History
A 10-year-old 57-kg sexually intact female alpaca was presented because of a 3- to 4-month history of aggressive behavior (attacking and charging herdmates). The alpaca previously had several successful pregnancies, with her last cria born approximately 1.5 years earlier. There had been no other male exposure since that breeding, as the owners only have females and 1 gelding (housed separately). The referring veterinarian collected blood for hormone testing through the Cornell University Animal Health Diagnostic Center in Ithaca, NY. Serum progesterone concentration was 10.49 ng/mL, consistent with progesterone concentration reference limit of > 2 mg/mL during pregnancy in camelids. Serum testosterone concentration was < 0.01 ng/mL (no reference range). The alpaca was referred to the veterinary teaching hospital for further evaluation.
On physical examination, the alpaca had a rectal temperature of 38 °C (reference range, 37.5 to 38.9 °C), heart rate of 80 beats/min (reference range, 60 to 90 beats/min), and respiratory rate of 40 breaths/min (reference range, 10 to 30 breaths/min). The alpaca was sedated with IM administration of ketamine hydrochloride (0.5 mg/kg), xylazine hydrochloride (0.5 mg/kg), and butorphanol tartrate (0.1 mg/kg) for transrectal ultrasonographic evaluation of the reproductive tract (Figure 1). The left ovary was smaller and had 2 hyperechoic structures that were 3.28 and 5.41 mm in diameter. The right ovary was larger and contained a singular mass-like structure that was 17.6 mm in diameter and fairly homogenous except for a prominent hyperechoic band spanning the structure, similar to a mediastinum testis. The size and echogenicity of the uterus appeared to be consistent with that of a nonpregnant female with no obvious abnormalities.
Transrectal ultrasonographic images of the left (A) and right (B) ovaries of a 10-year-old alpaca with a history of aggressive behavior. The portions of the uterine horns in the images appear ultrasonographically normal and homogenous, with no edema or intraluminal fluid present. The left ovary (circled; A) is smaller than the right ovary (circled; B) and contains 2 hyperechoic structures (5.41 mm [between the blue calipers] and 3.28 mm [between the green calipers] in diameter). The right ovary contains 1 large mass-like structure (17.6 mm in diameter between the blue calipers) that appears fairly homogenous except for a prominent hyperechoic band spanning the structure, similar to a mediastinum testis.
Citation: Journal of the American Veterinary Medical Association 260, 10; 10.2460/javma.22.02.0087
Question
What are the most likely causes for aggressive behavior in this alpaca?
Answer
The most likely causes for aggressive behavior in this alpaca were persistent nonpregnant luteal phase (pseudopregnancy), granulosa cell tumor, and interstitial cell tumor.
Results
The owners elected to have the alpaca undergo bilateral ovariectomy due to the inability to completely rule out the presence of a tumor on the basis of hormone analyses and ultrasonography.
The alpaca was sedated by IM administration of xylazine hydrochloride (0.25 mg/kg), ketamine hydrochloride (0.5 mg/kg), and butorphanol tartrate (0.2 mg/kg). Anesthesia was induced by IV administration of alfaxalone (0.7 mg/kg) and maintained with isoflurane delivered in oxygen. Penicillin G procaine (22,000 U/kg, IM), ceftiofur crystalline-free acid (4.4 mg/kg, SC), flunixin meglumine (1.0 mg/kg, IV), and pantoprazole (1.0 mg/kg, IV) were administered preoperatively. A transversus abdominis plane block was performed to desensitize the parietal peritoneum, anterior abdominal wall muscles, and overlying skin using 57 mg of bupivacaine on each side of the abdomen.
The ovariectomy was performed laparoscopically with the alpaca positioned in dorsal recumbency. The first portal was created 2 cm caudal to the umbilicus, and the second and third portals were created approximately 5 to 6 cm caudal to the first and 5 to 6 cm abaxial to both sides of midline. The left ovary was visualized using atraumatic laparoscopic forceps (Supplementary Figure S1). Traumatic forceps were introduced to stabilize the ovary while a 10-mm electrothermal vessel-sealing device transected the mesovarium, proper ligament of the ovary, and ovarian blood vessels. The ovary was removed by exteriorization of the forceps and cannula at the umbilical portal. The right ovary was similarly visualized, transected, and removed. The body wall at the portal sites was closed with size 0 polydioxanone suture in a simple continuous pattern. Subcutaneous tissue and skin layers were closed with 2-0 poliglecaprone 25 in a simple continuous pattern. An additional IM dose of procaine G penicillin was given 12 hours postoperatively. Additional IV doses of flunixin meglumine and pantoprazole were given 24 hours postoperatively, after which meloxicam (0.5 mg/kg, PO, q 24 h for 5 days) was prescribed. The alpaca was discharged 4 days after surgery.
The ovaries were grossly normal in appearance (Figure 2), consistent with ultrasonographic findings. Histologic examination revealed that the right ovary contained a 2.0-cm, well-demarcated, and densely cellular aggregate of luteal tissue that compressed normal ovarian tissue with multiple normal follicles in various stages of development. The luteal tissue consisted of sheets of cells upon a fine fibrovascular stroma with many large blood vessels. Approximately 90% of individual cells were large and polygonal, with abundant hypereosinophilic and frequently vacuolated cytoplasm and a central, round nucleus with indistinct to single nucleoli. The remaining 10% of cells were small, with indistinct cell borders, scant and lightly eosinophilic cytoplasm, and irregularly shaped, vesiculate nuclei. The left ovary contained a 0.7-cm aggregate of luteal tissue that looked similar to that described in the right ovary as well as a second 0.2-cm focus composed of a more even distribution of large (50%) and small (40%) luteal cells. The final diagnostic interpretation of these microscopic findings suggested that the corpus luteum (CL) in the right ovary was well-developed and likely persistent, whereas the left ovary contained 2 CL of different sizes and cellularity. No neoplasia was present in the submitted sections.
Gross and photomicrographic images of the ovaries removed from the alpaca in Figure 1. A—Both ovaries are normal in size and appearance, with the left ovary containing 2 small structures (arrows) and the right ovary containing 1 large structure (arrow). B—The left ovary has a central corpora luteum surrounded by normal ovarian tissue. Inset—Higher magnification of luteal cells outlined by the box in the main image. H&E stain; bar = 200 µm (B) or 25 µm (inset). C—The right ovary has a well-demarcated and densely cellular aggregate of sheets of luteal cells and many large blood vessels (upper right) and normal ovarian tissue (lower left). Inset—Higher magnification of the luteal cells outlined by the box in the main image. H&E stain; bar = 200 µm (C) or 25 µm (inset).
Citation: Journal of the American Veterinary Medical Association 260, 10; 10.2460/javma.22.02.0087
Discussion
Neoplasia was initially suspected in this alpaca given the onset of aggressive behavior and lack of exposure to a sexually intact male. Ovarian tumors are rare in camelids, with only 1 case reported out of 551 camelid submissions to a diagnostic laboratory.1 An ovarian benign interstitial (Leydig) cell tumor was the cause of aggressive male-like behavior in a female alpaca previously.2 Similar to the current case, a large, well-demarcated mass was found on 1 ovary. However, histologic findings in their case were consistent with neoplasia, and serum testosterone concentration was 969.1 pg/mL (reference range,2 11.7 to 62.1 pg/mL), compared with < 10 pg/mL in the alpaca of the present report. Additionally, the serum progesterone concentration of the alpaca in the previous case2 was 0.3 ng/mL, compared with 10.49 ng/mL for the alpaca of the present report. Although serum anti-Müllerian hormone and inhibin concentrations have been used in other species for diagnosis of granulosa cell tumors, these assays are species specific and not validated or commercially available for camelids. Given the lack of data in camelids, we were unable to confidently rule neoplasia in or out based on hormone or ultrasonographic findings and relied on histopathology to provide a final diagnosis.
Interestingly, structures on the ovaries were identified as normal luteal tissue, despite the female not being in contact with sexually intact males for several years. In camelids, ovulation is induced through the absorption of a seminal plasma protein from the uterus at copulation.3 Spontaneous ovulations in camelids are rarely reported, with some speculation that olfactory or auditory cues from the male could be sufficient to generate a preovulatory luteinizing hormone surge.4 Still, whether camelids can undergo spontaneous ovulation or not is controversial, with some authors suggesting that luteinization without ovulation may be more likely.3 In the current case, the latter seems to be more probable given that no sexually intact males were housed with this group of female alpacas and no other females seemed to be similarly affected.
Based on the duration of clinical signs, we suspected that a spontaneous ovulation or luteinization may have occurred in this alpaca approximately 3 to 4 months prior to presentation, resulting in the development of a persistent CL. When a sterile mating occurs in camelids, the CL usually undergoes regression between 9 and 11 days after ovulation, with estrus occurring by day 12.3 To the authors’ knowledge, a prolonged nonpregnant luteal phase (pseudopregnancy) has never been confirmed in alpacas.4 One study5 reported pseudopregnancies of 56- and 134-day durations in 2 llamas after unsuccessful matings with a sexually intact male. In camelids, luteolysis is typically triggered by the pulsatile release of prostaglandin F2α from the endometrium in the absence of pregnancy at 8 to 9 days after mating.3 Therefore, lesions or defects within the uterus could alter endometrial function and prevent the release of prostaglandin F2α, resulting in a persistent CL. Given the normal appearance of this alpaca’s uterus on ultrasonography and laparoscopy, the presence of endometrial-disrupting lesions within the uterus seems unlikely but could not be ruled out completely as the cause of pseudopregnancy in this case.
Outcome
The alpaca recovered from the ovariectomy with no complications, and the owners reported that the behavioral issues completely resolved within 4 months. Several months later, the alpaca was euthanized by its regular veterinarian after becoming recumbent and anorexic. Given the findings in this case and the period of recovery, we do not suspect that the death was directly related to the pseudopregnancy or ovariectomy but cannot rule it out completely.
Supplementary Material
Supplementary materials are posted online at the journal website: avmajournals.avma.org
Acknowledgments
The authors declare that there were no conflicts of interest.
The authors thank the referring veterinarians, Drs. Lincoln Montgomery-Rodgers and Jamie Horstmann. We also acknowledge Drs. Jorge Adarraga and Barbara Schanbacher from the Animal Health Diagnostic Center at Cornell University for assisting with hormone analysis interpretation.
References
- 1. ↑
Valentine BA, Martin JM. Prevalence of neoplasia in llamas and alpacas (Oregon State University, 2001–2006). J Vet Diagn Invest. 2007;19(2):202–204. doi:10.1177/104063870701900213
- 2. ↑
Gilbert R, Kutzler M, Valentine BA, Semevolos S. Hyperandrogenism from an ovarian interstitial-cell tumor in an alpaca. J Vet Diagn Invest. 2006;18(6):605–607. doi:10.1177/104063870601800616
- 3. ↑
Vaughan JL, Tibary A. Reproduction in female South American camelids: a review and clinical observations. Small Rumin Res. 2006;61(2-3):259–281. doi:10.1016/J.SMALLRUMRES.2005.07.015
- 4. ↑
Brown BW. A review on reproduction in South American camelids. Anim Reprod Sci. 2000;58(3-4):169–195. doi:10.1016/S0378-4320(99)00081-0
- 5. ↑
Adam CL, Moir CE, Shiach P. Plasma progesterone concentrations in pregnant and non-pregnant llamas (Lama glama). Vet Rec. 1989;125(25):618–620. doi:10.1136/vr.125.25.618
