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Nutritional and Environmental Relationships with Lambs^1,2,

University of Missouri, Columbia

Abstract

Relationships between concentrate levels of pelleted rations and some environmental effects were studied with lambs fed individually ad libitum and pair fed for equal feed intake. Rations containing approximately 35% (LC) and 70% (HC) concentrates were fed in three trials in cool (0 to 5° C.) and warm (23 to 29° C.) environments. Feedlot performance, carcass quality, ruminal VFA levels and energy utilization were evaluated.

Lambs housed in cool environments had greater feed consumption and live gains. Groups fed LC consumed more feed and had greater rumino-reticulum fill (P<.05). Those receiving HC had higher ruminal propionate levels (P<.05). Lambs fed HC in warm environments usually had greater live gains, carcass weights and grades. Those fed LC in the cool environment usually had higher rates of live gain.

Lambs on LC in one trial ate more feed (P<.01) and had greater HI losses (P<.01) than those fed HC. Apparent DM digestibility was greater (P<.01) for lambs receiving HC. The greater ad libitum consumption of both diets at 5° C. was reflected in the larger (P<.01) HI losses for these groups. The low heat increment of HC in the pair feeding trial was insufficient to maintain body temperature in the cold environment and a greater portion of net energy was required for maintenance. However, the high heat increment of LC was a burden at 29° C. and a large expenditure of NEm was required to dispose of excess heat and resulted in less NE_P.

Over a wide range of environmental temperatures, lambs can be expected to consume as much digestible energy from pelleted rations containing 30% concentrate as they do from those containing 70% concentrate. Under ad libitum feeding conditions, the higher heat increment associated with high roughage rations will contribute to the maintenance of body temperature and spare NE_P at 0–5° C. environments. At environmental temperatures above 25° C, the high heat increment can seriously impair the efficiency of utilization of these rations as compared to more concentrated rations. The magnitude of the differences are sufficient to justify a consideration of environmental temperature in the formulation of ruminant rations to be fed under productive conditions.

¹ Contribution from the Missouri Agricultural Experiment Stations. Journal Series No. 3014. Approved by the Director.

² This paper is part of a thesis submitted by the senior author to the Graduate School, University of Missouri as part of the requirement for the Ph.D.

³ Present address: 649 Spruce Street, Glenview, Illinois.

⁴ Department of Animal Husbandry.

⁵ The authors are grateful to H. D. Johnson, Department of Dairy Husbandry; M. D. Shanklin, Department of Agricultural Engineering; and LeRoy Hahn, A.E.R.D., U.S.D.A., for provision of the Psychroenergetic Laboratory for one trial.