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Functional Underline Sections Affect Pig Weight at Weaning

by 5m Editor
8 June 2009, at 12:00am

The term 'functional underline' refers to a teat and its associated section of the mammary gland. This report in the June issue of North Carolina State Extension Swine News was submitted by Justin Fix and Todd See, and describes an experiment demonstrating the importance of the sow's functional underline on piglet growth and survival to weaning.

Prior to weaning, even with access to creep feed, piglets obtain nearly all of their energy from sow milk (Sørensen et al., 1998). Cross-fostering pigs within the first 48 hours of birth is a management technique used to reduce the variation in numbers of pigs nursed, which potentially provides pigs in larger litters greater access to and less competition for sow’s milk. However, not all sows have the same number of underline sections or produce the same amount of milk. Studies have shown milk production also varies between underline locations; Fraser and Lin (1984) reported milk production was greatest in the most anterior glands.

Pigs establish a ‘teat order’ very early in life, even before the last pig is born (McBride, 1963). After selecting teats early in life, pigs will continue to nurse the same location until weaning. Because ‘teat order’ is established early in life and continues till weaning, the number of functional underline sections available for pigs to nurse is important. Underline sections are nonfunctional for several reasons: they were never functional or became nonfunctional over time due to injuries or mastitis.

The objective of this study was to determine the effect of two factors on pig weight and quality at weaning: (1) the number of functional underline sections at farrowing and weaning, and (2) loss of functional underline sections from farrowing to weaning.

Materials and Methods

Litters (n=392) from Large White × Landrace sows bred to Duroc boars farrowed from 6 July to 3 August 2008 at a commercial sow were used for this study. Within 24 hours of farrowing and three days prior to weaning, all sows’ underlines were evaluated. Underline sections were deemed functional if a mammary gland filled the palm of the evaluator’s hand and no visual injury or defect was evident for the corresponding teat. During evaluation, locations of nonfunctional underline sections were recorded. Loss of functional underline sections from farrowing to weaning was individually calculated for each sow.

All pigs (n=3,702) were individually weighed and identified within 24 hours of birth. Two days prior to weaning (18.7±0.03 days of age), all pigs were individually weighed and given a quality score of 1, 2 or 3. The quality score was based on a combination of weight and health: 3 = healthy pig; 2 = slightly small (3.2-4.1 kg) and/or slightly unthrifty; 1 = small (< 3.2 kg) and/or unthrifty. Pigs were weaned once weekly in four separate groups. Sows that had their underlines scored at both farrowing and weaning were used in the analysis. Only pigs that were farrowed and weaned from sows that had their underlines evaluated were used in the analysis.

All data were analyzed using the Mixed procedure of SAS (SAS Inst., Inc, Cary, NC), except quality score, which was analyzed using the GLIMMIX procedure of SAS (SAS Inst., Inc, Cary, NC).

Results

Effect of sow parity on functional underline sections

Descriptive statistics for total number of underline sections at farrowing, functional underline sections, and loss of functional underline sections are presented in Table 1. Means and number of animals evaluated, separated by parity are presented in Table 2.


Total number of underline line sections at farrowing was not different between parities (Table 3). However, older sows had a tendency for a decreased number of functional underline sections at farrowing. With each increase in sow parity, the number of functional underline sections at weaning decreased and females experienced a greater loss of functional underline sections from farrowing to weaning (Table 3). In both instances, number of functional sections at weaning and loss of functional sections, an increase of 1 parity resulted in a change of approximately 0.25 sections. Subsequently, increasing from parity 1 to parity 5 would result in a decrease of 1 functional underline section at weaning and loss of nearly 1 additional functional underline section from farrowing to weaning.

Differences in the number of functional underline sections at farrowing account for a portion of the differences in the number of functional underline sections at weaning. After accounting for parity, number of functional underline sections at farrowing and weaning were correlated (0.30; P < 0.01). Specifically, a 1-unit increase in the number of functional underline sections at farrowing would result in an increase, although smaller, in the number of functional underline sections at weaning.

Effect of functional underline sections on pig weaning weight

Weaning weight was not affected by the number of functional underline sections at farrowing. However, each one-section increase in the number of functional underline sections at weaning resulted in pigs being 72.8g heavier at weaning. Also, every additional functional underline section lost from farrowing to weaning led to a 52.8g reduction in pig weaning weight (Table 4). To account for difference in number of pigs nursed, which may affect the number of mammary glands being used, both the loss of functional underline sections and number of functional underline sections at weaning were adjusted for number of pigs weaned.

Effect of functional underline sections on pig quality at weaning

Pigs nursing sows with a greater number of functional underline sections were more likely to be a superior or higher quality score at weaning (Figure 1). Pigs weaned from sows that lost more functional underline sections from farrowing to weaning, were more likely to have poorer or lower quality scores (Figure 2).


Conclusion

Increased sow parity slightly reduced the number of functional underline sections at farrowing, increased the loss of functional underline sections from farrowing to weaning, and consequently reduced the number of functional underline sections at weaning.

A greater loss of functional underline sections from farrowing to weaning and fewer functional sections at weaning resulted in pigs that weighed less and were of poorer quality at weaning.

Based on these results, it may be important to be conscientious of the number of functional underline sections during the lactation period. Pigs nursing sows with fewer functional underline sections may be lighter and poorer quality at weaning, both of which affect the profitability of swine producers.

Sow parity and the number of functional underline sections at farrowing influence the number of functional underline sections at weaning, but they are not the only factors affecting the loss of functional underline sections and number of functional underline sections at weaning. Therefore, other causes need to be looked into further, to determine what other factors may be affecting the number of functional underline sections at weaning. Future research needs to be conducted to determine potential management practices to help alleviate these adverse effects on pig weight and quality.

References

Fraser, D. and Lin, C.S. 1984. An attempt to estimate teat quality of sows by hand milking during farrowing. Can. J. Anim. Sci. 64: 165-170.
McBride, G. 1963. The “teat order” and communication in young pigs. Anim. Behav. 11: 53-56.
Sørensen, M.T., Danielsen, V. and Busk, H. 1998. Different rearing intensities of gilts: I. Effects on subsequent milk yield and reproduction. Livest. Prod. Sci. 54: 159-165.

June 2009
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