Progress 09/01/02 to 08/31/07
Outputs
OUTPUTS: Perfusate collections were made from in vitro hypothalamic tissue preparations from goats that were destroyed after being subjected to long (14 h Light : 10 h Dark) and short photoperiod (10 h Light : 14 h Dark) treatments. Gonadotropic releasing hormone (GnRH) profiles were developed from the collections to correlate photoperiod response, and also to establish relationship with LH profiles for the treatments. The results suggest LH pattern that is in concert with GnRH, demonstrating that the effect is exerted at the hypothalamic level. Studies were conducted to determine the effect of photoperiod and glutamatergic stimulation on growth hormone (GH) and testosterone (T) secretion in bucks. Exposure to long daylength (LD) significantly reduced T secretion relative to short daylength (SD) bucks (0.41 +/-0.15 vs 1 +/- 0.15 ng/ml, P<.01). However, GH secretion was enhanced in LD bucks (3.3 +/- 0.17 vs 1.1 +/- 0.16 ng/ml, P<.001). The response of GH to N-methyl-D,-L Aspartate
(NMA), a potent agonist of the excitatory amino acids (EAA), aspartate and glutamate was dependent on photoperiod history. A highly significant immediate and sustained increase (P<.001) was observed in LD bucks within 10-min. Overall, a dose-dependent increase (P<.01) in T secretion was stimulated by NMA in both LD and SD bucks. These results suggest that daylength may also influence GH secretion in the goat and that divergent effects are exerted on GH and T secretion. Further studies were carried out to determine the contribution of pregnancy-induced suppression of LH secretion as a factor in postpartum anestrus in dairy goats. Eighteen dairy goats were injected with 5 gm GnRH i.v. on either day 140 of gestation (d -10; n = 6), day 3 (d 3; n = 5), or day 20 (d 20; n = 7) postpartum. Blood samples were obtained at 15-min intervals for 1 h followed by GnRH injection and sampling continued for 2 h at frequent intervals. Injection of GnRH on d -10, d 3 and d 20 induced LH release with
mean peak concentrations of 1.5 +/-0.4, 1.8 +/- 0.5, and 2.2 +/- 0.2 ng/ml, respectively. Baseline LH concentrations were similar across all days. Total LH concentration tended (P=.09) to increase from 6 +/-2 ng/ml on d -10 to 9+/-2 ng/ml on d 3 and reached 13 +/- 2 ng/ml on d 20 postpartum. The injection - first LH peak interval decreased (P<.01) with days postpartum averaging 55 +/- 7, 39 +/- 8 and 20 +/-7 min on d -10, d 3, and d 20, respectively. On d -10, GnRH injection stimulated a spike-like LH release while a distinctly bimodal pattern of release was observed on d 20. Area under the curve (AUC, ng/ml/h) for plasma LH increased (P <.04) with days postpartum from 0.5 +/- 0.2 on d -10 to 1 +/- 0.2 on d 20. These results indicate a progressive increase in the responsiveness of the anterior pituitary with time postpartum, suggesting that although the suppression of anterior pituitary function during late pregnancy may be reversed as early as d 3 postpartum, a marked increase in
anterior pituitary responsiveness occurs between d 3 and d 20 in the doe.
TARGET AUDIENCES: Scientific community, Animal Science faculty, students and producers
Impacts
The results provided a better understanding of the neuroendocrine basis of the goat's seasonal reproduction pattern. They also, provided basis for the development of a more cost effective technology for controlling stimuli to improve productivity.
Publications
- Amoah, E.A. 2002. Aspects of Technological Advances in Goat Reproduction. Scientific Conference on Goats. IGRC, Prairie View A&M University, Prairie View, TX. Oct 28.
- Berckman, B., Amoah, E.A., and Mobini, S. 2004. Superovulation and recovery of goat embryos during the non-breeding and breeding seasons using PG 600. International Conference on Goats, Pretoria, South Africa. July 3-9.
- Kouakou, B, Gazal, O.S., Terrill, T.H., Kannan, G., Gelaye, S., Amoah, E.A. 2008. Digestibility, hormones and blood metabolites in dairy bucks subjected to underfeeding and refeeding. Small Rumin. Res., 75: 171-176.
- Gazal, O.S., B. Kouakou, E.A. Amoah, C.R. Barb, J.B. Barrett, and S. Gelaye. 2002. Effects of N-methyl-D,L-aspartate on LH, GH, and testosterone secretion in goat bucks maintained under long or short photoperiods. J. Anim. Sci. 80:1623-1628.
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Progress 01/01/06 to 12/31/06
Outputs
Excitatory amino acid (EAA) stimulation as a regulatory factor for luteinizing hormone (LH) and other hormones including growth (GH) and testosterone were shown to be mediated through photoperiod changes in the goat. Using N-methyl-D,-L Aspartate (NMA), a potent agonist of the EAA, to test males subjected to short and long day-lengths, it was shown that LH production was mediated at the hypothalamic level through photoperiod exposure. Inhibitory photoperiod regimen i.e. long day-length for more than 30 days may be necessary to delineate the role of EAA in photoperiod-induced suppression of LH secretion. NMA also affects GH and testosterone secretion in photoperiodically stimulated bucks suggesting that day-length changes influence GH and testosterone secretion in goats.
Impacts
The results provided a better understanding of the neuroendocrine basis of the goat's seasonal reproduction pattern. They also, provided basis for the development of a more cost effective technology for controlling stimuli to improve productivity.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
Studies were conducted to determine the effect of photoperiod and glutamatergic stimulation on growth hormone (GH) and testosterone (T) secretion in bucks. Exposure of bucks to long daylength (LD) significantly reduced T secretion relative to short daylength (SD) bucks (0.41 + 0.15 vs 1 + 0.15 ng/ml, P<.01). However, GH secretion was enhanced in LD bucks (3.3 + 0.17 vs 1.1 + 0.16 ng/ml, P<.001). The response of GH to N-methyl-D,-L Aspartate (NMDA), a potent agonist of the excitatory amino acids (EAA), aspartate and glutamate was dependent on photoperiod history. A highly significant immediate and sustained increase (P<.001) was observed in LD bucks within 10-min. Overall, a dose-dependent increase (P<.01) in T secretion was stimulated by NMDA in both LD and SD bucks. These results suggest that day-length may influence GH secretion in the goat and that divergent effects are exerted on GH and T secretion. The mechanism of enhanced glutamatergic stimulation in bucks
exposed to photoinhibitory environments will be further investigated.
Impacts
The results provided a better understanding of the neuroendocrine basis of the goat's seasonal reproduction pattern. They also, provided basis for the development of a more cost effective technology for controlling stimuli to improve productivity.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
Studies were carried out to determine the contribution of pregnancy-induced suppression of LH secretion as a factor in postpartum anestrus in dairy goats. Eighteen dairy goats were injected with 5 gm GnRH i.v. on either day 140 of gestation (d -10; n = 6), day 3 (d 3; n = 5), or day 20 (d 20; n = 7) postpartum. Blood samples were obtained at 15-min intervals for 1 h followed by GnRH injection and sampling continued for 2 h at frequent intervals. Injection of GnRH on d -10, d 3 and d 20 induced LH release with mean peak concentrations of 1.5 + 0.4, 1.8 + 0.5, and 2.2 + 0.2 ng/ml, respectively. Baseline LH concentrations were similar across all days. Total LH concentration tended (P=.09) to increase from 6 + 2 ng/ml on d -10 to 9 + 2 ng/ml on d 3 and reached 13 + 2 ng/ml on d 20 postpartum. The injection - first LH peak interval decreased (P<.01) with days postpartum averaging 55 + 7, 39 + 8 and 20 + 7 min on d -10, d 3, and d 20, respectively. On d -10, GnRh injection
stimulated a spike-like LH release while a distinctly bimodal pattern of release was observed on d 20. Area under the curve (AUC, ng/ml/h) for plasma LH increased (P <.04) with days postpartum from 0.5 + 0.2 on d -10 to 1 + 0.2 on d 20. These results indicate a progressive increase in the responsiveness of the anterior pituitary with time postpartum, suggesting that although the suppression of anterior pituitary function during late pregnancy may be reversed as early as d 3 postpartum, a marked increase in anterior pituitary responsiveness occurs between d 3 and d 20 in the doe.
Impacts
The anterior pituitary responsiveness in the postpartum state could not be the limiting factor in the resumption of LH pulsability. A greater role may be played by the repletion of LH stores and possibly an enhanced GnRH receptor population.
Publications
- Berckman, B., Amoah, E.A.,and Mobini, S. 2004. Superovulation and recovery of goat embryos during the non-breeding and breeding seasons using PG 600. International Conference on Goats, Pretoria, South Africa. July 3-9.
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Progress 01/01/03 to 12/31/03
Outputs
Perfusate collections were made from in vitro hypothalamic tissue preparations from goats that were destroyed after being subjected to long (14 h Light : 10 h Dark) and short photoperiod (10 h Light : 14 h Dark) treatments. Gonadotropic releasing hormone (GnRH) profiles were developed from the collections to correlate photoperiod response, and also to establish relationship with LH profiles for the treatments. The results suggests that LH pattern is in concert with GnRH, demonstrating that the effect is exerted at the hypothalamic level. The long inhibitory photoperiod seemed to be necessary in inducing GnRH and LH suppression while the short photoperiod enhances hormonal response.
Impacts
The data will begin to provide basic information in establishing a mechanism of how day-length affects the seasonal breeding pattern of goats and consequently the development of methods of manipulating breeding efficiently in goat production
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
In October 2002, we obtained perfusate collections from in vitro hypothalamic tissue preparations from goats that were destroyed after being subjected to long (14 h Light : 10 h Dark) and short photoperiod (10 h Light : 14 h Dark) treatments. Gonadotropic releasing hormone (GnRH) profiles will be developed from the collections to correlate photoperiod response, and also establish a relationship with LH profiles for the treatments.
Impacts
The data will begin to provide basic information in establishing a mechanism of how day-length affects the seasonal breeding pattern of goats
Publications
- No publications reported this period
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