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The present study compared eight breeds of cattle differing in gender (heifers, bulls and steers) to determine associations between muscle characteristics and meat sensory qualities of the Longissimus thoracismuscle. Animal types differed in all the muscle characteristics and sensory qualities. Many correlations among muscle characteristics and among sensory qualities were consistent for most animal types. Isocitrate dehydrogenase (ICDH) activities allowed discrimination of muscles with respect to myosin heavy chain (MyHC)-I proportions for all animal types. Lactate dehydrogenase (LDH) and phosphofructokinase (PFK) activities were positively correlated for most animal types. Overall liking was correlated with beef flavour and abnormal flavour in all animal types and with global tenderness for all animal types except for Charolais cross breed steers. For all animal types except for Angus×Friesian heifers, beef flavour and abnormal flavour were negatively correlated. Overall liking was not correlated with juiciness. PFK, ICDH and citrate synthase (CS) activities were strongly associated with tenderness, beef flavour and overall liking when average values for all animal types were used. However, associations between muscle characteristics and sensory qualities within animal types were weak and inconsistent.

Polyphenol oxidase (PPO) activity in red clover (Trifolium pratense) has been reported to reduce both proteolysis and lipolysis, resulting in greater N use efficiency and protection of PUFA across the rumen. Although high levels of PPO have been reported in grasses such as cocksfoot (orchard grass; Dactylis glomerata), no in vivo research has determined whether grass PPO elicits the same response as red clover PPO. To test the hypothesis that silage ensiled from grass with high levels of PPO protects N and PUFA across the rumen, 6 steers with ruminal and duodenal cannulas were offered cocksfoot silage (CO; high-PPO grass), perennial ryegrass silage (PR; Lolium perenne; low-PPO grass), or red clover silage (RC; high-PPO control) at 16 g DM/kg BW daily with the experiment consisting of two 3 × 3 Latin squares with 21-d periods, consisting of 12 d of diet adaptation, 6 d of duodenal marker infusion, 2 d of duodenal sampling, and 1 d of ruminal sampling. All silages were well preserved, with DM of 34.4, 55.3, and 45.4% for CO, PR, and RC. Activity of PPO in silages was low due to deactivation but was greater in CO than either PR or RC (0.15 vs. 0.05 and 0.08 μkatal/g DM). Protein-bound phenol (mg/g DM) as a measure of the degree of oxidation and an indication of PPO protection was greatest for RC (15.9) but comparable for PR (10.1) and CO (12.2). Biohydrogenation of C18 PUFA was significantly lower on RC compared to the 2 grass silages with CO greater than PR. Despite lower levels of total fatty acid intake and subsequent duodenal flow, CO resulted in greater levels of phytanic acid and total branched and odd chain fatty acids in duodenal digesta than RC or PR. Ruminal ammonia concentration was greatest for RC, with no difference between the grasses. Duodenal flow of microbial N and efficiency of microbial protein synthesis were lowest for CO and comparable for RC and PR. The CO (high-grass PPO) did not result in elevated levels of C18 PUFA escaping the rumen or improve efficiency of total N transfer through the rumen compared to PR. The RC resulted in a greater flow of N and nonmicrobial N to the duodenum than the 2 grasses with PR greater than CO.

Because of the potential benefits to human health, there is interest in increasing 18:3n-3, 20:5n-3, 22:6n-6, and cis-9,trans-11 CLA in ruminant foods. Four Aberdeen Angus steers (406 ± 8.2 kg of BW) fitted with ruminal and duodenal cannulas were used in a 4 × 4 Latin square experiment with 21-d periods to examine the potential of fish oil (FO) and linseed oil (LO) in the diet to increase ruminal outflow of trans-11 18:1 and total n-3 PUFA in growing cattle. Treatments consisted of a control diet (60:40; forage:concentrate ratio, on a DM basis, respectively) based on maize silage, or the same basal ration containing 30 g/kg of DM of FO, LO, or a mixture (1:1, wt/wt) of FO and LO (LFO). Diets were offered as total mixed rations and fed at a rate of 85 g of DM/(kg of BW0.75/d). Oils had no effect (P= 0.52) on DMI. Linseed oil had no effect (P> 0.05) on ruminal pH or VFA concentrations, whereas FO shifted rumen fermentation toward propionate at the expense of acetate. Compared with the control, LO increased (P< 0.05) 18:0, cis18:1 (Δ9, 12–15), trans18:1 (Δ4–9, 11–16), trans18:2, geometric isomers of ∆9,11, ∆11,13, and ∆13,15 CLA, trans-8,cis-10 CLA, trans-10,trans-12 CLA, trans-12,trans-14 CLA, and 18:3n-3 flow at the duodenum. Inclusion of FO in the diet resulted in greater (P< 0.05) flows of cis-9 16:1, trans16:1 (Δ6–13), cis18:1 (Δ9, 11, and 13), trans18:1 (Δ6–15), trans18:2, 20:5n-3, 22:5n-3, and 22:6n-3, and decreased (P< 0.001) 18:0 at the duodenum relative to the control. For most fatty acids at the duodenum, responses to LFO were intermediate of FO and LO. However, LFO resulted in greater (P= 0.04) flows of total trans18:1 than LO and increased (P< 0.01) trans-6 16:1 and trans-12 18:1 at the duodenum compared with FO or LO. Biohydrogenation of cis-9 18:1 and 18:2n-6 in the rumen was independent of treatment, but both FO and LO increased (P< 0.001) the extent of 18:3n-3 biohydrogenation compared with the control. Ruminal 18:3n-3 biohydrogenation was greater (P< 0.001) for LO and LFO than FO, whereas biohydrogenation of 20:5n-3 and 22:6n-3 in the rumen was marginally less (P= 0.05) for LFO than FO. In conclusion, LO and FO at 30 g/kg of DM altered the biohydrogenation of unsaturated fatty acids in the rumen, causing an increase in the flow of specific intermediates at the duodenum, but the potential of these oils fed alone or as a mixture to increase n-3 PUFA at the duodenum in cattle appears limited.

Two experiments were conducted to determine whether the decreased proportion of fast muscle fibers seen previously in 2-wk-old lambs from ewes that were dietary restricted from d 30 to 70 of gestation are still evident in older lambs and what the consequences may be in terms of growth rates and carcass composition. Throughout both experiments, ewes were fed on an individual basis according to the recommended dietary allowance throughout pregnancy relative to metabolic BW (BW0.73). Control groups were fed as above, and the treatment groups had their nutrient supply reduced to 50% of this recommended allowance from d 30 to 70 (Exp. 1) or d 30 to 85 (Exp. 2) of gestation, after which they were returned to the same level of nutrition as the control group. All twin lambs were kept with their dams, and at 2 wk were given access to creep. After weaning, lambs were individually housed and fed ad libitum to 24 or 17 wk of age for Exp. 1 and 2, respectively. Although not significant (P= 0.18), growth to 24 wk (Exp. 1) resulted in a small decrease in the protein content and therefore an increase in the fat:lean ratio in the carcass of lambs subjected to maternal dietary restriction. This was not apparent when animals were slaughtered at 17 wk (Exp. 2; P> 0.68). Few significant effects of maternal dietary restriction on the fiber type composition of muscles were observed. In Exp. 1 the number of fast fibers increased (P< 0.008) with no effect on slow fiber number in LM. In Exp. 2 an increase in the total number of fibers in male lambs and an increase in type II (A and B) fibers in female lambs were observed in the LM, and an increase in IIB fiber number was observed in semitendinosus (ST) muscle from male lambs. Prenatal maternal dietary restriction during the time of muscle differentiation demonstrated an increase in type IIB muscle fibers and increase in intramuscular fat; although significant, effects on subsequent carcass quality of lambs were relatively small. These data suggest that the lambs adapted to changes in muscle fiber composition previously observed at 2 wk. However, lambs in this study were well fed during postnatal growth. Whether offspring would still have been able to compensate if they had received poor nutrition postnatally and whether that failure to compensate would have influenced carcass composition remain to be determined.

The experiment investigated the digestion of lipids from different forage silages in beef steers. Six Hereford × Friesian steers prepared with rumen and duodenal cannulas were given ad libitum access to a high-sugar grass silage, control grass silage, red clover silage, or mixtures of the red clover and each of the grass silages (50:50, DM basis). The experiment was conducted as an incomplete 5 × 5 Latin square, with an additional randomly repeated sequence. Total fatty acid and C18:3n-3 concentrations were greater (P< 0.05) for the high-sugar grass silage than the control grass silage or the red clover silage. Dry matter and total fatty acid intake were less (P< 0.05) for steers fed the control grass silage than for steers fed the other diets. Duodenal flow of C18:3n-3 was greater (P< 0.05), and flows of C18:0 and total C18:1 transwere less (P< 0.05), for the red clover silage compared with the 2 grass silage diets, with the mixtures intermediate. These results were supported by a reduction (P< 0.05) in biohydrogenation of C18:3n-3 for the red clover silage, with the mixtures again being intermediate. Flows of total branched- and odd-chain fatty acids were greater (P< 0.05) for the high-sugar grass silage diet, possibly as a result of greater microbial flow, because these fatty acids are associated with bacterial lipid. Duodenal flows of the chlorophyll metabolite, phytanic acid, were greater (P< 0.05) for animals fed the high-sugar grass silage treatments compared with the other treatments. These results confirm the potential for modifying the fatty acid composition of ruminant products by feeding red clover silage.

Two experiments were carried out to determine the effects of feeding grass silages differing in their water-soluble carbohydrate content, with or without red clover silage, on the efficiency of nutrient use. High-sugar grass, control grass, and red clover were ensiled in laboratory silos for use in an in vitro experiment (Exp. 1). For an in vivo experiment (Exp. 2), the same forage types were baled and ensiled. All silages were well preserved; within experiments the grass silages had similar composition, except for greater (P< 0.05) water-soluble carbohydrate concentrations in the high-sugar than the control grass silage. In Exp. 1, high-sugar grass, control grass, and red clover silages were fed alone or as mixtures (30:70, 50:50, or 70:30 on a DM basis, respectively) of each grass with the red clover silage to a simulated rumen culture system. There were no significant differences in microbial N flow or efficiency of microbial protein synthesis between individual forages. However, the corresponding values for the 70:30 ratio of high-sugar grass:red clover silage were greater (P< 0.05) than for the red clover silage. The value for the efficiency of N use (g of microbial N/g of feed N) was greater (0.86; P< 0.05) for high-sugar grass silage than the control grass silage. In addition, the high-sugar grass:red clover silage mixtures all gave greater (P< 0.05) values for the efficiency of N use than red clover silage alone; this difference was not achieved with the control grass mixture. Experiment 2 was an incomplete Latin square design conducted with 6 Here-ford × Friesian steers (163 ± 5.9 kg of BW) with rumen and duodenal cannulas fed the following 5 silage diets: high-sugar grass silage; control grass silage; high-sugar grass and red clover silage (50:50 DM basis); control grass and red clover silage (50:50 DM basis); and red clover silage. Rumen NH3-N concentration was lowest (P< 0.05) with the high-sugar grass silage. Microbial N flows to the duodenum and efficiency of microbial protein synthesis were greater (P< 0.05) for steers fed the high-sugar grass silage than for control grass and red clover silages, and mixing red clover with grass silages increased (P< 0.05) these values compared with red clover silage alone. In both experiments, the efficiency of incorporation of silage N into microbial N was more than 20% greater (P< 0.05) for high-sugar grass than for control grass silage. These data suggest that grass silage with high-sugar content provides a forage-based strategy for balancing N and energy supply and improving the efficiency of use of grass silage N in the rumen.