Emma Clowes, Vickie Baracos, and Frank Aherne

  Modern sows are larger, more prolific, and have higher milk yields but smaller appetites than sows of even five years ago. Because of these changes, many primiparous sows often supplement their dietary intake with maternal stores of energy and protein for milk production. This sometimes results in excessive weight loss, ultimately leading to a reduction in milk production and impaired subsequent reproductive performance. We believe that these reductions in animal productivity are a function of loss of lean tissue (protein), and an animal can lose 10 to 15% of her body protein before any detrimental effects are seen. We will test this hypothesis by feeding gilts to lose either a small (< 5%), moderate (10 to 15%), of a large (25%) amount of maternal protein during lactation and measure milk production (indirectly from litter growth rate) and reproductive status (from ovarian follicle population at weaning). Skeletal muscle is the main store of protein in the body, so changes in this tissue reflect changes in whole body protein stores. Sequential muscle samples taken in late gestation, mid lactation (day 14), and at weaning will assess the losses of maternal protein stores, and blood samples collected weekly during lactation will assess levels of various metabolites and metabolic hormones. It has been suggested that a sow has a ‘need’ to achieve a pre-determined lean (protein) body mass in her lifetime, and the closer the animal is to this lean body mass the smaller the drive to achieve this mass. So conceivably the ‘drive’ to gain lean tissue upon weaning is greater in a small animal such as a gilt than a larger animal such as a multiparous sow. We will create gilts with either a ‘normal’ or a ‘large’ lean body mass at parturition and feed these animals during lactation to either lose a small (< 5%) or a large (25%) amount of maternal protein during lactation. This will test whether it is the size of the maternal protein store at parturition and/or the relative depletion of these stores that influences the animal’s lactational and subsequent reproductive performance.