Limousin-cross steers ( n = 135; 258 ± 26 kg) were used to compare forage vs grain feeding on carcass composition and palatability attributes of beef when time on feed was controlled. Diets included a 95% alfalfa silage ration (AS) or a 68% highmoisture corn, 25% alfalfa silage ration (HMC). These were incorporated into six treatments to allow comparisons of end points based on similar days on feed or backfat finish. Dietary treatments included 1 ) HMC ( 4 mm), or cattle allowed ad libitum intake of HMC until slaughter at 4 mm ultrasound backfat; 2 ) AS (HMC-4), or cattle allowed ad libitum intake of AS until slaughter, regardless of finish, when HMC ( 4 mm) cattle were slaughtered; 3 ) AS ( 4 mm), or cattle allowed ad libitum intake of AS until slaughter at 4 mm backfat; 4 ) HMC (AS-4), or cattle allowed ad libitum intake of HMC until slaughter, regardless of finish, when AS ( 4 mm) cattle achieved 4 mm backfat; 5 ) HMC (RES), or cattle fed HMC at restricted intakes until slaughter at 4 mm backfat with feed offered at 75% of intake achieved by HMC ( 4 mm) and HMC (AS-4) cattle; and 6 ) AS ( 8 mm) or cattle allowed ad libitum intake of AS ration until slaughter at 8 mm backfat. Grain feeding generally increased ( P < .01) ADG, carcass weight, grade fat, and intramuscular fat content when compared with forage feeding at similar times on feed. Palatability attributes of ribeye roasts and ground beef were generally unaffected ( P > .10) by diet with the exception of slightly less beef flavor and more offflavor in forage-fed vs grain-fed beef. Higher ( P < .01) concentrations of linolenic acid and lower ( P < .10) concentrations of oleic acid in forage-fed beef may be partially responsible for diet differences in flavor.

Proteolytic activity of the bovine rumen microflora was studied with azocasein as the substrate. Approximately 25% of the proteolytic activity of rumen contents was recovered in the strained rumen fluid fraction, and the balance of the activity was associated with the particulate fraction. The proportion of proteinase activity associated with particulate material decreased when the quantity of particulate material in rumen contents was reduced. The specific activity of the proteinase from the bacterial fraction was 6 to 10 times higher than that from the protozoal fraction. Proteinase inhibitors of synthetic, plant, and microbial origin were tested on proteolytic activity of the separated bacteria. Synthetic proteinase inhibitors that caused significant inhibition of proteolysis included phenylmethylsulfonyl fluoride, N-tosyl-1-lysine chloromethyl ketone, N-tosylphenylalanine chloromethyl ketone, EDTA, cysteine, dithiothreitol, iodoacetate, and Merthiolate. Plant proteinase inhibitors that had an inhibitory effect included soybean trypsin inhibitors types IS and II-S and the lima bean trypsin inhibitor. Proteinase inhibitors of microbial origin that showed an inhibitory effect included antipain, leupeptin, and chymostatin; phosphoramidon and pepstatin had little effect. We tentatively concluded that rumen bacteria possess, primarily, serine, cysteine, and metalloproteinases. Ruminal proteolysis can result in a loss of high-quality dietary protein that would otherwise be directly digested and absorbed in the small intestine of the ruminant animal (7). The first step in protein degradation in the rumen is hydrolysis of proteins by proteinases to peptides and amino acids, which are either utilized directly by the microflora or degraded further by peptidases and deaminating enzymes to shortchain fatty acids and ammonia (12, 33, 34). Proteolysis has been suggested to be the ratelimiting step in the degradation of fraction 1 protein from alfalfa (31), although with other proteins, the utilization of amino acids was considered to be the limiting step (11, 26). Methods successful in improving protein utilization in ruminants by decreasing the apparent degradation of protein in the rumen have included chemical treatment of feed materials (11), defaunation (6), and inclusion of feed additives such as monensin and diaryliodonium compounds (13, 32). The most direct and perhaps the most effective means of decreasing the degradation of protein within the rumen is through the selective

Crossbred steers (n = 136) were used to assess breed differences in growth performance, carcass characteristics, fatty acid composition (total lipids and phospholipids), and palatability attributes of longissimus muscle. A multiple regression model was applied to crossbreeding data to estimate genetic differences between Simmental and Red Angus at the same level of backfat finish (10 mm). Simmental spent 71 more (P < 0.001) days on feed to acquire the same degree of backfat thickness as Red Angus, had heavier (P < 0.001) slaughter weights, larger (P = 0.002) longissimus muscle area, and increased (P = 0.023) lean yield. Average daily gain did not differ (P = 0.297) between breeds. Simmental were less (P = 0.012) efficient in converting feed to gain than Red Angus. Generally, there were few breed differences in palatability attributes for longissimus and semitendinosus muscles, with the exception of increased (P < 0.05) beef flavor scores for Simmental beef vs Red Angus beef across both muscles. For total lipids, concentrations of myristoleic acid (14:1), palmitoleic acid (16:1), and vaccenic acid (18:1n-7), along with n-6 to n-3 fatty acid (n-6:n-3) ratio, were greater (P < 0.05) in Simmental than Red Angus. In contrast, concentrations of margaric acid (17:0), eicosapentaenoic acid (20:5n-3), and total n-3 polyunsaturated fatty acids (n-3 PUFA) were greater (P < 0.05) in Red Angus than Simmental. For phospholipids, Simmental had lower (P < 0.05) amounts of 20:5n-3, docosahexaenoic acid (22:6n-3), and n-3 PUFA, with a greater (P = 0.017) n-6:n-3 ratio. Activity of delta9-desaturase enzyme in the conversion of palmitic acid (16:0) to 16:1 was greater (P = 0.001) in total lipids from Simmental as compared with Red Angus. A genetic basis for fatty acid differences is suggested, although the biological and practical significance needs to be demonstrated.

No abstract

We investigated the effects of fish meal (FM) in beef cattle diets on growth performance, carcass characteristics, and fatty acid (FA) composition of longissimus muscle in 63 yearling steers (335 +/- 23 kg). High-moisture corn and alfalfa silage diets were supplemented with either a corn gluten/blood meal mixture or FM at 10% of the diet. Fish meal contained (as-is basis) 5.87 g/kg eicosapentaenoic acid (EPA) and 9.84 g/kg docosahexaenoic acid (DHA). Seven strategies were developed to feed either a control diet (no FM) or diets containing 5 or 10% FM with FM fed for either 56, 112, or 168 d before slaughter. Average daily gain and feed efficiency were not affected (P > .10) by FM feeding but DMI decreased. Within FM diets, cattle fed 5% FM consumed more (P < .01) DM and gained more (P < .02) than cattle fed 10% FM. Carcass traits were not affected (P > .05) by feeding strategy except for fatter (P < .05) and lower (P < .06) yielding carcasses in cattle fed 5 vs 10% FM diets. Fish meal feeding increased (P < .01) concentrations of (n-3) FA, including EPA and DHA, and decreased (P < .05) concentrations of arachidonic acid. Increasing the amount of dietary FM further increased (P < .01) concentrations of EPA and DHA and decreased (P < .05) concentrations of (n-6) FA. We estimate that a 114-g steak from cattle fed 10% FM would supply 35 to 90% of the current average daily intake of EPA and DHA in North America. The results indicate that FM may have a role in niche marketing of beef provided that eating quality is not compromised.