A total of one hundred and fifty Shaver brown and Nera black hens in their 14th week of lay were used in a study conducted to determine the laying and physical characteristics of Shaver brown and Nera black hens under humid tropical environment. Hens were housed individually in separate cages. The hens were supplied water ad libitum and fed layers mash containing 16.5% crude protein and 2650 kcal/kg of metabolizable energy for 10 weeks. The hens were also divided into three classes based on their laying performance as follows: good layers, intermediate layers and poor layers and their physical conditions appraised. Temperature readings were taken 3-hourly at time intervals of 0900h, 1200h, 1500h, and 1800h using a standard air thermometer and the mean daily temperatures noted. The climatic data taken during the period of the experiment showed that the study area had the natural day-length of 13 to 14 hours; mean maximum weekly indoor and outdoor temperatures of 27.90C to 29.20C and 26.80C to 30.50C, respectively; mean minimum weekly indoor and outdoor temperatures of 20.50C to 22.30C and 20.00C to 23.600C, respectively; relative humidity of 73.1% to 76.6% and mean total monthly rainfall of 781.33mm. Results showed that the peak of lay was between 0700h and 0800h and declined gradually throughout late afternoon hours until no egg was laid between 1700h and 1800h. For Shaver brown hens, about 86.24% and 13.76% of the eggs were laid in the morning and afternoon hours respectively, while 88.75% and 11.25% of the eggs were laid in the morning and afternoon hours respectively, for Nera black hens. Mean egg weight of 70.05g±1.07 and 70.10g±0.92 for eggs laid between 0600h and 0700h for Shaver brown and Nera black hens, respectively were the heaviest (P<0.05) of all the mean egg weights observed in all oviposition intervals. For Shaver brown hens, first eggs laid in a clutch were significantly greater (P<0.05) than subsequent eggs laid in a clutch, while the first eggs in a clutch for Nera black were greater than other eggs in the clutch, although the differences were not significant (P>0.05). Hens with the longest clutches and shortest number of pause days produced the greatest number of eggs. The total number of pause days observed were 1410 and 1329 for Shaver brown and Nera black hens, respectively. Observations made on physical characteristics of the hens revealed that good layers had smooth combs and wattles, moist and enlarged vents with flexible pubic bone, soft abdomen and worn out feathers. Intermediate layers had similar features with good layers except that the eye rings, beaks and shanks were slightly bleached. Poor layers had dry combs and wattles, tight and hard abdomen and closed pubic bones. The Effect of ambient temperature on performance parameters showed that for Shaver brown hens, hen day egg production, average daily feed intake, egg shell weight, egg shape index, albumin height, yolk height, yolk height and Haugh units were significantly reduced (P<0.05) with increasing temperatures. All performance parameters measured for Nera black hens were significantly reduced (P<0.05) with increasing temperatures. Likewise, there was significant interaction (P<0.05) of strain and temperature on average daily feed intake and yolk height. The results of the present study indicate that although heat stress had effect on performance, Shaver brown and Nera black hens are adapted to humid tropical environment and can lay 86.24% and 88.75% eggs, respectively in the morning hours, with overall production rate of 66.43% and 68.36% respectively, for Shaver brown and Nera black hens.

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.....

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