GROWING AND FINISHING PERFORMANCE AND BODY COMPOSITION FOR ST. CROIX WETHERS CONSUMING GROWING DIETS DIFFERING IN GRAIN AND PROTEIN LEVELS

Authors: Goetsch, Arthur

Submitted to: Journal of Animal and Feed Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: In conventional growing-finishing ruminant production systems, protein is primarily deposited in the first phase and fat accumulates in the second. In terms of maximizing efficiency of energy and nitrogen use, these systems might be viewed as being somewhat poorly designed. Efficiencies would be enhanced if temporal patterns of protein and fat accretion were altered to minimize the time during which proteinaceous tissues must be maintained. Feeding St. Croix wether lambs 2.5% body weight of corn with 14.4% crude protein grass hay consumed ad libitum during a growing phase resulted in performance and body composition similar to 1.25% body weight of corn and supplemental protein sources, whereas the high amount of corn plus protein sources elicited greater live weight gain primarily through elevated fat deposition. In the subsequent finishing phase with a 20% protein, 80% concentrate diet, performance and final body composition did not differ among treatments, although much of the increase in fat mass for the high level of corn plus protein sources achieved during growing was maintained through finishing. In conclusion, there does not appear potential to enhance early fat deposition and partially delay protein accretion by providing a marginal protein diet with a moderate to high level of dietary corn with St. Croix wethers. Further study facilitated by these results, entailing animal types possessing greater growth potential and perhaps more limiting dietary protein levels, may lead to improved ruminant production systems. Such systems will be of great economic importance to livestock producers (cow-calf, stocker, and feedlot), feed manufacturers, and end-product consumers.

Technical Abstract: Twenty-four 3-month-old St. Croix wethers (14.5 +/- 0.53 kg initial live weight) were used to determine for enhancing efficiency of feed utilization by feeding a growing diet marginal in protein (83 days) to elevate fat deposition and partially delay protein accretion until a subsequent finishing phase (65 days; 80% concentrate, 20% crude protein diet). Endophyte-free fescue hay (14.4% crude protein) was consumed ad libitum during growing (83 days), with 1.25% body weight of corn plus a mixture of high-protein feedstuffs (82% crude protein) (LC-P), 2.5% body weight of corn plus high-protein feedstuffs (HC-P), or 2.5% body weight of corn (HC). Growing phase dry matter intake was similar among treatments (923, 978, and 900 g/day; SE 64.1) and live weight gain was greater (P<0.05) for HC-P vs LC-P and HC (139, 188, and 148 g/day for LC-P, HC-P, and HC, respectively; SE 8.9). Empty body protein mass after growing ranked (P<0.05) HC < LC-P < HC-P (4.17, 4.31, and 4.10 kg; SE 0.011), and fat mass was greater (P<0.05) for HC-P vs LC-P and HC (6.07, 7.01, and 5.66 kg for LC-P, HC-P, and HC, respectively; SE 0.188) Dry matter intake and live weight gain during, and body composition after, finishing were similar among treatments, although much of the difference in fat mass after growing between HC-P and other treatments was maintained through finishing (13.6, 14.2, and 13.6 kg for LC-P, HC-P, and HC, respectively; SE 0.80).