Plasma LH levels and the effects of ovariectomy and of chronic and acute administration of oestradiol-17 beta were compared in post-partum (anoestrous) and cyclic Merino ewes during the breeding season. Plasma LH and LH pulses were detected in more post-partum (anoestrous) than cyclic (dioestrous) ewes (10/10 and 4/10 respectively). The post-partum ewes had a greater pulse frequency (1.8 +/- 0.42 compared with 0.4 +/- 0.16 pulses/6 h) and higher plasma LH levels (1.16 +/- 0.32 compared with 0.17 +/- 0.05 ng/ml). Ovariectomized post-partum ewes demonstrated fewer LH pulses (3.8 +/- 0.36 compared with 5.0 +/- 0.15 pulses/6 h) than did ovariectomized cyclic ewes. The depression of plasma LH following acute i.v. injection of 3 micrograms oestradiol-17 beta was similar (0.05 < P < 0.1) for the two groups (80.5 +/- 3.6 and 66.3 +/- 4.1%). At 7 days after ovariectomy and an oestradiol implant more cyclic ewes than post-partum ewes showed detectable plasma LH and LH pulses (6/10 compared with 1/9 ewes). By 66 h after implant removal pulse frequency was less in the post-partum ewes (3.2 +/- 0.55 compared with 5.5 +/- 0.56 pulses/6 h). These findings indicate that in post-partum ewes there is an increased inhibitory (negative-feedback) effect of oestradiol on LH release and a lower intrinsic frequency of pulsatile release of LH. These factors may be casually related to ovarian acyclicity.
The relationship between pituitary responsiveness to exogenous LH-RH, return of oestradiol-17 beta-induced positive-feedback effect on LH release and the resumption of oestrous cycles were studied in Merino ewes lambing in the breeding season. The mean (+/- s.e.m.) increase in plasma LH 2 h after 50 micrograms LH-RH i.v. was reduced (P < 0.001) in ewes tested in the last 4 weeks of pregnancy (8.6 +/- 2.1 ng/ml, N = 29) but was similar (P > 0.05) for non-parturient dioestrous ewes (N = 31) and for anoestrous ewes tested around 14 (N = 50) and 28 (N = 51) days post partum (30 +/- 3.9, 37.8 +/- 4.0, 39. 0 +/- 3.2 ng/ml, respectively). Oestradiol-positive feedback was absent in 68.6% (35/51) and 54% (27/50) of ewes tested around 14 and 28 days post partum, respectively. Neither LH-RH responsiveness nor the presence of oestradiol-postive feedback was related to the incidence of 61.9%, 166/268) or interval to (62 +/- 2.2 days, N = 99) first oestrus post partum. We suggest that these endocrine responses do not represent factor limiting the resumption of ovarian cyclicity post partum.
A hexaploid triticale from Mexico and local cultivars of wheat, rye and barley, each at five levels of fertilizer nitrogen (0, 35, 70, 105 and 140 kg N/ha) with four replications, were grown in a field experiment at Mintaro, South Australia. A visually discernible response to nitrogen fertilizer by all four genotypes from an early stage was confirmed by quantitative sampling at tiliering, anthesis and maturity. Responses in plant dry weight to 105 kg N/ha were maintained until anthesis but grain yield responses were significant only at 35 kg N/ha. Total dry matter production responses at maturity to more than 35 kg N/ha were small. Numbers of tillers and heads were increased by nitrogen additions up to 140 and 105 kg N/ha, respectively, and plant height measurements showed general increases to 70 kg N/ha with significant lodging at higher nitrogen levels in both rye and triticale. For all genotypes, thousand grain weight decreased with increasing level of nitrogen supply while grain and straw nitrogen increased up to levels of 140 and 105 kg N/ha, respectively. Nitrogen supply had little effect on maturity, plants at 0 and 140 kg N/ha reaching anthesis less than a day apart. The lack of a significant nitrogen x genotype interaction in nearly all the data suggests that the triticale does not differ in its nitrogen nutrition from the traditional cereals. Triticale consistently outyielded the other cereals in total dry matter production followed by the rye, wheat and barley in that order. Grain yield was highest in the wheat and least in the rye, the latter also being the least responsive to nitrogen. The advantage of the triticale lay in its high grain protein and lysine content combined with good yield.
Summary. The administration of LH-RH in a pulsatile regimen (100 ng i.v./h for 48 h) to acyclic ewes 26\p=n-\30 days post partum increased plasma LH concentrations, and both the frequency and amplitude of plasma LH pulses. In 12/14 ewes these increases were followed by plasma LH surges similar to the preovulatory surges observed in 10 control cyclic ewes. Subsequent luteal function in the post-partum ewes was deficient. Plasma progesterone was detected in 7/12 post-partum ewes showing plasma LH surges. The concentrations were lower (1\m=.\3\ m=+-\ 0\m=.\2 ng/ml) and detected for shorter periods (3\p=n-\10 days) than in cyclic ewes (2\m=.\4\ m=+-\ 0\m=.\2 ng/ml, 12/15 days). In the post-partum ewes the increases in plasma LH concentrations before the LH surge were higher but of shorter duration than in the cyclic ewes. The inadequate luteal function in the post-partum ewes could therefore have been due to inappropriate LH stimulation of the ovary before the LH surge.
Ovulation was studied in a flock of medium Peppin Merino ewes known to show little seasonal variation in the incidence of twin births. In the absence of rams, ovarian activity was lowest in the spring and highest in the autumn, but the proportion of twin ovulations did not vary significantly from a constant level throughout the year. The incidence of twin ovulations, following an advanced onset of the breeding season, initiated by the sudden introduction of rams in the early summer, did not differ from that occurring during the 'natural' breeding season.
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