Captive colonies of nonhuman primates may supply animals for biomedical, behavioral, and/or conservation purposes. It is important that these colonies are self-sufficient, in order to avoid the need of wild-caught individuals, which is unsustainable and unethical, especially nowadays, with the growing number of endangered species. The National Primate Center (Centro Nacional de Primatas, CENP) is an experimental breeding colony, located in northern Brazil, in Ananindeua, Pará. Therefore, it is important that it maintains reproductively sound animals.

The objective of this report was to compare semen quality of howler monkeys (Alouatta caraya) from CENP in two different periods, spring 2010 and summer 2014. In both periods we used six adult males, although only three of the males were present during both periods. Semen was collected by rectal probe electroejaculation, diluted in Ringer lactate solution¹, and analyzed.

Results for the whole colony and for the three males were compared using Student’s t test (α=0.05). Results (mean ± SEM) obtained in 2010 and 2014, respectively, were: volume (µL)=86.77±10.37 and 112.59±17.06 (P=0.1773); pH=7.45±0.06 and 7.75±0.05 (P=0.0006); concentration (10⁶ sperm/ml)=726.00±129.00 and 559.81±88.83 (P=0.2951); total motility(%)=60.00±5.57 and 70.65±6.17 (P=0.2179); progressive motility (%)=47.15±5.47 and 58.24±6.37 (P=0.1997); intact plasma membrane (%)=47.38±3.21 and 58.65±4.72 (P=0.0469); intact acrosome (%)=58.96±3.48 and 63.24±2.57 (P=0.3290); mitochondrial activity class I (%)=7.50±1.53 and 24.67±4.76 (P=0.032); class II (%)=51.17±4.23 and 51.93±3.13 (P=0.8850). These results show that semen quality was overall maintained in the colony along the years and in both seasons. Moreover, the percentage of sperm with intact plasma membrane and with mitochondrial activity class I improved.

Male 1 showed significant improvement (P≤0.05) of semen quality from 2010 (spring) to 2014 (summer), when volume went from 110.00±26.70 to 225.00±49.24 (P=0.0575), pH went from 7.60±0.07 to 7.87±0.07 (P=0.0542), progressive motility went from 48.50±12.37 to 80.00 (P=00514), percentage of sperm with intact plasma membrane went from 44.67±4.76 to 73.00±4.58 (P=0.0007), and mitochondrial activity class I went from 7.33±4.52 to 26.67±4.84 (P=0.0337). Male 2 only showed significant improvement (P≤0.05) in semen volume, which went from 65.40±6.62 to 101.67±15.39 (P=0.0442). Male 3 had no significant change in semen quality.

Although an increase in volume during the summer months has been reported,² this was not observed for the whole colony. Nevertheless, we found an increase in ejaculated volume for two of the three males used in both periods, indicating it could be affected by season. Moreover, other factors could be involved, such as age and captive management. It has been shown that stress causes reduction of semen quality.³ We believe the improvement in semen quality shown by male 1, might be a consequence of two main factors, involving stress reduction. One factor is that this individual was kept by itself in a small enclosure during the first period, while in the second period it was kept with a female in a larger enclosure. The other factor is that this animal was wild-caught during the implantation of a hydroelectric power dam and had only been in captivity for a few months, during the first period. Therefore, the improvement in semen quality of male 1 is probably a reflection of stress reduction due to (1) sharing the enclosure with a female, and (2) individual adaptation to the captive environment.

These results indicate that in order to have a reproductively sound colony, it is important to respect the species’ social and physiological needs, thus minimizing stress.

ACKNOWLEDGEMENTS: The authors would like to thank the São Paulo Research Foundation (FAPESP), the Andrology Lab at the School of Veterinary Medicine and Animal Science, University of São Paulo (FMVZ, USP) and the National Primate Center (CENP), Ministry of Health for their technical and/or financial support.