Relationship Among Follicular Growth, Oestrus, Time of Ovulation, Endogenous Estradiol 17β and Luteinizing Hormone in Bos Indicus Cows After a Synchronization Program

Circulating progesterone concentrations and preovulatory follicle diameters affecting ovulatory response in crossbred dairy heifers, following a 7-day progesterone-based synchronization protocol

The present study was aimed at evaluating the differences of ovarian follicular dynamics and circulating progesterone (P4) concentrations between crossbred Holstein heifers that ovulated and did not ovulate after a P4-based synchronization protocol. Twenty-one crossbred (Holstein × Thai native) heifers with random stages of the oestrous cycle were subjected to the ovulation synchronization protocol, using an intravaginal P4-releasing device (Eazi-Breed CIDR®) for 7 days. Out of 21 CIDR-treated heifers, 14 ovulating heifers were classified as the ovulatory group and 7 non-ovulating heifers were considered the anovulatory group. The heifers having new wave emergence in ovulatory and anovulatory groups were 11/14 (78.6%) and 4/7 (57.1%), respectively. In ovulating heifers, the mean (± SEM) diameter of preovulatory follicle (PF, mm) was significantly larger, compared to non-ovulating heifers (7.21 ± 0.32 versus 4.04 ± 0.44; P = 0.001), while the mean (± SEM) follicular growth rates (mm/d) in non-ovulating heifers tended to be lower, compared to ovulating heifers (0.73 ± 0.17 versus 1.06 ± 0.08; P = 0.07). The mean (± SEM) circulating P4 concentration (ng/ml) throughout the CIDR protocol (0-10 days) in non-ovulating heifers was significantly higher, in comparison with ovulating heifers (2.82 ± 0.27 versus 1.83 ± 0.16; P = 0.02). However, no significant difference in the mean corpus luteum volume between groups was observed. In conclusion, the present results suggested that elevated circulating P4 concentrations and smaller PF diameters could cause ovulation failure in crossbred Holstein heifers, following a 7-day CIDR-based synchronization protocol.

Calf presence and estrous response, ovarian follicular activity and the pattern of luteinizing hormone in postpartum Bos indicus cows

The main objective of the present experiment was to assess the effect of temporary weaning on the onset of estrus, ovarian follicular activity and secretion of luteinizing hormone in Bos indicus cows. Forty six mature cows were divided into three groups 1) calves were weaned for 72 h allowing auditory, olfactory and visual contact with their dams (VISUAL, n = 17), 2) calves without contact with their dams for 72 h (NC, n = 17) and 3) calves not weaned and in constant contact with their dams (CTRL, n = 12). Estrus was synchronized in all cows using CIDR for 9 days plus 2 mg of estradiol benzoate given at CIDR insertion. The VISUAL group had a greater (P < 0.05) proportion of cows in estrus (76.5%) compared to the CTRL group (16.7%), but no differences were found when compared to the NC group (58.8%). The VISUAL group had a greater proportion of animal that ovulated (76.5%) compared to CTRL (33.3%) and NC groups (64.7%; P = 0.059). Duration of estrus was shorter (P = 0.04) in the VISUAL (8.4 ± 4.4 hours) than in the NC (12.9 ± 13.4 hours) however, CTRL treatment (11 ± 1.4 hours) was not different from either of these two groups. LH concentration after implant removal was similar among treatments and started to increase at 36 h post CIDR removal. Only in the CTRL group was there an obvious increase by 54 h after implant removal. Follicular size increased in diameter from 36 h and were evident in treatments and control groups by 60 h (P < 0.05). The VISUAL treatment increased the number of cows ovulating and shortened the length of estrus. VISUAL and NC groups showed a similar response in follicular growth and pattern of circulating LH because of treatment.

Relationship between growth of the preovulatory follicle and its steroidogenic activity on the onset and expression of estrus behavior in CIDR-treated Bos indicus cows: an observational study

Estrus synchronization induces cows to gather in sexually active groups (SAGs) composed of females displaying mounting activity. Although this technique promotes the enhancement of sexual behavior, there are cows in estrus (CE) that delay estrus expression and also cows not displaying estrus (CNDE) even in the presence of a preovulatory follicle (PF). To elucidate the physiological mechanisms of the delay in the onset of estrus or absence of estrus behavior, an observational study was undertaken in 17 Bos indicus cows treated with exogenous progesterone (CIDR) to synchronize estrus and to monitor follicular growth and its steroidogenic activity. After SAGs formation, cows were ovariectomized at 24, 48, and 72 h post-CIDR. Among ovariectomized groups there were only 9 CE which: 1) showed differences in the onset of estrus; 2) displayed distinctive follicular growth patterns; and 3) at 72 h produced the highest intrafollicular estradiol concentration, and showed a linear trend to increase expression of P450scc and P450arom. Comparison of CE vs. CNDE showed that: 1) both groups had progesterone levels indicative of cyclic activity, and a PF which grew at a similar rate and size; 2) CE showed a stronger association between time and growth; and 3) CE produced more intrafollicular estradiol and progesterone, together with the expression of higher levels of P450arom. Results suggest that pending on the pattern of growth of the PF and its steroidogenic potential to produce estradiol, the onset and expression of estrus behavior may be delayed probably until the establishment of the appropriate conditions to ensure ovulation.

Influence of somatic cell count, body condition and lameness on follicular growth and ovulation in dairy cows

The objective of this study was to investigate the effect of somatic cell count (SCC), body condition score (BCS) or lameness score on ovarian follicular growth and ovulation in dairy cows. Seventy four animals 30–80 days post-partum were monitored for all three conditions before synchronization of ovarian follicular phases by administration of gonadotrophin releasing hormone (GnRH) followed seven days later with prostaglandin F2alpha (PG). Ultrasonography of both ovaries twice daily throughout the follicular phase revealed that fewer animals with combined high SCC and lameness (4/9) ovulated compared to healthy animals (19/21; P = 0.006) or animals with only high SCC (11/11; P = 0.004) or only lameness (21/27; P = 0.06). Overall, regardless of the presence of other concurrent conditions, fewer lame cows ovulated than Non Lame animals (30/42 and 30/32; P = 0.015). Mean follicular growth and maximum follicular diameter were unaffected by any of the three conditions. However, dominant follicle growth and maximum diameter were greater in the 60 animals that ovulated compared to the 14 that did not; 1.83 ± 0.16 versus 0.96 ± 0.26 mm/day (P = 0.014) and 19.4 ± 0.4 versus 16.4 ± 1.2 mm (P = 0.003), respectively. In conclusion, lameness reduced the proportion of cows that ovulated and the synergistic effect of high SCC and lameness reduced that proportion further. However, follicular growth and maximum follicular diameter were unaffected by high SCC, low BCS or lameness.