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Influence of Age at Weaning and Kind and Protein Content of Starter on Rate and Efficiency of Gain of Growing Swine, and Carcass Characteristics^1,2,

University of Minnesota, St. Paul

Abstract

One-hundred-eighty litters of pigs were used in six experiments to determine the effects of age at weaning (3 vs. 5 vs. 8 wk.) and protein content of the diet fed pigs weaned at 3 wk. (17 vs. 20%) on rate and efficiency of gain of pigs to 8 wk. of age, or about 20 kilograms. In experiments 4, 5 and 6, the effect of kind of starter (simplified vs. moderately complex) on these response criteria was also investigated. Twelve hundred pigs were continued through the growing period subsequent to 8 wk., or about 20 kg., to determine effects of early treatments on subsequent rate of gain and gain/feed; 928 pigs were slaughtered to investigate treatment effects on carcass leanness, and 157 of these were used to obtain additional data on the influence of dietary and management variables on tenderness and composition of the lean tissue from the l. dorsi.

In three of six experiments, pigs weaned at 8 wk. were significantly (P<.01) heavier at that age than pigs weaned at 3 or 5 wk., but this result was not found in the last three experiments involving 112 litters. Pigs fed 20% protein diets when weaned at 3 wk. had greater gain/feed ratios from 3 to 8 wk. in three experiments than those fed 17% protein diets.

Pigs weaned at 8 wk. had significantly (P<.01) less backfat than those weaned at 3 and 5 wk. in one experiment and significantly (P<.05) less backfat than those weaned to 20% protein diets at 3 wk. in two experiments. Dressing percent, cross-sectional area of the l. dorsi and percentage yields of trimmed ham and loin were not significantly affected by any of the treatments imposed on pigs during the early growing period. Warner-Bratzler Shear values, expressible moisture ratios and percentages dry matter, protein and ether extract of lean tissue from the l. dorsi were not altered by treatments to which pigs were subjected during the early developmental period.

The results of this series of experiments suggest that rapid gains are not essential during the early growing period of pigs weaned at an early age to assure maximum gains and gain/feed during the period subsequent to 20 to 22.7 kg., as well as to attain maximum carcass leanness. On the other hand, these results do not indicate that rapid early development adversely affects subsequent rate of gain, gain/feed and carcass leanness.

¹ Paper 6715, Scientific Journal Series of the Minnesota Agricultural Experiment Station.

² Acknowledgement is due Geo. A. Hormel & Co., Austin; Elliott Packing Co., Duluth; and Swift & Co., South St. Paul, Minn., for excellent cooperation and assistance in obtaining carcass data; appreciation is expressed to American Cyanamid Co., Princeton, N.J., and Merck Sharp and Dohme, Rahway, N.J., for generous supplies of some dietary essentials.

³ Present address: Department of Chemistry, University of Georgia, Athens.

⁴ Southern School and Experiment Station, Waseca, and West Central Experiment Station, Morris, Minn., respectively.

⁵ Present address: Allied Mills, Inc., P.O. Box 459, Libertyville, Ill.

⁶ Present address: Bigelow, Minn.