Introduction

This paper presents the rationale for segregating sows on a farm into age dependent sub-populations, from a nutritional perspective. The premise is that the amount and type of nutrients differs so much between young immature sows (one or two litters) and older females (more than five litters). Data is presented to show how the number of pigs born per litter and per sow life-time would benefit from an age specific approach to nutrition. An example format of age segregation is provided, using a recent application from the Hanor system. The authors believe that this proposed strategy compliments health and reproductive considerations.

Two Extremes in Life-Cycle Nutrition of the Sow

Two examples are provided to illustrate how nutrition constrains the expression of genetic potential for litter-size. The first litter female (P-1) is especially vulnerable to body protein loss during lactation. The foremost consideration is to formulate and feed to conserve body protein loss since there is direct relationship on wean-to-oestrus interval (WEI) and second litter-size (Boyd et al. (2000).

For example, a 4-kg body protein loss during first lactation is sufficient to reduce second litter-size by 0.75 pigs. In contrast, limiting protein loss to less than 2 kg can result in a 1.0 increase in litter-size, compared to the first. The WEI increases in proportion to body protein loss (King, 1987) (R²=0.63). It is not uncommon for WEI to be extended by more than ten days for the first weaned sow that raised a large litter, milked well and suffered 'too much' protein loss. Unfortunately, this is sometimes interpreted as 'reproductive failure' and may result in early cull from the herd.

The 'older' female is at risk for a premature decline in litter size with advancing parity (and perhaps viability) but for different reasons. Total pigs born and born alive increase to the third litter, then are constant until about litters 5 or 6; thereafter, a progressive decline is observed (Figure 1). Shape of the curve is similar for sows weaned early (at 15 days) or later (24 days) (Smits, 2003). This parity related decline in litter size for the prolific sow seems premature from a reproductive perspective. The lost opportunity is probably in the order of 1.8 to 3.3 pigs per sow life-time, depending on whether productive life-time is 8 or 10 litters. The authors hypothesize that this is due in part to the progressive decline in micronutrient profile as the sow ages. This concept was first proposed by Boyd (2004) and is discussed below.

Figure 1. Age-related reduction in litter-size is modulated by lactation length
^{(Smits, 2003)}

Disparity in Micronutrient Nutrition for Older Sows

micronutrients consist of vitamins and trace minerals (VTM). They represent 0.12 to 0.15 per cent of the diet but about 50 per cent of the nutrients. In concept, micronutrients are formulated in diets at levels that prevent deficiency and include a margin of safety. In practice, there is a steady decline in the safety margin, with increasing reproductive age. Progressive demineralisation is one result (Mahan and Newton, 1995). This most likely occurs because pregnancy feed intake is held about constant (once body condition has been restored) across all parities to limit growth, e.g. 2.3 kg per day. However, body weight progressively increases with reproductive age. This constant feed allocation is appropriate for protein and energy needs (NRC, 1998; PIC USA, 1999) but it probably does not work for VTM because the amount that is required to support normal tissue metabolism increases with the increase in tissue mass. This results in a marked decline in the amount of VTM per kilo of body weight with increasing parity (Figure 2). The problem is that this occurs with each pregnancy and it also occurs, albeit to a lesser extent, in lactation. Thus, the older (heavier) sow is placed at an increasing nutritional risk, reproductively and immunologically.

Figure 2. Example calculation of declining vitamin and trace mineral (VTM) intake with advancing reproductive age (g VTM / kg body weight)
(Calculated by Boyd and Hedges, 2004; using PIC USA 2002 average daily feed intake x sow weight parity assuming 0.149 per cent dietary VTM )

micronutrient Equalization in Older Sows and Litter-size

The first illustration that an age-related decline in litter-size may be nutrition related was tested in mature sow sections of two Hanor farms (P-3 through P-10) (Boyd, 2004). Parity segregation is practiced in each farm by designating one section (50 per cent) for mature and older sows (3 or more litters completed). Control sows received 0.15 per cent VTM per usual. Test Sow diets contained additional VTM and choline using a correction factor of 0.76 for pregnancy and 0.82 for lactation. This increase provided the same weight of VTM per kilo body weight for a P-7 female as a P-3 sow. The annual cost of this increase was approximately $1.69 per sow compared to control diets. Record evaluation initiated for sows after they completed a lactation period on test diets and then continued for a 12-month period. Litter size weaned was improved with VTM 'equalisation' for litters 4 to 10 (0.60 pigs/litter; 1.44 pigs per year) (Figure 3). Sow viability was not significantly improved for the term of this study (-0.26 per cent).

The axiom of the concept – organizing the sow farm to nutritionally manage maiden and first litter sows and then to adjust nutrient level for the older sow –’ is one that if practiced will increase sow life-time pig output. This was demonstrated using the 1996 Hanor Age Segregation model, which divided the sow herd into three sub-populations (P-0 and P-1; P-2 and P-3 and P-4 to P-12). This practical forum for age segregation study led us to the present template, which is to organise the sow herd into two sub-populations that can be fed and managed with sufficient specificity. Primary outcomes from this nutrition-specific format are: increased life-time pig output and reduced risk to sow viability with no increase in feed cost per weaned pig.

Table 1 provides a simplified format that we used to identify the 'young' sub-population from the 'mature' and 'senior' (or geriatric) population. This matrix required integration of:

• special nutrition needs over the life-span, and
• special physiological needs that could be addressed with nutrients or functional proteins.

Division into two sub-populations was also based on present nutritional knowledge and anticipated breakthroughs that are needed to improve pigs born alive (immune modulation at key points, e.g. animal plasma.

Since Hanor is aligned with a meat plant, the one-litter terminal female was included as a management method of increasing pigs reared per 'herd' sow bred per year (goal: 29-30 suitable weaned pigs per 'herd' sow). Specific examples of age-specific nutrition emphasis are provided in the bottom portion of Table 1.

Expected Outcomes for Two Sow Sub-populations

Organization of the sow herd into a 'young' sub-population (consisting of P-0 through P-2; two conceptions) and an 'older' sub-population, consisting of P-3 through P-10 (third to tenth conception) is a reasonable approach to address very different nutritional needs of sows. The expected outcome is to improve life-time pig output by producing a large first litter and then to manage her in a manner that does not compromise second litter size. Once P-1 females are successfully re-bred (P-2) and managed to 30 days pregnant, the need for specialized 'young' sow nutrition probably ends. However, there may be health-based reasons for keeping 'young' sows in this sub-population.

The decision to include P-3 and P-4 sows with the 'older' sub-population is driven by the need to reduce gestation and lactation diet cost. The expected outcome in this sub-population is to avoid the premature decline in pigs born and weaned, which will add 1.8 to 3.3 pigs per sow life-time. It is not clear whether the relative lower viability of older sows compared to younger sows can be improved by adjusting micronutrient level and perhaps form. Mature sows can also utilize cheaper ingredient by-products very well. A comparison of annual feed cost is presented in Table 2 for a two sub-population sow farm versus a standard sow farm.

The intent of the mature and 'older' sow sub-population is to extend productive life by 'Healthy Aging'. Special considerations for the senior sow probably include declining immune capability and nutrient absorption (or retention efficiency) if sows follow the pattern exhibited in aging dogs and cats ^{8, 9}. Aging brings about age-associated changes in metabolism and physiology that influence the way that older animals utilise nutrients. The decline in immune capability is especially noteworthy; the role of vitamin E (level and form) in improving immune response to protect against infection is also important. A recent report of animal plasma functional proteins to improve performance in older sows can also be accommodated in this second sub-population ¹⁰. Wound healing and advancing osteoarthritis are likewise considerations that could be more specifically addressed.

Conclusions

This paper describes the rationale for organizing a sow farm into two sub-populations for age-based feeding. This was shown to improve litter size in both the second litter and in 'geriatric' sows.

This arrangement is possible for existing sow farms, provided that a mental roadblock is not constructed and supported by old paradigms. The strategy was based on nutritional considerations but we believe that they compliment health (and reproductive) objectives with respect to PRRS, Mycoplasma pneumonia and piglet enteric disease. Inherent in this strategy is that a 'wean-to-breed' row is needed for dedicated feeding to promote litter size (four daily feeds).

The authors anticipate that this could evolve into a 'wean-to-30-days-bred' feeding strategy if improved embryo viability can result from early pregnancy immune modulation (based on research in humans and perhaps with plasma functional proteins).

The axiom of one gestation and one lactation diet is well overdue for change since this practice, albeit easy, has imposed a significant silent financial cost on systems with prolific sows, based on the authors' estimates (Table 2). Companion animal research is well advanced compared to food animals in this area and can serve as a potential means to advance.

References

1. Boyd, R.D., K.J. Touchette, G.C. Castro, M.E. Johnston, K.U. Lee and I.K. Han. 2000. Recent advances in amino acid and energy nutrition of prolific sows - review. Asian-Aus. J. Anim. Sci. 13:1638-1652.
   
2. King, R.H. 1987. Nutritional anoestrus in young sows. Pig News Info. 8:15-22.
   
3. Smits, R. 2003. Sow reproductive performance - a snapshot of the present with a view to the future. In: Nutritional biotechnology in the feed and food industries. Edited by T.P. Lyons and K.A. Jacques. Nottingham Univ. Press, Nottingham, UK, p237-246.
   
4. Boyd, R.D. 2004. A novel approach to improving litter-size in older sows. Proc. 24th Annual Prince Feed Ingredients Conf., Quincy, IL.
   
5. Mahan, D.C. and E.A. Newton. 1995. Effect of initial breeding weight and macro- and micro-mineral composition over a three-parity period using a high-producing sow genotype. J. Anim. Sci. 73:151-158.
   
6. NRC. 1998. Nutrient requirements of swine. 10th Revised edition. National Academy of Sciences Press, Washington, D.C.
   
7. PIC USA. 1999. Recommended nutrient specifications for PIC pigs. PIC USA Franklin, KY.
   
8. Meydani, S.N., M.A. Ceddia and M.G. Hayek. 2001. Vitamin E, immunity and aging. In: Current perspectives in senior dog and cat nutrition. Proc. Tufts Univ. Anim. Expo. The Iams Co., Dayton, OH. pp38-43.
   
9. Hayek, M.G., G.M. Davenport and M.A. Ceddia. 2001. Nutrition and aging in companion animals. In: Current perspectives in senior dog and cat nutrition. Proc. Tufts Univ. Anim. Expo. The Iams Co., Dayton, OH. p22-27.
   
10. Crenshaw, J.D., J.M. Campbell, L.E. Russell and R.D. Boyd 2004. Effect of spray-dried animal plasma in lactation feed in a segregated-parity sow herd. Proc. A.D. Leman Swine Conf. 31 (suppl.):33

Further Reading

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