Under tropical conditions, seasonal variations may also influence the sperm characteristics of Bos indicus. The objective was to evaluate the motility of thawed sperm of bulls from the Peruvian tropics throughout the year. Over 24 months, 129 ejaculates were evaluated based on semen quality and subjected to slow horizontal freezing in 0.5 mL straws. After thawing, the individual, seasonal period, and season effect on motility and kinetic parameters were analyzed using a Sperm Class Analyzer^® (Microptic S.L.U., Barcelona, Spain). There was an individual effect on volume, motility, fresh concentration, and kinetic parameters when thawed. In the dry period, higher straight-line velocity (VSL) (p < 0.05) and beat cross frequency (BCF) were found than in the rainy period (p < 0.01). In summer and autumn, there was greater total motility, fast, circular routes, curvilinear velocity, average path velocity, VSL, amplitude of lateral displacement of the head, and BCF (p < 0.01). Greater volume and motility were found in winter and spring, but in summer and autumn, greater speed and vigor of movement were obtained in thawed sperm. The variation in annual climate patterns influences the seminal quality of bulls, and its effect needs to be assessed to propose adaptation strategies to climate change in tropical areas.

Background: The implementation of routine fixed-time artificial insemination programs can generate significant waste and costs, which good management practices can help mitigate. The objective of the study was to assess the effects of second- and third-use progesterone devices on estrus characteristics and pregnancy rates in synchronized crossbred Gyr cows. Methods: Ten cows were synchronized with first-use Bovine Intravaginal Progesterone Devices (DIB), nine with second-use DIB and ten with third-use DIB. All cows were ³90 days postpartum, had an average milk production of 6.9±1.9 L/day and were aged 4-10 years. Estrus signs were recorded at insemination and pregnancies were confirmed at 60 days by ultrasonography. Result: No significant associations were found between DIB use intensity and estrus detection patch response, mucus color, body condition score (CC), calvings, or breed purity (p greater than 0.05). Body condition was associated with uterine turgor tone (p less than 0.05) and 100% of cows with CC 3.0 showed turgor tone 3. The highest pregnancy rate was found in second-use DIB (55.6%) and CC 2.8 (47.1%), though neither association was significant (p greater than 0.05). DIBs may be used up to a second-use, as cervical mucosal stimulation and pregnancy rate remain unaffected.

The performance of estrus synchronization protocols may be influenced by stressful environmental conditions, even in tropically adapted cattle. This study evaluated the efficacy of two synchronization protocols for fixed-time artificial insemination (FTAI) in crossbred Gyr dairy cows and their relationship with heat stress under Peruvian tropical conditions. Multiparous lactating cows under semi-intensive systems were synchronized and divided into two groups: the conventional protocol (PC9) and the prolonged proestrus protocol (J-Synch6). Estrus manifestation, pregnancy rate, and their association with the temperature–humidity index (THI) were analyzed across seven phases of the FTAI program (73 days). In PC9 cows, no significant effect of the number of hours in each heat stress category according to THI was found. Conversely, in J-Synch6 cows, more hours in Category 0 (THI < 72) during Phases 1 to 4 (follicular emergence to preovulatory follicle) had a positive effect on the estrus manifestation, whereas in Phase 3 (follicular growth), higher exposure to Category 3 (THI ≥ 83) had a negative effect on estrus manifestation. Both protocols demonstrated similar estrus and pregnancy rates, although heat stress affected estrus rates in J-Synch6, but not pregnancy. The choice of protocol should account for heat stress risks during specific periods of the year to maximize success.