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Effects of Protein Level Sequence and Sex on Rate and Efficiency of Gain of Growing Swine, and on Carcass Characteristics, including Composition of Lean Tissue¹

University of Minnesota, St. Paul 55101

Abstract

ONE-HUNDRED-FORTY-FOUR crossbred barrows and 144 crossbred gilts weaned at about 21 days of age and averaging 5.4 kg were used in a 3 x 3 x 2 factorial arrangement of treatments with two replications to study the effects of level of dietary protein during the early developmental period, and of protein level sequence used from 23.1 to 94 kg, on rate of gain, feed/gain, carcass characteristics and composition of lean tissue from the longissimus muscle.

During the period from 5.4 to 23.1 kg pigs fed 16 or 20% protein diets gained significantly (P<.01) slower than those fed 24% protein and pigs fed the 16% protein diet required significantly (P<.01) more feed per unit of gain than those fed the higher protein diets. Daily gain was not significantly affected by sex, but barrows required significantly (P<.05) less feed per unit of gain than gilts.

Pigs fed diets providing 19 to 16 and 16 to 13% protein level sequences during the feeding period from 23.1 to 94.1 kg gained faster and had smaller feed/gain ratios than those pigs fed at the lowest protein level sequence (13 reduced to 10%). Barrows gained faster (P<.01) than gilts and required nearly the same amounts of feed per kg live weight gain during both growing periods.

Pigs fed diets providing 13 reduced to 10% protein yielded carcasses with smaller cross-sectional area of the longissimus muscle and smaller percentage yields of trimmed ham and loin of both slaughter and chilled carcass weights than pigs provided with greater protein intakes during the final growing period. Inadequate dietary protein also tended to result in greater ether extract and smaller protein content of lean tissue from the longissimus muscle than found when pigs were fed adequate protein, or more, during the final developmental period. Carcasses from gilts were superior to those from barrows in all carcass measurements except dressing percent.

There was no evidence that level of dietary protein fed during the period from 5.4 to 23.1 kg exerted a significant carryover effect on rate of gain or feed/gain ratio subsequent to 23.1 kg, or on carcass leanness. Lack of significant first and second order interactions indicated that levels of dietary protein and sex acted independently on the response criteria.

¹ Paper No. 7485, Scientific Journal Series of the Minnesota Agricultural Experiment Station.

² Present address: P.O. Box 824, Paramaribo, Suriname.

³ Animal Scientist, North Central Experiment Station, University of Minnesota, Grand Rapids.