Factors influencing embryo quantity and quality in donor cows from Latvian Blue, Latvian Brown, and Danish Red breeds at risk in Latvia

The aim of this study was to find out what general factors influenced embryo quantity and quality in the framework of multiple ovulation and embryo transfer done in Latvia 2018–2020. The gene-pool cows from the cattle breeds Latvian Blue, Latvian Brown, and Danish Red (n = 30) were selected. Such factors as the donor`s blood biochemical and hematological parameters value, ovarian steroid hormones level, milk somatic cell count (SCC), parity, and environmental temperature were analyzed using a negative-binomial regression method. The variables significant at a liberal alpha level of 0.20 in univariable regression models were included in two multivariable models. The first model showed that the number of embryos (nE) was associated (P < 0.01) with a higher progesterone (P4) level and blood absolute count of eosinophils (Eo) on the first day of multiple ovulation (MO) treatment, with a lower SCC and average daily air temperature in the month preceding embryo collection, and lower parity. It can be predicted according to the nE model, if P4 level or Eo absolute count is increasing by the interquartile range (IQR), and provided that the other associated parameters remain constant, the nE will be higher by 2.9 and 4.4 embryos, respectively. If SCC or temperature is increasing by the IQR, the nE will be lower by 4.7 and 15.2 embryos, respectively. Additionally, the nE model predicted 13.3 more embryos in primiparous than in multiparous donors. The second model showed that the number of transferable embryos (nTE) was associated (P < 0.05) with a higher Eo and serum sodium (Na⁺) concentration on the first day of MO treatment, and with a lower SCC and average daily air temperature in the month preceding embryo collection. It can be predicted according to the nTE model, if Na⁺ level or Eo absolute count is increasing by the IQR, the nTE will be higher by 3.7 and 2.4 embryos, respectively. If SCC or temperature is increasing by the IQR, the nTE will be lower by 3.3 and 6.4 embryos, respectively.