Management of Bulls For Optimum Fertility : Maximizing fertility and performance

Management of Bulls For Optimum Fertility : Maximizing fertility and performance

After puberty, bull produces sperm throughout his lifetime in a continuous cycle. This cycle takes roughly 60 days from initial spermatozoa creation from germ cells up to ejaculation of mature sperm in semen. This means that the nutritional status of a bull for the previous 60 days will affect the quality of semen ejaculated today. It also means that fertility in a bull is ever-changing. Just because he was fertile last year doesn’t mean that he will be fertile today. Because sperm production is a continuous process, proper nutrition is critical to maintain peak fertility in bulls. The nutritional quality of feeds and forages can have a tremendous influence on the reproductive performance of bull. Although reproductive failure may occur for several reasons, nutritional management is one of the important contributing  factors.  If  nutritional  requirement  of  a  bull  is  not  met, reproduction is the first body function that is sacrificed therefore; outmost care should be given while feeding bulls for better reproductive performance.

Effect of various nutrients on reproductive performance of bulls

1) Energy: Energy is probably the most important nutritional consideration in cattle production. Animals require energy to grow and to keep the body functioning. Carbohydrates and fats are the primary source of energy in the diet.  Besides being a source of energy, carbohydrates are building blocks for other  nutrients. The  excess  energy  in a  diet is deposited  as  fat, which provides insulation and protection to the body. Energy level in ration has its indirect impact on testicular activities. In male calves, it has been reported that additional dietary energy enhanced onset of puberty primarily via enhanced testicular function, as measured by increased level of serum testosterone, testicular testosterone, Leydig cell size and sperm production (Nolan et al., 1990). Dietary energy up to a level accelerates pre-pubertal development, but beyond a limit there are no positive effects (Pruitt et al.,1986).  Excessive dietary energy (Morrow et al., 1981) as well as critically low dietary energy (Meacham et al., 1963) both can adversely affect libido of yearling and mature beef bulls (Wodzicka-Tomaszewska et al., 1981). In Holstein bulls, low energy intake early in life can delay puberty (VanDemark and Mauger, 1964), but if severely low, then it can permanently impair sperm output (VanDemark et al., 1964).

Level of dietary energy had profound impact on reproductive ability of a bull and should neither be too high nor too less. It should be balanced as per the growing  stage  and  body  condition  of  the  animal.  High  energy  diet  is preferable for growing bulls, but if the growing bull is over conditioned than it need to be cycled down from that high plane of energy, otherwise it will result in more scrotal fat deposition and hamper sperm synthesis. A bull with thin body condition requires to be kept on higher energy level to hasten the body weight gain. For a yearling growing bull, high energy diet is a common practice in commercial farms to achieve the mature body weight as early as possible so that bull may be sold at higher price in short period. But sometimes, high levels of energy have also been shown to impair sperm output and semen quality (Coulter and Kozub, 1984). It may be due to hampered   thermoregulation   at   testicular   level   creating   deteriorating condition for sperm growth.

2) Protein: Protein is the second limiting nutrient in most rations. It is the principal building block of most tissues. The amount of crude protein in an energy-sufficient diet ranges from 8 to 12 per cent. If dietary energy is not adequate to meet demands, it can be supplied by the breakdown of body fat and muscles. However, there is no way for the body to compensate for the prolonged deficiency of dietary protein. Therefore, diets deficient in protein is more critical as it leads to loss of body condition. Inadequate amounts of protein in the diet, further drops off the daily feed consumption, decrease feed passage rates and declines the overall digestive efficiency. Reduced feed intake results in both a protein and energy deficiency.

Protein is the main body building nutrient and its level in diet directly had bearing on animal’s growth and reproduction. It has been seen that ration having high protein (14.45% CP) level had resulted in significantly larger scrotal  circumference,  greater  body  weight,  higher  average  daily  gains, higher body condition score, higher volume of semen, high sperm motility, semen concentration and more total spermatozoa than the rations with low protein (8.51%    CP)  levels (Rekwot et  al.,  1987).  Reduced  CP% in  diet resulted in decreased weight of testes, epididymis and seminal glands. It decreased thickness and diameter of seminiferous epithelium and tubules, respectively (Meacham et al., 1964).

3) Minerals: Minerals play various important roles. Along with building block of skeleton tissue, they are cofactor for various enzymatic and biochemical reactions involved in metabolism, reproduction etc. Minerals as per their requirement  in  the  body  are  divided  into  macro-minerals  and  micro- minerals.       Macro-minerals  include  Calcium,  Phosphorus,  Magnesium, Potassium, Sulfur, Sodium and Chlorine. Micro-minerals include Cobalt, Copper, Iodine, Iron, Manganese, Selenium, Zinc etc. Copper, Selenium, and Zinc have major role on reproduction as they are the trace minerals most commonly to be deficient in the diet. Copper   (Cu):  Cu  is  required   for   connective  tissue  metabolism,  iron metabolism and for various enzyme activities. It also strengthens immunity. Low copper level reduces reproductive efficiency by inhibiting enzyme activities. Cu deficiency can result in reduced libido, infertility and central nervous system abnormalities in offspring. High levels of iron, sulfur or molybdenum        in  the  soil  or  additional  feed  supplements  can  further exaggerate these deficiency symptoms. Newborns are very dependent on copper acquired during the prenatal period since copper levels in milk are poor. Therefore, proper copper nutrition in gestating females is critical to maintain body stores in newborns. Selenium (Se): Most of the Se found in the testes is associated with phospholipid,    hydro   peroxide   glutathione   peroxidase,   which   is   an antioxidant that protects the cells from oxidative stress (Boitani and Puglisi, 2008). Se deficiency results in reduced semen viability (Slaweta et al., 1988). Se in association with thyroxin regulates metabolism and reproduction. Se form complexes with heavy metals to render them harmless. Severe Se deficiency result in white muscle disease, leads to stiffness and heart failure. Unfortunately, the amount of Se required is very close to its toxicity level, thus great care must be taken while supplementing Se. The maximum level of selenium that can be legally fed to cattle is 0.3 PPM in the total ration (dry matter basis). Zinc (Zn): Zn is essential for spermatogenesis (Apagar, 1985). Zn regulates sperm motility as along with ATP, Zn helps in sperm contraction (Hidiroglou and Knipfel, 1984). Zn affects the production and secretion of testosterone, insulin and adrenal corticosteroids. As an integral component of over 300 enzymes, Zn is associated with numerous biological processes (McDowell et al., 1993). Hypo-gonadism is observed in Zn-deprived bull calves (Pitts et al., 1966). Deficiency reduces pituitary gonadotropin output and androgen production in rats (Kellokumpu and Rajaniemi. 1981). Metabolic interactions may occur between Zn and vitamin A metabolism (Smith, 1982.). Zinc deficient rats have reduced vitamin A (Apagar, 1985). Zinc enhances vitamin A uptake in bovine sperm (Swamp and Sekhon, I975).

Calcium (Ca): Help in sperm capacitation which results increased influx of Ca through plasma membrane. This process assists fusion of the plasma membrane and the outer acrosomal membrane and subsequent initiation of the acrosome reaction (Triana et al., 1980). Ca is important for sperm motility.      Sperm  motility  is  correlated  with  cyclic  AMP  concentration. Calcium, along with magnesium and manganese, is a potent stimulator of adenylate cyclase, an enzyme that converts adenosine triphosphate (ATP) to cAMP       (Rojas et al., 1992). The  ratio of Ca to phosphorus should be maintained between 1.5:1 and 3:1 to avoid an imbalance.

      4) Vitamins

Vitamin-A:  The rat has been used extensively in studies of the effects of vitamin A deficiency upon mammalian reproduction. In the male rat, classic symptoms of vitamin A deficiency include inhibition of spermatogenesis, reduction        in  testicular  size,  and  decline  in  testicular  steroidogenesis (Ganguly et al., 1980). In the male, vitamin A deficiency is associated with degeneration of testicular germinal epithelium, resulting in either reduction or  cessation  of  spermatogenesis,  depending  upon  the  severity  of  the deficiency (Maynard et al., 1979). Bulls fed diets deficient in vitamin A have delayed puberty, reduced libido, and reduced spermatogenesis (Hodgson et al., 1946). Vitamin-E:   Vitamin  E  deficiency  has  a  deleterious  effect  on  germ  cell proliferation.  Effect  of  vitamin  E  occurs  directly  or  indirectly  on  the regulation of intra-testicular factors which regulate specific steps of germ cell development (Cooper et al., 1987). In the male rat, vitamin E deficiency causes a degeneration of the germinal epithelium (Scott, 1978), and Se deficiency results in an inhibition of spermatogenesis (Wu et al., 1973.). In the latter case, supplemental vitamin E does not alleviate the Se deficiency symptoms. Vitamin E deficiency in the male rat does not impair LH and testosterone or FSH and inhibin feedback loops, but rather causes testicular degeneration at the intra-testicular level (Cooper et al., 1987). Vitamin E may affect germ cell development through some mechanism other than as a cellular antioxidant.

5) The effect of calfhood nutrition on gonadotropic hormone secretions: Calf destined to become later maturing bulls with smaller testis had lower amount of LH secretion during the period of the early gonadotropin rise (8- 16 wk of age). Furthermore, increasing circulating LH concentrations at this time by treating calves GnRH hastened pubertal development. In addition, FSH treatments in calfhood also increased scrotal circumference and hastened spermatogenesis. In this regard, FSH has been considered a main driver of Sertoli cell proliferation in pre-pubertal animals. Since Sertoli cell multiplication ceases at 20-25 wk of age in bulls, final testis size in bulls is likely determined in calfhood. Experiments conducted to investigate the effect of calfhood nutrition on pubertal development confirms that superior calfhood nutrition augmented gonadotropin secretion (which is probably mediated by metabolic hormones); this resulted in larger testis at 1 year of age and earlier onset of spermatogenesis (Barth et. al., 2008).

      6) Effect of feeding Bull supplement developed by the NDDB:

A bull supplement containing chelated minerals, coated vitamins and herbs was developed by the Animal Nutrition group of NDDB after conducting series of feeding trials on breeding bulls of different breeds. Trial results and economic analysis of feeding the bull supplement of some of the trials are given below in brief. Feeding trials on bull supplement were organized for one full year at ABC, Salon and SAG, Bidaj, on 50 breeding bulls at each farm. One feeding trial was also conducted at BAIF’s Bull Station in Uruli-Kanchan, Pune for a period of 6 months on 9 breeding bulls, before commercial launching of the supplement. On feeding the supplement, there was average increase in semen doses by about 329 per bull per month at SAG, Bidaj, 476 at ABC, Salon and 800 at BAIF. In addition, there was also improvement in sperm plasma membrane integrity and per cent intact acrosomes, as recorded by the QC labs of respective semen stations.

The supplement is now commercially produced in 5 mm pellets by Indian Immunologicals Ltd., Hyderabad at its cattle feed plant, Rajkot, under the brand name “Nandi Bull Supplement” for improving the quality and quantity of semen in breeding bulls.  The supplement is available in packets of 250 g, each of the packets required to be fed daily per bull.

7) Anti-nutritional Factors hindering bull fertility:

1) Gossypol: Chinese researches reported gossypol as a potent male contraceptive. Feeding cottonseed products at high levels and/or for long periods of time hindered bull fertility (Chase et al., 1989). In routine use of 3- 5 lbs of cottonseed meal is most unlikely to expose the breeding animals to the levels of gossypol needed to cause reproductive problems (Martin, 1990). Add 4000 IU of vitamin E/head/day to neutralize the effects of gossypol.

2) Molybdenum toxicity: Displayed complete lack of libido, and histological examination showed seminiferous tubules and testicular interstitial tissue to be in various stages of degeneration and devoid of spermatids. Damage to germinal epithelial tissue was irreversible (Thomas and Moss, 1951)

HOME REMEDY TO ENHANCE THE FERTILITY RATE & PERFORMANCE IN BULL

Fenugreek seeds-daily 25 grams orally for 15 days

Ashwagandha- daily 25 gram orally for 15 days

Germinating seeds of Horse gram or green gram -100 gram orally daily for 30 days

Mustard oil cacke/linseed cacke -100 gram orally  daily for 30 days

HOMEOPATHY TO ENHANCE THE FERTILITY RATE & PERFORMANCE IN BULL

Pulsatilla 200 -20 drops tid for 30 days

Lycopodium 200- 20 drops tid for 30 days

Agnus castus-200- 20 drops tid for 30 days

Conclusion:

A planned and scientific approach in nutritional management can upgrade the reproductive quality of breeding bulls. Bulls fed as per their actual requirement since calfhood achieve the puberty in right time and have large scrotal circumference and higher gonadotropic hormone release, which result in healthy and fertile sperms.

REPRODUCTIVE DISORDERS OF DAIRY CATTLE & PRACTICES TO IMPROVE CONCEPTION RATE

Compiled  & Shared by- Team, LITD (Livestock Institute of Training & Development)

 

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Reference-On Request.

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