J. E. Kinder

Synchronization of estrus and ovulation and associated endocrine changes in Bos indicus cows

The effects of 4 estrus synchronization treatments on intervals to and synchrony of estrus and ovulation, on timing of the preovulatory LH surge and associated changes in plasma progesterone, LH, FSH, and 17beta-estradiol (E(2)) were investigated in 48 Bos indicus cows. Treatment 1 consisted of 2 injections of PGF(2alpha) 14 d apart (n = 12); Treatment 2 of a subcutaneous 3-mg norgestomet implant and an intramuscular injection of 3 mg of norgestomet and 5 mg estradiol valerate, with the implant removed 10 d later (n = 12; norgestomet-estradiol); Treatment 3 of norgestomet-estradiol, with a subcutaneous injection of PMSG given at time of implant removal (Day 10; n = 12); and Treatment 4 of norgestomet implant (as for Treatments 2 and 3) inserted for 10 d, with an intramuscular injection of PGF(2alpha) given at the time of implant removal (n = 12). The experiment was conducted in 2 replicates (24 cows/replicate, 6 cows/group). Estrus, ovulation and timing of the preovulatory surge of LH varied less in cows treated with norgestomet-estradiol and PMSG than in cows in Treatments 1 and 4 (P < 0.008). Treatment with PMSG reduced variation in ovulation times and timing of the LH surge in cows treated with norgestomet-estradiol (P < 0.02). Concentrations of E(2) were higher in cows in Treatments 2 and 3 on the final day of treatment and at about 6 h post ovulation compared with cows in Treatments 1 and 4 (P < 0.05). Different methods for synchronizing estrus did not alter sequential endocrine and behavioral changes in relation to the timing of the LH peak, and the results were consistent with current recommendations for insemination times in Bos taurus cattle.

Secretion of gonadotrophins change during the luteal phase of the bovine oestrous cycle in the absence of corresponding changes in progesterone or 17β-oestradiol

Abstract The hypothesis in the present study was that changes in circulating luteinizing hormone (LH) and follicle stimulating hormone (FSH) would occur during the luteal phase of the oestrous cycle (Days 4–19; Day 0, day of behaviourial oestrus) that were not related to corresponding changes in concentrations of progesterone and 17β-oestradiol. The stage of the oestrous cycle of cows (n = 18) was synchronised to obtain cows that were on alternate days of the cycle. Blood samples were collected every other day at 15 min intervals for 12 h from all cows: Days 4, 6, 8, 10, 12, 14, 16, 18 (n = 9) and Days 5, 7, 9, 11, 13, 15, 17, 19 (n = 9). Concentrations of LH, FSH, 17β-oestradiol and progesterone were determined in these samples. Data were compared across days to determine when significant changes occurred in concentrations or patterns of secretion of the gonadotrophins and ovarian steroid hormones during the oestrous cycle. There were significant changes in mean concentrations of FSH in circulation between Days 6 and 12. The most striking changes in secretion of gonadotrophins that could not be explained by changes in gonadal steroids were the fluctuations in amplitude of LH pulses between Days 7 and 12. Amplitude of LH pulses increased between Days 7 and 11 and subsequently decreased between Days 11 and 12 of the oestrous cycle. Some changes in gonadotrophin secretion that occurred in the present study can be explained by fluctuations in concentrations of progesterone and 17β-oestradiol in circulation. Other changes cannot be explained by fluctuations in circulating concentrations of these steroids. We accept our hypothesis because the concomitant changes in mean concentration of FSH between Days 6 and 11 and amplitude of LH pulses between Days 7 and 12 of the bovine oestrous cycle cannot be explained by changes in circulating concentrations of progesterone and 17β-oestradiol.

Estradiol Regulation of Luteinizing Hormone Secretion in Heifers of Two Breed Types That Reach Puberty at Different Ages

Abstract The working hypothesis was that 17β-estradiol (E2) negative feedback on the hypothalamic-pituitary axis in regulation of LH secretion decreases during peripuberty in heifers of 2 different genotypes. We investigated whether Bos indicus heifers had a period postpuberty, as compared with prepuberty, of greater E2 inhibition of LH secretion at a time when heifers of this genotype have been reported to have a period of anestrus. Prepubertal heifers 9 mo of age of 2 genotypes (B. indicus and B. taurus) were assigned to 3 groups (6 animals/group) to either remain intact (control), be ovariectomized, or be ovariectomized and implanted with E2. Variables evaluated from 10 to 28 mo of age were circulating concentrations of progesterone (P4), presence of corpora lutea, and pulsatile pattern of LH release. Results confirmed that B. taurus heifers attained puberty at younger ages (P < 0.001) and at lower live weights (P = 0.015) than did B. indicus heifers (507 ± 37 days of age vs. 678 ± 7 days of age; 259 ± 14 kg vs. 312 ± 11 kg; respectively). There was cessation of E2 inhibition of LH pulses coincident with the onset of puberty in heifers of both breed types but at a much younger age in B. taurus heifers. There was no evidence of enhanced negative feedback of E2 on LH secretion subsequent to puberty in B. indicus heifers nor was there cessation of estrous cycles in control heifers of either breed type after puberty.

Frequency of luteinizing hormone pulses and circulating 17β-oestradiol concentration in cows is related to concentration of progesterone in circulation when the progesterone comes from either an endogenous or exogenous source

Abstract The present study was designed to test whether progesterone from exogenous and endogenous sources modulates the frequency of luteinizing hormone (LH) pulses in a differential fashion. Our working hypotheses were: (1) the frequency of secretion of LH pulses and concentration of 17β-oestradiol in circulation would be directly related to circulating concentration of progesterone; (2) progesterone from an exogenous source would have a different effect on frequency of LH pulses and circulating concentration of 17β-oestradiol than progesterone from an endogenous source. Cows were treated with graded doses of PGF 2α or progesterone to result in varying concentrations of progesterone in circulation from endogenous and exogenous sources. Treatment with PGF 2α resulted in concentrations of circulating progesterone among animals in this group that ranged from 0.5 to 10.9 ng ml −1 of plasma. Treatment with progesterone resulted in circulating concentrations of progesterone among animals in this group that ranged from 0.8 to 11.8 ng ml −1 of plasma. Concentrations of progesterone in circulation and frequency of LH pulses were negatively correlated ( r = −0.59) in cows with functional corpora lutea and in cows treated with progesterone without corpora lutea ( r = −0.62). The frequency of LH pulses had the same relationship to the varying concentrations of progesterone in both treatment groups. Cows with higher progesterone levels had fewer LH pulses and cows with lower progesterone had a greater frequency of LH pulses. Mean circulating concentrations of 17β-oestradiol also had the same relationship with varying concentrations of progesterone in both treatment groups. Cows with higher progesterone levels had lower 17β-oestradiol and cows with lower progesterone had higher 17β-oestradiol levels. The results indicate that there is a direct relationship between circulating concentration of progesterone, frequency of LH pulses and circulating concentration of 17β-oestradiol. In addition, progesterone modulates the frequency of release of LH pulses from the pituitary and circulating concentration of 17β-oestradiol in a similar fashion when coming from either an endogenous or exogenous source.

Gonadotropin secretion and development of ovarian follicles during oestrous cycles in heifers treated with luteinizing hormone releasing hormone antagonist

The hypothesis tested was that reduced LHRH stimulation of the anterior pituitary would lead to attenuated development of ovarian follicles as a result of reduced gonadotropin secretion during oestrous cycles of cattle. Twenty heifers were randomly assigned to be treated ( n = 5/treatment) with an antagonist to LHRH (LHRH-Ant) 1) from Day 2 to 7 (Day 0 = behavioural oestrus), 2) Day 7 to 12, 3) Day 12 to 17, 4) or serve as untreated control animals. LHRH-Ant suppressed LH pulses of heifers in all treatment groups from treatment initiation through Day 17 as compared with untreated control heifers [Peters et al., 1994. Luteinizing hormone has a role in development of fully functional corpora lutea (CL) but is not required to maintain CL function in heifers. Biol. Reprod., 51 (1994) 1248-1254]. Circulating concentration of FSH from Day 8 to 10 of the oestrous cycle did not increase in heifers treated with LHRH-Ant from Day 2 to 7 or Day 7 to 12; however, there was increased (P < 0.05) FSH from Day 8 to 10 of the oestrous cycle in heifers treated with LHRH-Ant from Day 12 to 17 and control heifers. Compared with control heifers, heifers treated with LHRH-Ant from the Day 2 to 7 had suppressed (P < 0.05) size and persistence of the first and second dominant ovarian follicles. Heifers treated with LHRH-Ant from Day 7 to 12 had suppressed size (P < 0.05 and tended (P < 0.10) to have a shorter persistence of the second dominant ovarian follicle compared with control heifers. Heifers treated with LHRH-Ant from Day 12 to 17 had a similar (P > 0.10) size and persistence of dominant ovarian follicles but had reduced (P < 0.10) numbers of large follicles compared with control heifers. Heifers treated with LHRH-Ant from Day 2 to 7 had lower (P < 0.01) concentrations of 17 beta-oestradiol during the treatment period and tended (P < 0.10) to have lower concentrations of 17 beta-oestradiol from Day 7 to 12 of the oestrous cycle compared with control heifers. Heifers treated with LHRH-Ant from Day 7 to 12 or Day 12 to 17 had similar (P > 0.10) circulating LH concentrations of l7 beta-oestradiol compared with control heifers. Reduced LHRH stimulation of the pituitary from Day 2 to 12 of the oestrous cycle and the resulting modulation in circulating LH and FSH led to suppressed ovarian follicular development and oestradiol secretion. After Day 12 of the oestrous cycle, reduced LHRH stimulation of the anterior pituitary did not lead to altered ovarian follicular development to the extent as reduced LHRH stimulation before Day 12 although pulsatile release of LH was similarly suppressed by treatment with the LHRH-Ant.

Development of a persistent ovarian follicle and associated elevated concentrations of 17β-estradiol preceding ovulation does not alter the pregnancy rate after embryo transfer in cattle

It was hypothesized that prolonged elevation in 17beta-estradiol (E(2)) preceding ovulation as a result of a persistent ovarian follicle would have a detrimental effect on pregnancy rate after Day 7 (behavioral estrus = Day 0) of the estrous cycle. Cows were either treated with exogenous progesterone (P(4)) for 10 d or remained untreated (CON; n = 76). Cows were treated with 1 of 2 doses of P(4) from Day 6 to 16 which was intended to result in either elevated E(2) (EE(2); n = 76) or normal E(2) (NE(2); n = 76) concentration in the circulation. At the initiation of P(4) treatment, cows received prostaglandin F(2alpha) (PGF(2alpha)) to eliminate the endogenous source of P(4). On Day 16, the exogenous source of P(4) was removed from treated cows, while cows in the CON group received PGF(2alpha). A single embryo was transferred into each cow 7 days after observation of behavioral estrus. Blood samples were taken on alternating days during the treatment period to determine concentrations of P(4) and E(2). The pregnancy rate was determined by ultrasonographic examination 25 to 32 d after embryo transfer. There was a treatment-by-day interaction (P < 0.0001) on E(2) concentrations in the plasma during the 10-d treatment period. Cows in the EE(2) group had a higher concentration of E(2) by Day 8 (6.1 +/- 0.5 pg/ml) and this concentration remained elevated until PRID removal compared with that of cows in the NE(2) (2 +/- 0.2 pg/ml) and CON (2.0 +/- 0.3 pg/ml) groups, which had concentrations of E(2) similar to those at the initiation of treatment. Pregnancy rates after embryo transfer did not differ (P = 0.56; X(2) = 1.1) among cows in the EE(2) (30.7%), NE(2) (36.2%) and CON (32.9%) groups. Prolonged elevation of E(2) concentrations associated with the development of a persistent ovarian follicle preceding ovulation did not affect the pregnancy rate to embryo transfer after Day 7 of the estrous cycle in cows.

Influence of fenceline bull exposure on duration of postpartum anoestrus and pregnancy rate in beef cows

Two experiments (1991 and 1992) were conducted to test the hypotheses that fenceline exposure of cows to bulls following parturition shortens duration of postpartum anoestrus and improves pregnancy rate to artificial insemination (AI). In Experiments 1 and 2, 75 and 125 postpartum crossbred beef cows, respectively, were stratified by calving date and while maintaining equivalent primiparous cows in each treatment group were randomly assigned to be exposed to bulls through the fenceline (BE) or not exposed to bulls (NE). In each experiment, twice weekly blood samples were collected for 13 weeks beginning 1 to 4 weeks postpartum. These samples were used to assess concentrations of progesterone and determine time of onset of ovarian luteal function following calving. In Experiment 2, a 23 day program of AI was included in the study in which signs of behavioral oestrus were detected twice daily and cows were artificially inseminated 12 h following detection of oestrus. Pregnancy rate to AI was determined by concentrations of progesterone, detection of pregnancy by rectal palpation, and confirmed by calving date. Primiparous cows in the BE group had shorter durations of postpartum anoestrus in each experiment than primiparous cows in the NE group (Experiment 1: BE = 78 days, NE = 92 days, P < 0.05; 2: BE = 109 days, NE = 117 days, P < 0.10). There was no influence of fenceline bull exposure on the duration of postpartum anoestrus of multiparous cows in either experiment. Pregnancy rate to AI in Experiment 2 was not improved by fenceline bull exposure. We conclude that fenceline bull exposure was effective in shortening length of postpartum anoestrus in primiparous cows but this improvement did not translate into improved pregnancy rates during the subsequent breeding season.

Markov chains as a shortcut method to estimate age distributions in herds of beef cattle under different culling strategies.

Markov chains were used to estimate the age distribution at equilibrium and average age in herds of beef cattle and the age distribution and average age of culled cows. These estimates are essential in systems simulation and economic analyses of beef production alternatives because the biological input and output from a beef production system depend on the age structure of the cows in the system. Ten sets of data on age-specific probabilities of culling for different reasons were found in the literature and used in simulation of different culling strategies. Three different culling strategies were simulated using these data. In addition to culling on maximum age, culling was either based on health alone, health and reproductive failure in one year (not pregnant) or health and reproductive failure in two consecutive years (not pregnant twice). The average herd age in the data sets reviewed under the actual culling strategies ranged from 4.58 to 6.73 yr and the average age of culled cows ranged from 5.41 to 9.94 yr. Description of the culling process as a Markov chain enables calculations of the age distribution at equilibrium by simple matrix operations, an advantage over the methods presently used. The scarcity of estimated age-specific probabilities of health and reproductive failure points to the need for more population analyses of beef cattle.

Frequency of luteinizing hormone pulses in cattle influences duration of persistence of dominant ovarian follicles, follicular fluid concentrations of steroids, and activity of insulin-like growth factor binding proteins

The objectives of the present study were to determine how varying frequency of LH pulses as controlled by varying treatments with progesterone (P4) in cattle would affect: (1) concentration of steroid hormones and activity of insulin-like growth factor binding proteins (IGFBPs) in the ovarian follicular fluid and blood plasma, and (2) duration of persistence of largest ovarian follicles. There were four treatment groups (n=7 per group) and a control group (n=5) of mature, non-lactating beef cows. Treatments were: (1) two progesterone releasing intravaginal devices (PRIDs) for 16 days (2PRID); (2) a half PRID for 16 days (0.5PRID); (3) two PRIDs for 8 days, then a half PRID for 8 days (2-0.5PRID); or (4) a half PRID for 8 days, then two PRIDs for 8 days (0.5-2PRID). Treatment was initiated on the fifth day of the estrous cycle, which was designated as Day 0, and continued for 16 days. All P4-treated females were administered prostaglandin F2alpha on Day 0 and 1 to regress their corpora lutea. Frequency of LH pulses was greater during treatment with the smaller dose of P4 compared with treatment with the larger dose of P4 and the control group. Ovarian follicles were classified into five categories based on ultrasonographic observations: growing (G); atretic (A); growing dominant (GD); growing persistent (GP); or atretic persistent (AP). At ovariectomy on Day 16, the largest and second largest follicles collected were re-classified into five categories based on follicular concentration of steroids. Classification of the largest follicle collected on Day 16 was influenced by treatment (P<0.005), with the 2PRID group having A follicles, the 2-0.5PRID group GP follicles, the 0.5-2PRID group AP follicles, and the 0.5PRID group GD and GP follicles. Concentrations of 17beta-estradiol (E2) were greatest in GD and GP follicles (P<0.05). There was less (P<0.05) activity of IGFBP-2 in GD follicles and less (P<0.05) activity of IGFBP-3 in GD and GP follicles than other follicles. Activity of IGFBP-4 and -5 was greater (P<0.05) in A and AP follicles than G, GD, and GP follicles. Maintenance of a frequent release of LH pulses over a 16-day period did not result in maintenance of persistent follicles throughout this period indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia is associated with greater activity of IGFBP-2, -4, -5, and greater concentrations of P4 in follicles, whereas growing dominant and persistent follicles contained greater concentrations of E2, androstenedione (A4), and less IGFBP-2 activity than follicles of other classes. Follicle classifications based on ultrasonography or follicular concentration of steroids did differ (P<0.05) for the largest follicles from the 2PRID group. Two follicles in this group appeared as GD follicles by ultrasonography, but these were atretic based on follicular steroid contents. Objective 1 of the present study yielded the conclusion that concentrations of steroid hormones in follicular fluid and blood plasma could be predictably controlled by regulating the frequency of LH pulses with varying doses of P4. Objective 2 yielded the conclusion that maintain frequent release of LH pulses over a 16-day period could not maintain persistent follicles throughout this period, indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia in the present study was associated with increased follicular fluid activity of IGFBP-2, -4, -5, and P4, whereas growing dominant and persistent follicles contained greater concentrations of E2, A4, and less IGFBP-2 activity than follicles of other classes.

Luteal function and estrus in peripubertal beef heifers treated with an intravaginal progesterone releasing device with or without a subsequent injection of estradiol

The objectives of this experiment were to determine if treatment of beef heifers with progesterone (P4) using an intravaginal device alone or in combination with estradiol benzoate (EB) would induce estrus and cause development of corpora lutea (CL) with a typical life span. Peripubertal heifers (n = 311) were used when about 40% of the heifers had a functional CL. The heifers were assigned to receive one of the following treatments on Day 0: 1) a sham device for 7 d (C, n = 108); 2) an intravaginal device containing P4 for 7 d (P, n = 102); or 3) an intravaginal device containing P4 for 7 d plus an injection of 1 mg EB 24 to 30 h after device removal (PE, n = 101). Serum concentrations of P4 were determined on Days -7, 0, 8, 15 and 22. Weight and age of the heifers at the start of the trial averaged 292 +/- 45 kg and 365 +/- 38 d, respectively. A greater (P < 0.0001) proportion of the heifers from the PE than P group was in standing estrus (81 vs 37%) and formed normal CL (68 vs 44%) after device removal. Of the heifers exhibiting estrus, a greater (P < 0.05) proportion of PE (94%) than P (80%) heifers was active 1 to 3 d after implant removal. Short-term progesterone treatment increased the proportion of heifers in estrus and those forming normal CL, and adding EB to the progesterone treatment further enhanced these responses.