Key production traits that determine sow lifetime productivity in commercial practice

Introduction

Sow longevity is defined as the time elapsed from gilt entry into the breeding herd until removal as a result of culling or death. Increasing herd retention rate is important to maximize sow lifetime productivity. Higher removal rate implies an increase in the percentage of young females in the herd, a category with lower production potential, and a higher risk of early culling. Systematic gilt replacement is required for genetic gain. Still, it is essential to achieve a retention rate that allows the sows to reach their maximum production potential in the later parities. In this way, it is important to evaluate the reasons for removal and death to establish strategies for reducing involuntary culling and controlling mortality rates. Although reproductive failures persist as the main culling cause, its expressivity has been reduced. To increase sow retention rate, management intervention should start during gestation with a focus on improving the replacement gilt birth weight. Ensuring adequate colostrum intake is critical for achieving targeted pre- and post-weaning growth rate. Besides, approaches that improve gilt body development during the post-weaning phase and up to first breeding are critical steps to reducing culling for structural problems and low reproductive performance. In this sense, the use of gilt development units allows a constant flow of replacement gilts that meet the required parameters recommended by the different genetic suppliers. Because locomotor disorders are frequent reasons for early culling, inspection, and maintenance of the animal facilities should be prioritized in all phases. The opportunity to reduce sow mortality, culling for poor reproduction, and structural failure, resides in the ability to translate new research findings on gilt birth weight, growth, and body measures into improved lifetime pig production to the third parity.

Key production factors that determine lifetime productivity

Gilts are an important category in a swine breeding herd, representing around 15-20% of the breeding group females. Some key traits, such as gilt birth weight, age at puberty, lifetime average daily gain, and body weight at first mating, directly influence lifetime productivity.

1. Birth weight

The occurrence of low birth weight piglets is well documented in high prolific sows (Quesnel et al., 2008). The low weight at birth results in higher mortality rates until weaning and lower weights on the finishing phase. This phenomenon is also observed in gilts, leading to increased removal and mortality rates until selection at 170 d of age (Magnabosco et al., 2015). In this study, the authors observed higher mortality rates and losses until 170 days for female piglets born with less than 1000 g (P < 0.0001). Besides, when gilts were classified according to their birth weight into eight classes, the lightest birth weight class (410-990 g) was lighter at weaning than the heaviest birth weight class (1780-2400 g), and at selection (at 170 days of age), the gilts from the lightest class were lighter than the other classes.

Low birth weight also negatively influences female production and longevity. In the study of Magnabosco et al. (2016), the total number of piglets born (P = 0.08) and piglets born alive (P = 0.028) in the first farrowing were lower for gilts born with less than 1 kg. Moreover, these light gilts at birth produced fewer piglets (P = 0.055) over three parities than the heavier ones (Figure 1). The retention rate from selection up to third farrowing was not influenced by the birth weight. However, when the culling rate and mortalities from the pre-selection period were also considered, gilts with birth weight ≤ 1280 g remained in the her d for a shorter time than the heavier ones (Figure 2). Furthermore, cumulative mortality rate and cumulative losses until 170 days were higher for piglets born with less than 1000 g (Figure 3; P < 0.0001; Magnabosco et al., 2015).

Further investigations on litter-of-origin were studied by Vallet et al. (2016). The authors evaluated litter traits as sow parity order, birth weight, immunocrit, preweaning growth rate, and their relationship with body and reproductive traits at 260 d of age. All litter-of-origin traits were positively associated (P < 0.05) with female growth traits. The body weight at 240 d of age increased (P < 0.01) as the birth weight, immunocrit, and preweaning growth rate increased. However, sow parity order was negatively associated with the body weight; increased parity of birth was associated with decreased BW values (P < 0.01). In contrast to growth traits, reproductive traits were, in general, not affected by litter-of-origin traits. Age at puberty was associated with birth weight (positive; P < 0.01) and preweaning growth rate (negative; P < 0.01), indicating that age at puberty is delayed for heavier piglets at birth and slow growth piglets during the preweaning period. In this sense, more recently, Patterson and Foxcroft (2019) described a low litter birth weight phenotype as a “litter” trait. This trait is repeatable over consecutive parities, and gilts born from a sow with a low birth weight phenotype have lower retention in the herd.

Figure 1. Total piglets born over three parities (n = 497) according to the birth weight of swine females. Bars with one letter in common are not significantly different (P > 0.05) - Magnabosco et al. (2016).

Total piglets born over three parities (n = 497) according to the birth weight of swine females. Bars with one letter in common are not significantly different (P > 0.05) - Magnabosco et al. (2016).

Figure 2. The number of herd days according to the birth weight of female swine. Days counted are from birth onwards, including all female piglets weighed at birth (n = 1495). Bars with one letter in common are not significantly different (P > 0.05) - Magnabosco et al. (2016).

The number of herd days according to the birth weight of female swine. Days counted are from birth onwards, including all female piglets weighed at birth (n = 1495). Bars with one letter in common are not significantly different (P > 0.05) - Magnabosco et al. (2016).

In this context, reductions in puberty age might be accomplished by improvements in preweaning growth rates. Flowers (2009) observed that the number of suckling females within the litter in which gilts were raised (< 7 pigs or > 10 pigs) affected the sow longevity and reproductive performance. At the end of 6 parities, regardless of the age of puberty induction, significantly more sows raised in small litters (35%) were still in production compared with those raised in large litters (17%). The age in which puberty induction was initiated (140 or 170 days of age) also affected sow longevity and reproductive performance. Significantly more sows exposed to boars at 140 days of age (33%) remained in the herd compared with their counterparts given boar exposure at 170 days of age (16%). The effect of younger exposure to the boar and the size of litter in which gilt was raised were additive. In this way, 45% of the gilts exposed to boar with 140 days of age and raised on a litter with < 7 piglets were ready to be rebred after the 6th parity, compared to only 10% of the gilts exposed to the boar at 170 day of age and raised on a litter with > 10 piglets. Even though the results of Flowers et al. (2009) are promising to early puberty stimulation (< 140 d), we should critically evaluate the logistic and the cost-benefit of anticipating this management.

Figure 3. Culling and cumulative losses from birth until 170 days, according to birth weight classes of female piglets. Bars with one letter in common are not significantly different (P > 0.05) - Magnabosco et al. (2015).

Culling and cumulative losses from birth until 170 days, according to birth weight classes of female piglets. Bars with one letter in common are not significantly different (P > 0.05) - Magnabosco et al. (2015).

2. Colostrum intake

In swine, colostrum can be defined as the secretion of the mammary gland in the first 24 h after farrowing being responsible for piglets' nutrition, thermoregulation, immunity, and growth. The amount and composition of colostrum produced may vary according to sow characteristics, such as endocrine, nutritional and immunity status, stress level, and heat stress (Quesnel & Farmer, 2019).

The average amount of colostrum needed by piglet is around 250 g. This amount reduces the risk of mortality (Figure 4), provides passive immunity and weight gain (Ferrari, 2013). Ferrari et al. (2014) demonstrated that colostrum intake is positively related to birth weight (P < 0.0001) and to serum IgG concentration (P < 0.0001). In this study, the mortality was affected by the interaction between birth weight and colostrum intake. For piglets with birth weight > 1.3– 1.7 kg, the probability of mortality was low regardless of their colostrum intake. The probability of mortality decreased as colostrum intake increased for piglets with birth weight between 1.1–1.2 kg and > 1.2–1.3 kg, being necessary 200 and 250 g of colostrum, respectively, to reduce their probabilities to the same level observed for heavier piglets. Probabilities of mortality were similar among all birth weight categories when colostrum intake was > 250 g (Figure 5).

However, at least one-third of sows do not produce enough colostrum to fulfill the requirements of their litter (Quesnel et al., 2012). The energy concentration of lactation diets is an important determinant of energy consumption and is typically modified by the use of fat, oils, or fibers in the diet (Tokach et al., 2019). The authors suggest that a lactation diet would be designed for optimal milk production and subsequent reproduction. Furthermore, a reduction in sow body weight loss and an improvement in litter growth rate during lactation would be expected. Thus, increased energy or amino acid intake in the few days before farrowing, during colostrogenesis, could be beneficial to the colostrum quality.

Figure 4. Piglets mortality until 42 days of age according to birth weight and colostrum intake. White circles represent piglets that were still alive at 42 days of age, and black circles represent piglets that died between 24 h after birth and 42 days of age – Ferrari (2013).

Piglets mortality until 42 days of age according to birth weight and colostrum intake. White circles represent piglets that were still alive at 42 days of age, and black circles represent piglets that died between 24 h after birth and 42 days of age – Ferrari (2013).

Figure 5. Probability of death until 42 days of age according to the colostrum intake and birth weight of piglets. LBW: piglets with a birth weight of 1.1-1.2 kg; IBW: piglets with birth weight > 1.2-1.3 kg; HBW: piglets with birth weight > 1.3-1.7 kg - Ferrari et al. (2014).

3. Lifetime Average Daily Gain

Lifetime average daily gain (ADG) influences the age of puberty, weight at selection, and weight at first artificial insemination (AI). These three factors together might compromise sow productivity and longevity. ADG affects total piglets born, piglets born alive, and weaning-to-estrus interval in the subsequent cycles. Increasing 100 g/d on ADG leads to an increase of 0.3 to 0.4 piglet in the litter and a decrease of 0.2 to 0.4 days on weaning-to-estrus interval (Tummaruk et al., 2001). Amaral Filha et al. (2010) categorized gilts in three classes (GI: 600-700 g/d, GII: 701-770 g/d, and GIII: 771-870 g/d) according to the ADG from birth to AI. The authors observed that GII and GIII gilts had higher total piglets born than GI gilts (P < 0.05), however, return to estrus and farrowing rate were not affected.

Kummer et al. (2009) compared two ADG groups of gilts (G1: 577 g/d, and G2: 724 g/d) and no differences on the number of ovulations, total and viable embryos at 32 days of gestation were observed (P > 0.05). During gestation, G1 gilts showed higher ADG and weight gain than G2 (P = 0.007). These data explain the positive correlation between gestation ADG and embryo survival (r = 0.29; P = 0.08) and show that lifetime ADG can be compensated during gestation, without affecting the reproductive performance. The study of Magnabosco et al. (2014) corroborates to Kummer et al. (2009); no difference was observed on farrowing rate and total piglets born on the first parturition between lifetime ADG classes (500-575 g/d; 580-625 g/d; 630-790 g/d). These results might be due to the achievement of target for weight at AI (130 kg at the first AI).

Recently, Walter (2018) evaluated gilts from selection to first AI after weaning, according to the lifetime ADG at selection with 140 days of age (G1 ≥ 480 - ≤ 530g/d; G2 > 530 - ≤ 580g/d; G3 > 580 - ≤ 630g/d; G4 > 630 - ≤ 810g/d). It was observed that the number of total piglets born, born alive, lactation length, weaned piglets, and weaning-to-estrus interval were not different among the groups. Besides, at insemination, it was observed that 94.67%, 92.67%, 91.13% e 91.04% of gilts from G1, G2, G3 e G4, respectively, showed ADG > 630 g/d. These data corroborate with Kummer et al. (2009), where gilts with low lifetime ADG until selection were able to compensate ADG from selection to AI.

Walter (2018) also investigated the retention rate and culling rate by reproductive reasons (Table 1). Gilts from G2 showed a lower retention rate from selection to 1st and 2nd farrowing when compared to gilts from G4. Regarding the culling rate by reproductive reasons, gilts from G2 showed a higher culling rate from selection to 1st and 2nd farrowing when compared to gilts from G3 and G4. Amaral Filha et al. (2008) observed that gilts weighing between 151-170 kg had a higher retention rate when compared to gilts weighing between 171-200 kg at the first AI, whereas no difference was observed for gilts weighing between 130-150 kg. The authors also observed that heavier gilts showed higher culling rates by locomotor problems, while no difference was observed on the culling rate by reproductive reasons among weight classes (Table 2).

Table 1. Retention rate and removals due to reproductive reasons until 3rd farrowing of gilts according to their ADG from birth to selection - Walter (2018).

Table 2. Retention rate over three parities and culling reasons for gilts according to their weight at first insemination - Amaral Filha et al. (2008).

4. Nutritional management

Nutritional management is crucial for gilt development, ensuring satisfactory productive and reproductive performance. Each genetic company has a nutritional manual that contains the specifications to each phase of gilt development and gestation. In this scenario, flushing is a nutritional management applied before AI to increase the ovulation rate (Beltranena et al., 1991). The increased ovulation rate is important as it is the first step in establishing litter size. Traditionally, nutritional flushing consists of an increase in feed amount or feed energy (Beltranena et al., 1991; Peruzzo, 2000) for at least 14 days before the first AI. Beltranena et al. (1991) showed that gilts fed additional 0.8 kg/day (Flushed) between the first and second estrus had an increase in the number of eggs ovulated compared to Control (14.0 vs. 12.0, respectively). Later, Peruzzo et al. (2000) compared the ovulation rate of gilts fed 2.0 kg/d vs. ad libitum and observed 1.6 more follicles ovulated in gilts fed ad libitum. These findings suggest that flush feeding gilts are crucial before insemination to increase the litter size.

In another way, the genetic selection to increase total piglets reduced the piglet birth weight and increased within-litter variability (Quesnel et al., 2008; Quiniou et al., 2002). During the final phase of gestation, piglets grow at an exponential rate (Ji et al., 2005). This phase was the target of several studies that evaluated the influence of different nutritional management in late gestation on piglet birth weight (Gonçalves et al., 2016; Mallmann et al., 2019). Mallmann et al. (2019) evaluated the effects of increasing the feed amount in late gestation of gilts (1.8, 2.3, 2.8, and 3.3 kg/d) on reproductive traits. Still, no differences were observed among treatments in the total number of piglets born and mummified fetuses. Tendencies for a quadratic effect of feed amount were observed for piglets born alive (P = 0.079), average piglet birth weight (P = 0.083), and litter weight (P = 0.059). Gilts fed on lower feed amounts during late gestation had reduced percentages of stillborn piglets in comparison to gilts fed with greater feed amounts. No differences in the subsequent cycle were observed among treatments for the farrowing rate, born alive, stillborn piglets, and mummified fetuses (P > 0.05). Furthermore, the retention rate over four parities and days until the female removal (Figure 6), number of total piglets born over four parities (Figure 7) were also not affected by the feed amount provided during late gestation in the first reproductive cycle.

Overall, the main goal during gestation is to achieve the requirements and avoid over-conditioned females. Females that are overfed during gestation will have their performance during lactation compromised. As observed by Mallmann et al. (2019), the heavier the gilts at farrowing, the lower was the colostrum yield and the voluntary feed intake. Moreover, the heavier the females at farrowing, the higher are the lactation body losses. Lactational catabolism is associated with impairs on subsequent performance. So, during lactation, the main goal is maximizing the feed intake to sustain milk production without excessive body mobilization (Menegat et al., 2018). The recommendation for the lactation period is providing ad libitum feed. It is also important to mention that primiparous sows will need special care since these are not able to ingest the amount of the necessary nutrients to achieve the requirements. This approach is also valuable for the period of heat stress, where the females reduce the voluntary feed intake by 3.7% for each 1 °C that the temperature increases above 25 °C (NRC, 2012; Menegat et al., 2018).

During the wean-to-estrus interval, the objective of the feeding program is basically to improve the ovulation rate and, if necessary, to recover the body condition in females that had higher body losses during lactation. So, providing higher feed amounts during this period may help the recovering, which in turn needs to be extended during the early gestation period (Menegat et al., 2018). Whereas, for females in a good body condition, providing higher feed amounts is not necessary. Recent studies showed that there are no benefits to reproductive performance by providing higher feed amounts or more energetic diets y (Graham et al., 2015; Gianluppi et al., 2019). Gianluppi et al. (2019) compared females (primiparous and multiparous) fed 2.7 or 4.3 kg/d, with lactation or gestation diet, and no improvements on the farrowing rate and litter size were observed.

Replacement gilt flow is a key step for herd health, productivity, and longevity. Thus, the farm needs to be prepared to receive and introduce this category within the reproductive herd. Even though this is primary management in the farms, it is not always well managed by the farm team either for the lack of training, lack of information, or management failures. In this context, there are some recommendations that the farm manager can implement to have better results, healthy animals, and, consequently, a more productive herd.

The logistic of the herd to receive the replacement gilt is extremely important. Once the farm established the breeding group, it is necessary to guarantee the infrastructure to receive and prepare the gilts for breeding. In this context, the main step is having a schedule for gilt management. The farm manager needs to know the correct time and age to receive the gilts at the farm, and when to start the puberty stimulation to introduce them to the reproductive herd. In this way, the arrival at the farm and gilt preparation for breeding are crucial to obtain healthy and productive females. It means that the replacement gilts might be able to be bred with the scheduled breeding group. In consequence, the retention of old or unhealthy females will not be necessary to achieve the insemination target.

In our current situation in Brazil, gilts arrive at the farms with 140 to 160 days of age to be bred at 200 to 210 days of age, based on a target weight. However, this recommendation may vary among genetic companies. Gilts will stay in the gilt development unit (GDU) for about ten weeks, in pens or in individual crates. For each breeding group, new gilts will be introduced to the GDU. Thus, the GDU needs to be dimensioned, considering the number of animals housed, to support the replacement animals to the farms. One of the main management of gilts arrival is their acclimation. Each farm needs to have its acclimation protocol, based on the health status of each herd.

Figure 6. Retention rate and days to removal over four parities of gilts fed with different feed amounts during late gestation of the first reproductive cycle - Mallmann et al. (2020) – data not published.

Retention rate and days to removal over four parities of gilts fed with different feed amounts during late gestation of the first reproductive cycle - Mallmann et al. (2020) – data not published.

Figure 7. Total piglets born over four parities of females submitted to different feed amounts during late gestation in the first reproductive cycle - Mallmann et al. (2020) – data not published. Adequate replacement gilt flow in the herd.

Total piglets born over four parities of females submitted to different feed amounts during late gestation in the first reproductive cycle - Mallmann et al. (2020) – data not published. Adequate replacement gilt flow in the herd.

After receiving the gilts, under our current sanitary situation in Brazil (PRRS-free), they need to be prepared in a few weeks to be bred. This management includes feeding program according to the genetics recommendations (aiming target for weight and body condition score at first AI); individual identification sheet per gilt and pen; selection of gilts with good locomotor and general health status; satisfactory puberty induction management; following an adequate vaccinal protocol; individual adaptation at stalls (if necessary); flush feed before breeding for two weeks; attention with estrus detection for breeding and attention on the quality of semen doses. These managements are essential to have gilts in good corporal, reproductive, welfare, and health status. By following these key steps, we can expect good reproductive results at the first and subsequent farrowing.

Increase retention rate and controlling mortality in the breeding herd

As mentioned before, in a healthy herd, there is always a necessity of a good flow of replacement gilts. However, it is necessary to control the mortality rate to not lose sows with still a good reproductive and genetic potential. In Brazilian herds, the average mortality rate is around 8%; however, in the best 10% Brazilian herds, the mortality rate is about 4.3% (Bierhals et al., 2019). These data suggest that there are a lot of opportunities to decrease the sow mortality rate, and this can be accomplished mainly with good management strategies. This management includes: facilities climatization; floor quality (minimizing locomotor problems); adequate flow of replacement gilts (avoiding inadequate sow retention); avoid overweight sow herd; daily inspection of animals (identify overfed and thin animals; check every animal every day: locomotor, health, appetite); daily inspection on water quality; trained caretaker (responsible for medication and management of hospital pens) and a precise recording on mortality causes.

Conclusion

Sow and gilt management are the keys to the reproductive success of the herd. Sow longevity and reproductive performance are related to female early lifetime development (Figure 8). In this way, management protocols that ensure the selection at birth of female heavier than 1 kg and a good colostrum management (the intake of at least 250 g of colostrum), ensuring an adequate preweaning development, are crucial on gilt development. Consequently, selecting gilts with good corporal development, lifetime ADG ≥ 630 g/d at the selection, and between 130-150 kg at first AI, improves subsequent retention in the herd. However, an adequate growth curve until puberty and a target weight at first insemination are not enough. It is important to monitor the first parity sow until the first weaning. Thus, the female early reproductive lifetime would be well carried, and the retention chances increase as well as the productivity. A correct replacement gilt flow guarantees parity order structure within the herd, intending to maintain the genetic potential. The opportunity to reduce the mortality rate just using management protocol is an easy approach for the farm to have great results and ensure sow longevity within the herd.

Figure 8. Schematic view of gilt management from birth to first weaning. The recommendations may vary among genetics lines.

Published in the proceedings of the International Pig Veterinary Society Congress – IPVS2020. For information on the event, past and future editions, check out https://ipvs2022.com/en.