Relative roles of photoperiodic and nutritional cues in modulating ovarian activity in goats

Glutamate Supply Reactivates Ovarian Function while Increases Serum Insulin and Triiodothyronine Concentrations in Criollo x Saanen-Alpine Yearlings' Goats during the Anestrous Season

The possible effect of glutamate supplementation upon ovarian reactivation and serum concentrations of insulin (INS) and triiodothyronine (T3) in anestrous yearling goats was evaluated. Goats (n = 32, 12 mo., 26° North, 1117 m) with a similar live weight (LW) and body condition score (BCS) were blood sampled twice per week for two weeks (2 × 1 week × 2 weeks) to confirm the anestrus status (<1 ng P4/mL; RIA). Thereafter, goats were randomly assigned to either 1) Glutamate (GLUT; n = 16, LW = 27.1 ± 1.09 kg, 3.5 ± 0.18 units, IV-supplemented with 7 mg of glutamate kg^-1 LW), or 2) Control (CONT; n = 16; LW = 29.2 ± 1.09 kg; BCS = 3.5 ± 0.18, IV saline). During the treatment period, 16 goats (eight/group) were blood sampled twice per week for six weeks. Such serum samples (2 × 1 week × 6 weeks) were quantified by their P4 content to evaluate the ovarian-luteal activity, whereas a sample subset (1 × 1 week × 6 weeks) was used to quantify their INS & T3 content to evaluate their metabolic status. Neither LW (28.19 kg; p > 0.05) nor BCS (3.51 units; p > 0.05) differed between treatments. Goats depicting ovarian reactivation favored the GLUT group (50 vs. 12.5%; p < 0.05). Neither INS (1.72 ± 0.15 ng mL^-1) nor T3 (2.32 ± 0.11 ng mL^-1) differed between treatments, yet a treatment x time interaction regarding INS & T3 concentration across time favored (p < 0.05) the GLUT group. The results unveil exogenous glutamate as an interesting modulator not only of ovarian reactivation, but of metabolic hormone synthesis.

Highly precocious activation of reproductive function in autumn-born goats (Capra hircus) by exposure to sexually active bucks

Goats are seasonal breeders with the main cue controlling the timing of breeding season being photoperiod. Hence, the season of birth impacts puberty onset: spring-born goats reach puberty in autumn, at 7 mo of age, whereas autumn-born goats reach puberty at 1 yr during the next reproductive season. The aim of this study was to determine whether exposure of autumn-born young females to sexually active males could counteract the delay in puberty onset observed in autumn-born goats. Females exposed to sexually active males (n = 8) reached puberty earlier than isolated females (n = 8), with exposed females ovulating at a mean age of 3.5 mo. To our knowledge, such precocious puberty onset obtained through social stimulation has never been described in the literature. Moreover, those exposed females exhibited estrus behavior for most ovulations. Our results indicate that in goats born out of season, exposure to sexually active bucks is a really efficient approach to induce early puberty, suggesting that social interactions could have a crucial impact on the regulation of pubertal transition.

Sexually active bucks are a critical social cue that activates the gonadotrope axis and early puberty onset in does

In rodents, early exposure to adult male is well known to induce an early puberty in females (Vandenbergh effect). This phenomenon has been less studied in other mammals. In goats, despite our extensive knowledge about the "male-effect" phenomenon in adults (i.e. ovulation induced by the introduction of the male during the anestrous), there are few data on the consequences of an early exposure of females to males. Here, we evaluated the puberty onset of young alpine goats when raised since weaning with intact bucks (INT), with castrated bucks (CAS) or isolated from bucks (ISOL). The INT group had the first ovulation 1.5 month before the two other groups. Despite the earlier puberty the INT group of females had normal and regular ovarian cycles. Morphological study of the genital tract showed that at 6 months, uterus of INT goats was 40% heavier than CAS and ISOL goats. Moreover, INT females had a myometrium significantly thicker and INT was the only group having corpora lutea. In our study, INT females were pubescent in the month following the entry of bucks into the breeding season, suggesting that only sexually active bucks provide the signal responsible for puberty acceleration. By removing direct contact with the bucks, we showed that somatosensory interactions were dispensable for an early puberty induction. Finally, no difference in the GnRH network (fiber density and number of synaptic appositions) can be detected between pubescent and non-pubescent females, suggesting that the male stimulations triggering puberty onset act probably on upstream neuronal networks, potentially on kisspeptin neurons.

Reproductive outcomes of anestrous goats supplemented with spineless Opuntia megacantha Salm-Dyck protein-enriched cladodes and exposed to the male effect

The possible influence of the "male effect" upon reproductive outcomes of adult anestrous goats under marginal rangeland conditions and supplemented with protein-enriched Opuntia megacantha Salm-Dyck was evaluated. Reproductive variables included: estrus percentage (EST, %), estrus latency (ESL, hours), ovulation percentage (OP, %), ovulation rate (OR, units), average largest follicle at ovulation (LFO, mm), largest corpus luteum (LCL, mm), embryo number (EBN, units), and embryo implantation percentage (EIP, %). During early May, anestrous mix-breed adult goats (Criollo x Alpine-Saanen-Nubian; n = 38, 26° N) were randomly distributed to (1) Control (CC; n = 12), (2), Non-enriched Opuntia (NEO; n = 14), and (3) Protein-enriched Opuntia (PEO; n = 12). Neither LW (P > 0.05) nor BCS (P > 0.05) or any of the evaluated ovarian variables differed (P > 0.05) among treatments; EST = 89.66%, ESL = 53.66 h, OP = 70.33%, OR = 1.07 units, LFO = 4.5 mm, LCL = 9.6 mm, EBN = 0.94 embryos, and EIP = 48.66%. Irrespective of nutritional supplementation regime, all goats denoted an increased response to the male effect just in the middle of the anestrous season and managed under marginal grazing conditions during the dry season (May to June; 26° N). The use of the male effect successfully invoked neurophysiological pathways to re-activate ovarian follicular and luteal pathways during the natural anestrous season in the female goat. Yet, such successful physiological scenario was not equally exerted to promote an increased embryo implantation rate; this issue claims further consideration. Therefore, it is essential to align not only the peri-conceptional but also the peri-implantation stages to the best suited environmental conditions in the rangeland, in order to increase both reproductive and economic efficiency while promoting sustainability in those rangeland-based marginal goat production systems.

Effects of different supplemental soya bean oil levels on the performance of prepubertal Saanen goats: Oestrogen and progesterone release

The aim of this study was to investigate the effects of different levels of soya bean oil in the total diet on the growth rate, metabolic changes, and oestrogen and progesterone release in Saanen goats. After dietary adaptation, 21 prepubertal goats (weight of 29.12 ± 0.91 kg, 230 days old) were randomly distributed among three diets of D2: inclusion of 2% soya bean oil in the total diet; D3: basal diet - inclusion of 3% soya bean oil in the total diet; and D4: inclusion of 4% soya bean oil in the total diet. The basal diet (D3) was formulated to promote a daily gain of 0.140 kg. The goats were weighed, and their blood samples were collected weekly. Glucose, cholesterol, triglycerides, total protein, urea, non-esterified fatty acids, beta-hydroxybutyrate, oestrogen and progesterone in the plasma were measured. Prepubertal goats that were fed D4 exhibited a significantly lower dry matter intake, urea and cholesterol levels compared with the goats that were fed D2 and D3. Indeed, goats that were fed D4 displayed a significantly lower final weight than goats that were fed D2 and D3. In contrast, the inclusion of soya bean oil in the diet increased the progesterone and oestrogen concentrations, and goats that were fed D4 released a significantly higher concentration of progesterone than those that were fed D2 and D3. Furthermore, the percentage of goats with a progesterone level greater than 1 ng/ml (functional Corpus luteum) was significantly higher among the goats that were fed D3 and D4 than among those that were fed D2. In this study, although the inclusion of 4% soya bean oil in the diet decreased dry matter intake and growth rate, it increased progesterone concentration and the percentage of goats with a functional Corpus luteum, suggesting that the inclusion of soya bean oil accelerated puberty in prepubertal goats.

Eruption of first permanent incisors and live weight gain in grazing yearling Angora goats

OBJECTIVE

To investigate the effects of the timing and duration of eruption of the first permanent incisors, live weight, sex and other factors on contemporaneous live weight gain in Angora goats.

DESIGN

Goats were previously part of a pen study on the effects of energy intake of Angora does during pregnancy and lactation on kid development. The design was 3 levels of nutrition in mid-pregnancy by 2 levels of postnatal nutrition in 17 randomised blocks.

METHODS

Artificial insemination, ultrasound examination and feeding does in pens enabled accurate conduct of the study. After weaning, goats were grazed in sex groups. Live weight change between 14 and 20 months of age was related to deciduous first incisor loss and permanent first incisor development and other attributes assessed before the study.

RESULTS

Live weight change was related to the elapsed time for first permanent incisors to commence eruption and to the length of time for first permanent incisors to erupt. This response was affected by sex. Over summer and autumn, entire males with short eruption intervals gained 2-3 kg more than entire males with long eruption intervals. Females that reached first permanent incisor eruption by mid-summer had a live weight gain of 3 kg more than those that reached the same development 3 months later.

CONCLUSIONS

Live weight change in yearling Angora goats was associated with the process of first permanent incisor eruption. In females, live weight gain was greater when first permanent incisor eruption was earlier. In males, live weight gain was greater when first permanent incisor eruption was faster.

Long-term betacarotene-supplementation enhances serum insulin concentrations without effect on the onset of puberty in the female goat

The effect of betacarotene (BC) supplementation on the onset of puberty and serum insulin levels in goats was evaluated in the study. In June, prepuberal goats (n=17; 3 months old; 7/8 Saanen-Alpine; 26° NL) were randomly assigned to one of two groups: 1/ betacarotene group supplemented daily with 50 mg of BC (n=9; live weight [LW]: 17.3±1.0 kg; body condition score [BCS]: 3.34±0.12) or 2/ control group (CONT; n=8; LW:16.1±1.0 kg; BCS=3.17±0.12). From June to November, an intermittent blood sampling was performed twice per week in both groups to evaluate serum progesterone (P(4)), while monthly samples were intended for insulin (INS) determination. Initial mean LW (16.7±1.0 kg) and BCS (3.31±0.12) were similar (p>0.05) in both groups. Mean serum insulin (1.37 vs. 1.18±0.09 ng/ml), age of puberty (215.7 vs. 226.5±6.6 days) and the percentage of goats reaching puberty (44.4 vs. 25.0±17.0%) did not differ (p>0.05) between BC and CONT group, respectively. However, increase in serum insulin during the second half of the experiment was observed in BC group (p<0.05) which was positively correlated with LW (r=0.95; p<0.05). In addition, as LW (r=-0.89) and serum insulin (r=-0.76) levels increased, the natural photoperiod decreased, revealing negative correlations (p<0.05) between the respective variables. In this study, BC supplementation did not promote precocious puberty and did not affect the percentage of goats reaching activation of the hypothalamic-hypophyseal-gonadal axis during the establishment of puberty. Nonetheless, BC supplementation positively affected the release pattern of insulin suggesting a potential role of BC as pancreas-activating molecule.

Effect of nutritional supplementation upon pregnancy rates of goats under semiarid rangelands and exposed to the male effect

The aim of this study was to evaluate possible effects of improved protein and energy diet upon reproductive outcomes of adult goats under marginal rangeland grazing conditions and exposed to the male effect during the anoestrous-dry season. Adult goats (Nubian × Criollo, nonpregnant, nonlactating, n = 160, 22° 50' N, 100° 59' W, 1,653 m) were randomly divided in two experimental groups: Control (CG; n = 80) and Supplemented (SG; n = 80). Both CG and SG goats were kept together during the day for ranging a semiarid rangeland while separated accordingly at night. SG goats were individually supplemented [400 g kg(-1) day(-1); 14% CP and 2.92 Mcal DE kg(-1)] during a 30-day period. Thereafter, both the CG [35.5 ± 0.94 kg LW, 1.95 ± 0.06 U, body condition score (BCS)] and the SG [39.5 ± 0.94 kg LW, 2.29 ± 0.06 BCS] were exposed to adult males (Nubian, n = 4, two per group) of proven libido and fertility and kept together at night (1700-0900) during a 42-day experimental breeding period. At the beginning of the breeding period, both LW (P < 0.001) and BCS (P < 0.001) were higher in the SG, which was also reflected in higher pregnancy rate (92.5 vs. 76.3%, P < 0.01). Nonetheless, both CG and SG depicted an increased abortion rate (52.5 vs. 41.9% P > 0.05), respectively. Results suggest that nutritional supplementation and the male effect were able to successfully invoke neurophysiological pathways to increase ovarian activity and to promote a uterine milieu prone to the establishment of pregnancy during the anoestrus season. However, the increased abortion rates observed in the study occurred irrespective of the nutritional regime offered during the premating stage. Therefore, there is a need to align the last third of gestation to the onset of the grazing season in order to increase reproductive and economic efficiency in those rangeland-based marginal goat production systems.

The use of melatonin and progestagen-eCG to initiate reproductive activity in prepuberal Awassi ewe lambs

This experiment was conducted to evaluate the effect of administering hormonal treatments (melatonin and progestagen/equine chronic gonadotropin (eCG)) on advancing puberty in Awassi ewe lambs. Fifty-one 6-month-old ewe lambs of similar body weights (around 28 kg) were randomly assigned into four treatment groups; control (CON; n = 14), melatonin (MEL; n = 13), melatonin plus progestagen-eCG (MELPP; n = 11), and progestagen-eCG (PP; n = 13). Ewe lambs in the PP and MELPP groups were fitted with intravaginal progestagen sponges containing 60 mg medroxyprogesterone acetate for 14 days; 400 IU eCG were administered to each of these ewe lambs on the day of sponge removal. Ewe lambs in the MEL and MELPP groups received subcutaneous melatonin implants (Regulin®, 18 mg melatonin) 36 days before sponge insertion. Hormonal treatment had no effect on ewe lamb body weight change. Estrous behavior was greater (p < 0.001) in the PP and MELPP groups than in the CON and MEL ewe lambs. The duration from ram introduction to onset of estrus was shorter (p < 0.05) in the CON, PP, and MELPP than in the MEL ewe lambs. The number of ewe lambs showing luteal activity was greater (p < 0.001) in the MELPP and PP than in the CON and MEL groups. Lambing rate from mating during the first cycle following ram introduction differed significantly (p < 0.01) among treatments being greater in the MELPP and PP than in the CON and MEL groups. Based on these results, it can be concluded that progestagen-eCG appears to be more effective than melatonin in inducing reproductive activity. However, the majority of ewe lambs in the current study either failed to cycle or stopped cycling following the induced estrus. Such failure in advancing puberty may be related to body weight of ewe lambs at the time of mating.

Glutamate supply positively affects serum release of triiodothyronine and insulin across time without increases of glucose during the onset of puberty in female goats

The current study evaluated the effect of glutamate supply on the onset of puberty and possible links to changes in serum concentrations of insulin [INS], glucose [GLU] and triiodothyronine [T(3)]. The study was conducted from June to November in prepuberal female goats (n=18; 3 mo. old, 7/8 Saanen-Alpine, 1/8 Criollo, 26° north) randomly assigned to two experimental groups: (i) excitatory amino acids group (group AA, n=10; 16.52±1.04 kg LW, 3.4±0.12 body condition score [BCS], receiving an intravenous infusion of 7 mg kg(-1) live weight [LW] of l-glutamate, twice a week, and (ii) control group (group CC, n=8; 16.1±1.04 kg LW, 3.1±0.12 BCS) receiving saline. Blood samples were obtained twice a week, for assessing progesterone [P(4)], as well as in a monthly basis to evaluate INS and T(3) by RIA. Mean final LW and BCS were 23.2±0.72 kg, 3.53±0.10 units, without differences between groups. The AA group depicted an earlier onset of puberty (6.9±0.3 compared to 7.5±0.4 mo.; P<0.05) and an increased ovarian activity (70±0.28% compared to 25±0.26%; P<0.05). Neither serum INS concentrations nor serum glucose concentrations differed between treatments (1.2±0.06 ng mL(-1) and 89.6±1.8 mg 100 mL(-1); P>0.05, respectively). Serum T(3) concentrations, however, were greater in AA goats (1.55±0.03 compared to 1.39±0.04 ng mL(-1)). In addition, a treatment x time interaction occurred (P<0.05) across the experimental period for both T(3) and INS, with increases by the last third of the experimental period, time at which the onset of puberty occurred in both experimental groups. No differences (P>0.05) for glucose concentrations across time occurred between treatments. Results indicate that, in prepuberal goats, glutamate acts as a cue for sexual maturation in a glucose-independent pathway, while both T(3) and INS seem to act as metabolic modulators for the establishment of puberty in goats. Actions of INS and T(3) are mediated directly on hypothalamic centers regulating the pulsatile release of GnRH or indirectly by peripheral cues reflecting INS-T(3) actions on somatic development remains to be determined.