Increased litter size results in decreased average birth weights. But larger litters do not increase variability in body weight of the pigs in the litter at birth. Carcass quality is also unaffected by litter size.

Recent analysis suggests that increasing litter size by one piglet reduces average birth weight by 0.22 lb., and doubles the proportion of piglets with a birth weight below 1.8 lb.

The goal of this study was to gauge whether there is a relationship between birth weight and postweaning growth performance on carcass quality. The second question was whether increased litter size caused increased variability in piglet weight at birth and later in life.

Researchers at the Prairie Swine Centre collected data from 98 litters (1,114 piglets). Litters were divided into “small” (3 to 10 piglets born alive), “medium” (11 to 13 born alive) and “large” (14 to 19 born alive). Interestingly, 91% of the total born were born alive in the small and medium groups, while greater than 98% of those born in the large litters were born alive. Approximately 85% of all pigs born alive were weaned.

Average birth weight was 3.5, 2.5 and 3.0 lb. for the small, medium and large groups, respectively. Average birth weight in larger litters was reduced by about 6% compared to average litter size, but did not contribute to greater variation in body weight at birth, nor to reduced market weights.

Average weaning weight was 14.4 lb., which ranged from 3.41 lb. to 23.5 lb.

Dressing weight was 207.5 lb. and was similar between litter sizes.

Since increased litter size did not cause increased variability on body weight at birth or throughout the finishing period, Canadian researchers emphasize there is significant economic advantage in producing more hogs in a swine production unit.

Moreover, in a 600-sow, farrow-to-finish facility, increasing total born from 10 to 12 piglets would generate nearly an additional $14/hog marketed, as more hogs can be spread over all fixed costs.

Researchers: J.F. Patience, A.D. Beaulieu and T. Osmanagic, all of the Prairie Swine Centre (PSC) at Saskatoon, Saskatchewan. Contact the PSC by phone (306) 373-99232, fax (306) 955-2510, or e-mail Kenneth Engele, PSC assistant manager of Information Services, at Ken.Engele@usask.ca.

Table 1. The Effect of Litter Size on the Growth and Variability of Growth

	Small ⅓ of litters	Medium ⅓ of litters	Large ⅓ of litters	All Litters
Number of Litters	38	39	21	98
Total Born Alive
Minimum	3	11	14	3
Maximum	10	13	19	19
Total Weaned
Minimum	2	5	2	2
Maximum	10	13	17	17
Body Weight, lb.
Minimum	1.76	1.65	1.65	1.65
Maximum	5.50	5.50	5.17	5.50
Weaning Weight, lb.
Minimum	3.41	4.40	4.51	3.41
Maximum	23.54	21.45	22.22	23.54
Five-Week Weight, lb.
Minimum	18.26	24.97	17.05	17.05
Maximum	73.70	66.11	70.07	73.70
Seven-Week Weight, lb.
Minimum	26.18	41.25	31.90	26.18
Maximum	97.68	96.47	98.78	98.78
First Pull Weight, lb.
Minimum	131.78	144.76	140.14	138.89
Maximum	269.28	260.48	268.84	266.20

Table 2. The Effect of Litter Size on Carcass Quality

	Small ⅓ of litters	Medium ⅓ of litters	Large ⅓ of litters	All Litters
Number of Pigs	222	222	199
Dressing Wt., lb.
Minimum, lb.	175.78	166.32	163.46	163.46
Maximum, lb.	175.78	235.84	229.24	235.84
Yield, %
Minimum	55.10	55.20	54.90	54.90
Maximum	64.70	65.40	65.00	65.40
Loin depth, in.
Minimum, in.	1.84	1.76	1.36	1.36
Maximum, in.	3.12	3.24	3.18	3.24
Backfat, in.
Minimum, in.	0.44	0.40	0.44	0.40
Maximum, in.	1.44	1.40	1.30	1.44
Index
Minimum	50.00	50.00	50.00	50.00
Maximum	113.00	113.00	113.00	113.00