Table 6.

The effect of litter composition (litters with only similar-sized piglets [light weight or heavy weight; UNIFORM litters] vs. litters with equal numbers of light-weight and heavy-weight piglets [MIXED litters]) and birth weight class and their interaction on the performance of piglets born light (less than 1.25 kg) and heavy (1.50 to 2.00 kg) from birth to slaughter at different stages of production (weaner, grower, finisher, and slaughter)¹

	Litter composition
	UNIFORM		MIXED			Significance2
	Birth weight class					Birthweight class	Littercomposition	Litter composition × birth weight class
Item	Light	Heavy	Light	Heavy	SED
BW, kg
Day 03	1.06 [1.04, 1.09]	1.72 [1.69, 1.76]	1.10 [1.06, 1.13]	1.70 [1.66, 1.75]		<0.001	0.411	0.093
Day 28	7.37	7.96	6.93	8.93	0.099	<0.001	0.137	<0.001
Day 61	20.9	23.7	20.5	25.2	0.337	<0.001	0.282	0.072
Day 88	36.2	39.5	35.1	42.3	0.595	<0.001	0.326	0.020
Day 165	97.1	98.7	93.4	101	1.05	0.001	0.684	0.018
ADG, g/d
Day 0–28	264	280	252	324	3.97	<0.001	0.032	<0.001
Day 28–61	393	454	393	470	7.79	<0.001	0.596	0.570
Day 61–88	575	592	541	634	17.6	0.009	0.841	0.064
Day 88–165	777	778	754	780	11.0	0.299	0.415	0.327
Scaled ADG, g/(d∙kg BW)
Day 0–28	245	162	229	188	5.20	<0.001	0.402	<0.001
Day 28–61	55.8	57.7	52.9	51.4	2.61	0.940	0.140	0.561
Day 61–884	25.8 [22.0, 31.3]	23.8 [20.5, 28.4]	24.6 [20.8, 30.0]	23.6 [20.2, 28.3]		0.115	0.459	0.600
Day 88–165	21.7	20.8	22.6	19.6	0.540	<0.001	0.724	0.048

¹Light-weight and heavy-weight piglets were in UNIFORM litters or in MIXED litters. Data are expressed as least squares means or as otherwise stated. Piglets remained in the same litter from birth to d 61, after which they were randomly mixed according to their size. Pigs were weighed at birth d 0, when weaned (d 27.3 [SD 0.9]), when moved to the grower facility (d 61.3 [SD 1.2]), when moved to finisher accommodation (d 88.0 [SD 2.9]), and when reaching slaughter weight (d 164.2 [SD 13]).

²The experimental unit for performance up to d 61 was litter mean for light-weight or heavy-weight piglets; all data were blocked by litter nested within farrowing batch. Data were analyses with PROC MIXED in SAS (SAS Inst. Inc., Cary, NC); the statistical model used was y = birth weight class + litter composition + birth weight class × litter composition + farrowing batch (litter) + ε. Due to variability in the timing of transfer, age was added to the model from d 88 onward. The experimental unit for performance from d 61 to slaughter was pen mean nested within farrowing batch; the statistical model used was y = birth weight class + litter composition + birth weight class × litter composition + age + farrowing batch (pen) + ε. For both models, the variance components was used as covariance structure in the random statement. In addition, a weight statement was used to account for differences in the number of light-weight and heavy-weight piglets where the litter or pen mean was based on.

3Data are expressed as back-transformed (log) least squares means with the 95% confidence interval.

⁴Data are expressed as back-transformed (inverse) least squares means with the 95% confidence interval.