1.1 BACKGROUND OF THE STUDY
The growth in global demand for poultry products is tremendous as the market for these products is growing very fast. Poultry is probably the fastest route to achieve any appreciable improvement in the nutritional standard of the populace because of its short generation interval, quick turnover rate and relatively low capital investment (Smith, 2001; Ani and Okeke, 2011). Gueye (2000) asserted that 85% of rural households in Sub-Saharan Africa keep chickens or other types of poultry. Poultry are equally important to other smallholders in Asia, Latin America and other parts of the world (Mallia, 1999; FAO, 2003; Islam and Jabbar, 2005; Kyrsgarrd, 2007). Increased egg production is one sure way of achieving the target of providing quality animal protein at a minimum cost to the consumers (Oluyemi and Roberts, 2000). Advances in genetic selection make today’s commercial layers quite different from those of years ago. Body weight is less, age at housing is earlier, total egg number has increased, egg mass is greater and feed conversion has improved considerably (Miles and Jacob, 2000; Minivielle et al., 2006). Total egg production is affected both by the physical and laying characteristics of the hen. Laying characteristics of hens have been assessed by evaluating such indices as rate of lay, oviposition time, clutch/sequence length, number of pause days, lag time, hen housed egg production (HHEP), and hen day egg production (HDEP).
Physical characteristics of laying hens on the other hand, consist of those features that can be seen easily on their body such as condition of combs, wattles, eyes, beaks, pubic bones, abdomen and vent. They are used to determine whether a hen is laying or not (Gillespie, 1997; Reddy et al., 2004; Daghir, 2008; Ani and Nnamani, 2011).
Apart from egg laying characteristics which are cyclic and genetically influenced, egg production is affected by nutrition, variations in temperature, light intensity, day- length, relative humidity, disease and level of management. Hens lay sequentially (Wolford et al., 1997; Spradbrow, 1997; Gillespie, 1997; Miles and Jacob, 2000; Smith, 2003; Van Der Molen, 2004; Jakowski and Kaufman, 2004; Reddy et al., 2004; Clauer, 2005; Poultryhelp, 2005). Hens vary in their laying habits. The number of eggs in a sequence varies between one to forty and occasionally even more. Even if flock uniformity is high, not all hens in the flock lay at the same rate. While some hens may be laying at a very high rate of production, others may not even be laying at all (Miles and Jacob, 2000; Ani and Nnamani, 2011). The longer the clutch length, the more eggs a hen lays in a given period (Etches, 1996; Reddy et al., 2004; Jakowski and Kaufman, 2004 ). According to Butcher and Miles (2000), the exotic hen is capable of laying 240-270 eggs per annum, each weighing about 58 grammes under tropical condition. The success of birds as a class is largely due to the fact that they have evolved physiological mechanisms that cause them to lay eggs at a time of season, when such factors as weather and food supply are optimal (Koelkebeck, 2001). According to Daghir (2008), humid environment is very suitable for poultry production. Although all livestock are subject to environmental stress in the tropics, poultry appears to be less susceptible than mammals. One reason may be that with higher body temperature than mammals, birds spend less production energy than other livestock in homeostatic regulations (adjustments). Under suitable tropical housing and management practices, poultry performance in the tropics has in many instances compared favourably with the performance standards of the same breeds reared in temperate environments. In acclimatizing to hot climate, animals normally make physiological adjustments (Hahn et al., 2003). As the seasons change, two major kinds of changes occur in the environments: changes in temperature and changes in length of daylight. Hormones enable the animal to respond physiologically to these seasonal changes (Hahn et al., 2003). The pineal body in chicken’s brain controls its body temperature and its sense of environmental temperature. Normal body temperature lies between 39.80C and 43.60C being at its highest around 1600h and its lowest around midnight (Hahn et al., 2003; Daghir, 2008). Egg production is intimately linked with daylight hours. The light rays received through the eyes affect the pituitary gland, which releases hormone into the bloodstream thus stimulating the ovaries into action. As the day-length hours shorten, egg production correspondingly decreases. By midwinter in temperate environment, it is usually nonexistent. To ensure continued production, hens in temperate regions must have a minimum of 16 hours of light per day. As the hours of natural day-length decreases, artificial lighting can be gradually introduced for longer periods to make up the difference (Clauer, 2005; Hanson, 2005). Environmental condition of the area in which the hens are laying affects their sequence length.
1.2 STATEMENT OF PROBLEM
Advances in genetic selection make today’s commercial layers quite different from those of years ago. Body weight is less, age at housing is earlier, total egg number has increased, egg mass is greater and feed conversion ratio has improved considerably (Miles and Jacob, 2000; Minivielle et al., 2006). Although management and feeding practices are the key determining factors of egg production, the breed of laying hen affects egg production. The rate of adaptation and quality of egg production of different exotic breeds of hen vary when exposed to a variety of climate and environments. According to Miles and Jacob (2000), some hens may be laying at a very high production rate while others may not be laying at all. The climatic conditions of Nsukka in particular and those of South Eastern Nigeria in general depict a typical tropical climate (Egbunike, 2002). Findings by Okonkwo and Akubuo (2007) have revealed an average annual minimum and maximum temperature ranges of 220C – 24.70C and 330C -37oC, respectively. These ranges appear to fall outside the zone of thermo neutrality of laying hens which is 180C – 22oC as recently defined by Imik et al. (2009). As such, adverse effects of heat stress are suspected to clasp egg production parameters of laying hens in the tropics. Most African diets (including Nigerian) are deficient in animal protein which results in poor and stunted growth as well as increase in spread of diseases and consequently death (Apantaku et al., 2003). Apart from low egg production and poor performing breeds, other problems associated with poultry production in Nigeria are diseases and pests, poor weight gain/feed conversion, feeding and management problems and lack of capital (Eekeren et al.,1995; Isiaka 1998; Apantaku et al., 2003). Moreover, the environment to which poultry birds are exposed affect performance of the birds (Abeke et al., 1998; Isiaka, 1998). The optimal laying temperature is between 18-220C (Imik et al., 2009), while a relative humidity above 75 percent will cause a reduction in egg laying (Hahn et al., 2003). When the temperature rises above 280C , the production and quality of eggs decrease as seasonal temperature increase can reduce egg production by 10 percent (Oluyemi and Roberts, 2000; Smith, 2001). Lastly, egg production clearly requires planning for costs as well as for profit generation and for meeting market demand without which a commercial egg production venture may suffer serious setbacks.
1.3 OBJECTIVES OF THE STUDY
The study was aimed at evaluating the laying and physical characteristics of Shaver brown and Nera black hens in hot humid environment.
The specific objectives of the study were as follows:
- To determine the oviposition time, and clutch size of Shaver brown and Nera black hens in hot humid environment.
- To determine position of eggs in a clutch and their relationship to egg weight in hot humid environment.
- To determine the comparative performance of Shaver brown and Nera black hens in hot humid environment.
To establish the relationship between performance and environmental temperature