Genetic analysis of test-day milk yield in sheep recorded at two governmental breeding and multiplication centers in Ethiopia

Figures & data

Table 1. Characteristics of the two governmental farms located in the central highlands of Ethiopia.

Characteristic	Governmental farm^a
	DB-R	AG-R
Distance from Addis-Ababa	125 km	282 km
Altitude (m.a.s.l)^b	2780	1680–3600
Latitude and longitude	9°36 N–39°38 E	10°28 N–39°5E
Rainfall (mm per year)	920	800–1600
Rainy season, pattern^c	June–September, bi-modal	June–September, bi-modal
Temperature^d	8.2–18.6°C	8–18°C

^a DB-R = Debre-Berhan Sheep Breeding and Multiplication Center; AG-R = Amed-Guya Sheep Breeding and Multiplication Center.

^b m.a.s.l. = meters above sea level.

^c June to September is the main rainy season. A weaker and unreliable second rainy season occurs from February to March (Getachew, 2015).

^d Average minimum and maximum per day in a year.

Table 2. Number of ewes with test-day milk yield (TDMY) records and number of records in each genetic group.

Genetic group	No. of ewes	No. of records
0% Awassi (100% Menz)	28	107
50% Awassi	125	579
75% Awassi	37	183
100% Awassi	21	171
Total	211	1040

Table 3. Estimated variance components and genetic parameters (± SE), for test-day milk yield (kg day⁻¹) obtained with statistical models with or without additive genetic effect a.

Parameter	Estimate ± SE
	With a	Without a
Additive genetic variance $\left({\sigma }_a^2\right)$	0.016 ± 0.013	–
Permanent environmental variance $\left({\sigma }_{\mathrm{pe}}^2\right)$	0.009 ± 0.012	0.024 ± 0.005
Residual variance $\left({\sigma }_e^2\right)$	0.139 ± 0.007	0.140 ± 0.007
Phenotypic variance $\left({\sigma }_y^2\right)$	0.164 ± 0.007	0.164 ± 0.008
Heritability (h^2)	0.096 ± 0.078	–
Repeatability (r)	0.148 ± 0.031	0.145 ± 0.030

Note: With a: h² = ${\sigma }_a^2$/${\sigma }_y^2$, r = (${\sigma }_a^2$ + ${\sigma }_{\mathrm{pe}}^2$)/${\sigma }_y^2$; without a: r = ${\sigma }_{\mathrm{pe}}^2$/${\sigma }_y^2$.

Figure 1. Observed test-day milk yields (TDMY, kgday⁻¹) and fitted lactation curves for each genetic group.

Table 4. Least-squares means (LSM) of average test-day milk yield (kg day⁻¹) over 120 days in milk in each genetic group of ewes and estimated contrasts between groups. All estimates are given with standard error (SE).

Genetic group	LSM ± SE	LSM contrasts ± SE
		50% Awassi	75% Awassi	Awassi
0% Awassi	0.81 ± 0.03	0.22 ± 0.04*	0.25 ± 0.04*	0.88 ± 0.05*
50% Awassi	1.02 ± 0.02		0.04 ± 0.03	0.67 ± 0.04*
75% Awassi	1.06 ± 0.03			0.63 ± 0.04*
Awassi	1.69 ± 0.04

*p < 0.05.

Table 5. Number of individuals in each genetic group and corresponding minimum and maximum estimates of breeding values (EBV, kgday⁻¹) for test-day milk yield (sum of average genetic group effect for an individual over 120 days in milk and individual animal genetic effect).

Genetic group	Observed ewes			Sires of observed ewes
	N	Min	Max	N	Min	Max
0% Awassi	28	0.60	1.08	9	0.61	1.09
50% Awassi	125	0.76	1.39	6	1.01	1.18
75% Awassi	37	0.79	1.43	–	–	–
100% Awassi	21	1.39	2.17	36	1.55	1.97

Table 6. Mean, minimum and maximum accuracy of estimated breeding values for test-day milk yield in each genetic group of ewes and sires of ewes.

Genetic group	Observed ewes			Sires of observed ewes
	Mean (%)	Min (%)	Max (%)	Mean (%)	Min (%)	Max (%)
0% Awassi	48.7	33.3	57.8	51.8	40.7	63.7
50% Awassi	55.3	40.5	65.9	55.7	41.4	66.7
75% Awassi	55.3	42.3	64.9	–	–	–
100% Awassi	60.0	50.7	68.6	49.4	26.8	71.6a

Getachew, T. (2015). Genetic diversity and admixture analysis of Ethiopian fat tailed and Awassi sheep using SNP markers for designing crossbreeding schemes. PhD thesis, University of Natural Resources and Life Sciences, Vienna, Austria.

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