Objectives: This study aimed to evaluate the effectiveness of gonadotropin-releasing hormone-loaded chitosan–TPP nanoparticles (GnRH-CNPs) and prostaglandin F_2α-loaded chitosan–TPP nanoparticles (PGF_2α-CNPs) within the Ovsynch protocol for enhancing reproductive performance in heat-stressed dairy cows. Methods: Thirty-six cyclic purebred Friesian cows not detected in standing heat for more than 90 days postpartum were randomly allocated to three treatment groups. The control group (OVS, n = 12) followed the standard Ovsynch protocol with conventional doses. The ½ OVS group (n = 12) received 5 µg GnRH-CNPs on days 0 and 9, along with 250 µg PGF_2α-CNPs on day 7. While the ¼ OVS group (n = 12) was administered 2.5 µg GnRH-CNPs on days 0 and 9, with 125 µg PGF_2α-CNPs on day 7. Ovarian follicular dynamics and corpus luteum (CL) development were monitored on days 0, 4, 7, and 9 of the protocol. Serum progesterone (P₄) concentrations were measured throughout the synchronization period and on days 15 and 30 post-AI. Pregnancy was diagnosed on day 30 post-AI. Results: The ¼ OVS protocol achieved a significantly greater follicular response (p < 0.05) than other protocols. On day 4, following the first GnRH administration, the OVS group exhibited a higher number of subordinate follicles (p < 0.05) and a greater diameter of the dominant follicles (DFs), whereas the ¼ OVS group showed a greater subordinate follicle diameter (p < 0.05) and a higher number of DFs. On day 9, after PGF_2α administration, the ¼ OVS group maintained an elevated number of subordinate follicles, while larger subordinate follicle diameters were observed in the ½ OVS and OVS groups. No significant differences in DF numbers and diameters were observed among groups. P₄ concentrations remained similar across groups during treatments. Compared to control, a significantly higher value of P₄ concentration (p < 0.05) was recorded on day 15 post-AI in the ½ OVS group and on day 30 post-AI in the ¼ OVS group. These findings correlated with a higher pregnancy rate in the ¼ OVS group (65%) compared to the ½ OVS and OVS groups (40% in each). Conclusions: Nanofabrication reduced GnRH and PGF_2α dosage by 50% and 75% without impairing ovarian response and pregnancy rates. The ¼ OVS protocol notably enhanced the ovarian activity and fertility, highlighting the use of GnRH-CNPs and PGF_2α-CNPs as promising and practical approaches to enhance the fertility in dairy cattle under heat stress (HS).

The current study was designed to investigate the effect of elevated testicular temperature caused by scrotal insulation on some hormonal profiles (testosterone T2; triiodothyronine T3; and cortisol), growth performance (body weight, femur length, and chest circumference) and thermal indices (rectal temperature RT; respiration rate RR) in 10-month-old bucks. Ten Damascus bucks were divided into an uncastrated group (control, n = 5) and a castrated group (n = 5). The testicular hyperthermia was conducted by scrotal insulation using sheep-skin pouches applied for 60 days. Blood samples were obtained biweekly for 100 days. Concentrations of T2, T3, and cortisol also RR, RT, as well as body weight, femur length, and chest circumference were measured concurrently. Results showed that the overall concentrations of T2 and cortisol were comparable between castrated and uncastrated bucks (314.26 vs. 316.22 and 40.33 vs. 39.44, respectively). However, the castrated bucks had significantly high T3 concentrations, body weight, and femur length compared to uncastrated bucks (18.14 vs. 15.82 ng/dl; 20.35 vs. 19.06 kg and 17.28 vs.16.97 cm, respectively). All T2 concentrations, body weight, femur length, and chest circumference were increased by time. Despite fluctuated T3 concentrations throughout the study period, a notable difference appeared at day 28, as the castrated bucks had a significantly higher T3 compared to uncastrated bucks. In conclusion, the physiological castration did not influence T2 and cortisol concentrations but increased T3 and enhanced growth performance. This technique may offer an alternative to physical or surgical castrations with potential benefits for animal welfare and productivity.