised under high summer ambient temperature was determined. Twenty-four female lambs (∼10 months of age; live weight = 27.7 kg) were randomly assigned to one of two dietary treatments: 1) a control diet (including zinc oxide 10 mg/kg dry matter (DM); n = 12) or 2) a control diet supplemented with 30 mg/kg DM of organic zinc (n = 12) for 5 weeks during natural summer conditions (ambient temperature range = 25-46°C and temperature humidity index (THI) range = 72.6-92.2%). Relative to control, organic zinc supplementation improved growth performance (higher final live weight, P = 0.01; greater weight gain, P ≤ 0.001) and carcass characteristics (increased carcass weight, P ≤ 0.001; higher dressing percentage, P ≤ 0.001), along with better thermoregulation (lower rectal temperature (RT) by 1.7°C, P ≤ 0.01). Whole blood analysis revealed that organic zinc supplementation increased red blood cell count (P = 0.02), concentration of hemoglobin (P = 0.01), albumin, total protein, and glucose (P ≤ 0.01) while decreasing white blood cells (P = 0.02) and lymphocyte counts (P = 0.02). The organic zinc supplementation group had 1.5-fold greater follicular fluid estradiol concentrations (P ≤ 0.001) and elevated mRNA expression of key genes (StAR, FSHR, CYP19A1, and FOS; P ≤  0.001) involved in steroidogenesis. The organic zinc supplementation also enhanced follicle development, increasing surface antral follicle counts (P ≤ 0.001) and number of secondary (P ≤ 0.05). Additionally, it reduced ovarian fibrosis (P ≤ 0.001) and increased ovarian size (P = 0.01) and weight (P = 0.01). In summary, organic zinc supplementation effectively mitigated the high summer ambient temperature in Awassi female lambs by improving thermoregulation and ovarian function, thereby benefiting production and reproductive performance.