Background and Objective: Moulting of older breeders is a procedure to obtain or to increase reproductive performance of breeders by restoration of egg quality. A 15-week study was carried out to examine the effect of induced molting of Sasso broiler breeders by feed withdrawal for a period of 9 days on the production performance, egg quality, hatching traits and 1-week post-hatch chick performance. Materials and Methods: A total of 240 Sasso broiler breeders (72 weeks old) were randomly allotted to two treatment groups (non-molt and molt) of 120 hens each. Each group was further divided into six replicates with 20 hens per replicate and 2 cocks each. The hens in the molt treatment group were subjected to molting by feed withdrawal for a period of 9 days. After the commencement of egg production, eggs were collected from the two experimental groups and incubated (from the 7th week after molting). Collection and incubation were repeated 5 times. The chicks hatched from these incubations were reared for 1-week. Results: The eggs from the molted hens had a higher albumen height and haugh unit. The eggs from the molted hens had an improvement in fertility while the hatchability of the fertile eggs was not different in the 2 groups. The incubation duration, chick weight and quality at hatch showed no difference between the treatments. At the end of the 7 days post-hatch, there was no difference in chick performance. Conclusion: It was concluded that although induced molting procedure with feed withdrawal improved the production, quality and fertility of eggs of Sasso broiler breeders, it did not influence chick quality and 1-week performance.
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The age of breeders influences the number of eggs and egg quality1. Also, fertility, embryonic mortality and hatchability rates depend on the age of the breeder flock2-5. The production of eggs in laying flocks, fertility, hatchability of set eggs and hatchability of fertile eggs are limited by age and decrease with the increase in the breeder age6,7. The hatching egg weight and the weight of day-old chick at hatch are also dependent on the breeder age8. The chick quality is lower in chicks hatched from eggs from older breeders9,10. As shown by Tona, et al.11, the effect of age could be reversed by molting the breeders, to improve performance.
Induced molting is a management tool used to rejuvenate the reproductive system of egg-laying hens at the end of the laying cycle, which averagely ranges from 70-85 weeks in commercial layers and 60-65 weeks in breeders12. Generally, it is known that molting may be induced by feed and water withdrawal13, by variable nutrient diets or by diets high in minerals14, or by injection of hormones1. The most widely practiced method to induce a molt is feed withdrawal and a restriction of the photoperiod to the natural day length or less and occasionally restriction of drinking water15.
With induced molting a significant loss of weight, changes in the histo-physiology of the reproductive system, which in turn leads to interruption in egg production for a short period, subsequent improvement in egg quality and an increased post-molt egg production was observed16. It also affects fertility17, hatchability11 and chick quality. Generally, different strains of birds may respond differently to induced molting18. To our knowledge, there is scarcity of study on the response of Sasso broiler breeders to induced molting in the tropical environments. Thus, this study was carried out to evaluate the effect of induced molting on production performance, reproductive tract morphometry, egg quality, fertility, hatching traits, chick quality and the 1-week post-hatch performance of chicks after induced molting of Sasso broiler breeders using the feed withdrawal method.
MATERIALS AND METHODS
Experimental design: Two hundred and forty (240) 72 weeks old Sasso broiler breeder hens were used for this study. The birds were weighed and randomly allotted to 2 groups (non-molt and molt) of one hundred and twenty (120) hens each using a completely randomized design. Each group was further divided into six replicates with 20 hens per replicate.
Each replicate was housed together with two cocks. Molting was done by a short-term feed withdrawal technique. Feed withdrawal with water provided ad-libitum lasted for 9 days. During the first 6 days of the feed withdrawal period, the hens were offered 10 g hen1 day1 of oyster shell. During molting, hens were fasted of feed until they lost 17.35% of their initial weight and then feeding was recommenced on the 10th day with pullet diet by gradual refeeding of hens with 30 g bird1 day1 up to 118 g bird1 day1. At 5% of egg production, the birds were offered the normal breeder diet until the end of the experiment (i.e., experimental week 14). During the feed withdrawal phase the lighting program was 12L: 12D and in the post-molt phase the lighting program was 16L: 8D. From day 1 of the experiment, the non-molted birds were continuously fed the normal breeder diet. Eggs and required data were collected daily. Samples of eggs were used for egg quality measurements at different times. After molting and the recommencement of full egg production, [from the 7th week after molting i.e., at 81, 82, 84, 85 and 86 weeks of age of the breeders (AOB)], the total settable eggs in all the replicates of the molted and the non-molted hens were collected and incubated every week (i.e., total of 5 incubations). Each batch of the hatched chicks were reared for a period of seven days to ascertain the 1-week post-hatch juvenile chick performance.
Management of Sasso broiler breeder: The birds were weighed daily and quantity of feed offered and the leftover was weighed and recorded weekly. Weekly feed intake was determined as the difference between the quantity of feed offered and the quantity of feed leftover.
The experimental birds were weighed at the beginning of the experiment and on weekly basis until the end of the experiment. During the molting period, the body weights of the molted birds were recorded 3 times in a week and the percentage weight loss was determined until they lost 17.35% of their initial weight. At this point of weight loss, feed withdrawal was stopped.
The daily egg production was recorded throughout the experiment and used to calculate the weekly egg production percent in each experimental group. The egg production was expressed as the laying rate and calculated using the following formula as described by Dikmen et al.19:
The egg mass is the average egg weight multiplied by the total number of eggs for that week.
Daily mortality was recorded and at the end of the experiment, mortality was calculated as the ratio of the number of dead birds to the number of birds per treatment, expressed as a percentage.
Gross morphometry of the reproductive tract: The gross morphometry of the oviduct and the ovary was assessed. This was done at the end of the feed withdrawal period (0% egg production) just before recommencement of feeding and at 40% lay (5 weeks after the end of the feed withdrawal period). Two hens were randomly selected per replicate to examine the oviduct. The hens were sacrificed by cervical dislocation and then cut open along the rib cage to expose the organs in the abdominal cavity and all the reproductive tract was removed. The length and weight of the different sections of the oviduct (infundibulum, magnum, isthmus, uterus and vagina) were measured.
Egg quality: The internal and external egg quality was assessed 6 times during the experiment. Five freshly laid eggs were collected per replicate (i.e., 30 per treatment, from the 5th week after molting at experimental week 7, 9, 10, 12, 13 and 14) and used to assess egg quality parameters. The freshly laid eggs were collected before 11:00 am on the days of egg quality assessment. The egg quality parameters were determined using a semi computerized system ‘Bröring’ software (Futura 2A 2011, manufactured by Bröring Technology GmbH, Niedersachsen, Germany); the egg weight, albumen height and Haugh unit were automatically recorded by this software. The external egg quality parameters assessed were the egg weight, egg length and diameter, shell weight, shell thickness while the internal egg quality parameters assessed were albumen height, albumen Haugh unit, yolk color yolk and albumen weight. The proportions of shell, yolk and albumen were also calculated as described by Dikmen et al.21:
Incubation: For incubation, the settable eggs were numbered, weighed individually and set in single stage incubators (Pas Reform) at the temperature of 37.5°C (later reduced to 36.5°C after the 18th day), humidity of 60% and automatic egg turning (eggs rotate through 90°) set hourly. On the 18th day of incubation, eggs were candled and the fertile eggs were transferred from the turning trays to the hatching baskets in the hatcher.
Fertility was calculated as the number of fertile eggs divided by the total number of eggs set multiplied by 100. The fertile eggs were determined by candling on day 18 of incubation. The hatchability percentage was determined by dividing the number of hatched eggs per replicate by the total number of fertile eggs in each replicate and then multiplying by one hundred.
The hatching times were recorded to ascertain the duration of incubation. The duration of incubation was determined as the average time of hatch.
Chick quality: At the end of each incubation period at hatch, the average weights of hatched chicks in the two treatment groups were recorded and then the quality of the hatched chicks was assessed immediately after hatch using Tona score23.
One-week post-hatch performance of chicks: The initial body weight of the chicks was recorded and the chicks were reared under normal brooding conditions and fed a broiler starter diet (2,926 kcal kg1, 21% crude protein). The quantity of feed consumed was recorded and the final body weight at the end of 7 days was measured. The juvenile growth performance of the chicks was evaluated for the first week after hatch in terms of the final body weight and relative growth as described by Tona et al.10:
Statistical analysis: The software Graph Pad Prism 8.0.2 was used for data analysis. The student t-test was used to compare the sample means. The generalized linear regression model was used to analyze the effects of molting on egg production, egg weights and egg components, feed intake, feed ratio conversion, duration of incubation and post hatch weights. Differences of p<0.05 were considered statistically significant. When the means of the general model were statistically different, then the means were further compared using Tukey’s test. In a second analysis, hatchability was considered as binomial distribution. A 2-tailed test for comparison of variances was used to analyze the effect of molting on hatchability.
Weekly body weight and feed intake: Figure 1a shows that molting significantly (p<0.05) influenced the average weekly weight of the hens throughout the course of this experiment.
There was a drop in weight of the molted hens at the commencement of feed deprivation and the subsequent regain of the weight after the recommencement of feeding. The molted hens attained 17.35% weight loss on the 9th day of the experiment. Molting significantly (p<0.05) influenced the average daily feed intake of the hens throughout the experimental duration. The overall feed consumption of the molted hens was lower than those of the non-molted (control) hens (Fig. 2a).
Weekly laying rate: Generally, molting significantly (p<0.05) influenced the laying rate. The egg production was higher in molted hens after recommencement of laying (Fig. 3a). Cessation of lay in the molted hens was observed averagely on the 6th day of feed withdrawal. Recommencement of lay was averagely on the 23rd day (week 3 of the experiment) of the experiment i.e., 2 weeks after the FW period. Molted hens reached a peak of lay (60.24%) at week 9 and 10 of the experiment while the highest laying rate (47.73%) was recorded in the non-molted hens during the entire duration of the study. The laying rate was significantly (p<0.05) higher in molted hens from the 7th week of the experiment until the end of the experiment.
Overall production performance: Table 1 shows that feed intake and feed conversion ratio (FCR) were lower (p<0.05) in molted hens compared to the non-molt group while egg production was higher in the molted hens. However, there were no significant differences (p>0.05) in the average egg weight and the mortality among the two treatment groups.
Ovary and Oviduct morphometry: Table 2 show that the number of yellow follicles, weight of yellow follicles, the length and weight of the oviduct and its segments at the end of feed withdrawal period were significantly higher (p<0.05) in the non-molted hens when compared to the molted hens. Nevertheless, with regard to the same parameters, there were no significant differences (p>0.05) across the two treatment groups after 5 weeks of the feed withdrawal period.