Lactating sow feeds: Nutritional strategies for improving feed intake, milk production and lifetime productivity

Introduction

Modern piglet production has continuously increased the amount of piglets born per sow year (PSY) through improving genetics, farm management and nutrition. In the Netherlands in 2016 on average 30.0 piglets were weaned per sow per year. This was achieved in 2.36 cycles with 14.7 piglets/litter born alive (PSY 34.7). With larger litters, the heterogeneity in birth weights increases and mortality increases with a higher percentage of small piglets. The mortality till weaning is high with 13.7%. Mortality doubles with a birth weight of under 800 grams and increases fivefold with a birth weight below 700 grams. The emphasis on prolificacy and milk production in combination with lean meat production of the progeny has led to high weight losses during lactation, resulting in difficulty in rebreeding. The replacement rate of sows is high (46% in the Netherlands). Since both litter size and birth weight of piglets is reduced with young sows the emphasis for increasing sow productivity should be on increasing longevity of sows.

Lactation

Milk production increases rapidly after farrowing and typically maximizes around day 10-14 of the lactation period. Feed and nutrient intake increases comparatively slower and will typically not maximize until day 12-18 of the lactation period, depending on the feeding schedule used. Resultantly the lactating sow is in a negative energy balance during the first 2 weeks of the lactation. During early lactation, both nutrient intake via the feed, as well as the mobilization of nutrients (energy, protein and minerals) from reserves, will determine the onset of milk production and development of the mammary gland. In the latter part of the lactation period, when body reserves are depleted, milk production will be determined by the feed intake capacity of the sow and the nutrient composition. The window of opportunity for maximizing milk production potential lies in early lactation with developing the mammary gland while that for achieving maximum milk production lies in the latter part of the lactation period.

At a recent Schothorst Feed Research trial, a litter growth of over 80 kg during a 26 day lactation period was achieved with multiparous sows. This resulted in an average 3.1 kg litter growth/day and a calculated milk production of 14.0 kg/d or 365 kg during the lactation period. Topigs 20 sows were used, litter size was standardized at 13 piglets.

Litter size and vitality of piglets are determining factors for the development of the mammary gland (and potential milk production capacity) by stimulating the utter and frequently emptying the milk glands (milk gland is refilled 35 minutes after suckling). Early growth of piglets will increase the milk demand and milk production potential. Modern sows will continue to produce milk even if it is the expense at their own body reserves and other body functions. Nevertheless, the milk production will become limiting for piglet growth 8-10 days after farrowing. An early introduction of prestarter feeds will, therefore, be needed to increase piglet growth and weaning weight and reduce weaning stress and mortality.

Potential milk production and feed intake: energy

With an average milk composition of 6.6% fat (36.6 MJ/kg), 5.2% crude protein (24.1 MJ/kg) and 5.8% lactose (16.6 MJ/kg), the Gross Energy content of sow milk will be 4.63 MJ/kg. With an assumed energy efficiency of 75% (Hansen, 2012) and a Net Energy content of 9.25 MJ/kg, it can be calculated that 1.0 kg of lactation feed fed above maintenance can provide enough energy to produce 1.5 kg sow milk (9.25/(4.63/0.75)). In practice roughly 1/3 of consumed energy is used for maintenance, meaning that 1.0 kg of lactation feed provides on average enough energy for 1.0 kg sow milk (see table 1). Nevertheless up to 2.4 kg milk is produced/kg lactation feed, as in the SFR experiment, the other energy is derived from body reserves (fat + protein).

From milk production, the litter growth can be calculated assuming an efficiency of energy deposition of 50% (Van den Brand, 2000). With an energy density of piglet gain of 10.7 MJ/kg (17.2% fat, 16.7% crude protein and 0.5% glycogen), the litter gain from 1.0 kg sow milk is 0.22 kg ((4.63 MJ/kg *0.50)/10.7) or 4.6 kg milk is needed for 1.0 kg litter gain. Assuming again that 1.5 kg lactating sow feed is needed for 1.0 kg sow milk, 4.6/1.5 = 3.1 kg feed (above maintenance) is needed for 1.0 kg litter gain.

Theoretically, the feed intake needed to achieve the desired milk production and litter gain (assuming a 2.5 kg feed requirement for maintenance (=1% body weight)) is as follows:

Table 1. Milk production and calculated feed intake needed for litter gain without energy mobilization.

Lactating sow feeds: Nutritional strategies for improving feed intake, milk production and lifetime productivity - Image 1

The feed efficiency increases from 5 kg feed/kg litter gain to around 4 when milk production (due to feed intake) increases. A typical feeding schedule is 1% of body weight + 0.4 kg lactation feed/piglet. Clearly, the feed intake levels calculated in table 1 are not achieved in practice, therefore both the energy (feed) intake and the ability to mobilize energy from body reserves will determine milk production and litter growth.

Potential milk production and feed intake: lysine

The crude protein content of sow milk varies from 4.5-5.5% and the lysine content of milk protein from 6.5-7.8%. Assuming an average crude protein content of 5.2% in sow milk and a lysine content of 7.5% in milk protein, the lysine content is 5.2*0.075 = 0.39% in sow milk. Assuming that all lysine is retained from feed (and not partly from body protein mobilization) and that 3 gram lysine/day is needed for maintenance, the daily requirement of ileal digestible (SID) lysine is calculated in table 2. As the milk production/ kg lactation feed varies in practice between 1.5 and 2.5, the lysine content of the lactating sow feed needs to be respectively 0.63% with a milk production of 1.5 kg per 1.0 kg feed intake, 0.83% with 2.0 and 1.03% with 2.5.

Table 2. SID lysine requirement for milk production, based on calculated feed intake needed for litter gain without protein mobilization.

Lactating sow feeds: Nutritional strategies for improving feed intake, milk production and lifetime productivity - Image 2

Since it is difficult to measure feed intake or litter gain it is easiest to express the SID lysine requirement per unit of energy intake. When assuming a 90% utilization of lysine for milk production and an energy efficiency for milk production of 75%, a balanced requirement will be 0.70 gram SID lysine/ MJ NE lactation feed (3.9 gram SID lysine/kg milk/ 0.90 lysine efficiency)/(4.61 MJ Gross Energy/kg milk ) * 0.75 energy efficiency. In practice often higher SID amino acid levels are used but this does not reduce body weight losses nor increase milk production, on the contrary, it will reduce feed intake.

Mobilisation of energy and protein from body reserves

Feyera, 2014 showed that regardless of the body weight loss of lean sow, roughly 1/3 of the body weight loss is fat and 2/3 protein tissue. Muscle contains 75% moisture and 25% protein, depot fat 15% moisture. The energy content of 1.0 kg body weight loss will therefore be 12.2 MJ: fat contributing (333 gram/kg * 85% dry matter * 36.6 MJ/kg) = 10.36 and protein (666 gram/kg * 25% protein *10.8 MJ/kg) = 1.80 MJ. The energy content of depot fat is 36.6*0.85/(10.8*0.25) = almost 12 times higher than that of body protein. Resultantly modern lean sows will lose large amount of weight during (the first part of) the lactation period, the energy content of muscle being relatively low, milk production high and feed (energy) intake insufficient.

With an efficiency of energy utilization of 87.5% (Hansen, 2012), 1.0 kg body weight loss can provide enough energy for 2.3 kg milk production ((12.2 MJ/kg BW*0.875 efficiency)/4.63 MJ/kg milk ). However, 1.0 kg body weight loss will also provide 12.5 gram lysine (666 gram muscle * 25% protein *0.075 (lysine%). The SID lysine/NE ratio as related to feed is then 12.5 gram SID lysine/12.2 MJ NE is 1.02 gram SID lysine/MJ NE. This is clearly in excess of the requirement of 0.70 calculated as being balanced in the feed. An average daily weight loss from farrow to weaning of 1 kg/day is common with modern lean sows under European conditions, this mobilization will provide only up to 10% of the NE requirement but up to 25% of the SID lysine requirement. If only fat could be mobilized 1.0 kg body fat would provide enough for energy for 5.9 kg milk (36.6*0.85*0.875/4.63). There will be therefore large differences between genetics and sows depending on body condition.

Feed formulation

It is recommended to formulate gestating sow feeds with high levels of fermentable carbohydrates (FCHO) in order to reduce embryonic death losses, increase the feed intake capacity during the lactation period and improve animal welfare. 2-phase gestation feeds are recommended in order to increase birth weight and vitality of piglets in the 2nd phase. A smooth transition to the lactating sow feed is needed around farrowing.

In order to increase milk production and reduce weight losses of the sow, feed (energy) intake should be increased as quickly as possible after farrowing and maintained at high levels (ad lib). Starch and sugars are the main glucogenic nutrients increasing blood insulin levels, driving lactose (milk) production and reducing mobilization of body reserves. Increasing the amount of lipogenic energy, derived from added fat to the feed and fat mobilization, results in an increased milk fat content but has limited effects on reducing weight losses of the sow or increasing milk production. Both FCHO and crude protein, when used as an energy source, will increase the metabolic heat production and negatively affect feed intake. High quality proteins (balanced amino acid pattern and a high ileal digestibility) and synthetic amino acids will alleviate metabolically induced heat stress. Inert carbohydrates (iCHO) will not increase heat stress but still increase gut fill and detoxification and prevent constipation. Different fiber sources in different concentrations should, therefore, be used in gestating and lactating sow feeds.

It is recommended to base feed formulations on the Net Energy values of feedstuffs taking into consideration the ability of (gestating and lactating) sows to ferment complex carbohydrates and the ileal digestibility of amino acids. The Net Energy content can vary depending on the season and feedstuff market but a fixed digestible amino acid/NE ratio should be used for each phase of the gestation and lactation period. This will help to reduce feed costs and increase performance. When weight losses are high in early lactation, the ileal digestible amino acid/NE ratio needs to be increased in the second part of the lactation period and in early gestation, the sow being in a positive energy balance, in order to restore lean tissue. At least a two-phase feeding program for lactating sows is recommended, eventually, a transition feed can be used around farrowing (see table 3).

Table 3. Phase feeding with different production goals and feed compositions.

Lactating sow feeds: Nutritional strategies for improving feed intake, milk production and lifetime productivity - Image 3

*Depending on heat stress (nursery temperature and humidity). **NSP= Non-Starch Polysaccharides consisting of fermentable (FCHO) and inert carbohydrates (iCHO).

In transition or phase 1, a smooth transition from gestation to lactation feeds is needed, moderate levels of inert carbohydrates are recommended. In phase 2 milk production is maximized by feeding high levels of starch rather than fat.

This article originally appeared in International Pig Topics. Also presented at the Pig Gut Health 2017 technical conference Bangkok in Thailand.