Predicting post-farrow maternal weight for primiparous and multiparous sows.

Maternal weight at the end of gestation is needed to calculate maternal and fetal weight gains throughout gestation. However, maternal weight after farrowing is difficult to obtain in commercial farms. Therefore, equations were developed from an analysis of 150 females (Line 1050, PIC, Hendersonville, TN) to predict the weight of conceptus by difference of pre- and post-farrowing weight change in multi-parity sows. Females were individually weighed as they were moved into the farrowing house at d 110 to 112 of gestation and again at 12 to 24 h after farrowing. Sows were provided with ad libitum access to feed in the farrowing house. Data was divided into 4 parity groups: 1, 2, 3, and 4+. Three predictor variables were evaluated within each parity group: pre-farrow weight, total born and difference in days between the pre- and post-farrow weights. Prediction equations were then developed using models with significant terms based on the Bayesian Information Criterion. The optimum equations to predict maternal BW were similar for all parities except for the intercept (b) and can be described as:

Post-farrow maternal BW (kg) = b + (0.897 × pre-farrow BW, kg) - (0.508 × total born, n) + (3.123 × days pre to post-farrow, d);

Where the intercept (b) for parities 1, 2, 3, and 4+ were -2.70, 2.34, 5.41, and 14.69, respectively.

The prediction equations were then used to estimate post-farrow maternal BW using 332 mixed parity sows (PIC 1050). Pre-farrow weights were taken on d 113 of gestation and maternal BW were taken within 24 h of farrowing. Feed intake was limited to 2.7 kg/d prior to farrowing. On average, the predicted post-farrow maternal BW was overestimated by 1.5 kg of the actual (P=0.002). Although the difference between the actual and estimated post-farrow maternal BW was significant this difference is negligible when partitioning maternal and fetal weight gains throughout gestation. When applying this difference (1.5 kg) to sow gestation models, the impact on daily maintenance requirement is a difference of only 32 kcal. We hypothesize the difference in feed allowance in the farrowing house prior to farrowing may have contributed to the overestimation of post-farrow maternal BW. The post-farrow BW prediction equation is a tool that can be applied to sow gestation models for an understanding of the females maternal and fetal weight gains throughout gestation.