Improving reproduction through nutrition

By Walter Scharlach

Adequate nutrition of the breeding herd is essential in order to maximise herd productivity and profit. If one compares the reproductive efficiency of herds obtaining average productivity with those obtaining higher levels of performance (table 1), considerable room for improvement is evident.

In this paper the influence of nutrition on reproduction is discussed.

A minimum body condition exists to support the genetic potential for reproduction. The body nutrient reserves consist of protein, fat and minerals. During lactation the sow is normally unable to satisfy her nutrient requirement within the limits set by appetite, and she will loose body reserves to overcome the deficit. As long as the minimum backfat levels are maintained, the ability to mobilise and restore body energy reserves is beneficial. An excessive loss of any component has however detrimental effects on sow reproduction efficiency and survival. Energy-restricted sows mobilize more fat during lactation compared with non-energy-restricted sows (Brendemuhl et al., 1989) and may mobilize up to 25 to 30% of their body protein stores to maintain milk production (Mullan & Williams, 1990). Severe weight loss is a big problem for first-parity sows who, due to a smaller body size, consume less feed and tend to loose more body weight. Poor preservation of body reserves is often seen as high culling rates and sow mortality.

Mahan & Newton (1995) determined the body mineral content of sows after weaning the third litter. The data is split into litter weaning weights of less than 55kg or more than 60kg per litter (Table 2).

This data clearly shows that higher producing sows are more vulnerable to nutritional deficiencies.

King (1987) observed that increases in body protein loss during lactation were associated with extended wean to oestrus interval in young sows. There was a closer relationship between protein loss and wean to oestrus interval (@ =0.63) than between fat loss and wean to oestrus interval (r² = 0.43). Thus, either absolute body protein mass, or degree of protein loss exerts a greater influence on days to rebreeding than body fat. Conservation of body protein mass during lactation in first litter females also appears to be important to second litter size. Touchette et al. (1998) observed an increase in second litter size (+1.7 pigs) at the lysine intake (52 g/d) that minimised muscle loss during first lactation (17 d). This confirmed a report by Tritton and co-workers (1996) who observed that first litter females fed 60 g lysine/d during lactation (28 d) had more pigs at the next farrowing when compared to sows receiving 28 to 45 g/d.

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High culling rate of gilts and 1^st litter sows may be related to low body fat stores (Whittemore, 1995). Data by Brisbane and Chesnais (1996) shows a positive relationship between backfat at selection and sow survival percentages throughout 6 parities (Table 3).

Hughes (1993) reported that a P2 fat depth below 12 mm at farrowing and below 10 mm at weaning compromised the wean to oestrus interval (>2 d) and next litter size (> 2 pigs) in second to sixth litter sows.

Minimizing weight loss during lactation: Data summarized by Aherne (1994) suggest that increasing feed intake of lactating primiparous sows by 1kg per day increases the subsequent litter size by 1 piglet. Increasing feed intake during lactation also reduces the weaning-to-oestrus interval Koketsu, Dial, Pettigrew and King, 1996). The effects of excessive weight loss during lactation on subsequent reproduction are well documented. A trial by Kirkwood and Aherne (1985) shows that the low intakes in lactation did not only increase the empty sow days but also had a negative impact on embryo survival (Table 4).

Table 4 Effect of lactation feed intake on reproductive performance after weaning (Kirkwood and Aherne, 1985)

Numerous reports have shown a positive correlation between feed intake and reproductive efficiency. The data in Figure 1 summarizes weekly feed intakes on 2 commercial herds. Although the daily feed intake between these two herds was only 0.5kg per sow per day the herd with the variable intake was achieving 19.4 pigs weaned per mated sow per year compared to 24.8 pigs weaned per mated sow per year in the herd with more consistent feed intakes.

Figure 1: Weekly feed consumption data of two breeding herds (MacDougald, 2000)

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The status of body protein is difficult to assess in practice; however, body fatness can be estimated easily since fat deposits tend to be deposited externally. This is normally done by visual appraisal (condition scouring) or by using ultrasonic technology.

Williams, Muhs, Wilson and Hill (2000) correlated sow herd condition with herd productivity and mortality on seven sow farms ranging from 1250 to 5000 sows. Sows where scored on a 1 to 5 scale in one-quarter increments. A score of 3 was considered perfect. The results are shown in table 5:

Table 5: Sow condition effects on mortality and reproduction (Williams et al 2000)

The data shows that the herds with more sows in perfect condition had a lower mortality (R² = -0.83) and weaned more pigs per mated sow per year (R² =0.88).

Lactation: The pattern of weight loss and dynamic changes in metabolic state are likely the key regulators of the reproductive status of lactating and weaned sows. Unexpected periods of reduced appetite lactation can produce significant effects on LH secretion during lactation with negative effects on post-weaning fertility (ovulation rate, embryonic survival, litter size, and weaning-to-service interval (Koketsu et al., 1996). Extensive studies have led to the conclusion that the pattern of LH secretion immediately before weaning is the most critical determinant of subsequent fertility. It is suggested that periods of catabolism in late lactation, which carry over into the period just after weaning when ovarian development occurs, will be the most detrimental to fertility.

Parturition is often followed by feed intake depression for several days. The major nutritional factor in post partum feed intake depression is related to high feed intake level with excessive fat gain during the gestation period. Alterations in metabolism resulting from overfeeding and fatness during gestation create a physiological condition in which the sow adjusts her feed consumption below her nutritional requirements (Trottier & Johnston, 2000). In lieu of the low post-partum feed intake the nutrient requirements during the first 10d of lactation are very high. In a study by Boyd et al. (2000) it was found that the predicted dietary lysine need was very high in early lactation because sows maximized milk output by day 12-post partum while feed intake continued to increase throughout lactation (Table 6).

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Table 6 : Predicted Energy and Lysine Needs for Prolific First Litter Sows (Boyd et. al. 2000)

Pig units having low reproduction or high culling on first and second litter sows should focus on getting higher intakes during the first 10 days of lactation. Alternatively a higher protein diet should be fed to first and second parity sows (Pettigrew 1998).

In many units sows do not return to oestrus as quickly as expected. Although nutritional intervention after weaning is fairly ineffective in improving post weaning breeding performance (Trottier & Johnston, 2000) the use of high feeding allowances between weaning and re-mating maximise the chance of a prompt return to oestrus, a strong heat and a high ovulation rate. Sows should be satisfied at 3 to 5 kg per day with intakes gradually falling as the sow approaches oestrus.

While research during the late 1970’s suggested that elevated feeding rates after mating negatively affected embryo implantation, more recent studies have demonstrated no connection between the early-pregnancy feed allowance and subsequent litter size in older sows. Several researchers have however reported that high intake before day 30 of gestation decreased embryo survival in gilts. Recent data from the University of Alberta suggest that the first 72 hours after mating may be of critical importance in determining the effect of feeding level on embryo loss. Increasing feed intake from 1.8 to 2.5 kg/day during the first 72 hours of gestation, significantly increased embryo mortality whereas increasing feed intake after 72 hours did not increase embryo mortality. The increased mortality in the first 72 hours was associated with a 10-hour delay in the normal rise in plasma progesterone due to increased blood flow and hepatic clearance of progesterone. A rise in progesterone, early in pregnancy, enhances the uterine environment and makes it more supportive of the embryo (Jindahl et al 1997). Feed intake should be limited to less than 2.25kg per day for at least the first 3 days after mating.

Table 7: Effect of Feed Level in Early Gestation on Plasma Progestone Levels and Embryo Survival (Dyck et. al 1980)

Feeding during the dry period: There is now general agreement that 20 to 33 MJ/day is satisfactory for pregnant sows housed under reasonable environmental conditions when free of parasite infestation and individually fed (Patience, Thacker & deLange, 1995). Young et al. (1991) suggested that 22 to 30kg of total gestation weight gain are required to prevent loss of fat reserves during pregnancy. This gestation weight gain may maximize the birth weight of newborn piglets, increase embryonic survival, reduce farrowing difficulties and increase feed intake during the next lactation.

During the last 21 days of gestation each foetus will gain approximately 40 % of its final weight. On strict rationing program sows often loose backfat before farrowing, thus indicating that sows experience a negative energy balance in the last week of gestation. This decline in backfat may be undesirable for high performance and longevity. It is recommended that the energy intake is increased from day 90 of gestation.

Feeding before farrowing: Due to a slight increase in insulin resistance at the end of gestation blood glucose levels rise before parturition (Shaefer et al. 1991). Excessive energy intake can exacerbate gestational diabetes and depress post-farrowing performance (Revell et al., 1998). It is therefore best to limit energy intake to less than 25 MJ during the last week before farrowing. This allows the digestive tract to empty, which may reduce the sow’s inclination to a prolonged farrowing and reduce the incidence of periparturient hypogalactic syndrome.

Phases of the reproductive cycle are interrelated. Consequently, nutrition in one phase of the reproductive cycle not only affects sow performance in that phase but it also influences performance in subsequent phases. Because of the interrelation between each production stage, feeding practices must be geared to long-term beneficial reproductive outcome. The young gilt represents the future of any pig enterprise and if not fed properly, is unlikely to achieve her reproductive potential of rearing 60-70 piglets over 6-7 parities. Feeding of the pregnant sow is not only concerned with optimising foetal survival and growth but also with maximizing voluntary intake during lactation. The short-term objective of feeding lactating sows is to maximize litter growth rate, the long- term objective is to minimize empty sow-days and to maximize the size of the next litter.