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Abstract
Five trials were conducted with cattle and sheep to evaluate the effects of previous rate of growth on subsequent growth performance, alterations in body composition and changes in mass and in vitro metabolism of visceral tissues. Growth restrictions of varying severity and duration were imposed by limiting intake of metabolizable protein or energy. In Trial 1, lambs with restricted energy intake deposited lean tissue at the expense of body fat, while lambs restricted in metabolizable protein intake maintained body composition similar to that of unrestricted lambs. Liver weights were reduced with either protein or energy restriction. In Trial 2, reductions in mass of liver and intestines that occurred during the restriction period persisted after 2 wk realimentation, but no compensatory growth was evident during this time. Compensatory growth, relative to unrestricted controls, was expressed during the period between 2 wk realimentation and attainment of 50 kg live weight, and was not different for protein and energy restricted lambs. Composition of gain during the realimentation period was similar for previously restricted and unrestricted lambs. Lambs in Trial 3 did not express compensatory growth as a consequence of previous metabolizable protein or energy restrictions. Compensatory growth of cattle in Trial 4 was influenced by severity and duration of restriction to a greater extent when energy, as opposed to metabolizable protein, was the first-limiting nutrient. Compensation was greater for energy restricted cattle as a consequence of longer and more severe growth restrictions. In Trial 5, cattle that experienced severe metabolizable protein deficiencies made greater compensatory growth if provided supplemental escape protein during the realimentation period. Compensatory growth was made primarily during the grazing period that followed the winter restriction. Differences in finishing performance were not related to differences in rate of gain during the preceding spring-summer grazing or wintering periods. Finishing performance was associated in a positive manner with gain during the preweaning period, which may be the consequence of genetic or early post-natal developmental effects.
