The modern lactating sow
The productivity of sows increased substantially in the past 15 years due to advances in management and genetic selection based on parameters such as litter size, weaning-oestrus interval and efficiency in lactation. Most data demonstrates the efficiency of balanced breeding, which brings a higher reproductive capacity of sows, and increased survival rates of piglets, enabling the production of larger litter sizes without increasing piglet mortality. Modern sows mature earlier, are more productive, are heavier and have lower body adipose tissue mass reserves than older genotypes. In addition, they have higher nutritional requirements and are less resistant to environmental, immune and nutritional challenges (Silva et al., 2009 and 2013). The selection for high prolificacy negatively affects sow catabolic status during lactation and, consequently, the performance of their litters (Foxcroft, 2008). In order to supply the nutritional requirements of sows during lactation, their BW, milk production and composition, and environmental housing conditions must be known.
Although it is difficult to measure the nutritional requirements, milk production accounts for 75 to 80% of the total requirements of lactating sows, whereas the remaining 20 to 25% are maintenance requirements (Aherne and Foxcroft, 2000). In addition, modern sows present reduced feed intake capacity as a result of the genetic selection for higher feed efficiency in growing and finishing pigs (Bergsma et al., 2009). This reduced feed intake affects mammary gland growth and milk synthesis (Kim et al., 1999). Although milk production is relatively unaffected by marginal deficiencies in dietary protein and energy because sows are capable of mobilizing body protein and energy to supply amino acid and energy requirements for milk synthesis (Revell et al., 1998), severe protein and energy deficiency reduces milk production (Knabe et al., 1996; Jones and Stahly, 1999). When sows are not fed adequate amino acid and/or energy amounts in the diet, nutrients from different body tissues, particularly skeletal muscles and fat are mobilized to supply milk production requirements. In addition excessive mobilization of maternal protein commonly results in subsequent reproductive failure (Jones and Stahly, 1999; Vinsky et al., 2006). Sow body condition and its dynamic is an indicator of its physiological status. Adequate nutrient supply for lactating sows may positively influence their body condition, maximizing their productivity in terms of milk production and piglet growth (Oelke et al., 2008), and minimizing reproductive problems after weaning (Dourmad et al., 2008).
Can lactating sows be fed restrictively?
The effects of nutrient restriction and consequent catabolism during lactation on sow reproduction and longevity have been extensively studied in the last few years (Foxcroft et al., 1995; Vinsky et al., 2006; Quesnel, 2009; Schenkel et al., 2010; Patterson et al., 2011). However, the metabolic behaviour of sows under intense catabolism needs to be further understood (Bergsma et al., 2009; Patterson et al., 2011). In this sense, we conducted a study (Table 1) with the objectives of evaluating the impact of feed restriction during the lactation of hyper-prolific sows on their performance and to determine if the body tissue mobilization during lactation imposed by feed restriction could affect litter size and sow performance in the subsequent lactation.
Table 1. Impact of feed restriction on sows on the performance of their litters during 28 d of lactation and on next lactation performance (Adapted from De Bettio et al., 2016)
|Number of sows||20||20|
|ADFI (d 1- weaning), kg d-1||6.43||4.14||0.24||TL***|
|Sow BW Loss, kg||7.8||28.2||8.5||TL***|
|Weaning-to-estrus interval, d||4.3||4.3||0.5|
|Piglet average weight, kg|
|Litter weight, kg|
|Litter weight gain, kg d-1||2.70||2.43||0.36||TL*TL*|
|Milk production, kg d-1||8.33||6.99||1.16||TL**|
|Lactation efficiency3, %||72.93||82.30||8.77||TL*|
|Litter size Next Farrowing||15.10||14.07||1.52||TL†|
1 RSD= residual standard deviation.
2 Obtained by analysis of variance (GLM including the effects of parity (O), treatment (TL), and sow replicate (G) and their interactions (TLxO; TLxG))
3Lactation efficiency (LE) was calculated by the equation of Bergsma et al. (2009). LE (%) = energy input (derived from feed intake and body mobilization) by energy use for sow maintenance and litter maintenance and growth.
***P<0.001; **P<0.01; *P<0.05; †P<0.10.
The sows submitted to feed restriction presented higher body weight loss than the control sows, corresponding to 12.9 and 3.3% of the initial body weight, respectively. Similarly, other studies evaluating the effects of feed restriction in primiparous sows during lactation reported body weight losses of 3.1 and 8.7% (Vinsky et al., 2006) and 3.7 and 11.0% (Patterson et al., 2011) in sows fed ad libitum compared to sows fed restrictively, respectively. The greater body weight loss observed in restricted-fed sows in our study can be attributed to the fact that they produced, on average, 34% more milk than that reported in the above-mentioned studies, explaining their higher nutritional requirements, and consequent greater body weight loss. In addition, the sows submitted to feed restriction presented greater backfat thickness loss. Although backfat thickness does not reflect total fat body reserves, changes in this parameter may indicate that the sow is in negative energy balance (Jittakhot et al., 2012). Therefore, these findings indicate that the observed backfat thickness reduction reflects insufficient energy intake during lactation.
When sows are not fed adequate nutrient amounts, particularly of protein and lipids, skeletal muscle proteins are mobilized to supply milk production needs. Restricted-fed sows present higher protein and lipid losses compared with non restricted sows. Several studies suggest that the nutritional and metabolic changes in lactating sows may have deleterious effects on dam biology, with negative impacts on follicle development, and consequently on embryo development and on the number of piglets born in the next litter (Foxcroft et al., 2007; Ashworth et al., 2009; Quesnel, 2009; Schenkel et al., 2010; Hoving et al., 2011). According to Foxcroft et al. (2009), the mechanisms affecting fertility may involve hormonal changes, as well as epigenetic changes and/or changes in the expression of genes related to embryo development. Sows under severe catabolism present reduced IGF-1 (insulin growth factor 1) levels (Patterson et al., 2011), inducing the mobilization of endogenous protein (Zak et al., 1997). Protein mass losses higher than 12% during lactation may reduce follicle number and diameter, and decrease IGF-1 levels in sows submitted to dietary protein restriction during lactation (Clowes et al., 2003 a, b). Schenkel et al. (2010) recently reported reduced size of the next litter when sow’s body mass and protein mass losses exceeded 8 and 9%, respectively.
In our study, the size of the next litter of the sows previously submitted to feed restriction tended to be lower relative to the ad libitum group (15.16 vs. 14.13 piglets). The observed -1.03 piglet difference may be related to the 12.9 and 13.8% losses in body mass and protein mass, respectively, observed in restricted-fed sows of the present study. It must be noted that these losses are greater than the 12% reported in literature. This indicates that the predisposition of excessive mobilization of protein mass in hyper-prolific sows submitted to feed restriction may have a negative impact on the next litter size.