Cyathostomins are the most prevalent equine intestinal parasites and resistance has been reported in these nematodes against all 3 licensed anthelmintic classes. Strategies need to be developed that are less dependent upon drugs and more reliant on management-based control. To develop these we need to understand natural transmission patterns better. Here, we analysed longitudinal fecal egg count (FEC) data from 5 pony populations used for conservation purposes. We tested how egg excretion varied amongst populations and individuals, and how this was affected by age and climate. There was evidence for consistency in FECs over time at the individual level; this was generally weak and accounted for <10% of the total variance. Animals <5 years old had higher FECs and there was profound seasonal variation in FECs, with highest levels recorded in spring/summer. Effects of monthly temperature and rainfall explained most, but not all, of the observed seasonal variation and associations between climate measures and FECs were stronger in younger versus adult animals. One population was occasionally treated with anthelmintics and analysis of this population suggested that treatment substantially altered the seasonal dynamics. This paper highlights the variability in strongyle egg excretion amongst individuals and the factors involved in this variation.

Quantitative aspects of follicle initiation and development have been studied in a series of N-type and New Zealand Romney foetuses. Density of the follicle population and ratios of secondary to primary follicles were examined on 13 positions of the body which covered the main wool-bearing areas, the face and head, and the limbs. Primary follicle development is initiated first on the head and limbs and throughout subsequent development these regions are most advanced. Primary follicle density reaches a maximum between 75 and 90 days of foetal age, after which it decreases as a result of skin growth. Secondary follicle initiation is more rapid on the wool-bearing areas of the body, and higher ratios of secondary to primary follicles are recorded from these regions. No real differences have been found between N-type and New Zealand Romney foetuses in population density of the different follicle types at any age or in the number of secondary follicles developed per primary follicle. The growth of larger primary fibres and follicles in N-type foetuses is not accompanied by, and does not result from, a lower density of primary follicles. There does not appear to be any marked relation between the decreasing density of primary follicles after 90 days of foetal age and the initiation of secondary follicle anlagen. This fact, and the absence of any differences in the number of secondary anlagen formed per primary follicle in N-types, suggest that crowding in N-types is not a limiting factor in the formation of secondary follicle anlagen.

The rates of entry of cystine into the extracellular compartment, and the concentrations of cystine in this compartment, were measured during 12-14 hr infusions ofL-[35S]cystine in Peppin Merino ewes_ The ewes were sampled from flocks selectively bred for high or low clean fleece weight per head; and were fed either 500 or 1100 g of chaffed lucerne hay daily during the experiment.The mean entry rate of cystine was similar for sheep in the two flocks, but was greater in those sheep eating the 1100 g of lucerne daily (73 v. 35 mg/hr: P < 0·05). The concentration of free cystine in the plasma was approximately 20% less in those ewes from the flock selected for high clean fleece weight, relative to those selected for low clean fleece weight (P < 0·05). Although the concentration of free cystine in plasma increased with the amount of feed given (P<0'05), the difference between the flocks was independent of feed intake.The proportion of the cystine disulphide bound to plasma proteins relative to total cystine in the plasma decreased as the amount of feed given increased (P < O· 05), but the proportion was similar for the two flocks. The [35S] activity associated with sulphate sulphur increased linearly between 4 and 14 hr of infusion, with no significant differences in the slopes of the regression coefficients between flocks or levels.The conclusion was drawn that genetic differences in efficiency of conversion of food into wool resulting from selective breeding for fleece weight were not associated with differences in the entry rate of cystine.

Growth, and the relative growth gradients over the body, have been studied in N-type and normal Kew Zealand Romney foetuses. Body weights, and a series of linear measurements taken between different points over the body, have been obtained from a series of foetuses of known ages. Huxley's allometric growth ratios have been calculated from these measurements by using the least squares regression. There are no significant gromth differences between foetuses belonging to the different AT-genotypes of the New Zealand Ronmey. Foetuses belonging to the New Zealand Romney and some British breeds grow at a faster rate than South African Merino foetuses studied by Malan and Curson (1936a) and Cloete (1939). Relative growth gradients over the body are, in general, similar to those of other mammals, but the results do not support the theory of Cloete (1939), that the relative growth rate of a part of the body is solely a function of the age of the part.

The dominant and recessive mimic genes N and nr produce increased birthcoat hairiness in New Zealand Romney lambs. This hairiness has been studied in lambs of different genotypes by three different methods. It has been found: (i) that in individual lambs there is a gradient in hairiness from the shoulder patch to the britch; (ii) increases in hairiness with increasing dosage of the N and nr genes conform to this gradient; (iii) with any single increase in N-gene dosage there is a differential rate of increase in hairiness on different positions. These results are explained on the hypothesis that the primary gene action is linear, but the gradient is modified by a threshold and possibly by a ceiling effect in the production of birthcoat medullation.