On a breeder farm the only valuable egg is the one which is fertile. To a large extent this depends on the condition of the males in the flock. Various factors are key in this respect. Rearing and managing them properly will have a positive influence on their fertility.
By Dr Avinash Dhawale, Diamond Hatcheries, Hyderabad, India
In the ovary of the female bird, the mature egg yolk leaves the ovary and within 20 minutes it is captured by the infundibulum. The egg yolk is surrounded by the perivitalline membrane (PVM) which has the germinal disc (GD), the seat of fertilisation. The sperm bind to the PVM, makes a hole and tunnel into the GD. Here genetic material of the sperm fuses with that of the female and embryonic development begins.
Around 30 sperms must enter the egg near the germinal disc to insure a 95% chance of fertilisation although only one sperm is necessary. After about 15 minutes the yolk leaves the infundibulum (fertilised or not) and descend down into the uterus.
Early growth (0-12 weeks)
During the first 28 days protein intake greatly influences the reproductive potential of the males. During this period a minimum intake of 200 grams of protein is a must. First segregation according to bodyweight (grading) is recommended at five weeks of age. After week 10 there is no benefit in grading as the skeletal size is 85% grown and leaves no opportunity for the manager to further influence the skeletal size.
Although the male can produce trillion of sperms, the actual number of mature sperms produced is limited by the number of sertoli cells in the testes. Sertoli cell proliferation occurs between 2-12 weeks of age but not at any time after this point. Therefore the maximum potential for sperm production is established in the first 8-10 weeks of age. Anything that may cause unnecessary stress to the developing male at this time, may interfere with proper development of these very important testicular cells.
During this early period of development, a portion of the brain (hypothalamus) and pituitary are also establishing a critical hormonal relationship with the testes. The early stage of maturation that help to establish the “feed back loop” are important in establishing the settings that will regulate pituitary function over the remaining life of the male.
Mild stressors which cause either weight loss or reduced water intake, can lead to a complete shutdown of testes function when occurring during critical stages of development. It is possible to disrupt the normal pattern of testes development with too severe feed restriction between 6-8 weeks. This results in reduced testes size, sperm production and the theoretical maximum number of sperms produced.
Growing tall roosters with few skeletal abnormalities, requires a good quality starter diet (20% protein and 2900 kcal ME) during the first five weeks. For underweight males (discovered at the first grading) continue this high density feed for a couple more weeks as such males respond poorly to developer rations. Developer rations are generally introduced from the 6thweek and are low in protein and energy.
From week 10 to 17
From the 10th week onward it is critical to not lose impetus in growth rate. From the 15th week, there is rapid development of the testes and growth profile must be followed or fertility will be delayed or lost. From the 16thweek, stimulate male birds constantly with feed to maintain body weight and testes development. It is important to ensure that they reach standard body weight by the time they are photostimulated.
From week 18 to 30
One of the most important factors affecting testicular development is the males growth from light stimulation until full sexual maturity at the end of the light stimulation period (week 20-28).
Males and females should normally be photostimulated at the same time although it is possible to stimulate males 1-2 weeks earlier if their maturity looks clearly behind that of females.
From week 30 onward
Ensure that male weight does not go out of control (not more than 4.1 kg at the 30th week) and then to depletion (approx. 4.9 kg at 68th week). The body weight differential goal from 20-40 weeks should be closer to 500-600 grams and post 40 week the difference increases to finish between 800-900 grams. This type of growth curve will promote enough testicular development while keeping the males active and physically able to mate.
Evaluating males breast effect on fertility by hand is a good way of estimating body condition. Aim to keep the “V-shape” breast for as long as possible. The breast should be tight in consistency. An average peak allowance of 150-170 grams (14% protein and 2750 kcal ME) is generally enough and shall be maintained throughout the life. After week 30 it is common to get some weak and depressed males. Such males shall be separated, given additional feed (+20 g/day) and vitamins and rested for at least 2-3 weeks before allowing mating again.
Research suggests that nutrition can improve sperm quality especially by lowering protein levels down to 11-13%. This helps to control body weight and breast muscle growth. Vitamin E at 200 mg/kg diet enhanced sperm count and viability when supplemented to stress induced birds.
Diet composition and feeding level can have a dramatic and absolute effect on fertility. Both over and underfeeding will lead to loss of semen production. Even 9-10% dietary crude protein can produce optimum semen production and improve fertility by 2-3%. Obesity in males is negatively associated with semen production and more importantly with mating activity. Such obesity is more commonly caused by general overfeeding or excess of either protein or energy in the feed. Feeding high protein (16% CP equivalent) most frequently causes extra muscle growth and this itself causes problems with weight control. If roosters are underfed males will quickly decline in semen production.
Testes and semen
The testes are quite small prior to maturity being only 1-2 gram each and 15-20 gram at around 18 weeks. There is a direct relationship between sperm production and testes size. The hormone testosterone is produced by the testes under regulation of gonadotrophins and overall control of the breeding cycle is ultimately dictated by the photoperiod. Comb size is a sensitive indicator of the testosterone level and so can be used to evaluate stage of maturity in the developing roosters.
Sperm formation takes about 15 days. The rooster’s semen can contain around 5 billion sperms/ml. The fertilising potential of roosters vary even within a flock. Once a rooster is mature and if he is maintained properly he will produce about 35000 sperms/second.
Daily sperm production is 100 million/gm of testes weight. Sperm production is fairly constant regardless of mating or collection frequency. Therefore with higher frequency of mating there will be fewer sperms/ejaculate. If ejaculate doesn’t occur over a 2-3 day period then any sperm stored in the vas deferens are absorbed.
Heat stress (HS) can lower the fertilisation rate of sperms. It can adversely affect binding proteins on the sperm surface that are necessary for binding to oviductal epithelium before transport to the site of fertilisation. Heat stress has deleterious effects on testicular function, semen consistency, spermatozoa concentration and seminal volume.
The weights of the testes are more closely associated with body size than with the level of dietary protein. The weight of the testes in chickens constitutes about 1% of the total body weight, or about 9-30 gram per testis at sexual maturity depending on the breed. Semen that is viscous and white has a high spermatozoa concentration, while semen that has a watery appearance is low in spermatozoa concentration. It is reported that broiler breeder males ejaculated five times per week produced the highest total number of sperm per ejaculate.