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Ammonia emissions, feeding and defecation dynamics of W36 pullets and laying hens as affected by stocking density and manure accumulation time
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A great deal of effort has been given through intensive research toward studying the sources of gaseous emissions from animal feeding operations (AFOs) and their influencing factors. Ammonia (NH3) is the most predominant noxious gas released from poultry production facilities and it is mainly affected by diet composition, manure temperature, moisture content and stacking configuration and manure surface area exposed to ambient air. However, current literature lacks information on bird age effects on NH3 emissions, even though changes in diet composition with bird age are expected to affect the emissions. Also, some producers have been using different bird stocking densities (SD) as an attempt to improve bird welfare. Nevertheless the effects of different bird SD regimens on NH3 emissions remain unknown. Moreover, it has been shown that different housing styles can have significant impacts on the magnitude of NH3 emissions from laying-hen facilities in that the high rise (HR) systems (typical of US egg production) emit 61 to 71 % more ammonia than the manure-belt (MB) systems (gaining more popularity in the US). The impact of manure accumulation time on the belts in MB systems on NH3 emissions needs to be quantified. Hence, a research study was conducted in a laboratory setting that resembled a commercial MB system for laying hens. The results of the study are presented in this thesis. Chapter 2 describes the effect of different SD regimens (155 to 619 cm2 bird-1 or 24 to 96 in2 bird-1) and manure accumulation time (MAT, 1 to 6 d) of pullets (hens < 18 weeks of age) and laying hens on NH3emissions. Results showed that daily NH3 emission rate (ER) for pullets and laying hens increased exponentially with bird age and MAT, while SD effect on NH3 ER was more pronounced for MAT ≥ 3d (P<0.0001). In general, higher SD led to higher ER. Specifically, for the laying hens, NH3 emissions from the 3rd to 6th d MAT ranged from 41 to 251 mg/hen-d for the high density (HD) and from 29 to 160 mg/hen-d for the low density (LD). This outcome supports the current egg industry practice of removing manure at 1- to 3-d MAT for the MB house systems. Chapter 3 assesses the dynamics of feeding, defecation and NH3 emissions of pullets and laying hens under different SDs (as used in the trials described in Chapter 2), MAT (1 to 6 d) during light and dark periods of the day. Results indicate that SD did not adversely affect feed disappearance or fresh manure production (P = 0.17 – 0.81) at any of the tested ages. For each gram of feed use, the fresh manure produced varied from 0.58 to 1.15 g bird-1 (P < 0.0001) varying according to bird age. The light and dark partitioning of feed disappearance was 92% to 8%, respectively, while the partitioning for fresh manure production was 80% to 20%. Results also revealed that 37% of the total daily NH3 emission occurred during the dark period vs. 63% during the light hours.
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