Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: February 28, 2001
Publication Date: March 21, 2001
Citation: Freetly, H.C., Nienaber, J.A., Brown Brandl, T.M. 2001. Relationship between aging and nutritional controlled growth rate on heat production of ewe lambs [abstract]. Journal of Animal Science. 79(Suppl. 2):106. Technical Abstract: The objective was to determine how nutritionally reducing growth rate alters the relationship between specific activity of heat production and aging. Fasting heat production of 12 Dorset ewe lambs at 114 +/- 2 d of age was determined and ewes were assigned to treatments. Treatments consisted of two different feeding levels. The HIGH treatment was offered 4.5% of their weekly BW and the LOW treatment was offered 2.5% of their weekly BW. Each treatment consisted of six animals and animals remained within treatment for the remainder of the study. Calorimetry measurements were repeated every 6 wk. Treatments differed in both the linear and quadratic term for fasted BW on age (P<0.001). The rate of BW gain decreased as ewes aged in the HIGH treatment and the rate of BW gain increased as ewes aged in the LOW treatment. The HP:BW ratio decreased in the HIGH treatment as ewes aged and was described by a previously reported prediction equation but the ratio in the LOW treatment was not described b this same equation. Fitting the data with treatment specific decay functions for HP:BW on age fit the data better than the pooled function. The HP:BW ratio decreased rapidly in the LOW treatment following feed restriction but remained elevated compared with the HIGH treatment as animals aged. After excluding the initial measurements in the LOW treatment when ewes were on the HIGH level of feed the HP:BW ratio was best described by a linear decrease. This study suggests that a model taking into account proportion of mature body size is a reasonable predictor for heat production across breeds of sheep growing in nutritionally adequate environments; however, it cannot be extended to sheep that are a lower proportion of their mature BW due to nutritional restriction.