1.0                                                       INTRODUCTION
            Puberty is the point of sexual development at which the animal becomes capable of reproduction (first ovulation in the female and first spermatozoa in the ejaculate of the male), but animals are not yet fully sexually mature at this stage. Sexual maturity is the time when the animal expresses it’s full reproductive capacity. In the ruminants like sheep and goat, puberty may often be reached without adequate physical growth to support reproduction and in the females the first ovulation may not necessarily coincide with first estrus.

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            In males, puberty is the time when complete separation of the prepuce and the penis occurs and motile spermatozoa are first detected in the ejaculate. In immature rams and bucks the penis has adhesions that prevent it from being fully extended. At puberty, these adhesions dissolve under the influence of testosterone and the penis can be fully extended. However, fully reproductive competence may not occur until 15 months of age. Spermatogenesis has been found to begin as early as 84 days of age, with spermatozoa present in the epididymis at 140 days of age.

          The pubertal process is characterized by an activation of physiological events within the hypothalamic-adeno hypophyseal-gonadal axis which culminate in reproductive competence. Excessive weight gain and adiposity during the juvenile period is associated with accelerated on set of puberty in females.
            The mechanisms and pathways by which excess energy balance advances puberty are unclear, but appear to involve an early escape from estradiol negative feedback and early initiation of high frequency episodic gonadotropin releasing hormone (GnRH) secretion.
            Hypothalamic neurons, particularly neuropetide Y and proopiomelanocortin neurons are likely important components of the pathways sensing and transmitting metabolic information to the control of GnRH secretion.
            Recent studies indicate that leptin-responsive neurons within the ventral pre-mammillary nucleus play a critical role in pubertal progression and challenge the relevance of kissipeptin neurons in this process.

            Pubertal development involves physical and behavioural changes that are linked to the activation of the hypothalamic –adenohypohyseal-gonadal axis (Sisk and Foster, 2004). The progression of events is controlled largely by genetic and environmental factors, among which nutrition has a major influence. However, evidence that the weight gain and adiposity during early stage are associated with early onset of puberty in females (Lee et al.,2007; Jasik and Lustig, 2008; Rosenfield et al., 2009). And indications that precocious puberty is associated with increased risks for development of polycystic ovarian syndrome, reproductive cancers, and psychological distress (Golub et al., 2008) has renewed interest in understanding the mechanism by which nutrient sufficiency supports reproduction maturation.
            A decrease in sensitivity to negative feedback of gonadal steroids-allowing higher levels of gonadotropin (FSH and LH) required for cyclicity and spermatogenesis result in the initiation of puberty.
            The first heat of the pubertal animal is often “silent”, that is the reproductive system is ready for mating to occur, with ovulation, yet there is no external manifestation of sexual receptivity. It is believed that the central nervous system requires to be primed with progesterone before it will respond and the animal show behavioral signs of heat.

            Puberty is controlled by sexual hormones in bucklings and doelings, this process generally occurs when they reach 60-70lbs or 30-50 percent of adult body weight. Testosterone is the bucklings and estrogen is doelings. These hormones cause physiological and behavioural changes in the both sexes leading up to puberty.
            The ovaries are essentially inactive from birth until puberty. Because of hormonal support from the hypothalamus and anterior pituitary gland is insufficient. The ovaries become active as the hypothalamus and anterior pituitary gland begin to produce stimulating hormones such as the gonadotropin-releasing hormone
(GnHR), the follicle-stimulating hormone (FSH) and the luteinizing hormone (LH).
Photo period, an environmental factor, also greatly affects the onset of puberty especially in does. In does, puberty and estrus cyclicity in general depend on photoperiodic changes. The onset of puberty typically occurs during the short days of autumn. Spring-born animals are exposed to long days and achieve puberty during the short days of autumn in the same year. In contrast the October-born animals are exposed to short days thereby decreasing days to reach puberty during the winter of the following year. However, puberty can be manipulated through management techniques such as permanent exposure to the buck, enhanced nutrition and breeding management practices in the females.
            In the male, puberty contrast, it involves testicular growth and spermatogenesis (spermatozoa production). Photoperiodic changes, does not affect male in attaining puberty. The season of birth also does not appear to significantly affect the onset of puberty in bucks.

Figure 1: Factors Affecting Female Puberty.
 Source: Alabama Cooperative Extension System, 2009

Fig 2: Factors Affecting Male Puberty.
Source: Alabama Cooperative Extension System, 2009

            There are several factors that affect puberty which are; nutrition, body weight, breed, season of birth and growth rate. Nutrition is among the most significant factors influencing reproductive development and the onset of puberty.
·                     A low plane of nutrition delays first estrus and reduces uterine and ovarian development in ruminant animals.
·                     Increasing the overall plane of nutrition generally advances the on set of puberty.
·                     Overfeeding will decrease subsequent fertility and impair mammary gland development and, therefore care must be taken to avoid overfeeding.
·                     In most sheep and goats breeds, attainment of puberty is dependent on achieving satisfactory body weight, usually between 40-70% of the mature body weight. A late-maturing breed like the Somali goat is known to attain puberty at a later age.
·                     Energy and protein restriction influences age at puberty, with energy restriction having a greater influence on delaying on set of puberty than protein restriction.
·                     Age, weight and growth rate seem to be interacting in determining the process of on set of puberty. In general, faster growth rates resulting from higher planes of nutrition enables kids to attain puberty at a younger age and heavier body weight than kids reared on low planes of nutrition
·                     Complete separation of males and females during the early growth period may delay the on set of puberty.
Different investigations on the reproductive performance of Ethiopian sheep and goats have shown the following: ewe lambs of the Menz breed attain puberty at 10 months of age and 16.2kg mean weight or 56% of mature body weight. The onset of puberty was earlier in animals with higher weaning weights. Somali kids were 19 months and weighed 26kg at puberty, indicative of a late maturing breed.
In Horro sheep, kept under low-to high nutritional regime, age at first maturing was reported to be 206 to 285 days while weight was 18-21kg. From on-farm monitoring work on Ada District, weight and age at first successful mating for sheep was reported to be 20kg and 8.7 months, respectively, while for goats it was 17kkg and 7.4 months.

            Puberty is not synonymous with sexual maturity. Dairy heifers and bulls may not produce ova and spermatozoa at 6-8 months of age, conception at this early age can be disastrous because the animal has not attained physical maturity. Puberty is more closely related to body weight that age in domestic animals, except in swine. Diary cattle usually reach puberty when their body weight is 30-40 percent and sheep 40-60 percent adult weight. Small breeds usually reach puberty earlier than large breeds. Based on these finding, it has been recommended that Holstein and Brown Swiss heifers should not be bred until they weight 750lbs,Aryshires about 650lbs, Guernseys about 550lbs and Jerseys about 500lbs. For beef cattle, it is recommended that Charolais heifers should not be bred until they weight 725lbs, her, Brahman and Brahman crosses about 700lbs, Hereford about 650 lbs, Angus 600lbs and Angus and Hereford crosses at about 600lbs.
            In ewes and does, there are two schools of thought regarding their appropriate age of mating. One school of thought advocates early mating regardless of what is called critical body weight. It is argued that this will increase the life time productivity of the females, despite the fact that some abortions are evident. However the concept of “critical body weight” is favoured. According to this concept, animals should attain a minimum body weight in order to avoid growth retardation (in most cases two-third of mature body weight) before they are mated. This reduces reproductive wastage (abortion) that could result from mating small-sized and sexually immature animals.

            Following the onset of puberty in ruminant animals there is the development of physiological rhythm of the reproductive system, called the estrous cycle. This pattern is characterized by periods of sexual receptivity of the male during estrus. In cow estrus activity may occur throughout the year and is said to be polyestrous. In ewes, nannies, estrus activity occurs during certain seasons of the year and they are referred to as being seasonally polyestrous. The estrous cycle is divided into four phases or periods which blend one into the other they are; proestrus, estrus, metestrus, diestrus.
But some theriogenologists also divide the estrus cycle into two periods based on the dominant secretary structure on the ovary-the estrogenic or follicular phase comprising proestrus and estrus, and the progestational or luteal phase comprising of metestrus and diestrus.

5.1       PROESTRUS
            This phase immediately preceding estrus, there is follicular growth and increased secretion of estrogen and regression of the corpus luteum of the previous cycle (in polyestrous species) and decreasing levels of progesterone. The principal distinguishing feature of proestrus is the occurrence of rapid follicular growth and late in this period the effect of estrogen on the tubular tract or diet system and the behavioural symptoms of approaching heat can be felt. The proestrus period directly proceeded that heat period which is a period of increasing estrogenic activity and all the symptoms associated with it.
5.2       ESTRUS
            This is the period of acceptance of the male. The onset and end of this phase are the only accurately measurable points in the estrus cycle and hence are used as the baseline for determining cycle length. Ovulation occurs during this phase in ruminant animals except in cow. Ovulation is a spontaneous process in all species of ruminant animals.
            There are certain psychological and physiological changes in the brain which manifests in some characteristic behaviour by the female largely described as behavioural estrus. In the cattle the animal will stop grazing, become restless, refuse to rest while others are resting and attempt to mount other females and at the late stage of this period, it will stand for the male to mount and mate with her and this point the 1st meiotic division will have taken place in the secondary oocyte within the Graafian follicle which is now large and matured. Estrogen secretion is more profound and the tubular tract is made ready to accept the ovum/ova at ovulation judging by the increasing contact between the fabriae of infundibulum and ovary as well as the increase in the erectile nature of the cilia. There is also corpus mucus secretion by the oviduct and other parts of the tubular tract and this time is thin and copious. In the cow and goat, the mucus can be seen draining from the vulva.
5.3       METESTRUS
            This is the phase succeeding estrus. The granulosa cells of the ovulated follicle give rise to lutein cells which are responsible for the formation of the corpus luteum and increasing amounts of progesterone ovulation occurs at this stage in cows and does. Also a phenomenon known as metestrus bleeding occurs in the cows. This bleeding should not be confused with the menstruation bleeding in humans but it is simply the bleeding that resulted from the rupturing of blood vessels when the estrogen sensitized tubular tract are trying to return to normal. It is just noticed as a patch of blood at the upper part of the tail adjacent to the vulva and occurs in about 90% of all metestrus period in heifers and 45% in matures cows this period lasts 4-8 days in the cow, 3-4 days in the sheep and goat.

5.4       DIESTRUS
            This is the period of corpus luteum when it is fully functional in the cow it starts at about day 5 of the cycle when an increase in blood concentration of progesterone can first be detected and ends with the regression of corpus luteum on day 16 or 17 of the cycle. But ewe extends from about day 4 through days 13, 14 and 15. At the end of third phase development of another set of follicle that is if pregnancy did not occur but where it occurs, the corpus luteum persists ad the influence of progesterone will continue until the end of the pregnancy.

Table 1.0 different phases of the estrus cycle in does
Day of cycle
1 - 2
Final growth and ovulation of 1-2 pre ovulatory cycles. Sexual receptivity of does. Cervical mucus thinner and more corpious, cloudy towards ovulation
Functional organization of corpus luteum
Luteal phase
Growth of pre-ovulatory follicles.
Source: Ethiopia sheep and goat productivity improvement, 2003

            Estrus cycle is controlled by Gonadotrophic releasing hormone (GnRH) released by the hypothalamus. Just before the onset of estrus, the pituitary gland, under the control of the phypothalamus in the brain, releases an increasing amount of luteinizing hormone, (LH) and follicular stimulating hormone (FSH) (Ulfina, et al., 2000).
            The growth of the follicles being regulated by pituitary hormone (luteinizing hormone and follicle stimulating hormone). The luteinizing hormone stimulates the final maturation of the follicle containing the eggs and stimulates follicle to produce the hormone estrogen (Ugwu, 2012). The estrogen brings the animal into behavioural estrus or heat (Ugwu, 2012).
            The rising concentration of estrogen stimulates a surge in luteinizing hormone that stops further secretion of estrogen by the follicle (Ugwu, 2012). Once the egg has been released, luteinizing hormone transforms the follicle into a corpus luteum (Mukasa, 1986).
The corpus luteum produces progesterone which in turn suppresses pituitary activity (Ugwu, 2012). Therefore if pregnancy does not occur, lysis (destruction) of the corpus luteum occurs due to endogenous release of prostaglandin from the uterus, thus causing a fall in the progesterone level, and the cycle starts again (Ugwu, 2012)

            The onset of puberty in animals is characterized by an activation of the hypothalamic- adeno-hypophyseal-gonadal axis that precedes the establishment of cyclic ovarian activity. The peripubertal increase in pulsatile release of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH) supports final maturation of ovarian follicles and enhances ovarian steroidogenesis (Kinder et al., 1987). Elevated circulating concentration of estradiol includes the pre-ovulatory surge of GnRH/LH, which leads to first ovulation (Kinder et al., 1987). During juvenile period, the hypothalamic-adenohypophyseal-gonadal axis remains relatively quiescent and the frequency of LH release is low (Foster and Jackson, 2006; Plant and Witchel, 2006). A major limiting factor for increased secretion of LH and Development of Pre-ovulatory follicles during the juvenile period is the lack of appropriate stimulation of the gonadotropes by GnRH. This assertion is supported by the observation that ovarian function is stimulated in immature female monkeys treated with GnRH (Wildt et al., 1980). And in lambs treated with Luteinizing hormone (Foster et al., 1984). Because estradiol can lead to a surge-like release of LH in Pre-pubertal female (Foster and Karsch, 1975; Andrews and Ojeda, 1977), it is believed that the estradiol positive feedback is functional before reproductive maturation is established. However, the lack of an appropriate stimulatory signals that restrain GnRH neural activity, may explain the infrequent release of GnRH characteristic of the Pre-pubertal period increased sensitivity to estradiol negative feedback contributes to the inhibition of GnRH release in ewe, lambs and heifers (Foster ad Ryan, 1979; Day et al., 1987). The ability of low circulating concentrations of estradiol to inhibit the pulsatile release of LH is diminished during maturation, and frequency of LH pulses increase (Ebling et al., 1990)

            Adequate growth and adiposity are critical for normal progression of puberty in ruminant animals. Growth restriction (Foster and Olster, 1985, Suttie et al., 1991) and excessive exercise (Manning and Bronson 1989, Malina, 1994) during the juvenile period delay puberty, likely by decreasing the release of GnRh (I’Ason et al., 2008) in association with heightened negative feedback sensitivity to estrodiol (Foster and Olster, 1985). In contrast, increased adiposity seems to facilitate reproductive maturation and advance the onset of puberty (Kaplowitz et al., 2001; lee et al., 2007; Rosen field et al.,2009). In cattle, a high proportion of heifers fed to gain weight at high rates during the juvenile period exhibit precocious puberty (Gasser et al., 2006 a,b). This occurrence is associated with attenuation of estradiol negative feedback and increased pulsatile release of LH (Gasser et al., 2006 a). Therefore, nutritional cues interact with gonadal steroid feedback to time the onset of puberty in females.
            Studies investigating adiposity and adipocyte derived hormones as essential factors for the initiation of puberty have revealed that leptin; a hormone secreted predominantly by adipocytes has a critical role for the progression of puberty in various species, including ruminants (Zieba et al., 2005). Although leptin does not affect secretion of LH in adequately fed ewes (Henry et al., 1999) and cows (Amstalden et al., 2002) leptin prevents fasting-induced reduction in LH pulsatility in pre-pubertal heifers (Maciel et al., 2004), leptin’s action on GnRH/LH release in ruminants are likely mediated by intermediate pathways. In addition to leptin, information from other hormones like (insulin, and ghrelin) and nutrient (glucose, fatty acids, and amino acids) is also likely to be integrated in a complex neural network that perceive and signal availability of metabolic fuels to the control of reproductive functions (Schneider, 2004)
            Critical neuronal pathways mediating signals of nutrient sufficiency and insufficiency have been identified. Hypothalamic neuropeptide Y (NPY)/agouti-related protein (AgRP) neurons, and proo-piomelanocortin (POMC) neurons are considered major pathways by which nutritional signals are affected (Crown et al., 2007). These populations of neurons in the arcuate nucleus expressed the leptin receptor and are responsive to changes in nutritional status (Kalra and Kalra, 2003). Specifically, NPY has been shown to mediate the inhibitory effects of under nutrition on reproductive function. (Kalra and Crowley, 1984). Contrary to rats in which NPY has both stimulatory and Inhibitory effect on LH release depending on gonadal steroid milieu (Sahu et al., 1987), NPY has a predominant inhibitory action on the release of LH in ruminants in the presence and absence of estradiol (Gazal et al., 1998; Estrada et al., 2003; Morrison et al., 2003). This effect of NPY has been shown to largely due to inhibition of GnRH release (Gazal et al., 1998) and may be mediated by direct NPY actions on GnRH neurons (Klenke et al., 2010). An animal with elevated body weight at a high rate between 4 and 6.5 months of age, the expression of NPY In the arcuate nucleus was decreased compared to heifers that gained weight at lower rates (Allen et al., 2009). Using a similar dietary treatment, we also observed that the proportion of GnRH neuron is close proximity of NPY fibers in the preoptic area and hypothalamus was reduced in heifers gaining body weight at high rate (Alves et al., 2011). Therefore structural and functional changes involving hypothalamic NPY circuitry during the early juvenile period may involve in the mechanisms by which excessive nutrition and adiposity support early on set of puberty. In a study during hypothalamic tissue from non-human primates and rats (Rot et al., 2007) suggested that a network of genes involved in a range of cellular functions, including control of transcription and cellular metabolism, is activated at the time of puberty. In a recent study using microarray technology to investigate changes in gene expression in the arcuate nucleus to pre-pubertal heifers fed to gain weight at high or low rates, we observed that genes involved in a variety of biological functions are responsive to nutritional input during the juvenile period (Allen et al., Unpublished). Differentially- regulated genes included those associated with regulation of cellular metabolic processes, receptor and intracellular signaling and neuronal communication. Therefore, the pre-pubertal, growing female seems exquisitely sensitive to nutrient inputs because changes in the regulation of metabolic-sensing and effectors pathways are in tune for the fine control of neuroendocrine functions. Mechanism involved may include regulation of gene expression, control of cellular functions, and plasticity of functional structures within the hypothalamus.

8.1       AGE
            It has been found that in bulls, age and testicular development have a curvilinear relationship (Hahn et al., 1969; Coulter and Foots, 1976; Elmore et al., 1976; Lunstra et al., 1978 and Osinowo et al., 1981). Work done by Coulter et al., (1975) showed that increase in scrotal circumference with age is up to a certain limit. Correlation between age and scrotal circumference in young Bunaji Bulls was 0.88 (Osinowo et al., 1981). In ram, Watson et al., (1956) reported a general increase in testicular weight and mean cross-sectional area of the seminiferous tubules, with increase in age. Testicular size increased steadily in young bulls and declines in the old bulls (Coulter, 1979; Coulter and Foote 1979). Although spermatogenesis was found to have started by 13 months of age in Bunaji bulls, consistently large gonadal and epididymal sperm reserves were only found in bulls age 17 months and above (Osinowo et al., 1981 Wildeus and Entwistle, 1983).

8.2       NUTRITION
            Under nourishment has been reported to delay growth and puberty in rams and bulls, and age of selecting Holstein bulls for artificial insemination by many months (Foots and Trimberger, 1968., Leathern 1975). Nutrition affects age at puberty there is a correlation between body weight and testicular weight in males or age at the first oestrus in the dams. If nutrition is maintained at a normal level, puberty occurs when body weight reaches 60% of the adult body weight in sheep and 45% of the adult weight in cattle (Thinbault and Levasseur, 1974). If growth is accelerated by overfeeding body weight at the time of puberty is higher that normal and the animal reaches maturity at a younger age. On the otherhand, if growth is slowed down by underfeeding, puberty is delayed and body weight does not reach the level of that of normally fed animals (Thibault and Levasseur, 1974(. Dietary protein deficiency results in a loss of testes mass, spermotogenic arrest and lowering of the secretary ability of the interstitial cells of the secretary ability of the interstitial cells of leydig (Tripathi et al., 1968). Lambs reared on a high plane of nutrition reach puberty earlier that those on a low plane (Ward, 1980). This is partly a reflection of the tendency to reach puberty only above a certain body weight, and partly of a direct effect of nutrition on the reproductive system. In rams testis size, which is highly correlated with spermatogenesis activity, responds to nutrition, and sperm production can be increased by flushing with high protein supplement for about 8 weeks before mating states (Pryot, 1980). This is especially impotent both under natural mating conditions and when semen is to be collected for artificial insemination Vitamin A deficiency it could lead to testicular malformation and aspemia (Barones et al., 1969).
            Reports indicate that amino acid, carbohydrates, a few essential fatty acid and mineral are necessary for the production of the fluid medium, produced by the cellular environment of the testes, which is necessary for sperm transport (Leatherm, 1975). The number of motile spermatozoa in the ejaculate of underfed ruminants was found to be 50% of normal, if the underfeeding was pre-pubertal (Flipse and Almguist, 1961). However, low protein intake has been found to be produced more adverse effect on immature animals than mature ones (Leathem, 1975)

            Age at sexual maturity in sheep varies form breed to breed (Terrill, 1974). The rate of testicular development is found to be higher for fast growing like merino (Chag and Rae, 1970).
            Lunstra et al., (1978) found the scrotal circumference of various breeds of cattle to be almost the same (22.9±0.2cm) at puberty, but the age body weight and testosterone content of the plasma at the time of puberty varied from breed to breed. In Nigeria however, Osinowo et al., (1981) reported a scrotal circumference of 19-24 cm for Bunaji bulls at puberty. The difference could be due to breed, level of nutrition and management practice.
Work on Angus and Holstein bulls by Coulter et al (1975) showed that the Angus had a larger testis up to 3 years of age when they were surpassed by the Holstein. The Angus breed thus reached maximum testicular size at a younger age than the Holstein breed. The Heritability estimate of scrotal circumference in bulls was reported to be about 0.67 (coulter et al., 1976).

            It has been shown that changes in season have profound effect on sexual activities and reproduction in general. Seasonal changes in the spermatogenic and androgenic activities of the testis occur in a wide range of ruminants (Lincoln, 1976). Weight and scrotal circumference measurements taken on some rams by Motimer and Lincoln (1982) during the non-breeding season showed a decrease in their testicular weight and size, with about one third decrease in weight recorded. Seasonal variation has been observed in the episodic secretion of LH and testosterone in rams, with increase from the non-breeding to the breeding season (Lincoln 1976, Pelletier et al., 1982). This shows that seasonal changes affect testicular development in the young animals but affect the weight of the testes in mature animals.

            The sex differentiation of the male sex organs is guided under the influence of a masculinizing mechanism that emanates from the secretion of androgen if these testicular hormones are absent, the mullerian ducts and the urogenital sinus develop into female sex organ. If the testicular androgens are present, the Wolfian ducts and the urogenital sinus develop into male sex organs. The regression or involution of the Mullerian ducts seems to be affected by the testes (Josso et al., 1977) it has been shown that the proliferation of gonocytes is stimulated by the pituitary gonadotropin. The gonadototrophin releasing hormone from the hypothalamus stimulates the anterior pituitary to release Luteinizing hormone (LH) and follicle stimulating hormones (FSH) (White, 1974). The LH stimulates the leydig cells to produce testosterone which in turn stimulates the germinal cells, and maintains spermatogenesis (Gemzell and Roose, 1966). Androgen also helps in the development and maintainance of the accessory sex glands, stimulation of sexual behaviour and spermatogenesis (White, 1974).
            The final differentiation of permuted to spermatozoa requires FSH and probably, testosterone. The FSH stimulates the testes and causes a significant increase in the diameter of the seminiferous tubules (White, 1974). Lunstra et al., (1978) found that testosterone production in bulls was related to growth which was in turn related to testicular development. Androgen stimulates protein anabolism causing increased nitrogen retention which accounts for the more rapid growth and greater ultimate weight of makes in many animals (Frandson, 1974; Nalbandoo, 1976).

            Epididymitis has been reported as one of the diseases affecting testicular development (Konig, 1964). It may result to testicular degeneration, which has been found to be the most frequent cause of infertility in rams and bulls (Konig, 1964; Smith et al. 1970).
            Orchitis is another disease which may lead to degeneration of the testes. It is usually due to hermatogenous mataslasis of infection, and less frequently through spread of the infection from the genitor- urinary passage (Konig, 1964. Jubb and Kenedy, 1970). Orchitis may be interstitial, intratubular or necrotic (Konig, 1964). Infections which lead to epididymilis and orchilis have been found to cause testicular degeneration in bulls (Kumi-Diaka, 1978). In rams epididymilis produces by Actinobacilus seminus hinders testicular development and result in a decrease in semen quality and quantity (smith et al., 1970). Similarly, testicular hypoplasia effects testicular development but may not be observed until after puberty (Jubb and Kennedy, 1970). Some testicular disorders like cryptorchidism (White, 1961; Swift, 1968; Smith et al., 1970; Bishop 1972; Jumi-Diaa et al, 1981) and testicular hypoplasia (Erickson, 1943; Laing and Young, 1956; Bishop, 1972; Lundgren, 1972) have been reported to be of genetic origin. Many infectious agents that interfere with the general well being of the animal may adversely affect the function of the testis depending on the duration and severity of infection.     
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