Response to kisspeptin and gonadotropin-releasing hormone agonist administration in Holstein-Friesian dairy heifers with positive or negative genetic merit for fertility traits

Abstract

Previous research has identified that Holstein-Friesian dairy heifers with positive (POS) genetic merit for fertility traits (FertBV) reach puberty earlier than heifers with negative (NEG) FertBV. The hypothalamuspituitary-gonadal (HPG) axis is functional in heifers before the onset of puberty, with increased LH release evident as heifers progress toward puberty. We investigated the functionality of the HPG axis in peripubertal Holstein-Friesian dairy heifers with divergent POS or NEG FertBV, hypothesizing that the earlier puberty onset of POS heifers is associated with earlier activation of the HPG axis than in NEG heifers. In experiment 1, we tested the dose responsiveness of POS heifers to an intravenous injection of either kisspeptin [Kiss; 2, 4, or 8 µg/kg of body weight (BW); n = 3 per dose] or a GnRH agonist (buserelin; 5, 10, or 20 ng/kg of BW; n = 3 per dose). The use of these 2 agonists investigates the status of the HPG axis in both the hypothalamus (Kiss) and pituitary (buserelin) glands. Doses of 4 µg/ kg BW of Kiss and 10 ng/kg BW of buserelin produced submaximal LH responses and were used in experiment 2, in which previously unused POS (n = 22) and NEG (n = 18) FertBV heifers were challenged with both agonists at 10 and 12 mo of age in a partial crossover design. Heifers were randomly allocated to treatment groups, balanced for age and BW. The LH response to buserelin was greater in POS heifers than NEG heifers at 10 mo of age, with no difference in response at 12 mo. The FSH response to buserelin and the LH and FSH responses to Kiss did not differ between the POS and NEG heifers at either age. These results indicate an association between divergent genetic merit for fertility and the LH release to buserelin at 10 mo of age, supporting the hypothesis that gonadotropin respon-siveness to a GnRH agonist is more advanced in POS heifers than in NEG heifers.

SWATH-MS Analysis of Blood Plasma and Circulating Small Extracellular Vesicles Enables Detection of Putative Protein Biomarkers of Fertility in Young and Aged Dairy Cows

“…Cattle were monitored for luteal activity via the assessment of plasma progesterone (P4) levels 7 days prior to blood collection. Following plasma P4 assessment, all heifers were administered an intravaginal P4 secreting device to prevent spontaneous ovulation and maintain a static P4 level, as previously described …”

“…Heifers selected for the Young study were a part of a larger experiment performed by DairyNZ (Lye farm, New Zealand) between April and September 2019. 23 Cattle were peripubertal and of high-and low-genetic merit for fertility (n = 39; 21 high, 18 low) based on their parentage (as described in Section 2.3). Heifers were 311 ± 0.8 days of age at the time of sampling (∼10 months of age).…”

Micro-RNA (miRNA) epigenetic profiling of plasma small extracellular vesicles (sEV) – sEV miRNA as diagnostic biomarker of fertility

“…A cattle cohort of young heifers were used for the validation studies of targeted miRNA qRT-PCR analysis. This dairy cow cohort was a part of a larger experiment performed by DairyNZ (Lye farm, New Zealand) between April and September 2019 (59). The young heifers were peripubertal and were 311 ± 0.8 days (~10 months) of age during the plasma collection.…”

“…Luteal activity of cattle were monitored via an assessment of plasma progesterone (P4) levels from day -7 (relative to day 0 of saline infusion), which was administered as part of larger experiment. Further, an intravaginal P4 secreting device was administered to prevent ovulation and maintain a static P4 level (59). Speci cally, these animals were included as the control group in the study (involving the challenge of Kisspeptin and Gonadotrophinreleasing hormone) and did not undergo any challenge during the time of plasma collection, in contrast to the other animals in the group (59).…”

“…Further, an intravaginal P4 secreting device was administered to prevent ovulation and maintain a static P4 level (59). Speci cally, these animals were included as the control group in the study (involving the challenge of Kisspeptin and Gonadotrophinreleasing hormone) and did not undergo any challenge during the time of plasma collection, in contrast to the other animals in the group (59). For validation experimental studies, plasma samples from two distinctly separated HF (n=8) and LF (n=8) dairy cows were selected.…”