Effect of different feed density during gestation for group housed and fed sows on litter size and farrowing rate

Many studies have focused on creating the best feeding strategy for sows in the gestation period. The conclusions show that the feeding strategy must follow the daily needs for maintenance, adjusted to the body condition of the sow (Quesnel et al. 2010; Athorn et al. 2011). In Europe, loose housing systems based on small, stable groups with floor feeding during gestation are common, because these systems are cheap and easy to manage. However, this leads to aggressive behaviour during feeding. One possible way to reduce aggressive behaviour is to increase the daily feed intake or the eating time with low-density diets. It was hypothesised that feeding sows with a low density commercial pelleted diet during the gestation would increase farrowing rates but not affect the litter size.

The study took place in one production herd, where sows were housed in pens of 13–14 from immediately after mating to farrowing and fed twice daily on the floor with commercial pelleted feed. A total of 1556 multiparous DanAvl sows were assigned to two groups blocked by parity: Low (11 MJ digestible energy (DE)/kg) and High (13 MJ DE/kg) energy density. The sows were weighed and scanned for backfat depth at the P2 site just after mating and just before farrowing. Sows followed the same feeding strategy based on MJ DE/day, but it was possible to shift the feeding curve parallel up/down for each pen depending on the average P2 backfat depth just after mating. The aim of the feeding strategy was to have the same average P2 backfat depth at farrowing in all the pens.

The difference in MJ DE/kg was achieved by increasing the level of oats in the Low diet. The diets used in the two groups had different levels of crude fiber but the same content of minerals, vitamins and protein per MJ DE and followed common standards for nutrients for gestating sows. Therefore, sows in the Low Group had to eat 15% more feed daily to receive the similar intake of DE and nutrients as the sows in the High group (based on the Danish feed evaluation system). At farrowing the number of total born piglets per litter was recorded per sow, but the averaged litter size from all the sows in each pen was used in the statistic model. The farrowing rate was calculated as percentage of sows in each pen transferred to the farrowing.

Litter size, body weight (BW) and backfat P2 gain to farrowing were analysed in a linear model by ANOVA under the GLM procedure, while farrowing rate was analysed by logistic regression in the MIXED procedure (SAS^®; USA). The covariates were pen, parity, body weight (BW) and P2 at mating.

The Low- and High-density diets resulted in the same (P > 0.05) increased BW gain and P2 backfat gain (Table 1). Using the Low-density diet caused a higher (P = 0.04) litter size, but there was no difference (P > 0.05) in farrowing rate between groups. In conclusion, in this study the density of the diet (based on change in crude fiber content) was detrimental to litter size, but not to the farrowing rate.

Table 1.  Effect of two diets of different density fed during gestation on litter size and farrowing rate. Values are mean ± SE (per pen)