| Abstrakt: |
Three experiments were conducted to study the effects of low birth weights on postnatal growth and carcass composition at slaughter in swine. In Exp. 1, high (> 1,600 g), medium (1,300 to 1,400 g) and low (1,000 to 1,100 g) birth weight pigs (16 pigs per group) were studied. At weaning, pigs were penned according to birth weight group and grown to slaughter at 96 kilograms. In Exp. 2, a large (1,500 to 1,600 g) and a runt (900 to 1,000 g) littermate pig from each of 16 litters and eight very low birth weight (<850 g) runts of similar breeding to the large and runt littermates were studied. Large and runt littermate pigs suckled with their natural litters, while the very low birth weight pigs were fostered to one of two sows to assure their survival. After weaning, birth weight groups were penned separately (four pigs per pen) and grown to slaughter at 96 kilograms. Eleven artificially reared pigs (five large barrows, X̅ = 1,592 g birth weight; three runt barrows, X̅ = 827 g; three runt gilts, X̅ = 910 g) were used in Exp. 3. Pigs were reared in individual cages and pens from birth to slaughter at 109 kilograms. Low birth weight pigs in Exp. 1 grew slower than medium or high birth weight pigs, but feed utilization was not significantly affected. Quantitative and qualitative carcass traits were similar among groups. In Exp. 2, runt littermate and fostered runt pigs grew slower and took significantly longer to reach slaughter weight than large pigs. Runt littermate pigs consumed less feed per day but had feed conversion ratios and carcass composition similar to those of large pigs. Fostered runt pigs were less efficient in utilizing feed for gain and produced fatter, lighter muscled carcasses. In Exp. 3, runt barrows and gilts grew slower and less efficiently than their large barrow littermates. Runt barrows produced fatter, lighter muscled carcasses, while runt gilts were similar to large barrows in carcass composition. In both Exp. 2 and 3, runt pigs had higher marbling scores and percentage lipid in the longissimusmuscle. Results indicate that birth weights as low as 1,000 g were not a severe detriment to carcass composition or efficiency of gain but that there was some reduction in rate of gain. Pigs weighing less than 1,000 g at birth grew slower and less efficiently and produced carcasses with a higher proportion of fat and less muscle than larger pigs when compared at constant slaughter weights. |
