Effect of reduced dietary protein and roughage intake on metabolites in plasma, urine and milk from gestating and lactating organic sows during winter

Summary

Organic sows are fed excessive dietary protein. Current thesis investigates the effect of reducing the dietary concentration of protein during gestation, on the metabolism and productivity of organic sows during winter conditions, using metabolites in plasma, urine and milk as indicators. Moreover, the nutritional contribution of roughage is studied.
Organic agriculture is shaped on a set of coherent values, namely the principle of health, ecology, fairness and care. The organic legislation is shaped by these values, which is expressed in the sow production, where sows have outdoor access, are supplied roughage, have a longer lactation period, among others. The organic production system is a contrast to the indoor conventional sow production, and consequently the requirement of the sows differs. Most noticeable organic sows have a greater requirement of energy, due to an increased need for cold thermogenesis, especially in winter conditions. The organic sow’s requirement for protein is however not different from the indoor sows’ requirement. Nevertheless, organic and conventional sows are fed according to the same feeding standards. Another important aspect affecting the nutrition of organic sows is the access to roughage. Besides providing several benefits in terms of welfare and health, roughage contributes to the nutrition of the sows. When fed restricted, roughage may contribute with up until half of the daily total energy intake and a substantial proportion of the amino acids required, depending on the type and quality of roughage.
In addition to physical measurements, metabolites found in plasma, urine and milk are useful indicators and provides a detailed view upon the metabolism of the sow. The five major metabolites contain information about specific parts of the metabolism, where glucose, lactate and TG are correlated to the energy metabolism, urea to the nitrogen metabolism and NEFA to body mobilization. Besides these five main metabolites, a large range of minor metabolites exists and provides even more details about the metabolism. In addition to the metabolites, milk production and chemical composition of milk are affected by the metabolism and feeding of the sows and are central in the reproductive performance of sows.
Adjusting the protein supply to sows is a matter of balance. Feeding sows too much protein, increases the amino acid oxidation and urea production, which is energy-costly and ultimately reduces the feed efficiency. Moreover, it constitutes an environmental problem. On the contrary supplying sows insufficient protein may reduce productivity and causes body mobilization to accommodate the nutritional needs for the highly prioritized reproductive traits. Thus, the dietary concentration of protein must be carefully optimized.
A total of 21 sows (Topigs Norsvin; TN70) was included in current study from day 30 of gestation until weaning at day 49 of lactation. The sows were housed under typical production conditions of outdoor organic sows in winter conditions. During gestation sows were on one of two isoenergetic diets: An organic commercial diet containing 76 g SID CP pr. kg or a low-protein diet containing 63 g SID CP pr kg. In the lactation period all sows were fed the same organic commercial lactation diet. Besides, sows were fed either clover-grass silage or barley-pea whole-crop silage during the entire experimental period.
At day 60 and 100 of gestation blood, urine and feces were sampled and at day 5 and 20 of lactation blood, milk, urine and feces were sampled. At all sampling days, including day 30 of gestation and day 49 of lactation, sows were weighted and backfat scanned and piglets were individually weighted. Besides, plasma, urine and milk from sows fed different protein levels during lactation from a previous study, was analyzed for a range of minor metabolites.
During gestation the deposition of body reserves was not affected by dietary protein level. An interaction (P<0.05) showed that the concentration of urea in urine from control sows only at day 60 of gestation was 23 % higher compared to sows fed low protein diets. Moreover, the roughage intake during gestation supplied a substantial amount of nutrients, where clover-grass silage in average supplied 1.7 MJ ME/d and 0.36 g SID lysine/d, equal to 14 % ME, and 13 % and 17 % SID lysine of the total intake, for sows fed control and low dietary protein diet, respectively. The nutritional contribution of barley-pea whole-crops silage was approximately a fourth of this. During lactation the reproductive performance of the sows were very good, with an average peak milk yield of 16.2 kg/d at day 20. Consequently, the litter gain was very good, and sows weaned in average 13.3 piglets, that each weighed 19.9 kg at day 49. However, as indicated by plasma NEFA, body mobilization was high, and the sows’ metabolism was under significant pressure indicated by plasma glucose. From day 5 to 20 the milk yield of sows fed low protein during gestation, became gradually higher compared to control sows (P<0.05). Accordingly, the litter gain was greater (P<0.01), thus the litter weight became gradually heavier as lactation proceeded (P<0.001). Despite, the higher milk production, low protein sows did not mobilize more body reserves compared to control, presumably due to a slightly higher feed intake. Of the minor metabolites, urinary urea was the only metabolite affected by dietary protein level (P<0.05), showing that control sows were fed excessive amounts of protein. Moreover, the metabolites provided several details of how the lactational period affected the metabolism of the sow.
In conclusion reducing the dietary content of SID CP in gestational compound feed to 63 g/kg does not affect the productivity of organic sows during winter conditions negatively. On the contrary, it seems to improve the nitrogen balance in gestation and improve the reproductive performance. Thus, there seems to be no obstacles preventing a reduction in the protein content in compound feed for gestation sows in commercial organic sow production. Moreover, clover-grass silage can contribute a substantial amount of nutrients, which should be accounted for in the feeding strategy.