Split Suckling, Birth Order, and Birth Weight Affects Colostrum Intake and Pre-Weaning Weight Gain

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Introduction
Colostrum is an important source of nutrients and immunoglobulins for newborn pigs.As litter size increases, the access to colostrum may not be equally distributed, particularly to low birth weight (LBW, < 1.4 lb) pigs and pigs later in the birth order.Temporary removal of part of the litter (split suckling) is often employed to afford more equal access to colostrum; however, the practice is not standardized.The objective of the study was to determine the effects of split suckling on pig immunoglobins, colostrum intake, and growth of low birth weight pigs and pigs that are born later in the birth order.

Procedures
Thirty sows (DNA Line 241, n = 10/treatment) and litters (sired by DNA Line 600, n = 412 pigs) were used.Sows were observed when they neared farrowing, and the time the first pig was born was recorded.Each pig was dried with a towel and weighed after removal of its umbilical cord.Pigs were then tagged and returned to the farrowing crate behind the sow.Sows that had fewer than 9 pigs born alive, or farrowing was longer than 7.5 h were not included.Six hours after the birth of the first pig, the litter was randomly assigned to 1 of 3 split suckling treatments: 1) control, all pigs suckled ad libitum; 2) weight based, the heaviest 6 pigs were removed for 1.5 h; or 3) birth order Swine Day 2017 based, the first half of the litter was removed for 1.5 h.During separation from the sow, pigs were in a plastic storage tote behind the crate and a heat lamp was provided.The pigs remaining with the sow were observed to confirm at least one suckle occurred during separation.After 1.5 h, all pigs were returned to the farrowing crate and allowed to nurse ad libitum.
Pigs were weighed 24 h after birth of the first pig and at d 7 and 20 post farrowing.Also during the 24 h weighing, blood was collected from the cephalic or mammary vein (0.5 mL).Serum was separated by centrifugation and 50 μL of a 40% (wt/vol) of ammonium sulfate in distilled water was added to precipitate immunoglobulins.The precipitated sample was centrifuged (12,000 × g in a hematocrit centrifuge tube) for 10 min at room temperature.The immunocrit, a measure of colostral immunoglobulins (described by Vallet and co-workers1 ), was calculated as the ratio of the precipitate to the total length of the column.The colostrum intake was estimated according to the method of Amdi and co-workers 2 as: Colostrum/24 h = 1.55 × 0.944 × body weight gain 24 h + (115).

Data Analysis
Data were analyzed using Proc GLIMMIX of SAS (Version 9.4, SAS Institute Inc., Cary, NC).Sow was the experimental unit with treatment nested within sow.The model included birth weight group: High > 1.45 kg (HBW); Middle > 1.11 and < 1.45 kg (MBW); Low < 1.11 kg; and birth order (1 st or second half of pigs born).

Results and Discussion
Birth weights were not (P < 0.10) different across treatments (Table 1) and weight gain to d 1 and d 20 were not (P > 0.10) affected by treatment.However, weight-based split suckling litters gained more (P < 0.05) than the controls to d 7. Pigs in the HBW category had greater (P < 0.01) weights on d 1, 7, and 20.
Colostrum intake (Table 2) was less (P < 0.01) for the MBW and LBW compared to HBW pigs, and for LBW compared to the MBW pigs.There were no (P > 0.10) differences in immunocrit ratios due to treatment or birth weight category.However, a tendency (P = 0.15) for a treatment × birth order effect may indicate a benefit for split nursing for later born pigs (Figures 1 and 2).Overall, pigs born in the second half of the litter had lower (P < 0.01) immunocrit values than pigs born in the first half of the litter.Immunocrit and colostrum intake were positively correlated (r = 0.49, P < 0.01).
Our data indicate that both birth weight and birth order affect pigs in the preweaning period and weight-based split suckling improved growth to day 7. Two methods for estimating colostrum intake are those based on weight gain during the first 24 h after birth and the circulating immunoglobulins.We found a tendency for birth-orderbased split suckling to increase colostrum intake for the second half of the pigs born.

Figure 1 .
Figure1.Colostrum intake as affected by birth order and treatment.There was a tendency (P = 0.15) for a birth order × treatment interaction.(SEM = 13.20).