Reproduction in Domestic Animals

218 BS Prakash, M Sarkar and M MondalProgesterone, LH (ng/ml)4.03.53.02.52.01.51.00.50.0Progesterone LH GHGroup-I Group-II Group-III Group-IV Group-V Group-VIGroupsFig. 1. Changes in plasma progesterone, LH and GH for consecutive6 weeks in mithuns of six different age groups from birth throughadulthood. Group I (0–3 months; n = 9), group II (>3–6 months;n = 7), group III (>6–12 months; n = 11), group IV (>12–18months; n = 10), group V (>18–24 months; n = 10) and group VI(>24–31 months; n = 12). Blood samples were collected from allanimals for six consecutive weekspulses occur at frequent intervals throughout the dayand night and alterations in GH levels and patternsare elicited more by pulse amplitude than frequencymodulation. LH pulses occurred at an average rate of0.54 ⁄ h (5 pulses ⁄ 9 h). The mean plasma LH levelwas correlated with body weight (r = 0.82; p < 0.05)and pulse amplitude in growing mithuns (Mondalet al. 2005c). There was higher LH concentrationswith higher pulsatility and greater amplitude in prepubertalmithuns than exhibited in growing mithuns(Mondal et al. 2005e). Our results showed increasingtrend of plasma progesterone and LH concentrationsin the process of onset of puberty in mithun (Fig. 1).Plasma GH levels were recorded to be doubled duringpubertal process (Fig. 1). The optimum LH pulsefrequency and amplitude required for onset of pubertyin mithun were ‡9 pulses ⁄ 24 h and ‡1.6 ng ⁄ ml,respectively.Possible use of GH-releasing factor as an inducer ofpubertyKeeping in view the promising results obtained recentlyof using exogenous GH-releasing hormone (GHRH)for growth enhancement (Mondal and Prakash 2004)and the suggestion of Gelato and Merriam (1986) thatGHRH being active in a wide range of species andhence its treatment could potentially be used toaccelerate growth of animals of commercial importance,we first standardized the dosage of GHRH inmithun (Mondal et al. 2006c) and then went on to testthe effects of exogenous GHRH on secretion patternsof GH and LH as a preliminary study for the first timeever in this ruminant species (Mondal et al. 2006e).Our results suggest that 10 lg GHRH per 100 kg BWis the dosage, which can be used for augmentation ofmithun production. Using this dosage, GHRH wasfound to increase plasma GH and LH pulse frequencyand amplitude with higher mean LH levels in growingmithuns suggesting the possibility of using such strategyfor enhancement of maturity and ⁄ or pubertyprocess in this species.160140120100806040200GH (ng/ml)Endocrine Changes Associated withReproductive Processes in Yaks and MithunsRelationship of plasma oestradiol-17b, total oestrogenand progesterone to oestrous behaviour in mithun cowsWe carried out studies to (1) establish the characteristicsof oestrous behaviour in mithun cows and (2) determinethe relationships between this behaviour and theplasma concentrations of oestradiol-17b (E2), totaloestrogen and progesterone. Among the behaviouralsigns of oestrus, the cow to be mounted by bull (100%)was the best indicator of oestrus followed by standing tobe mounted by other females (92% Mondal et al.2006b). Rectal examination of the reproductive tractrevealed a relaxed cervix, turgid uterus and ovarieshaving palpable follicles in all animals (Mondal et al.2006g). The length of oestrous cycle and duration ofoestrus were recorded to be 21.8 ± 0.69 days and12.6 ± 1.34 h, respectively. E2 and total oestrogenprofiles during the peri-oestrous period (Mondal et al.2006f) showed that the mean highest peak concentrationsof E2 (27.29 ± 0.79 pg ⁄ ml) and total oestrogen(45.69 ± 2.32 pg ⁄ ml) occurred at 3.90 ± 2.27 and3.89 ± 2.26 h prior to the onset of oestrus, respectively(Fig. 2a). Plasma progesterone concentration was basal(0.14 ± 0.001 ng ⁄ ml) during the peri-oestrous period.Plasma E2 and total oestrogen were found to increasefrom 6 days before oestrus to reach a peak level on theday of oestrus and decline thereafter to basal level onday 3 of the cycle (Fig. 2b). The plasma progesteroneconcentration was the lowest on the day of oestrusshowing gradual increase to register a peak level on day15 of the cycle.Plasma prolactin and oxytocin profiles during cyclicity inmithun and yak cowsIn yaks the plasma prolactin concentration althoughhigh at oestrus, its level fluctuated throughout the cycle,without any definite trend (Sarkar 2004).In mithuns, the plasma prolactin concentration washigh at oestrus and showed fluctuation thereafter withno definite trend throughout the cycle (Mondal et al.2007a). Results on prolactin profile suggest an involvementof prolactin in the ovulation process in this species.The mean plasma oxytocin concentration duringdifferent days of the oestrous cycle was found to besignificantly different (p < 0.001; Mondal et al. 2006d).The plasma oxytocin concentration was low at oestrus.In mithun cows, two peaks of oxytocin were recorded ondays 6 and 18 of the oestrous cycle.Timing of ovulation in relation to onset of oestrus and LHpeak in mithun cowsMondal et al. (2006g) found that the preovulatory LHsurges in mithun cows consisted of several pulses(2.92 ± 0.26 pulses ⁄ animal). The peak level of LH forindividual mithun varied from 6.99 ± 0.44 to 12.69 ±2.10 ng ⁄ ml. The concentration of LH during surge was10.83 ± 0.76 ng ⁄ ml. The duration of LH surge was6.98 ± 0.22 h. LH surge started 1.23 ± 0.18 h afteronset of oestrus. Ovulation occurred at 26.92 ± 0.31Ó 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag