Statistical models for estimating lamb birth weight using body measurements

Figures & data

Table 1. General data of birth weight and measurement lambs.

Variable	N	Mean	Std Dev	Min.	Max.
BW (kg)	101	4.58	0.889	2.5	6.5
SC (cm)	101	7.23	0.773	5.0	9.0
HC (cm)	101	27.22	1.527	23.0	32.0
CC (cm)	101	38.32	2.661	30.0	43.0

N: number of observations; Std Dev: standard deviation; Min.: minimal value; Max.: maximal value; BW: birth weight; CC: chest circumference; SC: shin circumference; HC: head circumference.

Table 2. Partial correlation coefficients of birth weight dependence on body measurements.

Variables	BW	SC	HC
SC	0.345**
HC	0.679***	0.514***
CC	0.795***	0.290**	0.658***

BW: birth weight; CC: chest circumference; SC: shin circumference; HC: head circumference; **p < .01; ***p < .001.

Table 3. Statistical models for estimation birth weight of lambs from body measurements.

		GLM procedure		MIXED procedure			Significance of fixed effects
		R^2	p-Model	AIC	AICC	BIC	Breed	Age	Sex	LS
A	BW = 1.138^n.s. + 0.524 × SC***	0.608	***	190.9	191.0	193.4	***	*	n.s.	***
B	BW = −4.459*** + 0.343 × HC***	0.741	***	154.3	154.4	156.8	***	*	n.s.	***
C	BW = −3.997*** + 0.225 × CC***	0.781	***	139.8	139.8	142.3	n.s.	n.s.	n.s.	***
D	BW = −4.539*** + 0.172 × SC^n.s. + 0.301 × HC***	0.751	***	153.7	153.8	156.2	***	n.s.	n.s.	***
E	BW = −4.672*** + 0.243 × SC*** + 0.198 × CC***	0.804	***	132.8	132.9	135.4	**	n.s.	n.s.	***
F	BW = −5.932*** + 0.175 × HC*** + 0.154 × CC***	0.818	***	127.2	127.3	129.8	**	n.s.	n.s.	***
G	BW = −5.973*** + 0.144 × SC^n.s. + 0.142 × HC** + 0.151 × CC***	0.825	***	127.1	127.1	129.6	***	n.s.	n.s.	***

BW: birth weight; CC: chest circumference; SC: shin circumference; HC: head circumference; R²: coefficient of determination; p-Model: p value of model; LS: litter size, Age: ewes’ age category; Sex: sex of lambs; n.s.: non-significant; *p < .05; **p < 0.01; ***p < .001

Table 4. Comparison of real vs. estimated birth weight.

MODEL	RBW ± Sd	EBW ± Sd	RBW vs. EBW ± Sd	MinD	MaxD	CORR
A	4.58 ± 0.889	4.93 ± 0.405	−0.353 ± 0.773	−2.334	1.691	0.498***
B	4.58 ± 0.889	4.89 ± 0.524	−0.313 ± 0.603	−1.814	1.686	0.753***
C	4.58 ± 0.889	4.63 ± 0.599	−0.054 ± 0.500	−1.333	0.991	0.845***
D	4.58 ± 0.889	4.90 ± 0.552	−0.325 ± 0.602	−1.796	1.704	0.747***
E	4.58 ± 0.889	4.68 ± 0.632	−0.102 ± 0.481	−1.362	0.950	0.854***
F	4.58 ± 0.889	4.71 ± 0.630	−0.135 ± 0.465	−1.471	1.607	0.867***
G	4.58 ± 0.889	4.72 ± 0.645	−0.148 ± 0.463	−1.462	1.132	0.865***

RBW: averaged real birth weight (kg); EBW: averaged estimated birth weight (kg); RBW vs. EBW: averaged difference between real birth weight and estimated birth weight (kg); MinD: minimal difference between real birth weight and estimated birth weight; MaxD: maximal difference between real birth weight and estimated birth weight; CORR: Pearson correlation coefficients between real birth weight and estimated birth weight; ***p < .001.

Data availability statement

The data that support the findings of this study are available on request from the corresponding author, A. M. The data are not publicly available due to their containing information that could compromise the privacy of research participants.