A specific carbohydrate diet fed in late lactation to enhance post-weaning fertility in primiparous sows

In primiparous lactating sows, feed intake is generally insufficient to meet energy requirements for milk production, causing excessive mobilisation of body reserves, and potentially compromising post-weaning reproductive performance. Besides feed intake, the dietary energy source during lactation can also influence post-weaning reproductive performance through luteinising hormone secretion and insulin production (van den Brand et al. 2001). Chen et al. (2013) showed that glucose and insulin secretion were elevated and subsequent litter size increased by feeding a supplement of carbohydrates rather than fat during the last week of lactation. The object of this study was to use a fully formulated carbohydrate diet (CHO) to increase gonadotrophin by stimulating insulin and glucose secretion in late lactation to improve subsequent litter size in a commercial piggery.

The study was conducted on a commercial production unit in South Australia. Eight days before weaning, primiparous sows (n = 119) weighing 200 ± 6.4 kg (mean ± SD) were allocated based on suckled litter size to a CHO diet (14.3 MJ digestible energy (DE)/kg, 198 g/kg crude protein) or a standard lactation diet (Control; 14.2 MJ DE/kg, 195 g/kg crude protein). The CHO diet was to provide glucogenic content (wheat extruded, dextrose and sugar) instead of fat, and without changing total dietary energy. Only litters with 10 or more piglets remaining 8 days before weaning were included in the study. Feed allowance was increased gradually from farrowing until maximum feed intake was achieved. Feed intake in lactation was recorded daily. Sows and piglets were weighed after litters had been standardised to ≥11 piglets at beginning of lactation, and at weaning. Mating dates, pregnancy status, sow removals and second litter size were recorded. All statistical analyses were performed using the GLM procedures (SAS^®; USA).

Body weight loss was less (Table 1) than generally reported (around 10%) for primiparous sows during lactation (Schenkel et al. 2010). For sows that were mated within 10 days of weaning, the weaning-mating interval was reduced by half a day (P < 0.05) by feeding the CHO diet. However, conception rate and subsequent litter size did not differ between treatments. In conclusion, providing an enriched CHO diet fed in late lactation did not improve subsequent reproductive performance in the present study. This may due to there was no second litter syndrome in those primiparous sows and, therefore, there was little margin to improve fertility. However, there were physiological effects on post-weaning gonadotrophins from the CHO diet in terms of a shorter weaning-mating-interval.

Table 1.  Body weight loss and energy balance during lactation, and post-weaning reproductive traits, in primiparous sows fed either a Control diet or a high carbohydrate diet (CHO). Values are mean ± SEM