Identifcation of Risk Factors Associated with Slow Growth Rate of Swine in Commercial Conditions

Body weight (BW) variability in swine production hinders farm efficiency and occupies time, especially in growing-finishing facilities. Pigs with a slower growth rate perform worse than their faster counterparts, increasing the period until reaching the market BW and, hence, reducing the farmer’s income. The aim of this observational study was to identify risk factors associated with a reduced growth rate of swine regarding the whole production cycle. The study was conducted in a commercial farm, in which pigs were slaughtered in three times, at d 163 (n=423), d 188 (n=402) and d 205 (n=203). A total of 1028 male and female crossbreed pigs [Pietrain x (Landrace x Large White)] from 110 dams were included in the trial. Piglets were weighed weekly from birth to weaning and then every three weeks until slaughter. Piglets that did not survive until the finishing period were excluded from the trial. Variables including length of gestation, length of lactation, parity, litter size, sex, birth BW and ADG (0-7, 21-64, and 65-83 d) were considered. Pigs leaving the farm in the third group were defined as slow growing pigs (20% of pigs). Statistical analyses were performed with the R software (R Core Team, 2015). A multiple logistic regression, taking the growth rate as a binary response (1=slow; 0= fast), was calculated to identify and rank all the variables that were significant (P<0.05). None of the variables included presented collinearity (VIF<5). The Risk Ratio (RR), Odds ratio (OR) and the Population Attributable Risk (PAR) were calculated for all the significant variables, after transforming all them into binary factors using 25th percentile as the cutting point. The results showed that lactation length <19 d (RR:1.53, OR:1.73), birth BW <1.2 kg (RR: 2.01, OR: 2.49), ADG from 7 to 14 d <140 g/d (RR:2.74, OR: 3.79), ADG from 21 to 64 d <200 g/d (RR:4.52, OR: 7.70) and ADG from 65 to 83 d <550 g/d (RR:5.70, OR: 11.21) were associated with a slow growth rate. If animals with these five risk factors were eliminated, the percentage of slow growth pigs would be a 5.1% instead of a 20%. In fact, the differential PAR associated to lactation, transition and the beginning of the fattening period were 4.5%, 3.9% and 2.6% respectively. These results suggest that the most critical risk factors associated with retardation of growth rate in swine are lactation and transition.