Managing growth and wellbeing
The thickness of the gilt’s back fat is particularly critical. According to research, 12 to 15mm of back fat is both an advantage for future longevity as a sow and the ideal thickness for influencing the secretion of leptin – the hormone that stimulates the release of luteinising hormone (LH) and, in turn, the reproductive cycle.
If the gilt is too lean or obese, longevity and productivity are likely to be compromised. A focus on gut health and strength of joints and bones is similarly important to animal performance and wellbeing.
Steps in the feeding strategy
This is where the right feeding strategy with controlled daily weight gain can bring farmers a long way to optimising body composition and overall health.
A daily weight gain of 750 to 800g is the recommended optimum for gilts from a weight of 30kg and up to 140kg prior to insemination. While ad libitum feeding is unproblematic in gilts up to 60kg, feed intake should be limited from then on to obtain the necessary weight gain control (figure 1). If ad libitum feeding is the only option, however farmers should adjust the feed by lowering the protein content and raising the level of fibre.
From 110kg and up, a reduction in the feed’s digestible protein content can support the growth of back fat deposits and minimise the development of excessive muscle. Several experiments have shown that too high a weight at the first insemination gives a higher percentage of the gilts later exposed too early as sows, partly because a high growth during the growing period increases the risk of osteochondrosis.
The next step in the feeding strategy should be initiated around seven to 14 days before insemination is due to take place. Feed should then be increased to 3.5 to 4kg a day, including a higher protein content to raise plasma levels of LH. Due to this so-called flush feeding, the level of glucose, insulin and estradiol hormone in the blood plasma increase, stimulating the production of eggs.