Between March and August 1968 to 1970, Chlormadinone acetate (CAP), 10 mg/head/ day, was administered to 668 Zebu cows and heifers for oestrous cycle synchronization for 14, 12, or 9 days, the latter schedule supported by an injection of 5 mg estradiol valerate on day 2 to achieve luteolysis. Applied orally over a period of 14 days, CAP provided a reliable method for cycle synchronization. The severe anoestrous rate experienced in all herds reduced the overall percentage of synchronized animals. Fertility from insemination during the first synchronization period (day 2 to 10 after treatment) was slightly, yet insignificantly reduced, but was completely restored during the second synchronization period (day 20–30). Insemination only during this second synchronization period resulted in conception and pregnancy rates similar to those combined from the first and second synchronization period.

Of factors tested for influencing synchronization and fertility, presence or absence of penis-deviated teaser bulls (psycho-stimulation) had no effect on the percentage of animals synchronized, or on post-treatment fertility. In well-managed herds, the percentage of animals responding to treatment was predetermined by the number of animals already cycling, reflecting their phase of reproductive life. Levels of management had an important impact on the success of cycle synchronization combined with artificial insemination. Both methods are managerial tools for improvement of already good management. Their failure under insufficient management conditions has diagnostic value.

Possibilities and limits shown for oestrous cycle synchronization in Zebu cattle were similar to those reported in European cattle. Within these limits, CAP can be employed successfully as a means for cycle synchronization, providing sufficient synchronization and acceptable fertility and allowing economical use of artificial insemination.

Two hundred and forty mature Merino ewes were used in a factorial experiment to investigate the effects of single injections of either 0, 40, 80 or 160 mg progesterone on the length of the subsequent oestrous cycle. Equal numbers of ewes (15 per group) received subcutaneous and intramuscular injections, and equal numbers were treated either on the day of oestrus or the following day.

Oestrous cycle length was significantly reduced in all treated groups, with a minimum cycle length of 7–10 days following treatment with 80 or 160 mg progesterone. Neither route of administration nor day of treatment significantly affected the response. The conception rate achieved by treated ewes at the first post-treatment oestrus did not differ significantly from that in comparable controls.

The results suggest that a single massive dose of progesterone on the day of oestrus is an effective means of shortening the oestrous cycle of the ewe without loss of fertility.

In the first paper of this series it was shown that Lolium perenne material required hardening periods involving low, but above freezing, temperatures before frost tolerance was achieved. The present experiments show that the light conditions during the hardening and prehardening periods are also important. At both stages a reduction in total light energy reduced subsequent cold tolerance but the relative effects of light intensity and photoperiod differed between the prehardening and hardening treatments. Thus low light input during the hardening period at 2 CC reduced cold tolerance most when given at higher intensities over shorter days (8 h) while during the prehardening growing period at 20 °C the reduction was greatest when the lower light input was given at low intensity over longer days (16 h).

Varieties of different climatic origins reacted differentially to the treatments. The Mediterranean variety Fano was particularly adversely affected by low light intensities during hardening and also benefited from higher temperatures during the prehardening growing period. With higher light intensities and higher growth temperatures this Mediterranean variety approached the more northern material in cold tolerance; but as a corollary it was clear that the N. European variety Veja was able to harden under lower light conditions, and lower growing temperatures. The varieties Melle and S. 321 from intermediate latitudes, were intermediate in response.

Although water soluble carbohydrate content was increased during the hardening period, except at the lowest light intensity (2·9 W/m2), no simple relationship between the WSC content and the cold tolerance of the different varieties could be detected.

The results provide a useful guide to the pre-treatments necessary to discriminate between varieties for cold tolerance in such a way that the results can be correlated with field performance.

Detached, fully turgid leaves of S. 24 perennial ryegrass were sprayed with 1, 3 and 5 mg of a solution of 85% formic acid per leaf and dried in controlled conditions (temperature 28 ± 1 °C, relative humidity 22 and 64%, air speed 40 cm/s). The lowest rate of application increased the rate of leaf drying approximately four times when the relative humidity was 64%. Increasing the rate of formic acid or reducing the relative humidity to 22% did not enhance the drying further. The mode of action of formic acid is discussed. It is suggested that formic acid might be utilized to obtain quicker drying of grass for hay, and further investigations are called for.