Table 7.

Results of a simulated backcrossing design to restore lines from the frozen semen of the cryobank; from the production of F₁ birds after insemination of commercial layers with frozen-thawed semen¹

Line	Stage	Males, n	Dams, n	Artificial inseminations per dam, n	Fertile eggs, n	Chicks, n	Females, n	Layers, n	Straws, n	Donor genome, %
R+	F1	5	20	4	53	48	24	18	80	50
	BC1	5	18	5	60	54	27	20	90	75
	BC2	5	20	6	64	58	29	22	120	87.5
	BC3	5	21	9	76	68	34	26	189	93.75
	BC4	10	26	9	78	70	35	26	234	96.87
	BC5	10	26	10	87	78	39	29	260	98.4
Total									973
Gauloise dorée	F1	5	20	2	45	41	20	15	40	50
	BC1	5	15	3	51	46	23	17	45	75
	BC2	5	17	4	61	55	28	21	68	87.5
	BC3	5	21	6	85	77	38	29	126	93.75
	BC4	8	29	7	114	103	51	39	203	96.87
Total									492
Y33	F1	5	20	3	83	75	37	28	60	50
	BC1	5	26	2	72	65	32	24	52	75
	BC2	5	23	2	64	57	29	22	46	87.5
	BC3	7	20	4	111	100	50	37	80	93.75
	BC4	10	34	4	188	170	85	64	136	96.87
	BC5	10	40	4	222	200	100	75	160	98.4
Total									536
B4	F1	5	20	3	54	48	24	18	60	50
	BC1	5	18	3	48	44	22	16	54	75
	BC2	5	16	4	46	41	21	15	64	87.5
	BC3	5	15	9	60	54	27	20	135	93.75
	BC4	10	20	8	29	26	13	10	160	96.87
Total									473

¹BC 1, 2, 3, 4 = successive backcrossing with frozen-thawed semen from a line. Changes in fertility rates with backcrossing generations: BC2, 80% of F₁ for B4, R+ and GLD lines. BC₃, 60% of F₁ for R+ and GLD lines and 50% of F₁ for B4. BC4 and after, 50% of F₁ for R+ and GLD lines and 20% of F₁ for B4. Fertility rate decreased with an increasing percentage of donor genome for the R+, Gauloise dorée breed, and B4 lines. Different males were used to produce F₁, BC1, BC2, and BC3 females.