How many chickens does it take to make an egg? Animal welfare and environmental benefits of replacing eggs with plant foods at the University of California, and beyond

Cleveland, David Arthur; Gee, Quentin; Horn, Audrey; Weichert, Lauren; Blancho, Mickael

doi:10.1007/s10460-020-10148-z

Table 1 Estimation of eggs per chicken^a in the US egg production industry

From: How many chickens does it take to make an egg? Animal welfare and environmental benefits of replacing eggs with plant foods at the University of California, and beyond

	1. Table egg-type chicks hatched^c	Layers^b removed from flock during the month				Layers^b on hand during the month				10. Table egg production^d
	1. Table egg-type chicks hatched^c	2. Layers sold for slaughter^d	3. Layers eliminated, other^d	4. Total layers removed from flock: columns (2 + 3)	5. Table egg-type layers^c removed from flock: columns {4*[(6 + 8)/(6 + 7)]}	6. Table egg-type table egg layers^d	7. All hatching layers (broiler egg-type + table egg-type)^d	8.Table egg-type hatching egg layers^d	9. Total table egg-type layers^e: columns (6 + 8)	10. Table egg production^d
2016 December	45,731,000	14,359,000	10,307,000	24,666,000	21,075,102	318,956,000	58,415,000	3,477,000	322,433,000	7,953,900,000
2017 January	45,367,000	15,899,000	9,494,000	25,393,000	21,671,142	318,495,000	58,703,000	3,417,000	321,912,000	7,916,400,000
February	48,127,000	15,099,000	9,010,000	24,109,000	20,539,489	317,258,000	59,083,000	3,363,000	320,621,000	7,095,800,000
March	55,919,000	16,192,000	10,530,000	26,722,000	22,728,156	316,664,000	59,593,000	3,358,000	320,022,000	7,861,500,000
April	52,762,000	13,524,000	13,479,000	27,003,000	22,928,274	315,770,000	59,978,000	3,278,000	319,048,000	7,572,800,000
May	53,506,000	16,679,000	9,347,000	26,026,000	22,054,625	313,464,000	60,178,000	3,163,000	316,627,000	7,764,500,000
June	49,722,000	14,347,000	9,481,000	23,828,000	20,172,066	312,162,000	60,268,000	3,126,000	315,288,000	7,513,800,000
July	41,862,000	14,930,000	9,096,000	24,026,000	20,348,326	312,412,000	60,220,000	3,181,000	315,593,000	7,782,100,000
August	45,861,000	15,121,000	8,783,000	23,904,000	20,269,310	313,841,000	60,060,000	3,207,000	317,048,000	7,755,200,000
September	42,725,000	13,038,000	8,637,000	21,675,000	18,383,671	315,502,000	60,246,000	3,189,000	318,691,000	7,456,600,000
October	51,495,000	14,586,000	8,796,000	23,382,000	19,849,167	317,758,000	60,270,000	3,153,000	320,911,000	7,763,300,000
November	48,344,000	12,893,000	7,516,000	20,409,000	17,363,299	320,748,000	60,072,000	3,241,000	323,989,000	7,676,300,000
Mean	48,451,750	14,722,250	9,539,667	24,261,917	20,615,014	316,085,833	59,757,167	3,262,750	319,348,583	7,676,016,667
SD	4,190,526	1,141,193	1,403,673	1,844,518	1,574,477	2,606,555	631,661	110,095	2,676,239	228,060,989
Total annual	581,421,000	176,667,000	114,476,000	291,143,000	247,380,168					92,112,200,000

^aChicken = both male and female of any age
^bLayer = mature female chicken producing marketable eggs, usually at least 20 weeks old (USDA NASS 2005, p. 9). "Layers" in columns 2–4 refer to all three types of layers: broiler-type hatchery supply layers, table egg-type hatchery supply layers, and table egg-type layers
^cData from (USDA NASS 2018c). Unless otherwise specified "table egg-type" refers to all table egg-type chickens, both those designated to produce table eggs and those designated to produce hatching eggs
^dData from (USDA NASS 2018b)
^eTable egg-type layers in this table refers to both table egg-type table egg layers and table egg-type hatching egg layers
Additional calculations:
0.0063: Chicken lives (table egg)⁻¹ = (mean table egg-type chicks hatched)/(mean eggs produced), = (column 1 ave.)/(column 10 mean)
24.04: Table eggs (table egg-type layer)⁻¹ mo⁻¹ = (column 10 mean mo⁻¹)/(column 9 mean)
372.35: Table eggs (table egg-type layer)⁻¹ over life as layer = (mean table eggs (table egg-type layer)⁻¹ mo⁻¹) * (life expectancy as table egg-type layer in months)
2.35: Chickens (table egg-type layer)⁻¹ = (column 1)/(column 5) = (egg-type layers hatched mo⁻¹) / (mean table egg-type layers added to flock mo⁻¹) = [mean life expectancy as table egg-type layer (months)]/[mean life expectancy table egg-type layers at hatching (months)]
158.43: Table eggs chicken⁻¹ over life = [table eggs (table egg-type layer)⁻¹ over life]/[chickens (table egg-type layer⁻¹)], = [(column 10)/(column 1)], = (mean life expectancy at hatching, months) * [Table eggs (table egg-type layer)⁻¹ mo⁻¹]
0.0063: Chicken lives egg⁻¹ = [1/(Table eggs chicken)⁻¹ over life]
6.59: Mean time table egg-type chickens live (months), from hatching = (column 9 mean.)/(column 1 mean. mo⁻¹)
15.49: Number of months before all birds in the flock are completely replaced, = (column 9 ave.)/(column 5 mean mo⁻¹). Assumes population size is stable, so that table egg-type layers removed = table egg-type layers added
0.57: Mean mortality rate of table egg-type chickens, from hatching to entering table egg-type layer flock

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