Administración estratégica de gonadotropina coriónica humana (hCG) en vacas lecheras de alta producción sometidas a estrés térmico para mejorar la fertilidad a primera inseminación posparto
Inmaculada Cuevas-Gómez1, Iris Cuchí Cava2, Javier Jiménez Bejarano3, Javier Lozano4, Guillermo Lorenzo Díaz5, Carles Porta Sabaté6, Raul Troya Ruiz7, Eber Rojas Cañadas8, José María Sánchez9
(1)-Instituto Andaluz de Investigación y Formación Agraria, Pesquera, Alimentaria y de la Producción Ecológica (IFAPA), Hinojosa del Duque, 14270, Córdoba, España (2)-Departamento de Producción Animal, Universitat de Lleida, 25198, Lleida, España/ Grupo de Producción y Reproducción Animal, Centro Agrotecnio-CERCA, 25198, Lleida, España. (3)-Laboratorios Calier, 08520, Barcelona, España.
(4)-Las Rozuelas del Valle S.L. Torrecampo, 14410, Córdoba, España. (5)-Gando Nuevas Tecnologías SL, Ferrol, 15403, A Coruña, España. (6)-Selergan SAU, Almancelles, 25100, Lleida, España.
(7)-Grupo Medivetnova SL, Almuñecar, 18690, Granada, España. (8)-Departamento de Producción Animal, Universitat de Lleida, 25198, Lleida, España./ Grupo de Producción y Reproducción Animal, Centro Agrotecnio-CERCA, 25198, Lleida, España. (9)-Instituto Andaluz de Investigación y Formación Agraria, Pesquera, Alimentaria y de la Producción Ecológica (IFAPA), Hinojosa del Duque, 14270, Córdoba, España.
Low fertility in dairy cows compromises farm profitability and sustainability. Suboptimal concentrations of circulating progesterone (P4) during the early post-ovulatory period have been associated with reduced fertility observed in high-producing dairy cows. Human chorionic gonadotropin (hCG) increases the size of the nascent corpus luteum (CL) and/or induces an accessory CL, depending on the timing of administration, thereby increasing P4 concentration. Our previous work, performed under thermoneutral conditions, demonstrated that hCG administered on Day 2 of the estrous cycle increased circulating P4 concentration earlier and improved fertility at first artificial insemination (AI) only in >2-lactation cows, whereas other studies suggest that first-lactation cows may benefit from hCG treatment later in the cycle (around Day 5). We hypothesized that parity-targeted timing of hCG administration would increase luteal area and thus increase circulating P4 concentration, resulting in overall improved fertility at first post-partum AI in high-producing dairy cows exposed to heat stress. Therefore, we aimed to evaluate the effect of a single hCG administration on Day 2 after fixed-time AI (FTAI) in cows with >2 lactations and on Day 5 in cows with 1-2 lactations on total luteal area and pregnancy per AI (P/AI) at first FTAI. Pregnancy loss between 30 and 60 days, and P/AI at second AI were also evaluated. A total of 522 Holstein-Friesian cows from 5 Spanish dairy farms, geographically distributed to represent different production systems (one in northwestern, two in northeastern, and two in southern Spain), were enrolled between July and September 2025 (mean daily temperature-humidity index (THI): 69.8 +/- 5.1, mean +/- SD; mean daily maximum THI: 76.6 +/- 5.3). Cows followed one of the three synchronization protocols for FTAI (Double Ovsynch (n=131), G6G (n=362), or GGPG (n=29); days in milk (DIM) at FTAI: 83.3 +/- 13.6). Within farm, cows were blocked by parity, DIM, synchronization protocol, and body condition score (BCS) and were randomly assigned to receive 2,500 IU (i.m.) of hCG on Day 2 (hCG2: >2-lactation cows; n=81) or Day 5 (hCG5: cows with 1-2 lactations; n=179) after FTAI or no further treatment (control2: >2-lactation cows; n=80; control5: cows with 1-2 lactations; n=182). Luteal area, CL number, and incidence of accessory CL were assessed by transrectal ultrasound in a subset of cows (hCG: n=66; control: n=70) on Days 7 and 14. Pregnancy diagnoses were performed by transrectal ultrasound around 30 and 60 days after FTAI (P/AI=number of pregnant cows/number of inseminated cows). For P/AI at second AI, only cows inseminated before pregnancy diagnosis on Day 30 were included. The effect of the independent variables on binary response variables was determined using generalized linear mixed models in SAS. For the analysis of luteal area, a repeated measures mixed model was applied, with time point defined as the repeated measure. Fixed effects in each model included treatment, parity, DIM and BCS. Farm was included as a random effect in all models. The incidence of multiple ovulations (>1 CL) was similar between hCG and control cows on Day 7 (35.4% vs. 35.4%, respectively). The incidence of accessory CL (defined as a new CL between Day 7 and 14) was greater in hCG than in control cows (41.3% vs. 0%, respectively, P<0.01). Most accessory CLs were observed following hCG administration on Day 5 (54.4% of cows with accessory CL), whereas only 5.9% occurred after hCG administration on Day 2. Cows treated with hCG tended to have greater total luteal area than control cows on Day 7 (4.6 +/- 0.3 vs. 4.1 +/- 0.3 cm2, respectively; P=0.09) and had a greater total luteal area on Day 14 (5.6 +/- 0.3 vs. 4.7 +/- 0.3 cm2 respectively; P<0.01). Overall, hCG treatment increased P/AI compared with controls (39.6% [103/260] vs. 28.6% [75/262], respectively; P=0.01). This improvement was observed both after treatment on Day 2 in >2-lactation cows (hCG2: 42.0% [34/81] vs. control2: 27.5% [22/80]; P=0.05) and on Day 5 in cows with 1-2 lactations (hCG5: 38.5% [69/179] vs. control5: 29.1% [53/182]; P=0.05). The overall incidence of pregnancy loss between Day 30 and 60 was 13.5% and was not influenced by hCG administration on either Day 2 (hCG2: 20.6% [7/34] vs. control2: 18.2% [4/22]) or Day 5 (hCG5: 13.0% [9/69] vs. control5: 7.5% [4/53]). No differences in P/AI at second AI were observed between hCG2 and control2 cows (26.9% [7/26] vs. 33.3% [11/33], respectively); however, hCG treatment on Day 5 increased P/AI at second AI compared with control5 cows (43.5% [27/62] vs. 20.9% [14/67], respectively; P=0.01). In conclusion, a parity-targeted timing of hCG administration increased total luteal area and was associated with improved fertility at first post-partum AI in heat-stressed dairy cows. Additionally, administration of hCG on Day 5 improves fertility at second AI in >2-lactation cows. Further studies evaluating circulating P4 concentrations are ongoing. Funding: MCIN/AEI/10.13039/501100011033 and FEDER,EU (PID2023-146910OA-C22) and Next GenerationEU/PRTR (RYC2021-033574-I). Grant DGP_POST_2024_00045, funded by Junta de Andalucia/CUII and FSE+.
