A study of sweat gland characters and their relationship to adaptation in Jersey cattle.

Abstract

A STUDY OF SWEAT GLAND CHARACTERS AND THEIR RELATIONSHIP TO ADAPTATION IN JERSEY CATTLE J. S. F. BARKER* and T. NAY I. INTRODUCTION Nay and Hayman (1956) showed differences in sweat gland morpholog y between European cattle (Bos taurus L.) and Zebu-type cattle (Bos indicus L.). This finding has been extended by Nay and Dowling (1957), Nay (1959), and Walker (1960). Sweating ability is important in heat regulation (Ferguson and Dowling 1955; Dowling 1958), and sweating activity increases generally with gland volume (Hayman and Nay 1958). The Jersey is apparently more heat tolerant than other European dairy breeds (Seath and Miller 1947; Maule 1952), so that its sweat gland morphology is of particular interest. The Australian Jersey breed descends largely from animals imported since 1900 from cool temperate countries, particularly the Island of Jersey, the United Kingdom, and New Zealand (Barker 1957, 1959). Although the herds in this study are all located in a temperate climate, extremes of heat occur in the summer months. Assuming then that imported Jerseys are less well adapted to this climate, relationship to imported animals provides a measure of opportunity for adaptation. As adaptation, due to natural and/or artificial selection, is likely to involve changes in sweat gland dimensions (Nay 1959), correlations between these and relationship to imported animals may provide evidence of such adaptation. II. MATERIAL AND METHODS Between 7th July and 4th August, 1959, skin samples were collected from 285 mixed-age registered Jersey cows in ten herds within 30 miles of Sydney, New South Wales. They had at least commenced their first lactation at the time of sampling. The relationship (R) of each to imported animals was determined from its four generation pedigree. Collection and histological techniques were as described by Nay and Dowling (1957), with the modification of Nay (1959). Ten glands per animal were measured, four measurements being made on each: one of length, and three of width at three positions along the length. In calculating the volume, each gland was treated as a cylinder of length equal to the measured length of the gland (L), and diameter equal to the mean of the three width measurements (D). Gland shape has been expressed numerically as the ratio L/D. The means of the ten measurements of each of L, D, L/D, and volume in each animal were used in all analyses as estimates of gland characters. All measurements were done by one of us (T.N.). Nay and Dowling (1957), and Hayman and Nay (1958) have shown the repeatability of these gland dimension measurements in duplicate skin samples to be very high (80-90%). *Department of Animal Husbandry, University of Sydney, Sydney, N.S.W. tC.S.I.R.0. Division of Animal Genetics, Delhi Road, North Ryde, Sydney, N.S.W. 173 TABLE 1 Means and standard deviations of the four sweat gland characters, relationship to imported animals (R), and age at sampling for each of the ten herds sampled (listed in order of increasing mean R). Fig. 1. -Various types of sweat glands found in Jerseys. III. RESULTS (a) Sweat gland morphology The morphological results are summarized in Table 1, types of sweat glands found in Jerseys are shown in Figure was some variation in length and diameter, most animals had which can be considered characteristic of the breed (Nay volume plotted against L/D are presented for each herd in while the various 1. Although there small baggy glands, 1959). Graphs of Figure 2. (b) Adaptation Some of the sampled herds had a low average relationship to imported animals, others a high relationship (Table 1). The total number of imported animals in the pedigrees was 120, with 77 of these in the ancestry of animals in one herd only, 21 in 2 herds, 9 in 3 herds, 7 in 4 herds, 2 in 5 herds, and 4 in 6 herds. Differences between herds may therefore have been partly due to the different samples of imported animals contributing to each. Correlation coefficients among the six variates are given in Table 2. The regressions of sweat gland characters on relationship and age did not differ significantly from herd to herd, as indicated by comparing the deviation from average regression with the residual variance. Accordingly, the pooled withinherd coefficients in Table 2 were calculated. The correlations among the four sweat gland characters show that herd differences do not contribute to the overall correlations. However, the betweenherd correlations for the sweat gland characters and relationship are positive (0.45, O-36, 0 a 11, and 0 -47 for L, D, L/D, and volume respectively), while those for the sweat gland characters and age are `negative (-0~57, -0.42, 175 Fig. 2.-Distributions of volume plotted against L/D for each of the ten herds sampled. 176 TABLE 2 -057 in the same order as above), None of these between-herd correlations are significant, as they are based on only ten herds. However, for herd means, higher age implied lower relationship to imported animals, and smaller sweat gland dimensions. This, of course, does not imply any causal relationship, but it does result in the between-herd and within-herd correlations of sweat gland characters with relationship being of opposite sign (except for L/D). In this case, the within-herd correlations, where these herd differences in average age are discounted, are more meaningful. Since variation in age at sampling could have affected the within-herd correlations between gland characters and relationship, partial correlation coefficients, holding age constant, were also calculated. Those between D and R (-O-14), and volume and R (-O* 12) are both significant (P<O.O5). -0.16, an d The within-herd correlation coefficients (Table 2) also suggest strongly that gland size increases with age. The regressions of sweat gland characters on age TABLE 3 177 Fig. 3.-Photomicrographs of horizontal sections of cattle skin showing sweat glands in cross section. Magnification 75 X approx. a - sweat glands, b - hair follicles, c - blood vessels. ( 1 )-Sahiwal. (2)-Jersey. 178 at sampling are 0.12 p/month for L and D, O-05 for L/D, and Oe21 ~3 x 10-h/ month for volume. (c) Heritability of sweat gland characters Among the animals sampled, there were 228 paternal half-sisters, the progeny of 49 sires, located in nine herds. The number of daughters per sire ranged from 2 to 15, the weighted average number per sire calculated according to the formula of Wearden (1959) being 4.7 1. Each sire, however, was represented in only one herd. Estimates of heritability were obtained from the within-herd correlations between paternal half-sisters (Fisher 1948). Analyses of variance and estimates of heritability obtained are given in Table 3. The estimates for diameter and volume are significantly different from zero. IV. DISCUSSION Small baggy glands are characteristic of the Jersey breed, as only a few animals had an L/D over 10 (Fig. 2). Also, only a few had gland volumes over 10 units, which brings them within the size range of the glands of Sindhi and Sahiwal (B. indicus) breeds. These baggy glands, especially in animals with larger glands (Figure 3 (a) and (b)), result in the 'honeycombed' skin structure characteristic of Sindhi and Sahiwal animals (Nay 1959), and support the hypothesis that the Jersey breed may have had Zebu-type cattle among its ancestors (Boston 1954). There is no historical evidence for such a relationship, but it is also supported by the distribution of bovine haemoglobins in different breeds (Bangham 1957; Blumberg 1958). Alternatively, the small baggy gland of the Jersey may be the primitive type, from which the large baggy gland of the Zebu has developed. Nay and Dowling (1957), and Nay (1959) found that in Shorthorns selected for heat tolerance, gland volume had increased due to a lengthening of the coiled tubular glands typical of this breed. In Jerseys with typically baggy glands, adaptational changes may proceed differently. In this sample of Australian Jerseys, those which have had the greatest opportunity for genetic adaptation, that is, those with a low relationship in recent generations to imported animals, have wider and more voluminous sweat glands (partial correlations, R and diameter -0.14, R and volume -0.12). The high heritabilities for gland diameter (0.60 -t- 0.26) and volume (0.47 2 0.25) further support the hypothesis that adaptive selection is favouring Jersey animals with larger Zebu-type glands. V. ACKNOWLEDGMENTS We are indebted to those Jersey breeders who generously allowed us to take skin samples from their animals, and for their assistance during this sampling, and to Mr. L. N. Balaam, Department of Agriculture, University of Sydney, for statistical advice. Thanks are due to Robyne Spalwit, Dorothy Allingham, Gillian Davey, and Robin Johnston for technical assistance. This study was supported in part by a University of Sydney Research Grant. VI. REFERENCES B ARKER J. S. F. , ( 1957). 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