Calving rates in a tropical beef herd after treatment with a synthetic progestagen, norgestomet, or a prostaglandin analogue, cloprostenol

Maiden heifers and lactating cows of known ovarian status and of several breeds were treated with a synthetic prostaglandin, cloprostenol, or a synthetic progestagen, norgestomet, at the start of an artificial insemination (AI) program. Animals in the cloprostenol treatment received 2 injections 10 days apart. Over the next 26 days those animals that showed oestrous behaviour were inseminated. Synchronisation rates and calving rates to insemination over the first 7 days were calculated. Those in the norgestomet treatment received an implant of norgestomet plus an injection of norgestomet and oestradiol valerate. The implant was removed 10 days later and the animals were given an injection of pregnant mare serum gonadotrophin (PMSG). They were inseminated at 48 h (maiden heifers) or 56 h (lactating cows) after implant removal. Calving rates to fixed-time insemination were recorded. After completion of the AI program the animals in both treatments were joined with bulls. Overall calving rates (AI plus bulls) were calculated. By day 7 of the program, 82% of the maiden heifers and 76% of the lactating cows in the cloprostenol treatment had been detected in oestrus. By day 21 the respective figures were 99% and 81% Norgestomet treatment had an immediate and a prolonged effect on ovarian activity in those females classified as having inactive ovaries at the start of the AI program. Calving rates of those females to fixed-time AI and overall were similar to those of the females with active ovaries in both treatments. Their calving rates to fixed-time insemination, and overall calving rates for the lactating females, were significantly higher than the corresponding values of their contemporaries treated with cloprostenol and inseminated on observed oestrus over 7 days. For those females classified as having active ovaries at the start of the AI program, calving rates to first insemination and overall were similar for both treatments. Overall calving rates of lactating cows of each breed were, with one exception, higher in the norgestomet treatment than in the cloprostenol treatment. Although norgestomet treatment was more expensive than cloprostenol treatment, the advantage in calf crop resulted in an overall monetary advantage to the norgestomet treatment.     

Guidelines for the future of equine locomotion research

This paper describes the major areas that require investigation in equine locomotion and outlines a plan for such research in both the Thoroughbred and Standardbred. Fifteen topics for future investigation have been selected and given an order of priority. These topics deal with characteristics of normal locomotion, factors which influence locomotion, the epidemiology and economics of lameness and the clinical identification of lameness.     

The effect of artificial photoperiod at the end of the breeding season on plasma testosterone concentrations in stallions

Testosterone concentrations in stallions showed a seasonal trend with peak concentrations in the spring (April and May in Britain) and lowest concentrations in the period from December to February. The effect on this pattern of changing the length of the photoperiod at the end of the normal breeding season (mid-summer's day) was studied in 2 experiments. In the first experiment artificial illumination was organised from 21 June to mimic the effect of transfer to a southern hemisphere spring and summer, that is short days becoming longer. The stallions had low concentrations of testosterone in February and high concentrations in April. Concentrations in July, August and September were extremely low with a return to high values in late November/early December. In the second experiment, illumination was maintained at the equivalent of a 16 1/2-hour day from 21 June to mid December. These stallions had high testosterone concentrations in April, after which they fell until August, later rising to a maximum in October. These results are discussed in relation to transfer of stallions between the northern and southern hemispheres.     

Lymphocyte alterations in zinc-deficient calves with lethal trait A46

Lymphocyte numbers and activities were evaluated at 2, 4, 8 and 12 weeks of age in two calves with lethal trait A46 (A46), a genetic disorder affecting intestinal zinc absorption. Plasma zinc concentrations declined to subnormal by 3 weeks of age, after which anorexia, diarrhea, alopecia and hyperkeratosis occurred. Lymphocyte response to phytohemagglutinin-P (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) stimulation was variably reduced. CD4+ T-lymphocytes were subnormal on at least one observation period following onset of zinc deficiency, and relative numbers of B lymphocytes were decreased at 8 weeks. Secondary antibody responses to bacteriophage phi X 174 were significantly reduced. The results demonstrate that calves homozygous for the A46 trait have normal numbers of functional lymphocyte subpopulations at birth, and that the activity of their lymphocytes is altered once the calves become zinc deficient.