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Diet Energy and Steer Type Effects on Adipose Composition, Lipogenesis and Carcass Composition¹

Kansas State University, Manhattan 66506

Abstract

Fourteen Angus x Hereford (AHX) reciprocal crossbred steers and 30 Brown Swiss (BSX) sired steers out of AHX reciprocal crossbred dams represented cattle of different biological types. Steers were slaughtered at an energy efficiency end point (EEP) of either 9.0 Meal NEp/kg gain (EEP₁) or 11.5 Meal NEp/kggain (EEP₂). The 14 AHX steers were fed a low energy (LE) diet; seven were killed at EEP₁ and the other seven at EEP ₂. Seventeen BSX steers received the LE diet; eight were slaughtered at EEP₁ and nine at EEP₂. Thirteen other BSX steers received a high energy (HE) diet, and eight and five were slaughtered at EEP₁ and EEP₂, respectively. Although differences between EEP₁ and EEP₂ steers were not significant, EEP₁ cattle tended to have lower 12th rib adjusted fat thicknesses, lower yield grades and higher predicted percentages of separable lean. EEP₂ cattle required more days on feed (P<.10), gained slower (P<.05) and were slightly less efficient in converting dry matter (DM) to gain (P<.05). However, average daily gain and feed DM conversion (F/G) did not differ between EEP₁ and EEP₂ cattle during the last 70 days on feed (P>.10). BSX cattle gained faster (P<.05) and had trimmer carcasses (P<.05) and slightly more desirable F/G than AHX cattle slaughtered at a comparable EEP. Days on feed were similar for biological types. Carcass traits were similar for HE and LE steers slaughtered at constant EEP, but HE steers were superior in F/G (P<.05). No differences (P>.10) in adipose chemical composition between EEP₁ and EEP₂ steers or diet type were observed. No differences (P>.10) were detected in lipogenic enzyme activities of 6-phosphogluconate dehydrogenase (6PG), glucoses-phosphate dehydrogenase (G6P) or NADP-isocitrate dehydrogenase (ICDH). The similarity in adipose chemical and lipogenic enzyme activities indicates that the steers may have been of comparable physiological maturity.

¹ Contribution 80-12-J, Dept. of Anim. Sci. and Ind., Kansas Agr. Exp. Sta., Manhattan 66506.

² Present address: Loeffel Meat Lab., Univ. of Nebraska, Lincoln 68583.

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