Characterisation of white facial markings in Pura Raza Española horses (a worldwide population genetic study)

Figures & data

Table 1. Description of the white facial markings scoring system in the pura raza español horse.

Score 0	Score 1	Score 2	Score 3	Score 4
No white facial Markings	Small white markings on the forehead	Big white markings on the forehead	White markings on front-nose	White markings all over the head

Table 2. Number and proportion (%) of Pura Raza español horses according to the white facial markings scores and Generalised Non-Linear Model analysed depending on coat colour.

		Affected				p value
	Score 0 (No affected)	Score 1	Score 2	Score 3	Score 4
Total Population (n)	27,697	2,645	8,629	2,634	475	<.001
(%)	(65.8)	(6.3)	(20.5)	(6.3)	(1.1)
Bay (n)	11,091	1,322	3,762	601	175
(%)	(65.4)	(7.8)	(22.2)	(3.6)	(1.0)
Chestnut (n)	1,482	204	1,114	583	89
(%)	(42.7)	(5.9)	(32.1)	(16.7)	(2. 6)
Black (n)	3,851	431	1,022	115	33
(%)	(70.6)	(7.9)	(18.8)	(2.1)	(0.6)
Grey (n)	11,273	688	2,731	1335	178
(%)	(69. 6)	(4.3)	(16.9)	(8.1)	(1.1)

Table 3. Results of matings of Pura Raza española horses regarding the presence of white facial markings according to coat colour.

Parents	Total population	Offspring
		Number of foals	% With markings	% Without markings
		4,484	33.6%	66.4%
With markings (father) × With markings (mother)	Bay	243	55.9%	44.1%
	Chestnut	242	72.3%	27.7%
	Black	30	50.0%	50.0%
	Grey	70	51.4%	48.6%
With markings (father) × Without markings (mother)	Bay	464	31.9%	68.1%
	Chestnut	257	50.6%	49.4%
	Black	91	30.8%	69.2%
	Grey	162	28.4%	71.6%
Without markings (father) × With markings (mother)	Bay	469	33.1%	66.9%
	Chestnut	214	57.0%	43.0%
	Black	103	34.0%	66.0%
	Grey	104	32.7%	67.3%
Without markings (father) × Without markings (mother)	Bay	1,125	19.2%	80.8%
	Chestnut	311	31.5%	68.5%
	Black	265	20.7%	79.3%
	Grey	334	22.77%	77.3%

Table 4. Generalised non-linear model (GLZ) between white facial markings and systematic risk factors and significance level.

Risk factors	Class	Population (%)						p-value
		n	Score 0	Score 1	Score 2	Score 3	Score 4
Sex	Females	26,704	66.3	6.3	20.3	6.0	1.1	<.05
	Males	15,376	65.0	6.3	20.9	6.7	1.1
Geographical area	Spain	32,470	63.5	6.3	21.6	7.3	1.3	<.05
	Europe	2,085	71.1	8.3	16.1	3.9	0.6
	North America	2,956	76.3	6.4	13.8	3.3	0.2
	Central South America	4,569	73.1	5.5	18.7	1.7	1.0
Inbreeding coefficient	≤0.625	24,355	65.1	6.8	21.1	5.9	1.1	<.05
	>0.0625 ≤ 0.125	13,160	67.6	5.6	19.5	6.3	1.0
	>0.125 ≤ 0.1875	3,109	66.3	5.1	18.7	8.2	1.7
	>0.1875	1,456	60.8	5.7	23.8	7.9	1.8
Birth period	2006–2013	23,649	67.1	6.3	19.3	6.2	1.1	<.05
	2014–2021	18,431	64.2	6.3	22.0	6.3	1.2

Table 5. Genetics parameters (mean and median for additive genetic variance (σ_u) and residual variance (σ_e) and heritabilities (h²) and fitting parameter deviance information criterion (DIC) for white facial markings according to coat colour, calculated with different genetic models.

Model		σu		σe		h^2	HPD 95%	DIC
		Mean	Median	Mean	Median
Dichotomic		1.7	1.7	1.0	1.0	0.63^1 0.38^2	0.60–0.66 0.36–0.41	−32298.34
Linear		0.4	0.5	0.6	0.6	0.43	0.41–0.46	113184.05
Linear with heterogeneity	Chestnut	0.5	0.5	1.0	1.0	0.32	0.30–0.34	112344.19
	Bay			0.5	0.5	0.47	0.45–0.49
	Black			0.4	0.4	0.53	0.51–0.56
	Gray			0.7	0.7	0.40	0.38–0.42

¹Heredability underlying scale 2 heredability real scale.

HPD 95%: 95% higher posterior density. All Monte Carlo sampling error were lower or equal than 0.0001; Geweke Z-Score ranged between −1.8 and −0.9 and p > 1.

Data availability

The data underlying the results presented in the study are available from https://zenodo.org/records/10623667 Sánchez-Guerrero, M.J. (2024), ‘white markings dataset’, doi:10.5281/zenodo.10623666.