Small Ruminant Research, 2 (1989) 367-374 367 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Morphometr ic Studies on Horn Glands of N iger ian Breeds of Goat

D.O. CHUKWU and E.C. IHEMELANDU

Department of Veterinary Anatomy, University of Nigeria, Nsukka (Nigeria)

(Accepted 6 September 1988)

ABSTRACT

Chukwu, D.O. and Ihemelandu, E.C., 1989. Morphometric studies on horn glands of Nigerian breeds of goat. Small Rumin. Res., 2: 367-374.

Twelve goats (six males, six females), four West African dwarf goats (WADG) and two red Sokoto goats (RSG) per group, were studied. The age ranged form 1 to 3 years. Skin samples were taken from the head area, caudomedial to the horns (horn glands), and from ten other areas of the body. Samples were fixed in formol calcium and alcohol. Thick free-hand sections were stained with Celestine blue and preserved in Canada balsam. Routine paraffin wax sections were stained with hematoxylin and eosin (H and E). The H and E stained sections were projected at a mag- nification of 200 × and sebaceous gland sections were traced on graph paper.

Sebaceous glands in the horn glands showed significantly larger cross-sectional areas than se- baceous glands elsewhere in the body, but anatomically they were similar to them. Ducts of the sebaceous gland of horn glands usually open into hair follicles but a few ducts open on the surface. The cross-sectional area of sebaceous glands in the horn glands was significantly larger in males than in females and larger in WADG than in RSG.

INTRODUCTION

Male W e s t Af r i can d w a r f goats ( W A D G ) a n d to a lesser ex ten t , ma le red Soko to goats ( R S G ) s p r e a d an of fens ive odor. T h i s odor is respons ib le for cha rac t e r i s t i c s o f goat pens . Sec re t ion of modi f i ed sebaceous g lands is be l ieved to be invo lved in th i s odor p r o d u c t i o n (B rouwer a n d N i j k a m p , 1952; S a r a n d Ca lhoun , 1966; J e n k i n s o n e t al., 1967; Ba l a n d Ghosha l , 1976). F r e n c h (1970) inc luded the p r e se nce of od i fe rous tai l g lands in t he ma le as one of t he char - ac te r i s t ics of I t a l i an goats , bu t it was no t s t a t ed w h e t h e r these tai l g lands were sebaceous glands. S a r a n d C a l houn ( 1966 } descr ibed large, b r a n c h e d alveolar , s ebaceous g lands a t t he base of h o r n s a n d ears , a t the j unc t ion of hoo f and skin, a n d in t he pe r inea l region of A m e r i c a n goats . J e n k i n s o n e t al. (1967) no t ed t h a t the odor in Br i t i sh S a a n e n goats m a i n l y c a m e f r o m en la rged sebaceous

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glands of the head and neck. Bal and Ghoshal (1976) reported that the cross- sectional diameter of sebaceous glands in horn glands in American goats was larger in males than in females and castrated males, and that the glands were more active during the breeding season.

Sar and Calhoun (1966) and Bal and Ghoshal (1976) described the seba- ceous glands in horn glands as simple or branched, alveolar glands whose lobes are separated by delicate strands of connective tissue and ducts open into hair follicles below the opening of sweat glands. Brouwer and Nijkamp (1952) re- ported that the secretion of sebaceous glands (hair grease) in goats contains C2, C3, C4, C5, C6, Cs, C1o fatty acids (with a predominance of Cs and Clo acids) and other unidentified fatty acids. Jenkinson et al. (1967) also found n-deca- noic and Ci2-branched acids. Brouwer and Nijkamp (1952) suggested that the offensive odor may be associated with C6 and Cs acids, but Jenkinson et al. ( 1967 ) suggested it may be associated with n-decanoic and Ci2-branched acids. Bal and Ghoshal (1976) found no characteristic odor in females and castrated males although the sebaceous glands were present. Testosterone has been re- ported to increase the size and activity of sebaceous glands (Ebling, 1957; Strauss et al., 1962).

Horn glands, which may possibly function as scent glands, have not yet been described in Nigerian goat breeds. In his study of follicle arrangements in the skin from wild sheep and primitive domestic sheep, Ryder (1958) included data on hair follicle arrangements in one Nigerian goat but did not describe sebaceous, horn or scent glands. Burns (1965), in a study of the skin of some Nigerian goats, sought to determine factors responsible for the high leather quality of the RSG. He mentioned sweat and sebaceous glands in relation to leather quality but not horn or scent glands. Onwuka (1983) described the morphology of the skin of WADG, West African dwarf sheep, and measured the thickness of different layers of the skin in wet and dry seasons. He did not include, however, sebaceous, horn or scent glands.

There is a need for anatomical studies of sebaceous glands in the horn glands and other parts of the body of goats, including Nigerian breeds. The findings will be useful in the understanding of scent production in the Nigerian breeds, apart from providing basic information on sebaceous glands. The purpose of this study was: (1) to locate the area or areas occupied by enlarged sebaceous glands; (2) to take measurements of the cross-sectional area of sebaceous glands to see how they compare in different parts of the body; (3) to determine rela- tive development of sebaceous glands in male and female; (4) to compare horn gland development in the WADG and the RSG.

MATERIALS AND METHODS

Twelve goats were studied (six males, six females). Of the six goats in each group, four were WADG and two RSG. Age determined by the teeth was 1 to 3 years. Samples were taken in the dry season (December-June). Goats were

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killed by exsanguination. Skin samples were taken with a scalpel blade from ten areas in males and females as follows: the caudomedial area at the base of the horn (horn gland), the area of the head caudal to the horn gland, the lateral side of the neck, the humerus region, the mid-lateral t runk over the eleventh rib, the ventral abdominal region, the hip, the perineum, the thigh and skin- hoof junction of the forelimb. Skin samples were also taken from the prepuce and scrotum in males and udder in females. All samples were taken from the left side of each animal.

Samples were fixed for 24 h in formol calcium according to recommendations of Baker (1958) for the preservation of lipids. Each sample was divided into two halves; one half was processed through the routine paraffin wax technique, and transverse 10 pm sections were taken. Sections were stained with hema- toxylin and eosin (H and E). Slides were projected with a microprojector at a magnification of 200 ×. Sebaceous gland sections were traced on graph papers. The area of gland sections was determined by planimetry, according to Jen- kinson et al. (1967). Planimeter readings (in cm 2) were divided by 40 000 to correct for the magnification. For each sample section, 20 sebaceous glands were measured. The mean area for each sampled site was determined for in- dividual goats and groups. Values were compared statistically and significant differences determined by the Student 's t-test.

The other half of each sample was further fixed in 70% alcohol for 24 h. Free-hand sections (300-500 ~m thick) were made perpendicular to the skin surface and parallel to the direction of hair growth. These sections were stained with Celestine blue for 15 min, dehydrated in alcohol and mounted in Canada balsam. Sections were used for visualizing the shape of the sebaceous glands and the relationship between sebaceous gland ducts, hair follicles and sweat gland ducts.

RESULTS

Horn glands consist of large sebaceous glands, mainly located within a cres- centic skin fold at the caudomedial aspects of the base of the horns. The glands are simple or branched alveolar glands. The lobules and aveoli are separated by loose connective tissue. Usually one hair follicle is associated with two of the sebaceous glands but, in a few cases, especially in females where the glands are not well developed, three or four gland ducts (Fig. 1 ) may be seen opening separately into a hair follicle. Ducts of the sebaceous glands open into a hair follicle at about the same level, below the opening of the duct of the single associated sweat gland (Fig. 2). In a few cases, sebaceous gland ducts in the horn gland were observed opening on the skin surface (Fig. 2 and 3).

Sebaceous glands in other parts of the body look like those in the horn glands, except that they have smaller cross-sectional areas. Sweat gland ducts open at

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Fig. 1. Horn gland. Female, X 80. h = hair follicle; small arrow head = sweat gland duct; large arrow head = sebaceous gland duct.

Fig. 2. Horn gland. Male; ×80. f=hair follicle; small arrow head=sweat gland duct; large arrow head= sebaceous gland duct opening on the surface; d= sebaceous gland ducts opening into hair follicle; r = alveolus of sebaceous gland.

Fig. 3. Horn gland. Male; × 120. E = skin furrow; small arrow head = sweat gland duct; large arrow head=hair follicle; black on white arrow=sebaceous gland duct opening into skin furrow; s = sebaceous gland.

t he n e c k o f t he ha i r follicles, v e r y c lose t o t h e su r face o f t he sk in or a l i t t le deeper , b u t a lways a b o v e t h e o p e n i n g o f t h e t wo s e b a c e o u s g lands .

T h e m e a n c r o s s - s e c t i o n a l a reas o f s e b a c e o u s g l ands in h o r n g l ands a n d o t h e r s a m p l e d a reas for m a l e a n d f ema le goa t s a re in T a b l e 1. I n males , t h e l a rges t c r o s s - s e c t i o n a l a reas were f o u n d in h o r n g lands , w i t h a m e a n o f 0.097 m m 2. T h i s was fo l lowed in d e c r e a s i n g o r d e r b y t h e p r e p u c e (0.057 m m 2 ) , t h e a r e a o f

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TABLE 1

Mean cross-sectional area (ram 2) of sebaceous glands in sampled areas of male and female goats

Male Female Probability (P)

Horn gland 0.097 0.039 < 0.001 Head fold 0.027 0.013 < 0.001 Neck 0.010 0.007 < 0.001 Humerus 0.010 0.005 <0.001 Mid-trunk 0.006 0.004 < 0.001 Hip 0.005 0.005 > 0.05 Thigh 0.005 0.004 < 0.001 Ventral abdomen 0.008 0.005 < 0.001 Perineum 0.014 0.005 <0.001 Prepuce 0.057 - - Scrotum 0.005 - - Udder - 0.008 - Sk in /hoof junction 0.015 0.012 <0.001

the head caudal to the horn glands i.e. head folds (0.027 ram2), sk in /hoof junc- t ion {0.015 m m 2), the per ineum (0.014 m m 2), humeral region (0.010 m m 2), lateral side of the neck (0.010 m m 2), the ventral abdominal region (0.008 m m 2), and the mid-lateral t runk (0.006 mm2). The smallest areas were measured in the hip (0.005 m m 2 ), scrotum (0.005 m m 2 ), and thigh (0.005 m m 2 ) areas.

In females, the largest gland cross-sectional areas were also found in horn glands with a mean of 0.039 m m 2. The mean cross-sectional areas of sebaceous glands in other sampled parts in the female were as follows: area of head caudal to the horn glands 0.013 m m 2, skin-hoof junct ion 0.012 m m 2, udder 0.008 m m ~, lateral side of neck 0.007 m m 2, pe rn ineum 0.005 m m 2, hip 0.005 m m 2, mid- ventral abdomen 0.005 m m 2, humerus 0.005 m m 2, mid-lateral t runk region 0.004 m m 2, and thigh region 0.004 m m 2.

Generally, cross-sectional areas of the sebaceous glands in horn glands and other sebaceous glands of males were larger t han those of females. Except in the hip region where no difference was observed between males and females, all other cross-sectional areas were significantly larger (P < 0.001 ) in males than in females (Table 1).

Preput ia l sebaceous glands in the male had alveoli with very small cross- sectional areas as compared with horn glands, a l though they were enlarged, when compared with other sebaceous glands. The cross-sectional area of the alveoli was significantly larger (P < 0.001 ) in horn glands (Table 2).

Cross-sectional areas of the glands t raced from horn glands were signifi- cantly larger ( P < 0.01 ) in WADG than in RSG (Table 3). Significant differ-

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TABLE 2

Mean cross-sectional area of 20 alveoli of horn and preputial glands of six male goats

Horn gland Preputial gland

Goat 1 0.095 0.006 2 0.114 0.008 3 0.077 0.007 4 0.041 0.011 5 0.067 0.007 6 0.057 0.005

Mean 0.075 0.007

Probability of significance: P < 0.001.

TABLE 3

Mean cross-sectional area (mm 2) of sebaceous glands in WADG and RSG

WADG RSG Probability (P)

Horn gland 0.080 0.055 < 0.01 Head fold 0.021 0.018 > 0.05 Neck 0.008 0.005 < 0.001 Humerus 0.008 0.005 < 0.001 Mid trunk 0.005 0.005 > 0.05 Hip 0.005 0.006 < 0.001 Thigh 0.005 0.005 > 0.05 Ventral abdomen 0.007 0.005 < 0.001 Perineum 0.014 0.005 < 0.001 Prepuc 0.063 0.048 > 0.05 Scrotum 0.007 0.006 > 0.05 Skin/hoof junction 0.013 0.014 > 0.05 Udder 0.007 0.008 > 0.05

ences (P < 0.001 ) were also found in the neck, humerus , hip, vent ra l abdomen and per ineal areas {Table 3).

DISCUSSION

H o r n glands in W A D G and R S G were simple or b r a n c h e d alveolar sebaceous glands. T h e y were s t ruc tura l ly similar to sebaceous glands f rom other par t s of the body, bo th in males and in females. Like in o ther sebaceous glands, usually one hair follicle was associa ted with two ho rn glands but, in a few cases, three or even four sebaceous glands may be associa ted with one hair follicle. Each of these glands had a separate secre tory por t ion and a separate secretory duct which also opened separa te ly into the hair follicle. These observat ions differed

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from Jenkinson et al. (1967) and Bal and Ghoshal (1976) who considered two sebaceous glands associated with a single hair follicle to be two lobes of the same gland. Observations in this study agree with findings of Sat and Calhoun (1966) who described a single sebaceous gland opening on each side of the hair follicle in American goats, and of Strickland and Calhoun (1963) who reported two or three glands opening into a hair follicle in the cat.

Ducts of the horn glands, like those of other sebaceous glands, opened into the associated hair follicle at about the same level, below the opening of the duct of the associated single sweat gland. Aberrant cases of gland ducts opening on the skin surface, observed in this study, could have resulted from a break in the connection between the associated hair follicle and the duct of the gland. This has made it possible for the ducts to find way to the surface. Develop- mentally, most sebaceous glands originate as diverticula of hair follicles. Sebaceous glands that open independently of hair follicles have been reported in the eyelid (tarsal glands) and perineal region in American goats (Sar and Calhoun, 1966) and eyelid in the cat (Strickland and Calhoun, 1963).

The preputial, sebaceous glands, though large in size, had alveoli with small cross-sectional areas, compared with horn glands. Small sized alveoli means that there is higher epithelial tissue to secretory product ratio. This may mean, that the preputial glands are less active than the horn glands. It may also mean that the secretory product is extruded and lost at a faster rate than in the horn glands.

Largest cross-sectional areas were from sebaceous glands located at the base of the horn (horn glands). These were significantly larger in males than in females. Sebaceous glands in other parts of the body, apart from the hip area, also had significantly larger cross-sectional areas in males than in females. Jenkinson et al. (1967) observed that the enlargement of horn glands in Brit- ish goats was accompanied with variations in fatty acid composition of the secretory product. They also associated the enlargement of the glands with rutting and odor production in males. Significant differences in cross-sectional areas of horn glands and other sebaceous glands in males, compared with fe- males, suggest larger size and involvement of these glands in odor production in male Nigerian goats. Differences in cross-sectional areas of horn glands and sebaceous glands in some parts of the body between WADG and RSG may be due to genetic factors. The differences may also be due to differences in the climatic zones where they normally live. The WADG are in the tropical, humid forest zone of Southern Nigeria, while the RSG are in the savannah regions of the northern part of Nigeria. Climate may have some effect on these glands (Jenkinson et al., 1967; Bal and Ghosal, 1976) and seasonal changes in the size of horn glands of British and American goats have been reported. Factors really responsible for differences between these two breeds of Nigerian goats were not established in this study. However, most goats in the tropics have no specific breeding season, they breed all year round (Devendra and Burns, 1970 ).

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I t has been d e m o n s t r a t e d in ra t (Ebl ing, 1957; H a s k i n et al., 1953 ) a n d m a n (S t r aus s et al., 1962) t h a t t e s t o s t e r o n e causes increase in size and ac t iv i ty of sebaceous glands; S t r aus s a n d K l i g m a n (1961) r epo r t ed t h a t na tu r a l proges- t e rone had no effect on sebaceous g lands in man . J e n k i n s o n et al. (1967) did no t f ind an increase in size of ho rn g lands or sebaceous g lands in female goats. Bal a n d Ghosha l (1976) s t a t ed t h a t lobes of ho rn g lands were smal l in preg- n a n t female goats. I t is l ikely there fore , t h a t t e s t o s t e r o n e a lone is respons ib le for the large c ross -sec t iona l a rea of ho rn g lands and o the r sebaceous g lands in male goats.

CONCLUSION

Th i s work es tab l i shed that : (1) horn glands are ana tomica l ly s imilar to o ther sebaceous g lands in o the r p a r t s of the body in b o t h sexes; (2) sebaceous glands ( including ho rn g lands) have larger c ross -sec t iona l a rea in ma les t h a n in fe- males; (3) ho rn g lands have larger c ross -sec t iona l a rea in W A D G t h a n in RSG.

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