Productivity of Crossbred Dairy Cows Suckling their Calves for 12 or 24 Weeks Post Calving

An experiment on restricted suckling of crossbred dairy cows was conducted at the Livestock Research Centre, Tanga in northeast Tanzania. Thirty-six Bos taurus (Holstein Friesian and Jersey) x Bos indicus (East African Zebu) cows were allocated alternately as they calved to suckling their calves for either 12 or 24 weeks after calving. Cows grazed improved pastures and were offered 4 kg concentrate daily. Milking occurred twice daily by hand; calves were allowed to suck residual milk for 30 min following each milking. Calves were also allowed access to grazing and were offered a maximum of 1 kg concentrate daily to 24 weeks of age. Weaning age had no significant effect on lactation milk yield for human consumption, the mean (SE) yield being 1806 (102.0) L and 1705 (129.1) L for 12- and 24-week weaning, respectively. Cows from the two treatments suffered similar losses of live weight and body condition score during lactation and neither group had returned to the original body condition score 40 weeks following calving. Post-partum anoestrous intervals were prolonged. Although not significant, cows suckling calves to 24 weeks had a mean interval to first oestrus extended by 38 days compared with cows suckling calves to 12 weeks. The mean (SE) daily live weight gains of the calves to 52 weeks were 263 (14.1) g/day and 230 (18.1) g/day for calves weaned at 12 and 24 weeks, respectively, such that 12-month weights were 119 (5.6) kg and 110 (7.3) kg, respectively. Twelve-week-weaned calves consumed more concentrate (p<0.05) from 13 to 24 weeks than did 24-week weaned calves. Calculation of residual milk consumption removed by calves from birth to 12 weeks indicated that it accounted for 28%) of total yield. No benefits in cow and calf performance and welfare were found to justify prolonging the suckling period to 24 weeks.

The acyclic period postpartum in automatic and conventional milking

The acyclic postpartum period in cows is prolonged due to frequent suckling when compared with twice daily milking. In conventional milking systems twice daily milking is common, while in automatic milking systems (AMS) three or more milkings are performed in early lactation. In this study, the hypothesis was tested that an increased milking frequency in AMS causes a delay in resumption of ovarian cyclicity postpartum and increases days open in German Fleckvieh cows (n = 124). Calvings were equally distributed throughout the 1-year experimental period. All cows were housed in one barn. Sixty-three cows were milked in an AMS (AC) and 61 cows were twice daily milked in a conventional milking parlour (PC). Forty-two AC and 36 PC remained in the herd until conception. After parturition, milk samples were analysed for progesterone twice weekly to record the ovarian activity until pregnancy was diagnosed. The first and the second ovulation were determined by the progesterone profile of each individual cow. The mean milking frequency during the first 3 weeks after parturition was higher in AC (3.17 +/- 0.09 milkings/day) than in PC (milked twice daily). The individual mean milking frequency of AC for the first 3 weeks of lactation ranged from 2.0 to 5.9 daily milkings. The time span from parturition until the first and second ovulation did not differ between AC and PC. However, first ovulation was observed earlier in primiparous (23 +/- 1 days) than in multiparous cows (29 +/- 1 days, P < 0.05). Within AC no relationship between milking frequency and duration of the acyclic period was observed. Days open did not significantly differ between AC and PC and between primiparous and multiparous cows. In conclusion, the increased milking frequency in AMS did neither cause a delay in resumption of ovarian cyclicity postpartum nor did it increase days open.

Pre-pubertal and postpartum anestrus in tropical Zebu cattle

Bos indicus breeds, commonly known as Zebu cattle, have spread from their center of origin in Western Asia into large areas of Asia (including the Asia-Pacific basin), Africa, South and Central America (including the Caribbean islands). The original Zebu genotype, however, has been modified by planned and unplanned cross-breeding programs involving many native and Bos taurus breeds in their new habitats. Though accurate estimates are not available, more than half of the world's cattle population includes a proportion of B. indicus germ plasma. B. indicus native breeds have developed by natural selection over centuries for their ability to survive in rough, harsh tropical environments. Most of these non-described breeds still exhibit high fertility, in terms of calving rates, and disease resistance but they grow very slowly and take well over 3 years to reach puberty and produce only a few liters of milk over a short lactation period. Selection has been carried out in some areas and distinct Zebu breeds have been developed that have moderately high growth rate and milk production. However, they are slow breeders and have extended pre-pubertal and postpartum anestrous periods, compared to their temperate counterparts exposed to similar environment and management. The reproductive biology of B. indicus is similar to that of B. taurus. Most of the proven management, nutritional, hormonal and biotechnological interventions developed through experimentation with B. taurus breeds are equally applicable to B. indicus and their crosses. Zebu breeds predominate in most tropical countries where the majority of the human population lives. If meat and milk production are to be increased in the tropics, Zebu cow productivity, in terms of number of calves produced per lifetime or per unit area of land, must be increased and the time from birth to slaughter must be reduced. This goal could be achieved either by selection within local Zebu populations or through planned cross-breeding with B. taurus breeds. Because the productive and reproductive potentials of Zebu cattle are relatively low, worthwhile gains could only be achieved by selection over many generations. This would require substantial investment in labor, feed and drugs that may not be economic since the return from such investment is relatively low. However, many studies have shown that cross-breeding with B. taurus, which combines additive, dominance and epistatic effects of the two genotypes, ensures high productive and reproductive performance. Therefore, planned cross-breeding with suitable B. taurus breeds, although demanding additional investment in labor, feed and drugs, will still be economic because the return far exceeds the costs.

Patterns of Antral Follicular Wave Dynamics and Accompanying Endocrine Changes in Cyclic and Seasonally Anestrous Ewes Treated with Exogenous Ovine Follicle-Stimulating Hormone During the Inter-Wave Interval1

In the ewe, ovarian follicular waves emerge every 4 to 5 days and are preceded by a peak in FSH secretion. It is unclear whether large antral follicle(s) in a wave suppress the growth of other smaller follicles during the inter-wave interval, as is seen in cattle. In this study, anestrous (n = 6; experiment 1) and cyclic (n = 5; experiment 2) Western white face ewes were given ovine FSH (oFSH) (0.5 microg/kg; two s.c. injections, 8 h apart) during the growth phase (based on ultrasonography) of a follicular wave (wave 1). Control ewes (n = 5 and 6, respectively) received vehicle. In oFSH-treated ewes, serum FSH concentrations reached a peak (P < 0.05) by 12 h after oFSH treatment, and this induced FSH peak did not differ (P > 0.05) from the endogenous FSH peaks. In all ewes, emergence of follicular waves 1 and 2 was seen (P > 0.05). However, in oFSH-treated ewes, an additional follicular wave emerged approximately 0.5 days after treatment: during the interwave interval of waves 1 and 2 without delaying the emergence of wave 2. The growth characteristics and serum estradiol concentrations did not differ (P > 0.05) between oFSH-induced waves and waves induced by endogenous FSH peaks. We concluded that, unlike in cattle, the largest follicle of a wave in sheep has limited direct effect on the growth of other follicles induced by exogenous oFSH. In addition, the largest follicle of a wave may possibly not influence the rhythmicity of follicular wave emergence, as it does in cattle.

Response of anestrus rural buffaloes (Bubalus bubalis) to intravaginal progesterone implant and PGF2alpha injection in summer

An investigation was conducted to study the genital condition and response of intravaginal progesterone implant with and without administration of PGF2alpha in anestrus rural buffaloes during summer (April-June, 2001) in tropical climate. The ovarian status of 40 lactating (1st to 4th lactation) noncycling buffaloes and 15 noncycling buffalo heifers (3.5 to 5.0 years of age) maintained under village management condition were examined per rectum. Inactive genitalia with [12] and without [28] palpable corpus luteum (CL) were detected on per rectum examination in buffalo cows. The PGF2alpha-injection caused luteolysis and induction of estrus in 83% buffaloes having distinct corpus luteum. Implantation of progesterone in form of CIDR (Controlled Internal Drug Release device) intravaginally for 10 to 14 days induced resumption of estrus among 83% of anestrus buffaloes within 12 to 120 h after implant removal. Of those detected estrus about 80% of buffaloes conceived following natural service. Implantation of CIDR in combination with intramuscular injection of PGF2alpha was more effective than CIDR alone in terms of exhibition of estrus and conception rate. Long term of 10 to 14 days CIDR implant was superior to short term of 8 days in terms of resumption of estrous cyclicity. The observation suggests that during summer about 30% of rural buffaloes were cycling but due to lack of estrus detection they were declared anestrus, though they were having distinct corpus luteum on ovary. The summer sterility can be overcome by raising progesterone level for 10 to 14 days in buffaloes under rural managemental condition.

Evidence that thyroid hormones act in the ventromedial preoptic area and the premammillary region of the brain to allow the termination of the breeding season in the ewe

Thyroid hormones are permissive for various species to enter seasonal anestrus. In the ewe they act centrally to permit the onset of potent estradiol-negative feedback responsible for anestrus, but the specific sites of action are unknown. Therefore, we tested whether T(4) replacement via chronic microimplants in any of five brain areas could reverse the reproductive effects of thyroidectomy. Diffusion of (125)I-T(4) from the microimplant was largely (>98%) limited to a 1.2-mm radius. A marked decline in LH concentration in ovariectomized, estradiol-treated ewes was used as an index for anestrus. In experiment 1, all thyroidectomized (THX) ewes with microimplants in the medial preoptic area, A15 area, and medial basal hypothalamus failed to enter anestrus; instead, LH levels remained elevated, similar to those in untreated THX controls. In ventromedial preoptic area (vmPOA)-microimplanted ewes, only the two animals with the most caudal microimplants entered anestrus, as did thyroid-intact controls and THX ewes receiving icv or sc T(4) replacement. In experiment 2, all vmPOA-treated ewes with similar placements to those effective in experiment 1 along with all ewes microimplanted in the premammillary region entered neuroendocrine anestrus. Thus, the premammillary region and vmPOA are brain sites in which thyroid hormones act to permit the onset of seasonal anestrus.

Potential signals mediating the maintenance of reproductive activity during the non-breeding season of the mare

The seasonal nature of reproductive activity in mares is widely accepted and considerable attention has focused on the mechanisms that lead to the initiation of the breeding season. In contrast, considerably less information is available about the termination of the breeding season. It is interesting to note that each winter a sub-population of mares continues to undergo oestrous cyclicity during the non-breeding season. Continuation of reproductive activity during the winter occurs most frequently in mares that maintain a non-pregnant condition in successive years. The maintenance of a non-pregnant condition in successive years leads to an increase in the percentage of total body fat and it has been proposed that the degree of adiposity may be a determinant of reproductive activity during the winter months. To investigate this hypothesis we have manipulated fat stores by either pharmacological treatments or feed restriction. The studies described in this review demonstrate that manipulation of body fat during the autumn months fails to modify the mechanisms that lead to anoestrus or the proportion of mares that continues to show oestrous cyclicity during the winter months. On the basis of these and related studies two hypotheses are presented that may serve as a template for future work. The first hypothesis proposes that one aspect of the long-term regulation of seasonal reproductive rhythms in mares, specifically anoestrus, may reflect recognition of the availability of metabolic fuels before perception of a change in photoperiod. Alternatively, energy availability may need to reach a critical value before a presumptive inhibitory daylength signal initiates termination of the breeding season. This review describes previous and current studies that have led to development of these proposals.

Abnormal response of the neuropeptide Y-deficient mouse reproductive axis to food deprivation but not lactation

Neuropeptide Y (NPY) plays a key role in both food intake and GnRH secretion. Food deprivation elevates hypothalamic NPY activity and suppresses LH and gonadal steroid secretion. Similarly, lactation up-regulates NPY expression as food consumption increases and estrous cycles cease. These observations suggest that NPY coordinates reproductive suppression in response to energy deficiency; if so, the reproductive axis of NPY knockout (KO) mice should be impervious to lactation and food deprivation. We monitored food consumption, body weight, and estrous cyclicity during lactation in NPY KO mice with large and small litters. NPY KO mice with either litter size resembled wild types (WTs) in weight regulation and food consumption. Large-litter mothers had longer anestrous periods and smaller pups at weaning, but NPY KOs and WTs did not differ in either respect. We also examined the LH response of NPY KO mice to 48 h without food. Basal levels of LH in ovariectomized NPY KO animals decreased in response to fasting, but LH levels in intact and estrogen-treated ovariectomized NPY KO animals did not. In contrast, WTs consistently showed fasting-induced suppression of LH. Our findings suggest that other systems can sustain the hyperphagia of lactation and NPY alone is not responsible for suppressing cyclicity during lactation. Nevertheless, the suppression of basal LH release that accompanies food deprivation in normal female mice appears to require the steroid-dependent actions of NPY.

Evidence that estrogen receptor alpha, but not beta, mediates seasonal changes in the response of the ovine retrochiasmatic area to estradiol

In ewes, anestrus results from a reduction in LH pulsatility due to an increased sensitivity of the hypothalamic estradiol negative feedback system. Considerable evidence has implicated the A15 group of dopaminergic neurons in the retrochiasmatic area in this seasonally dependent estradiol effect. Moreover, estradiol administered to the retrochiasmatic area in ovariectomized anestrous ewes inhibits LH secretion. However, A15 neurons do not appear to contain the classical estrogen receptors (ERalpha). Therefore, we tested the hypothesis that beta-estrogen receptors mediate the action of estradiol in the retrochiasmatic area by comparing the effects of estradiol and genistein, a selective ERbeta agonist. We also examined whether there are seasonal changes in response of the retrochiasmatic area to these agonists and if these effects are mediated by dopamine. To test these hypotheses, ovariectomized ewes were implanted with bilateral guide cannulae targeting the retrochiasmatic area. Crystalline agonists were administered via microimplants inserted down the cannulae. Blood samples taken before and 4 days after microimplant insertion were analyzed for LH concentrations, pulse frequency, and amplitude. Genistein treatment produced no significant change in LH levels in either season. Estradiol treatment decreased both mean LH concentrations and pulse frequency in anestrous but not breeding-season ewes. Administration of the dopamine antagonist sulpiride to ovariectomized ewes with estradiol microimplants in the retrochiasmatic area returned LH pulse frequency to levels indistinguishable from controls. From these data, we hypothesize that estradiol acts on local ERalpha-containing neurons in this area to stimulate a dopaminergic pathway that inhibits LH secretion during anestrus.

Reproduction in female yaks (Bos grunniens) and opportunities for improvement

This paper reviews seasonal breeding, puberty, postpartum anestrus, embryonic loss and calf survival and their constraints in female yaks. Methods for improving fertility in postpartum yak cows are also considered. Yaks are seasonal breeders with mating and conception restricted in the warm season. Puberty generally occurs in the 2nd to the 4th warm season following birth, i.e. between 13 and 36 months of age. The cows usually have a long postpartum anestrus period; only a small proportion of the cows return to estrus in the 1st breeding season after calving, most come into estrus in the 2nd and 3rd years. Nutritional status is the most important determinant of reproduction in female yaks. Reproductive success is a direct result of the availability of pasture determined by climate, season, and management practices. Milking delays puberty by reducing milk intake (restricted suckling) and growth rate for the calf. Milking interferes with grazing and prolongs the duration of postpartum acyclicity in cows. Calves born early in the season have a longer suckling season than those born later in the season before the onset of winter. Thus, they can have their first cycle in the breeding season of the following year, while those born late in the season may not have their first estrus until 25 or 26 months of age. Cows calving early in the season are more likely to return to estrus in the year of calving because they have a longer period to recover from the demand on body reserves before the onset of winter. Inbreeding in smallholder yak farms is also discussed and minimizing inbreeding by exchanging bulls among different herds is suggested. Reproductive efficiency can be improved by nutritional supplementation during the winter, however, the most cost-effective and practical strategy for this needs to be determined. Early weaning or restricted suckling may shorten the duration of postpartum acyclicity, however, it is impractical due to reduced growth rates and increased winter mortality of early weaned calves. A single treatment with either GnRH, or PGF(2alpha)+GnRH can successfully induce estrus in yak cows that calved in previous years (with or without calf) but did not calve in the current year, however, it has little effect in cows nursing a calf born in the current year. The effects of administration of exogenous progestogens plus GnRH on the fertility of yak cows are worthy of further study.

Selective control of the estrous cycle of the dog through suppression of estrus and reduction of the length of anestrus

The objective of this study was to determine the effectiveness of testosterone in suppressing estrus in the bitch, and of cabergoline in shortening the length of the subsequent anestrous period. In Experiment 1, 12 diestrual Beagle bitches were randomly divided into two groups when plasma progesterone (P(4)) concentration was <1 ng/ml (Day 0). Starting on Day 0, bitches in Group 1 (n=6) were treated with testosterone cypionate every 14 days for a total of 239 days, and bitches in Group 2 served as untreated controls. On Day 274, bitches in both groups were treated with cabergoline for 40 days and blood samples were obtained on Days 274, 276 and 279 for determination of plasma prolactin (PRL) concentrations using RIA. All bitches were observed for proestrual bleeding during treatment with cabergoline. In Experiment 2, 12 Greyhound bitches previously treated with testosterone within the last 6 months were randomly divided into two groups. At the initiation of this experiment, P(4) concentration was determined to verify that all bitches had a concentration of <1 ng/ml (Day 0). Starting on Day 0, bitches in Group 1 (n=6) were treated with cabergoline for 36 days, and bitches in Group 2 (n=6) served as untreated controls. Blood samples were obtained on Days 0, 2 and 5 to determine PRL concentrations. All bitches were observed for proestrual bleeding during treatment with cabergoline. In Experiment 1, one bitch (Group 1) exhibited estrus after treatment with testosterone (1mg/kg body weight) for 43 days, and one bitch (Group 1) exhibited estrus after treatment with testosterone (2mg/kg body weight) for 113 days. None of the other four bitches in Group 1 exhibited estrus during the period of testosterone treatment (239 days). All bitches in Group 2 (control) exhibited estrus during the 239 days of the study. In addition, five of the six testosterone-treated bitches showed signs of proestrual bleeding within an average of 12.6 days (range of 5-25 days) after treatment with cabergoline; and, four of the six nontestosterone bitches showed signs of proestrual bleeding within an average of 28 days (range of 6-46 days). Prolactin concentrations in bitches in both Groups 1 and 2 significantly decreased after treatment with cabergoline. In Experiment 2, one of the six bitches showed signs of proestrual bleeding within 15 days after treatment with cabergoline. From the results of this study, it was concluded that exogenous testosterone was moderately effective (66%) in suppressing estrus in Beagle bitches, and cabergoline was effective in shortening the length of the anestrous period of Beagle bitches whose estrous cycle was previously suppressed with exogenous testosterone, but less effective in shortening the length of the anestrous period in Greyhound bitches previously treated with testosterone to suppress estrus.

Investigations on the re-establishment of the positive feedback of oestradiol during anoestrus in the bitch

To test for the re-establishment of the positive feedback of oestradiol (E2) during anoestrus in the dog, the hypothalamo-pituitary-ovarian axis of five beagle bitches was challenged by treatments with oestradiol benzoate (EB), mimicking the course of the pro-oestric E2 secretion. Treatments in anoestrus started 7 days following the decline of progesterone (P) <1 ng/ml; they were repeated in 5 week intervals until onset of pro-oestrus; another treatment was performed during dioestrus 50 days after onset of the preceding pro-oestric bleeding. Each dog served as its own control by receiving vehicle-treatments in one of the following cycles. Each observation period covered a time window of 168 h and blood samples were collected for the determination of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and E2 in 6 (0-24 h) and 8 h (24-168 h) intervals. In the control periods and as indicated by the parameters area under curve (AUC), basal and maximal values, the availability of LH, FSH and E2 decreased from dioestrus to early anoestrus to increase again during the course of anoestrus (p < 0.05), indicating a gradual desensitization of the hypothalamus towards the negative feedback of oestradiol. At all times treatments with EB lowered the availability of FSH (decreased AUC and basal levels). A delay in the occurrence of the first LH peak after treatments with EB (p < 0.001) and decreased maximal values (p < 0.001) indicated a suppression of the LH-release. In no case treatment with EB led to a pre-ovulatory like LH-surge. In each dog the last trial with EB in anoestrus passed over into pro-oestrus/oestrus, with a reduced AUC and peak value of the pre-ovulatory LH-surge being the only differences to the control group. The observed differences in the response of LH and FSH to treatments with EB point towards subtle differences in the mechanisms controlling the release of these two hormones during anoestrus. From the data obtained, it may be concluded that the time window for E2 to act via a positive feedback seems to be very small and restricted to the end of anoestrus, and that full follicular function is a pre-requisite to allow for this phenomenon.

Growth hormone-releasing hormone neurons in the anestrus cat do not express progesterone receptors

Ovarian steroids have been implicated in the regulation of growth hormone (GH) secretion in several species and increased progesterone secretion has been associated with elevated circulating GH levels in the cat. These high GH concentrations may be due, at least in part, to a direct action of progesterone on growth hormone-releasing hormone (GHRH) neurons. Using standard immunocytochemical methods coupled to high-temperature antigen retrieval, the objective of this study was to determine whether progesterone receptors were colocalized in GHRH neurons of the anestrus cat. GHRH perikarya were restricted to the infundibular nucleus and the ventral ventromedial nucleus and although frequently surrounded by numerous progesterone receptor-immunoreactive cells, none was colocalized. This study, therefore, provides evidence that, in the adult anestrus female cat, GHRH neurons do not express nuclear progesterone receptors.

Ovarian cyclicity in thyroid-suppressed ewes treated with propylthiouracil immediately before onset of seasonal anestrus

Two experiments were conducted to determine if propylthiouracil (PTU)-induced thyroid suppression immediately before onset of anestrus would extend the breeding season in mature ewes. In Exp. 1, twice-weekly serum concentrations of progesterone indicated that all ewes were cyclic before initiation of treatment. Beginning on d 0 (January 17), ewes received 0 (n = 4), 20 (n = 5), or 40 (n = 5) mg of PTU x kg(-1) of body weight (BW) x (-1) for 35 d. Blood samples were collected regularly throughout the trial and serum thyroxine and progesterone were quantified. Ewe BW were similar (P > 0.90) among treatments before the experiment began (mean = 78.2 +/- 4.5 kg). Likewise, serum concentrations of thyroxine averaged 86.5 +/- 8.0 ng/mL on d 0. After 11 d of PTU treatment, serum thyroxine was 90.2,75.2, and 44.2 +/- 14.0 ng/mL in ewes receiving 0, 20, and 40 mg of PTU/kg BW, respectively (linear effect, P = 0.04). On d 20, thyroxine values in the three respective groups were 73.0, 51.1, and 16.1 +/- 12.9 ng/mL (linear effect, P < 0.01). Fourteen days after PTU treatment ended, serum thyroxine did not differ (P = 0.53) among the three respective groups (71.4,73.3, and 57.5 +/- 11.8 ng/mL). Ewes receiving PTU tended to weigh less on d 42 (84.2, 78.2, and 71.8 +/- 5.1 kg for ewes treated with 0, 20, and 40 mg PTU/kg, respectively; linear effect, P = 0.10). Day of onset of anestrus was designated as the day on which serum progesterone decreased and remained below 1 ng/mL. Ewes treated with 0, 20, or 40 mg of PTU/kg BW became anestrous on d 16,40, and 81 (+/- 12) of the experiment, respectively (linear effect, P < 0.01). At the time the 35-d treatment period ended, 25, 60, and 100% of ewes receiving 0, 20, or 40 mg of PTU/kg exhibited normal estrous cycles. In Exp. 2, ewes received 0, 20, or 40 mg of PTU/kg BW for 14 d. The dose was then decreased to 0, 10, and 20 mg of PTU/kg BW for the remaining 21 d. Serum thyroxine decreased to concentrations below 20 ng/mL by d 9 after initiation of PTU treatment. Ewe weights did not differ throughout the trial and no BW loss was observed. The average day that each group entered anestrus was similar to those in Exp 1. Large doses of PTU dramatically lower serum thyroxine and this effect appears to inhibit onset of anestrus in ewes.

[The mammary gland, an endocrine gland]

Features of acromegaly had developed in a 6-year-old crossbred Belgian shepherd dog (dog A) following treatment with medroxyprogesterone and an 8-year-old beagle dog (dog B) during the luteal phase of the oestrus cycle. Discontinuation of progesterone administration in dog A and ovariohysterectomy in both dogs was followed by a regression of the soft tissue changes and a normalisation of the initially high plasma growth hormone concentrations. These cases illustrate that the mammary gland is not just a gland which delivers milk in response to certain stimuli, but that it also transmits humoral signals, i.e., the mammary gland is an endocrine gland. Progestin-induced growth hormone is produced in areas of hyperplastic mammary epithelium and in mammary tumours. This suggests that locally-produced growth hormone is involved in the proliferation of unaffected and tumorous mammary tissue in an autocrine or paracrine manner. Now that the expression of the growth hormone gene has also been demonstrated in the human mammary gland, further studies are needed to answer questions such as (a) does mammary growth hormone also reach the systemic circulation in women?, (b) what is the role of local growth-hormone production in tumourigenesis?, and (c) does this phenomenon provide possibilities for therapeutic intervention in women with breast cancer?

Bull exposure and an increased within-day milking to suckling interval reduced postpartum anoestrus in dual purpose cows

It is hypothesized that the combined effects of suckling and milking in the dual purpose cows is one of the main suppressors of reproductive efficiency in this production system. The experiment described here examined whether managing the interval between milking and suckling could reduce the postpartum anoestrous period and whether the presence of a teaser bull could enhance the effects of these managements. The experiment involved 39 Bos taurus x Bos indicus cows which had an average weight of 523.0 +/- 12.8 kg (mean +/- S.E.M.) and body condition score of 5-7 (scale 1-9) at calving. The cows and calves grazed separate pastures and the cows were supplemented with 2 kg 17% CP concentrates and 1 kg molasses per cow per day. The experiment was conducted over the first 100 days postpartum. Cows were hand-milked once per day in the presence of the calf to stimulate milk release. The factors in the 2 x 2 design were the milking to suckling interval (0 h, control suckling; CS versus 8 h prolonged-delay suckling; PDS) and no exposure versus exposure to a teaser bull (B). Cows were assigned at random within calving date to the four treatments: CS (n = 10), PDS (n = 10), CS-B (n = 9) and PDS-B (n = 10). Cows on treatments CS and CS-B had three-quarters of the udder milked and one-quarter was not milked. The entire udder was milked on those treatments where there was an interval between milking and suckling. The bull was introduced 7 days after calving in treatments where the cows were exposed to a teaser bull. Body weights of cows and calves and cow milk yield were recorded. Weekly blood samples were collected for plasma progesterone assay. Data were analyzed by ANOVA in a 2 x 2 factorial design and by chi(2)-test. There were no statistically significant differences between treatments in cow body weight at calving and at 100 days postpartum, nor in milk yield (overall mean 6.0 +/- 1.1 kg per day). Calf daily gain was 598 +/- 25 g for treatments CS and CS-B in which suckling immediately followed milking and 833 +/- 24 g for treatments PDS and PDS-B (P < 0.001). The proportion of cows ovulating was CS 80.0%, PDS 100.0%, CS-B 88.8% and PDS-B 100.0%. The difference between CS and PDS or PDS-B was significant (P < 0.05). CS-B did not differ significantly from the other three treatments. The calving to first ovulation interval was not improved when the interval between milking and suckling was increased from 0 h (56.5 +/- 5.0 days) to 8 h (64.8 +/- 4.5 days). Exposure to a teaser bull, however, significantly (P < 0.001) reduced this interval from 77.0 +/- 2.7 days (no bull exposure) to 44.4 +/- 2.7 days (exposure to teaser bull). Exposure to a teaser bull significantly reduced the calving to first anoestrus interval. Delaying the start of suckling after milking did not improve the reproductive performance of the cows or alter the effect of bull exposure, however, delaying suckling after milking improved the performance of the calves without affecting milk yield.

The role of nutrition in the regulation of LH secretion during anestrus by the serotoninergic and dopaminergic systems in Mediterranean ewes treated with melatonin

The steroid-dependent inhibition of LH secretion involves dopaminergic and serotoninergic systems but it is unclear how the plane of nutrition affects this inhibition during anestrus in melatonin treated ewes. Melatonin implants (18 mg) were inserted (Day 0) into ovariectomized, estradiol treated adult Rasa Aragonesa ewes on a high (H; n = 8) or low energy diet (L; n = 6) which were applied in early anestrus (Day 29-57) and late anestrus (Day 90-104). Cyproheptadine (0.1 mg/ kg), a serotoninergic (SHT2) receptor antagonist, was administered in early and late anestrus (Day 50 and 107) followed by pimozide (0.08 mg/kg), a dopaminergic2 receptor antagonist (Day 57 and 114). The H ewes had significantly higher LH concentrations (P < 0.05) before cyproheptadine treatment in early anestrus. The H and L ewes responded in a similar way to the antagonists in both early and late anestrus, except for L ewes who had a higher LH pulse amplitude after pimozide treatment in both periods (P < 0.05). During early anestrus, cyproheptadine tended to increase (P = 0.06) LH pulse frequency in L ewes and LH concentrations in H ewes. The LH secretion also increased in L ewes after pimozide administration during early anestrus (P < 0.05 for mean LH concentrations and LH pulse frequency and amplitude). However, pimozide dramatically increased LH secretion during late anestrus (Day 114) irrespective of the plane of nutrition (P = 0.06-0.08 for LH pulse frequency and P < 0.05 for LH concentrations and pulse amplitude). In melatonin treated Mediterranean ewes, the plane of nutrition appeared to modify the effect of dopaminergic and serotoninergic systems on the steroid-dependent inhibition of LH secretion throughout anestrus.

The Involvement of GABAA receptors in the control of GnRH and beta-endorphin release, and catecholaminergic activity in the preoptic area in anestrous ewes

This study examined role of GABA A receptors in the control of GnRH, beta-endorphin release and catecholaminergic system activity in the preoptic area and LH secretion in anestrous ewes. Stimulation of GABA A receptors in the medial preoptic area (MPOA) by muscimol attenuated GnRH release and dopaminergic system activity and increased extracellular noradrenaline (NE) and MHPG concentration. Muscimol has no evident effect on the extracellular concentration of beta-endorphin-like immunoreactivity (B-END-LI) in the MPOA. The decrease of LH pulse frequency and concentration of this hormone in blood plasma suggests that GABA A receptor agonist applied in the MPOA suppresses GnRH release from the GnRH axon terminals in the ventromedial hypothalamus-nucleus infundibularis region (VEN/NI) into the hypophyseal vascular system. Blockade of GABA A receptors with bicuculline did not change GnRH release, catecholaminergic activity, B-END-LI concentration in the MPOA, and LH release. The presented data indicate that activation of GABA A receptors in the MPOA decreases extracellular concentration of GnRH in this structure and LH level in the blood plasma thus suggesting that GABA may act in the MPOA to inhibit GnRH release in the VEN/NI. These results suggest that suppression of GnRH/LH release during muscimol treatment may result from activation of GABA A receptors on the GnRH perikarya and/or through GABA A receptor mechanism on the dopaminergic and noradrenergic system in the MPOA. Lack of changes in B-END-LI concentration during stimulation or blocking GABA A receptors suggests, that beta-endorphinergic system in the MPOA does not participate in the GABA A receptors mechanism modulating GnRH release.

Characterization of morphology and angiogenesis in follicles of mares during spring transition and the breeding season

The mare is a seasonal breeder and undergoes a period of ovarian transition in spring between winter anoestrus and cyclicity. During spring transition LH concentrations are low and many mares have successive large anovulatory follicular waves which reach the size of preovulatory follicles. Follicular angiogenesis is essential for growth and health of preovulatory follicles. The aim of the present study was to investigate the morphology and vascularity of transitional anovulatory follicles. On gross inspection, the wall of transitional follicles was visibly less well vascularized than that of preovulatory follicles. Histologically, it could be seen that the theca was only poorly developed in transitional follicles. Immunostaining for factor VIII showed that there were significantly (P < 0.05) fewer blood vessels in the theca of transitional follicles. There was substantially less (P < 0.001) proliferative activity, measured by immunostaining for Ki67, in the endothelial cells and granulosa cells of transitional follicles compared with preovulatory follicles. Preovulatory follicles had a heavy band of immunostaining in the theca for vascular endothelial growth factor (VEGF), whereas staining was sparse in the transitional follicles. It was concluded that the poor vascularity and development of the theca layer in transitional follicles could be related to low circulating LH, and possibly other trophic hormones, and are likely to be the key factors in explaining the steroidogenic incompetence of transitional anovulatory follicles.

Temporal requirements of thyroid hormones for seasonal changes in LH secretion

The transition between breeding and anestrous seasons in ewes is driven by an endogenous rhythm in responsiveness to estradiol negative feedback. One stage of this rhythm, the transition to anestrus, requires the presence of thyroid hormone during a window of responsiveness that opens in the late breeding season. The primary goal of this study was to assess when ewes lose responsiveness to thyroid hormone (i.e. when the window closes). In addition, we investigated whether thyroid hormone influences aspects of seasonality other than the transition to anestrus. Ovariectomized ewes maintained in a simulated natural photoperiod were implanted with estradiol, thyroidectomized, and treated with T(4) for 100 d beginning at progressively later dates during the anestrous season. Onset of neuroendocrine anestrus (decrease in LH), latency to anestrus, and time of onset of the subsequent neuroendocrine breeding season (rise in LH) were determined. Ewes gradually lost responsiveness to T(4) during the latter half of the anestrous season, as judged by increasing latency to the decrease in LH and, eventually, failure to exhibit a decrease in LH. Progressively later T(4) replacements also caused progressive delays in the subsequent breeding season. In contrast, the annual PRL cycle was not significantly affected by thyroidectomy or T(4) replacement. These findings indicate that 1) responsiveness to T(4) is lost gradually during the mid to late anestrous season; 2) thyroid hormones can influence the timing of the breeding season and thus may be required for the maintenance or entrainment of the endogenous reproductive rhythm; 3) thyroid hormones are not required for all seasonal neuroendocrine cycles.

Estrogen treatment suppresses forebrain p75 neurotrophin receptor expression in aged, noncycling female rats

There is increasing evidence that estrogen has beneficial effects on cognition, both in humans and in rodents, and may delay Alzheimer's disease onset in postmenopausal women. Several rodent studies have utilised the ovariectomy model to show estrogen regulation of the p75 neurotrophin receptor, TrkA, and markers of acetylcholine synthesis in the cholinergic basal forebrain. We studied estrogenic effects in aged (16-17-month-old), noncycling rats. Estrogen treatment for 10 days drastically reduced p75(NTR) immunoreactivity in the rostral parts of the basal forebrain. The number of p75(NTR)-immunoreactive neurons was decreased, and those neurons remaining positive for p75(NTR) showed reduced p75(NTR) staining intensity. In vehicle-treated rats, almost all choline acetyltransferase-immunoreactive neurons were p75(NTR) positive (and vice versa), but, in estrogen treated rats, large numbers of choline acetyltransferase-immunoreactive cells were negative for p75(NTR). Similar levels of p75(NTR) down-regulation in the rostral basal forebrain were found when estrogen treatment was extended to 6 weeks. There was no reduction in the number of p75(NTR)-immunoreactive neurons in the caudal basal forebrain after 10 days of treatment. After 6 weeks of treatment, however, there was evidence of p75(NTR) down-regulation in the caudal basal forebrain. There was no evidence of hypertrophy or atrophy of cholinergic neurons even after 6 weeks of estrogen treatment. Considering the evidence for the role of p75(NTR) in regulating survival, growth and nerve growth factor responsiveness of cholinergic basal forebrain neurons, the results indicate an important aspect of estrogen's effects on the nervous system.

Role of changes in the pulsatile secretion pattern of FSH in initiation of ovarian folliculogenesis in bitches

The results of two studies in which the pulsatile secretion patterns of LH and FSH were investigated in six Beagle bitches during early, mid- and late anoestrus and in six anoestrous Beagle bitches treated with bromocriptine are summarized to improve our knowledge of the endocrine changes that lead to a new follicular phase in bitches. Blood samples for the determination of secretory profiles were obtained via jugular venepuncture at 10 min intervals for 6 h. In untreated bitches, blood samples were collected during early, mid- and late anoestrus. In bromocriptine-treated bitches (20 micrograms kg-1 twice each day, starting 100 days after ovulation until the start of the next oestrous cycle), blood samples were collected before treatment and at 2 week intervals after the start of bromocriptine treatment until the next ovulation. In all bitches, FSH and LH were secreted in a pulsatile manner and FSH pulses coincided with LH pulses. Progression from early to late anoestrus was associated with an increase in FSH secretion without a concomitant increase in LH secretion. The bromocriptine-induced shortening of the interoestrous interval was also associated with an increase in FSH secretion without a concomitant increase in LH secretion. These results indicate that in bitches an increase in circulating FSH should be considered to be a critical event required for the initiation of ovarian folliculogenesis and consequently the termination of anoestrus.

Ability of ram introduction to induce LH secretion, estrus and ovulation in fall-born ewe lambs during anestrus

The ability of ram introduction (RI) and progesterone pre-treatment to induce increases in LH secretion and ovulation, and the ability of progesterone pre-treatment with or without estrogen to induce estrus and ovulation in fall-born ewe lambs during seasonal anestrus was investigated. In early July, lambs of mixed breeds (41.8+/-0.6 kg and 250.7+/-1.3 days of age) were assigned to receive no treatment (C, n=7), to be introduced to rams (7:1 ewe:ram ratio; R, n=7), to be treated with progesterone (a used CIDR device) for 5 days (P, n=5), to be treated with progesterone and introduced to rams at CIDR removal (PR, n=11), or to receive the latter treatment plus an injection of estradiol benzoate (25 microg, E2beta i.m.) 24 h after CIDR withdrawal/RI (PER, n=11). Blood samples were collected from all lambs every 4h for 60 h beginning at RI/CIDR withdrawal (0 h), to characterize the LH surge profile and in groups R and C every 15 min for 8 h between 12 and 20 h for determination of LH pulse frequencies. Ultrasonographic examinations of the ovaries were conducted at 0, 36 and 60 h. In ram-exposed groups lambs were also observed for raddle marks every 4h from 0 to 60 h. The LH pulse frequency (pulses/8 h) was higher in group R (P<0.01; 7.7+/- 0.5) than group C lambs (2.7+/- 0.8). More lambs in groups exposed to rams than in the C or P groups showed an LH surge (P<0.05; 0, 100, 0, 72.7 and 100%, for C, R, P, PR and PER groups, respectively). Time from RI/CIDR removal to initiation of the LH surge was greater in lambs in the PR (43.5+/- 3.8h) than in the R (32.6+/- 4.6h; P=0.08) or PER (33+/- 1.2h; P<0.01). Diameter of the largest follicle at 0 h (3.2+/- 0.2mm) was not different among groups. Growth rate of the largest follicle between 0 and 36 h was greater (P<0.05) in RI than in C or P groups. Diameter of the largest follicle at 36 h was larger (P<0.05) in lambs in R (5.6+/- 0.2mm) and PR (5.1+/- 0.5mm) than C (4.0+/- 0.6mm) or P (3.8+/- 0.4mm) groups, and in R than PER (4.3+/- 0.4mm) treatment groups. Only lambs in the RI groups ovulated. Among RI groups the percentage of lambs ovulating was greater in the R (P<0.05; 85.7%) than PR (33.3%) groups with an intermediate response observed in lambs in treatment group PER (71.4%). The estrous response in progesterone pre-treated groups was greater (P<0.05) in lambs also treated with estrogen (PER; 81.8%), than in lambs introduced to rams alone (PR; 45.5%). In conclusion, ram introduction by itself, but not progesterone treatment alone, induces increases in LH pulse frequency, follicular development, and ovulation in fall-born ewe lambs during seasonal anestrus, further, P4 pre-treatment and RI when combined with E2 results in a high estrous response.

Effect of treatment with progesterone and oestradiol benzoate on ovarian follicular turnover in postpartum anoestrous cows and cows which have resumed oestrous cycles

Two experiments were carried out to determine the effect of a low dose of progesterone (P) with and without the addition of an injection of oestradiol benzoate (ODB) on ovarian follicle dynamics, oestradiol production and LH pulsatility in postpartum anoestrous cows, compared with cows which had resumed oestrous cycles (cycling cows). In the first experiment, anoestrous Jersey cows were treated with (AN+P, n=8) or without (AN-3, n=3) a previously used intravaginal progesterone releasing (CIDR) device for 10 days, commencing 3 or 4 days after emergence of a new dominant follicle (DF1) as determined by transrectal ultrasonography. Contemporary cycling cows (CYC+P, n=8) were similarly treated with used CIDR devices and injected with prostaglandin F(2alpha) (PGF) at the time of device insertion. Follicle turnover was monitored by daily ultrasonography and pulsatile release of LH was measured on the ninth day after device insertion. During the period of CIDR device insertion, a second dominant follicle emerged in 4/8 of the CYC+P group and 7/8 of the AN+P group (P=0.14). Maximum diameter of DF1 was greater in cows in the CYC+P compared with the AN+P group (P=0.02), but did not differ between cows in the AN+P and AN-P groups (P>0.1). Frequency of LH pulses was greater in cows in the CYC+P than AN+P group (P=0.06), and in cows in the AN+P than AN-P group (P=0.02). In the second experiment, anoestrous (n=20) and cycling (n=11) Friesian cows were treated with a new CIDR device for 6 days commencing 3 days after emergence of a new dominant follicle (DF1). Cycling cows were also injected with PGF on the day of device insertion. Half of the cows in each group were injected with 2mg ODB on the day of device insertion. Daily ultrasonography was used to monitor follicular dynamics throughout the experimental period. Follicular turnover was increased by ODB in cycling (5/5 versus 1/6; P<0.05), but not anoestrous cows (5/9 versus 4/11). Persistence of DF1 was reduced by ODB treatment in both cycling and anoestrous cows (P<0.001). Maximum diameter of DF1 was influenced by ODB treatment and reproductive status (P<0.05). In anoestrous cows in which a second dominant follicle did not emerge during the period of device insertion, the interval from emergence of DF1 to emergence of a second dominant follicle was significantly delayed by treatment with ODB (P=0.04). In conclusion, P treatment of anoestrous cows increased pulsatile release of LH, but did not induce the development of persistent follicles. Injection of ODB in association with P treatment reduced the persistence of dominant follicles in both cycling and anoestrous cows, but delayed subsequent follicular development in a proportion of anoestrous cows.

Effect of alternating bulls as a management tool to improve the reproductive performance of suckled Zebu cows in the humid tropics of Costa Rica

A study was undertaken to evaluate the effect of alternating bulls between a single and a multiple sire mating (MSM) program on the reproductive performance of suckled Zebu cows raised under range conditions in the humid tropics of Costa Rica. Multiparous Zebu cows (n=94) suckling calves were distributed between two experimental trials (A and B) consisting of 47 animals each. A single sire mating (SSM) system was alternated weekly with a MSM system with three bulls. This period lasted for 8 weeks. To facilitate estrous expression, four cows were strategically synchronized (estrus-stimulated) in alternate weeks. Courtship predominated over mounting under non-stimulated estrus, for each mounting performed an average of 6.0 and 6.3 courtship activities were recorded in the SSM and MSM, respectively. Under the influence of strategic synchronization corresponding values were 3.9 and 4.2 in the SSM and MSM, respectively (P>0.05). Blood samples for progesterone evaluation were taken twice weekly. All cows in trial A were in anestrus at the start of the study. By second week, 5 out of the 47 cows had initiated estrous cycles and by the third week six were pregnant. In contrast in trial B, 9 out of 47 had initiated estrous cycles before interacting with the bulls and on week 3, only two females had become pregnant and three had initiated estrous cycles. Significant differences were found in the cumulative percentage of cows pregnant between trials A and B (P<0.05). Even though these results occurred, the rotation of the bulls (one or three), or the type of cows (estrus-stimulated or not) did not influence the results in this study.