Analyses of the variation in the interval from an injection of prostaglandin F2α to oestrus as a method of studying patterns of follicle development during dioestrus in dairy cows

Lactating dairy cows experiencing normal oestrous cycles were injected once with either 0.5 mg of an analogue of prostaglandin F_2α (PGF) (Cloprostenol, 435 cows) or 25 mg of a PGF-Tham salt (237 cows) when at days 7–16 of the cycle (oestrus = day 0). In these two trials, 91% and 93% of the cows were detected in oestrus from 3–10 days post-injection increasing from 81% to 98% with advancing dioestrus. Over 70% of detected cows injected on day 7 (early dioestrus) or day 16 (late dioestrus) were in oestrus from 48 to 72 h post-injection. Comparable response rates among cows injected on days 11 and 12 (mid-dioestrus) were less than 30% with most response intervals being at 4 and 5 days post-injection (73 h–120 h). The variability in response intervals generally decreased with advancing dioestrus. A regression model for ordinal data, with post-injection interval to oestrus as the ordinal response and stage of cycle at injection as the explanatory variable, showed that both the interval to oestrus and the variation in this interval varied with the stage of cycle at injection.These response intervals appear to reflect a wave-like pattern in ovarian follicle development during dioestrus. The probability of the presence of a follicle in a less advanced stage of development at the time of PGF injection is greatest among animals treated during mid-dioestrus.     

The abdominal motor system of the crayfish, Cherax destructor. II. Morphology and physiology of the deep extensor motor neurons

Two opposing muscle systems underlie abdominal contractions during escape swimming in crayfish. In this study we used extracellular and intracellular stimulation, recording and dye-filling to systematically identify each of the five deep extensor excitors and single inhibitor of the crayfish, Cherax destructor. Functional associations of each neuron were characterised by recording its responses to sensory and abdominal cord inputs, its extensor muscle innervation pattern, and its relationships with other neurons. Each excitor receives excitatory input from the tonic abdominal stretch receptors and the largest neuron also receives input from the phasic stretch receptor. The two largest excitors innervate the muscle bundle containing the fastest fibres and may be electronically coupled. The smaller neurons may also be electronically coupled and innervate the remaining deep extensor fibres which display dynamic characteristics from fast to medium-fast. The inhibitor does not receive input from the stretch receptors, but is strongly excited by tactile afferents. The implications of these findings for the current models of the control of abdominal tailflips and swimming are discussed. Accepted: 21 June 1998     

Effects of benzyl alcohol on the bovine oestrous cycle and subsequent fertility

A uterine infusion varying in volume from 5 to 40 ml and containing from 0.5 to 2.0 ml of benzyl alcohol shortened the length of the oestrous cycle in cows treated in the early luteal phase and prolonged the oestrous cycle in some cows in the late luteal phase. Results with 399 infusions produced a concentration of cows in oestrus from 8 to 13 days after treatment. The conception rate for 198 inseminations at the first post-treatment oestrus was 59.6% compared to 59.2% obtained in 471 untreated cows.     

Plasma gonadotrophins, prolactin and corticosterone concentrations in male mice exposed to high altitude

Groups of sexually-naive male NFR/N mice were maintained at sea level or exposed to simulated altitudes of 18 000 ft (5486 m) or 22 000 ft (6705 m) for 1, 3, 7, 14 or 28 days. Plasma LH concentrations were slightly but not significantly depressed after 1 day of hypoxia. Plasma FSH values were reduced (P < 0.05) after 1, 7, 14 and 28 days of exposure to 22 000 ft when compared to the values in the other groups. Prolactin concentrations fluctuated considerably, but were not uniformly affected by high altitude exposure. Exposure to 18 000 ft resulted in an elevation of plasma corticosterone concentration (P < 0.05) for 3 days, which was followed by a decline to control group values, whereas at 22 000 ft corticosterone levels remained elevated. These findings indicate that plasma LH values are transiently reduced during the initial 24 h of exposure to high altitude and that plasma FSH concentrations are depressed in a sustained manner during severe hypoxia.