Tierarztl Prax Ausg G Grosstiere Nutztiere. 2025 Aug;53(4):231-244. doi: 10.1055/a-2625-9116. Epub 2025 Sep 2.
ABSTRACT
In South American Camelids (SAC), determining a suitable time point for mating poses challenges as females ready for conception do not show estrus signs or behavioral changes. Therefore, the applicability of measuring sex steroids in milk and vaginal cytology as non-invasive methods for monitoring ovarian activity was investigated.Samples were collected from a total of 10 alpacas (A) and 9 llamas (L) over a period of 4 weeks following parturition. The concentrations of progesterone (P4), estradiol-17β (E2) and total estrogens (GOE) in blood and milk were measured using radioimmunoassays after sample extraction. Vaginal swabs were prepared and evaluated according to the procedure routinely used in dogs.In A and L, the estrogen concentrations in milk were significantly lower than those in blood (E2 in blood: A: 11.1±2.9 pg/ml, L: 14.6±5.0 pg/ml; E2 in milk: A: 6.2±3.1 pg/ml, L: 7.9±5.8 pg/ml; GOE in blood: A: 120. 2±26.9 pg/ml, L: 143.7±45 pg/ml; GOE in milk: A: 57.1±16.1, L: 75.9±34.6 pg/ml), while the differences between the two species were not significant. The correlations between steroid concentrations in blood and milk were statistically significant in L, but not in A. While in L, correlations between estrogen concentrations and vaginal cytological parameters showed several statistical significances with p-values partly <0.01, in A only GOE in the blood was negatively correlated with the proportion of basal-/parabasal cells.P4 measurement in milk allows the detection of luteal phases in SAC with high reliability. Despite statistical significance, the correlations between estrogen concentrations in blood and milk were also too weak in L to estimate blood concentrations with acceptable accuracy based on estrogen concentrations in milk at the level of the individual animal. Vaginal cytology could in principle be suitable for the identification of the maturation phase of follicular waves in L. However, improvements of the methodology and further validation are warranted before its routine use.
PMID:40897165 | DOI:10.1055/a-2625-9116
