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D. J. Cooke, M. A. Crowe, and J. F. Roche

Blood samples were collected from heifers (n = 6; 450 ± 7.7 kg) 2–4 times a day during the first and second follicular waves, and during the gonadotrophin surge to determine whether changes in circulating FSH isoforms occur during cyclic quantitative changes in FSH throughout the oestrous cycle. Serum was assayed for FSH, LH, oestradiol and progesterone. Selected samples collected during the first (samples 1–3) and second (samples 4–6) postovulatory recurrent FSH increase and during the subsequent gonadotrophin surge (samples 7 and 8) were analysed for FSH isoforms by chromatofocusing. No change (P > 0.05) in isoform profile occurred during the first or second recurrent FSH increase, when oestradiol concentrations were 0.6 ± 0.07 and 0.6 ± 0.09 pg ml−1 and progesterone concentrations were 0.03 ±0.01 and 2.4 ± 0.19 ng ml−1, respectively. The percentage of FSH eluting in the pH range 7.4–7.0 increased (P < 0.05) from 14.2 ± 2.2 during the luteal phase (samples 1–6) to 20.2 ± 2.3 (sample 7) and 31.4 ± 3.4% (sample 8) during the preovulatory gonadotrophin surge, while oestradiol concentrations were higher (P < 0.05; 4.9 ± 0.39 pg ml−1) than in the luteal phase of the cycle. In summary, FSH isoform patterns did not change during the cyclic quantitative changes in FSH associated with emergence of the first or second follicular wave. However, during the gonadotrophin surge, in association with increased oestradiol concentrations, an increase in the amount of less acidic isoforms of FSH was observed. Therefore, qualitative changes in FSH are not important in the physiological regulation of follicle turnover during the luteal phase of the oestrous cycle of heifers.

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M. A. Crowe, D. Goulding, A. Baguisi, M. P. Boland, and J. F. Roche

There is a low incidence of ovulation of the first dominant follicle that develops in the early postpartum period of beef suckler cows, which prolongs the interval from calving to first ovulation. The objective of this study was to determine whether a single injection of a GnRH analogue would ovulate the first postpartum dominant follicle. Limousin × Friesian beef suckler cows were assigned at parturition, over two years (16 cows in year 1; 19 cows in year 2), to one of three treatments: (1) untreated (control; n = 12), (2) GnRH analogue (20 μg buserelin i.m.) administered in the growing–plateau phase of the first postpartum dominant follicle (GnRH-G; n = 12) and (3) GnRH analogue administered in the declining phase of the first postpartum dominant follicle (GnRH-D; n = 11). From day 8 or 9 post partum, the ovaries of each cow were examined daily by ultrasound to determine the time of GnRH injection and ovulation. Blood samples were collected daily for progesterone measurement to confirm ovulation and in year 2 to determine the duration of the first oestrous cycle. The mean (± sem) number of days from parturition to development of the first dominant follicle was 11.0 ± 0.3, 10.3 ± 0.5 and 10.1 ± 0.7 for cows assigned to treatments 1–3, respectively (P > 0.05). The proportion of cows ovulating the first dominant follicle was higher (P < 0.05) following GnRH treatment (12 of 12 and 7 of 10; GnRH-G and GnRH-D, respectively) than with controls (2 of 12). The mean interval from parturition to first ovulation in all cows in the GnRH-G treatment was reduced (16.1 ± 0.8 days; P < 0.01) compared with the interval for cows in the GnRH-D treatment (24.5 ± 3.6 days) or controls (27.1 ± 2.5 days). There was no difference in the duration of the first luteal phase post partum in control (9.3 ± 3.0 days) and GnRH-treated cows (8.0 ± 1.0 and 9.6 ± 3.7 days; GnRH-G and GnRH-D, respectively) or in the proportion of cows with short cycles (4 of 7, 5 of 6 and 4 of 5; control, GnRH-G and GnRH-D, respectively). In conclusion, a single injection of GnRH analogue during the growing–plateau or declining phase of the first postpartum dominant follicle of beef suckler cows induced ovulation in most cows but did not alter the proportion of cows with short cycles compared with controls.

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S. J. Sunderland, M. A. Crowe, M. P. Boland, J. F. Roche, and J. J. Ireland

This study examined the correlation between measurement of follicle growth by ultrasound, and measurement of intrafollicular ratios of oestradiol and progesterone concentrations and the serum concentrations of FSH during selection, dominance and atresia or ovulation of dominant follicles in heifers. Heifers were ovariectomized on days 0 (before LH surge), 1 (after LH surge, preovulation), 1 (postovulation), 3, 6 and 12 of the oestrous cycle. Blood samples were collected at 4–6 h intervals. After ovariectomy all follicles ≥ 5 mm were measured and follicular fluid was aspirated. Follicles were classified by size according to ultrasound (F1, largest; F2, second largest; F3, all remaining follicles ≥ 5 mm) and by the ratio of oestradiol:progesterone concentrations. During the follicular phase, a single dominant oestrogen-active follicle increased in diameter while serum concentrations of LH increased and FSH decreased (P < 0.05). On day 1 (after LH surge, preovulation), serum LH and FSH decreased to pre-surge concentrations (P < 0.0001), while follicle size and intrafollicular progesterone concentration increased and oestradiol concentration decreased (P < 0.05). A dominant nonovulatory follicle, classified as oestrogen-active on days 1, 3 and 6 and oestrogen-inactive on day 12, increased in size from day 1 to day 7 and lost dominance during days 10–12, coincident with the growth of multiple oestrogen-active follicles. The serum FSH concentration increased transiently (P < 0.05) before each new wave of dominant follicular growth. The overall correlation of ultrasound measurements of follicle diameter with measures of follicle size after ovariectomy was high. The ratio of oestradiol:progesterone concentrations, but not of size, reliably distinguished potential dominant from atretic follicles. The size of the follicle and the oestradiol concentration were not determinants of subsequent dominance during a selection phase. We conclude that: (1) ovarian follicles go through selection, dominance and atresia phases coincident with transient increases and decreases in FSH; and (2) ultrasound is an accurate measure of follicle growth, but that size alone is not a sufficient measure to ascribe dominance and both ultrasound and the intrafollicular ratio of oestradiol:progesterone concentrations are needed to monitor selection, dominance and atresia of follicles accurately.

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K E Ryan, S M Casey, M J Canty, M A Crowe, F Martin, and A C O Evans

Dominant follicles are those that continue to develop and have the potential to ovulate while subordinate follicles regress. Characteristics of dominant follicles include a larger diameter, higher intrafollicular estradiol, and lower IGF-binding protein (IGFBP)-4 concentrations compared with other cohort follicles. Follicle development is regulated by endocrine hormones that act via intracellular signaling pathways. Here, we show the differences in Akt, Erk, c-Jun N-terminal protein kinase, and p-38 signaling pathways between dominant and subordinate follicles at the dominance stage of the follicle wave. However, earlier in the follicle wave (dominant follicle selection), there were only differences in the levels of Akt and Erk signal transduction proteins among dominant and subordinate follicles. Using this profile of Akt and Erk protein expression in granulosa and theca cells of selected dominant follicles compared with subordinate follicles, we suggest a predictive model to identify future dominant and subordinate follicles from the pool of otherwise similar cohort follicles at the time of follicle wave emergence. We conclude that the Erk and Akt signal transduction pathways are important for dominant follicle selection and development and, furthermore, that the observed differences in these pathways mark the future dominant follicle from subordinate follicles before differences in follicular diameter, follicular fluid estradiol, and IGFBP-4 concentrations are apparent.

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L A Okumu, N Forde, A G Fahey, E Fitzpatrick, J F Roche, M A Crowe, and P Lonergan

To investigate the effects of pregnancy or post-ovulatory progesterone (P4) supplementation on the expression of oestrogen and P4 receptors (ESRs and PGRs) in the bovine uterus, heifers (n=263) were randomly assigned to the following treatments: i) cyclic, normal P4; ii) cyclic, high P4; iii) pregnant, normal P4; and iv) pregnant, high P4 on days 5, 7, 13 and 16 of pregnancy/oestrous cycle. Elevated P4 was achieved through P4-releasing intravaginal device insertion on day 3 after oestrus, resulting in increased concentrations from day 3.5 to 8 (P<0.05) in the high groups than in the normal groups. Irrespective of treatment, PGR and ESR1 mRNA expressions were highest on days 5 and 7 and decreased on day 13 (P<0.05), while ESR2 mRNA expression increased on day 7 (P<0.05) and similar levels were maintained within the normal P4 groups subsequently. Expression in the high P4 groups decreased on day 13 (P<0.05). PGR-AB and PGR-B protein expressions were high in the luminal and superficial glands on days 5 and 7, but by day 13, expression had declined to very low or undetectable levels and high P4 concentration tended to decrease or decreased significantly (P<0.05) the expression in these regions on days 5 and 7. ESR1 protein expression was high, with no treatment effect. ESR2 protein was also highly expressed, with no clear effect of treatment. In conclusion, early post-ovulatory P4 supplementation advances the disappearance of PGR protein from the luminal epithelium on days 5 and 7, and decreases ESR2 mRNA expression during the mid-luteal phase, but has no effect on PGR or ESR1 mRNA expression.

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M. G. Murphy, W. J. Enright, M. A. Crowe, K. McConnell, L. J. Spicer, M. P. Boland, and J. F. Roche

Summary. Friesian × Hereford heifers (n = 19; mean ± s.e.m. body weight (BW) = 375 ± 5 kg) were used in a randomized incomplete block design. Heifers were fed 0·7 (n = 7; L), 1·1 (n = 7; M) or 1·8% (n = 5; G) of BW in dry matter (DM)/day for 10 weeks. Ovaries were examined by ultrasound, for one oestrous cycle, from week 5 of treatment. Maximum diameter of dominant follicles was smaller (P < 0·05) in L (11·8 ± 0·1 mm) than in M (13·7 ± 0·2 mm) or G (13·2 ± 0·3 mm) heifers. Growth rate (mm/day) of dominant follicles during the oestrous cycle was not affected (P > 0·05) by dietary intake. Persistence of dominant follicles was shorter (P < 0·05) in L (9·8 ± 0·2 days) than in M (11·9 ± 0·3 days) or G (12·7 ± 0·4 days) heifers. Three dominant follicles were identified during the oestrous cycle of 5 of 7 L, 3 of 7 M and 1 of 5 G heifers (P < 0·10); 2 dominant follicles were identified in the remaining heifers (n = 2 of 7, 4 of 7 and 4 of 5, respectively). Length of the luteal phase and luteal-phase concentrations of progesterone were not affected (P > 0·05) by treatment. Low dietary intake reduced the diameter and persistence of dominant follicles during the oestrous cycle of beef heifers and tended to increase the proportion of oestrous cycles with 3 dominant follicles.

Keywords: follicle; heifer; ultrasound; nutrition

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A M English, D A Kenny, C J Byrne, H Sauerwein, C Urh, M A Crowe, C Staub, S M Waters, and S Fair

The objective of this study was to examine the effect of nutrition during the first 18 weeks of life on the physiological and transcriptional functionality of the hypothalamic (arcuate nucleus region), anterior pituitary and testes in Holstein–Friesian bull calves. Holstein–Friesian bull calves with a mean (±s.d.) age and bodyweight of 19 (±8.2) days and 47.5 (±5.3) kg, respectively, were assigned to either a HIGH (n = 10) or LOW (n = 10) plane of nutrition, to achieve an overall target growth rate of 1.2 or 0.5 kg/day, respectively. At 126 ± 1.1 days of age, all calves were euthanised. Animal performance (weekly) and systemic concentrations of metabolic (monthly) and reproductive hormones (fortnightly) were assessed. Testicular histology, targeted gene and protein expression of the arcuate nucleus region, anterior pituitary and testes were also assessed using qPCR and immunohistochemistry, respectively. The expression of candidate genes in testicular tissue from post pubertal 19-month-old Holstein–Friesian bulls (n = 10) was compared to that of the 18-week-old calves. Metabolite and metabolic hormone profiles generally reflected the improved metabolic status of the calves on the HIGH (P < 0.001). Calves offered a HIGH plane of nutrition were heavier at slaughter (P < 0.001), had larger testes (P < 0.001), larger seminiferous tubule diameter (P < 0.001), more mature spermatogenic cells (P < 0.001) and more Sertoli cells (P < 0.05) in accordance with both morphological and transcriptional data. Overall, testicular gene expression profiles suggested a more mature stage of development in HIGH compared with LOW and were more closely aligned to that of mature bulls. Ghrelin receptor was the only differentially expressed gene between LOW and HIGH calves in either the anterior pituitary (P < 0.05) or arcuate nucleus region of the hypothalamus (P < 0.10) and was upregulated in LOW for both tissues. This study indicates that an enhanced plane of nutrition during early calfhood favourably alters the biochemical regulation of the hypothalamus–anterior pituitary–testicular axis, advancing testicular development and hastening spermatogenesis.