Semen Quality Characteristics and Effect of Mating Ratio on Reproductive Performance of Hubbard Broiler Breeders

A study was conducted at the National Animal Production Research Institute (NAPRI) Shika, Zaria, Nigeria to access some semen quality characteristics and to determine the effect of mating ratio on fertility and hatchability of Hubbard broiler breeders. 20 cocks were examined for semen quality characteristics. Parameters evaluated were: ejaculate volume, semen pH, sperm concentration and sperm motility. Sequel to semen quality evaluation, hens were divided into three groups according to mating ratio (cock to hen) which included ratios 1:6, 1:7 and 1:8 with each group replicated 3 times. Each replicate was housed separately in pens. Hatchable eggs were collected after ten days grace period of mating and were set in the incubator. There were six hatches and fertility and hatchability parameters were calculated. Results obtained for semen quality characteristics showed that mean values for volume (ml) was 0.55±0.04, motility (%) was 83.50, concentration was 3.91x10/ml, pH was 7.40 and average body weight was 4.73 kg. Correlations between the semen quality characteristics and body weight showed that pH was negatively but not significantly correlated with volume, concentration and body weight. The correlation between volume and concentration was high (0.92) and highly significant (p<0.001). Other correlations though positive were not significant (p>0.05). Mating ratio significantly (p<0.05) affected number of eggs fertile, number hatched and percent fertile. Birds mated in the ratio of 1:6 had the highest values for number fertile, number hatch and percent fertile but not significantly different from ratio 1:8. However the birds in the ratio of 1:7 had similar performance with those in the ratio 1:8 for percent fertile. High and significant correlation between ejaculate volume and concentration indicated that large ejaculate volume resulted in high concentration. Mating ratio of 1:6 was recommended to enhance fertility and hatchability especially in pedigree hatching.


Introduction
The production of hatching eggs is the primary goal of a broiler breeder industry. Semen quality is therefore important to the industry due to its effect on the fertility and eventual hatchability of the eggs. In domestic fowl, a number of factors have been identified to affect fertility. Strain effects on oviductal sperm storage was reported by Brillard (1992). Sperm concentration of 50x10 6 was reported to be adequate for good fertility in chickens and turkeys (Bratte & Ibe, 1989). The factors affecting hatchability include egg fertility and embryonic mortality (Fairchild et al., 2002). Failure of fertile eggs to hatch (embryonic mortality) could be as a result of prolonged egg storage, abnormal egg storage conditions, age of breeders and incubation problems (Fasenko et al., 1992;Wilson, 1997;Fairchild et al., 2002). The genetic effects of breeds, varieties and individuals within breeds on fertility and hatchability have been identified (Islam et al., 2002).
Studies to compare mating ratios are important for optimizing the breeding efficiency of broiler breeder flocks. Burke and Mauldin (1985) suggested that behavioral factors may be playing an important role in determining male reproductive success. Increased aggression and reduced frequency of courtship are behavioral characteristics affecting male broiler breeder reproductive ability . Reports of Casanovas and Wilson (1999) showed that a mating ratio of 1:10 in broilers gave the best fertility because it combined a good level of mating activity with relatively low interference and aggression. Bilcik et al. (2005) observed a high male fertility when housed individually with 4 hens. Reports on mating ratios for pedigree hatching in broiler selection experiment under natural mating are not available in Nigeria.
The objectives of this study were: (i) To access some semen quality characteristics of Hubbard broiler breeder cocks.
(ii) To determine the effect of mating ratio on fertility and hatchability of Hubbard broiler eggs.

Materials and Methods
This study was carried out at the poultry breeding unit of the National Animal Production Research Institute (NAPRI) Shika, Zaria, Nigeria. The poultry lies between 11°12′42″N and 7°33′14″E at an altitude of 691 m above sea level (Ovimaps, 2011).
A total of 63 broiler breeder hens and 20 cocks were used for this study. All the hens and cocks used for this experiment were housed in a deep litter floor pen using wood shavings about 3 cm layer deep covering on the floor. Feeders and drinkers were provided for each pen. Birds were vaccinated against Newcastle disease using intraocular (I/O) Newcastle disease vaccine and Marek's vaccine against Marek's disease at day old. At 14 and 28 days, birds were vaccinated against Gomboro while Lasota was administered at 21 days. At 8 weeks, fowl pox and kumorov were administered to the birds and at 16 weeks, a booster dose of Kumorov was also administered to the birds. Routine medications were also carried out. Birds were fed with chick starter ration from 0-4 weeks containing 18-20% Crude Protein, growers from 4-20 weeks containing 15-16% Crude Protein. From 21 weeks of age, females were fed pre-breeder ration with 16-17% Crude Protein and at 24 weeks or 1% production a Crude Protein of 15-16% was fed. The Metabolizable Energy of the feeds ranged from 2750-2800 kcal/kg. Feeding programme was according to the breeders' guide. Water was offered ad lib. 2.1 Experimental Procedure 20 cocks were examined for semen quality characteristics between 38-41 weeks of age. Semen was collected from cocks thrice once in a week. Parameters evaluated were, ejaculate volume, semen pH, sperm concentration and sperm motility. The hens were divided into three groups according to mating ratio (cock to hen). These included ratios 1:6, 1:7 and 1:8 with each group replicated 3 times. Each replicate was housed separately in pens. The cocks were then allowed to mate freely with the hens. Mating commenced from 42 weeks through 47 weeks of age. A ten day grace period was allowed before fertile eggs were collected for hatching. Fertile eggs were marked according to Sire number/pen number since there was only one cock in a pen. Eggs were weighed to the nearest 1g and were stored for a maximum of 7 days at a temperature of 16 o C. There were six hatches.

Candling and Hatching
After setting in trays, eggs were weighed then fumigated, before being set in the incubator during which period eggs were turned on a regular basis. On the 18 th day of incubation, eggs were candled using a bright electric bulb/fluorescent tube; the number of infertile eggs were recorded for each group and then removed from the set eggs. The number of fertile eggs were recorded after which the fertile eggs were transferred to the Hatcher for 3 days (until hatch). Data on fertility and hatchability were recorded for each hatch. Percent fertility, percent hatch and percent hatchability were calculated as follows. (ii) Number of chicks hatched per mating ratio.
All the data collected on semen quality and mating ratio were analyzed using the GLM procedure of SAS (2002). Differences between the means for mating ratio were seperated using Duncan's Multiple Range Test.  CV=Coefficient of Variation.

Means of Semen Quality Characteristics
The mean for semen volume (0.55 ml) obtained in this study was found to be in the range of 0.34 -0.59 ml reported by Bilcik et al. (2005)  Body weight was reported by Gebriel et al. (2009) to have significant effect on concentation and motility but not on semen volume and pH in Norfa chickens while Abd El Ghany et al. (2011) reported body weight influence on volume, concentration and motility but not pH in two local strains of chickens. These authors reported that the heavy weight had the advantage of high concentration but motility was to the advantage of the light weight group.
Age difference had been reported to affect concentration and motility but not volume and pH while season (hot or cold) affected volume, concentration, motility and pH. (Gebriel et al., 2009). Table 2 showed the correlations between the various semen quality traits and body weight. All correlations were positive except the correlation between pH and volume, pH and concentration, and pH and body weight. Most correlations irrespective of direction ranged from low to moderate and not significant. However only the correlation between volume and concentration was significant (p<0.001) and very high (0.92).  The high positive and significant correlation between volume and concentration had been reported. (Bilcik et al., 2005;Gebriel et al., 2009;Abd El Ghany et al., 2011). These authors also reported negative correlation between volume and pH, body weight and pH but positive correlation between concentration and pH which agreed with the results of this study. It was also observed from this study that body weight was positively but not significantly correlated with volume and concentration. Some other reports have shown positive relationship between these parameters (Gebriel et al., 2009;Abd El Ghany et al., 2011). Positive correlation between body weight and volume had also been reported by El Sahn (2007). However Makhafola et al. (2012) reported that body weight was negatively correlated with ejaculate volume, semen concentration and pH in Naked neck and Ovampo but positive correlation was reported between body weight and volume in Potchfstroom Koekoek strains of Southern African indigenous cockerels. Table 3 showed the effect of mating ratio on reproductive parameters. Number of fertile eggs, number of eggs hatched and percent fertile showed significant differences. Percent hatch and percent hatchability were not significantly different. Birds mated in the ratio of 1:6 had the highest values for number fertile, number hatch and percent fertile but not significantly different from ratio 1:8. However the birds in the ratio of 1:7 had similar performance with those in the ratio 1:8 for percent fertile. The inconsistencies in the results obtained due to mating ratio may be due to males behaving differently towards different females . It has been reported that males show mate preferences and will court some individual females more than others within a flock (Blohowiak et al., 1980). Male aggression towards females in commercial broiler breeder industry has been reported to make females less accessible to males due to previous injury (Mench, 1993). Generally, male fertility is based upon ability to perform a successful copulation and the quality of semen produced. The differences observed in the number of fertile eggs and percent fertile obtained due to mating ratios 1:6, 1:7 and 1:8 may be attributed to differences in the reproductive ability of the cocks. Each cock differs in its ability to produce semen. This agrees with reports made by McGary et al. (2003). Another factor to consider is the differences in the semen storage tubule capacity that might exist between the hens. Other factors that could influence the number of sperm at the site of fertilization include egg location within the oviduct and sperm characteristics such as mobility (Fronman et al., 1997;Donoghue et al., 1998) andviability (Baskt et al., 1994).

Conclusion
It was concluded that the semen quality of the cocks fell within reported values for other chicken breeds. High and significant correlation between ejaculate volume and concentration indicated that large ejaculate volume resulted in high concentration. Mating ratio of 1:6 was recommended to enhance fertility and hatchability especially in pedigree hatching.