By Mariana B. Menegat, Joel M. DeRouchey, Steve S. Dritz, Jason C. Woodworth, Mike D. Tokach and Robert D. Goodband, Kansas State University
Modern sows have remarkably increased the number of piglets gestated, nursed and weaned.
The ability of sows to provide nutrients to support the gestation of a large litter, produce milk to nourish fast-growing piglets and promptly return them to cycle after weaning has, therefore, been enhanced.
The improvements in productivity have prompted the reassessment of proper nutritional programs for the prolific and high-producing sow.
The purpose of this article is to provide an update on nutrition programs and feeding strategies for sows during wean-to-estrus interval, gestation, transition period and lactation.
The sow feeding strategy during wean-to-estrus interval is focused on recovering body reserves lost during lactation in preparation for the upcoming gestation.
It is known that increasing the feed intake of weaned sows in poor body condition improves reproductive performance, but sows in good body condition do not seem to benefit from high feed allowance or from lactation feed during the wean-to-estrus interval (Graham et al., 2015; Almeida et al., 2018).
In general, feeding 5.5 pounds per day of a conventional gestation diet after weaning seems to be sufficient to support the recovery of body reserves of weaned sows; it suggests that ad libitum feeding and offering lactation diets during the wean-to-estrus interval is not needed.
The goals of the nutrition program for gestating sows are threefold: 1) to meet the nutrient requirements for maintenance, weight gain and gilt growth; 2) to provide nutrients for adequate development of the embryo; and 3) to manage body condition. The majority of the nutrients and energy of gestation diets are used for maintenance, weight gain and gilt growth.
The first 30 days of gestation represents the best opportunity for replenishing body reserves lost during previous lactation, whereas in late gestation (the last third of gestation) energy and nutrient demands are greatly increased for fetal growth and mammary development.
Gestation feeding programs
In the immediate period after breeding, the key is to maintain pregnancy and ensure embryo survival. Feed intake after breeding has been conventionally limited to avoid a negative impact on reproduction (Jindal et al., 1996), but recent studies demonstrate the opposite.
Sows and gilts with feed intake restrictions or deprivation in early gestation (first 10 to 12 days of gestation) can have a reduction in embryo survival and litter size (Athorn et al., 2013; Langendijk et al., 2016). Therefore, it is recommended to avoid feed deprivation in the immediate period after breeding, and to feed thin sows to recover body condition as quickly as possible.
During most of the gestation course, the goal of the nutrition program is to maintain well-conditioned sows to improve reproductive efficiency, sow longevity and welfare. The use of a body condition scoring system helps to identify thin sows to bring back to an adequate body condition, and prevent fat sows at farrowing.
Underconditioned sows are predisposed to have reproductive failure, development of sores and higher risk of mortality, while overconditioned sows are prone to have farrowing complications, lower feed intake in lactation and higher risk of culling due to locomotive problems.
The traditional methods to estimate body condition of gilts and sows are visual scoring, flank measurement and backfat measurement with ultrasound. Recently, the sow body condition caliper was developed as an unbiased tool to assess body condition by using the sow back angle in the last rib as a measure. The caliper is based on the premise that the back becomes more angular as sows lose weight, fat and muscle.
The appropriate adjustment of feed allowance in gestation is important, because feeding sows above the requirements accrues unnecessary feed expenses and leads to an overconditioned breeding herd.
It is well-recognized that increasing feed allowance during most of the gestation period provides no benefit to piglet birth weight (Amdi et al., 2014). In turn, sows gain weight and accrue excessive backfat deposition during gestation, leading to a reduction in feed intake during lactation, excessive body weight loss at weaning and difficulties to maintain milk production and litter growth (Kim et al., 2015).
In the last month of gestation, the demands greatly increase due to rapid fetal growth and mammary development. Bump feeding is a common practice to support the increase in energy and nutrient demands of gestating sows in the last third of gestation.
However, recent studies with gilts and sows show some concerns about this practice. Bump feeding studies consistently demonstrate that increasing energy and amino acid intake in late gestation is only partially used to improve piglet birth weight by a modest 30 grams per piglet on average (Gonçalves et al., 2016). Instead, sows use the extra energy and amino acids for body weight gain, which leads to heavier gilts and sows at farrowing and an increase in the stillborn rate by 2% on average for both gilts and sows (Gonçalves et al. 2016; Mallmann et al., 2019).
It has been estimated that each 1-kilogram increase in daily feed allowance from Day 90 of gestation to farrowing is associated with an approximately 7-kg increase in body weight of gilts and sows.
The characteristics of modern gestating sows seem to consist of improved feed efficiency and propensity for growth. The nutritional impact on piglet birth weight is modest, while genetic selection can have a much higher impact in this regard.
General recommendations for gestating sows would be to provide 4.5 to 5.0 pounds per day of a gestation diet containing 1,497 kilocalories per pound metabolizable energy and 0.60% digestible lysine, adjusting feeding levels according to gilts and sows. As the modern sow is very resilient, simplification of gestation diets to a single phase throughout gestation seems to be an effective feeding strategy.
Gestation feeding systems
Worldwide housing systems of gestating sows are gradually shifting from individual stalls to group housing systems.
Group housing systems generally allow a similar nutritional program to individual housing, but they take into account some particularities regarding social interaction, activity level, environmental temperature, feed wastage and adjustment of body condition score.
Activity level and environmental temperature influence energy demands of sows. Group-housed sows have increased activity level compared to individually housed sows, as they have more social interaction and spend more time standing and walking and less time lying.
The energy demands of sows are also increased to maintain body temperature when environmental temperature is below their comfort zone. The lower critical temperature for individually housed gestating sows is 68 degrees F, but because group-housed sows are able to exchange body heat with each other, the lower critical temperature is decreased to 60 degrees.
This indicates that sows in groups can be housed at lower environmental temperatures before the energy demands begin to increase.
Group housing allows for a natural competition for feed that is typically imposed by dominant sows over the timid ones. However, it is important to notice that feeding strategy, feeder design and pen layout can ameliorate the dispute over access to feed. Another reasonable way to ameliorate aggression in these systems appears to be to increase feed intake.
Thus, many group housing systems create variation in sow weight and limit the ability to evaluate and control sow body condition. In most group housing systems, it is difficult to adjust individual feeding levels to get sows into an adequate body condition.
For example, in floor feeding or trough feeding, the overall feeding level should be adjusted to prevent sows from becoming over- or underconditioned.
However, this situation can create feed wastage and variation in body condition. In fact, observations in the field indicate feed wastage is higher in these systems.
On the other hand, in electronic sow feeding systems, the individual feeding level can be adjusted for each sow. However, it requires extra time and labor to assess individual body condition within the group of sows.
Observations in large-scale productions systems have indicated that there are not adequate guidelines for optimizing feeding at the individual sow level in group housing systems. Although the feeding level can be adjusted for the individual sow in electronic sow feeding systems, much of the nutrient requirement is dependent on sow body weight, which is unknown in group-housed sows.
Successful implementation of ESF program systems is focusing on feeding a constant level with the ESF system and simplifying system management. Also, acquainting sows with the feeding system and maintaining full feed intake is often a challenge, especially in gilts and first-parity sows.
Training of replacement gilts is becoming a priority in farms with ESF systems, because gilts unfamiliar with the system are reluctant to enter the feeding station to consume their daily feed allowance throughout the course of gestation, particularly for the first week after placement (Thomas et al., 2016).
The transition period is defined as the time from the last week of gestation to the first week of lactation. During this period, the goal is to supply the nutritional demands for rapid fetal growth and mammary development, for the farrowing process, and for the upcoming lactation. Feed allowance is traditionally restricted in the transition from gestation to farrowing to prevent low feed intake during lactation.
However, increasing feed allowance in the transition period has been shown to increase total feed consumption until weaning and reduce body weight loss during lactation (Cools et al., 2014; Decaluwé et al., 2014).
The benefits include improvements in piglet growth rate and weaning weight, as well as colostrum yield and nutritional composition. However, increasing the feed allowance in the transition period is recommended for well-conditioned sows, emphasizing the importance of not having overconditioned sows and gilts at farrowing.
Besides feed allowance in the transition period, recent studies have evaluated the effect of amino acids and fiber levels in sow diets around farrowing. Increasing lysine levels for a week before farrowing has been shown to improve piglet birth weight in gilts (Gourley et al. 2019).
Increasing fiber pre-farrowing has also been shown to improve piglet survival, reduce sow constipation around farrowing, and decrease sow body weight loss during lactation, but has no impact on piglet birth weight, weight gain or colostrum yield (Oliviero et al., 2009; Loisel et al., 2013; Feyera et al., 2017).
The nutritional recommendations for the transition period are not clearly defined, but the recent studies suggest it is a promising area in which to develop nutritional strategies to improve sow and piglet performance during lactation.
The main goal of the nutrition program for lactating sows is to maximize feed intake to sustain milk production without excessive body weight loss. The demands of high-producing sows for milk production have increased considerably to support a large and fast-growing litter, but have not been accompanied by a proportional increase in feed intake.
Thus, sows normally have to mobilize body tissues to support milk production. Because modern sows are leaner, greater mobilization of muscle protein is expected during lactation.
Ideally, a truly ad libitum feeding program should be practiced during lactation to maximize milk production, minimize mobilization of body reserves, increase litter growth rate and improve subsequent reproductive performance.
Dietary energy and protein are important to alleviate sow body weight loss during lactation. Fats and oils are extensively used to increase energy density in lactation diets. This nutritional strategy seems to be particularly important for lactating sows under heat-stress conditions, and for prolific and high-producing lactating sows.
As sows prioritize lactation, the additional energy is partitioned preferentially for milk and converted as milk fat output. Consequently, the benefits of greater energy intake are consistently evidenced as improvements in litter growth rate because of the greater amount of energy provided through milk (Rosero et al., 2016).
The supply of dietary amino acids and protein close to the requirements can improve milk protein output (Strathe et al., 2017) and reduce muscle protein mobilization in lactating sows (Gourley et al., 2017). Recent studies underline that both dietary intake of balanced protein and single essential amino acids are mutually important to sow and litter performance during lactation (Strathe et al., 2017; Huber et al., 2018; Pedersen et al., 2019).
Studies agree on the effect of increasing dietary lysine intake to reduce body weight loss and muscle protein mobilization, but are not consistent in terms of the influence of dietary lysine intake on litter growth rate and subsequent reproductive performance (Xue et al., 2012; Shi et al., 2015; Gourley et al., 2017).
Ultimately, lactation catabolism impacts subsequent reproductive performance of sows, particularly in the case of first-parity sows.
It is well recognized that excessive weight loss and mobilization of body reserves during lactation is associated with prolonged wean-to-estrus interval, high incidence of anestrus and return to estrus, low farrowing rate and fewer piglets born in the subsequent farrowing, as well as a high culling rate due to reproductive failure (Koketsu et al., 2017).
However, the reproductive performance of modern sows seems to be increasingly resilient to the negative effects of lactational catabolism (Patterson et al., 2011).
This could be related to changes in the biology of sows with modern genetics, as well as an increase in lactation length, use of advanced feeding systems in lactation and application of proper breeding techniques.
Mariana B. Menegat is a doctoral student; and Joel M. DeRouchey, Steve S. Dritz, Jason C. Woodworth, Mike D. Tokach and Robert D. Goodband are swine research faculty at Kansas State University.