The response of lactating ewes grazing grass to variations in effective rumen degradable protein (ERDP) and digestible undegradable protein (DUP) supply from concentrates was investigated. During the spring and early summer of 1993, 36 Friesland and 12 Finn Dorset ewes were offered continuous access to permanent pasture (Lolium perenne) and allocated to one of six concentrates (1·2 kg/day) formulated to be iso-energetic and to supply 149 (H), 126 (M) or 103 (L) g ERDP and 70 (A) or 45 (B) g DUP per kg dry matter (DM) in a 3 ✕ 2 factorial design. Herbage intake was estimated using the n-alkane technique and herbage samples obtained for analysis. Ewe milk yields, milk composition, live weights (LW) and condition scores (CS) were recorded weekly. The DM and nitrogen degradability characteristics of the grass samples and concentrates were determined using four Friesland wether lambs fitted with permanent rumen cannulae. Throughout the experiment the grass ERDP: FME ratio was lower than the optimum for maximal microbial protein synthesis. However, using a rumen solid phase outflow rate of 0·05 per h, estimated concentrate ERDP and DUP supplies were similar to those predicted. Increasing concentrate ERDP supply had no effect on herbage intake or LW and CS change but reduced milk fat concentration (P < 0·05) and increased milk lactose concentration (P < 0·05) and the yields of milk (P < 0·01), protein (P < 0·05) and lactose (P < 0·01). There were no significant effects of concentrate DUP supply. In conclusion, it is suggested that concentrate ERDP increased microbial protein synthesis and metabolizable protein supply, a proportion of which may have been deaminated to provide precursors for milk lactose synthesis, such that the marginal response in milk protein yield was 0·210.

This study reports improvements in the nutritional value of pork by including linseed in the diets of boar and gilt pigs. Two feeding strategies, either short-term or long-term, were employed: (i) 0 g or 114 g linseed per kg of food provided to 16 pigs of 87 kg live weight for 20 or 27 days; (ii) 0 g, 10 g, 20 g or 30 g linseed per kg of food provided to 64 pigs of 46 kg live weight for 54, 62, 68 or 75 days. All diets were supplemented with DL-α-tocopheryl acetate (0•2 g/kg). The 18 : 3n-3 contents (18 : 2n-6 :18 : 3n-3 ratios in parentheses) of the short-term 0 g and 114 g/kg, and long-term 0g, 10 g, 20 g and 30 g/kg linseed diets, were 2•1 g (7•75), 28•1 g (0•70), 1•0 g (8•86), 3•4 g (2•73), 6•0 g (1•66) and 8•1 g/kg food (1•25) respectively. The long-term 30 g/kg diet reduced the n-6 : n-3 ratio of muscle and adipose tissue as successfully as the short-term 114 g/kg diet to accord with guidelines for the overall human diet (5 :1 or less) but required only 0•73 as much linseed and increased the proportion of C20-22 n-3 fatty acids more effectively; compared with their respective control diets, the 114 g/kg and 30 g/kg diets more than halved the n-6 : n-3 ratios in muscle to 3•8 and 3•9, approximately trebled the concentrations of 18 : 3n-3 in muscle to 0•43 mg and 0•28 mg/g tissue, and doubled the concentrations of 20: 5n-3 in muscle to 0•08 mg and 0•10 mg/g tissue. Similar changes occurred in adipose tissue. With both strategies, the majority of the changes had occurred by the time the first groups were slaughtered. There was a strong relationship between the 18 : 2n-6 :18 : 3n-3 ratio of the food and tissues and the accumulation of all C20-22 n-3 fatty acids, except 22 : 6n-3, which was unaffected by dietary linseed. The improvements in nutritional value were obtained without changes in organoleptic characteristics, as measured by a trained taste panel, or significant loss of shelf-life, as measured by TBARS analysis and colour stability.

Four multiparous Holstein-Friesian cows fitted with simple cannulas in the proximal duodenum and the rumen were offered four diets in a 4 ✕ 4 Latin-square design to evaluate the effect on energy and nitrogen balance of crop maturity of maize when offered as ensiled food with grass silage and a concentrate. Forage maize (cv. Hudson) was ensiled at target dry matter (DM) contents of 230, 280, 330 and 380 g per kg fresh weight (FW). The mean values for volatile corrected DM (VCDM) and starch content of the maize forages as given were 226, 278, 319 and 357 g/kg FW and 180, 263, 327 and 401 g/kg VCDM respectively. Grass silage (GS) containing 247 g VCDM per kg FW was produced from the primary growth of a perennial ryegrass sward. The diets comprised 8·7 kg DM concentrate per day with one of four forage treatments offered ad libitum, in a 3 : 1 DM ratio of maize silage with GS, designated T23, T28, T33 and T38. Each period was of 6 weeks with energy and nitrogen balances conducted in respiration chambers over 6 days in either week 5 or 6. There were no significant effects of maturity on DM intake. Changes in milk yield and composition were not significant but milk protein yield increased significantly (P < 0·05) with maize maturity up to T33 and was linearly related (P < 0·05) to changes in maize silage starch and neutraland acid-detergent fibre (NDF, ADF) content. Total starch intake increased significantly (P < 0·01) with maturity but apparent digestibility of starch was significantly (P < 0·05) reduced only with the most mature maize silage (T38). NDF and ADF intake and amounts digested were not significantly different despite a numerical decline with stage of maturity. Total nitrogen intake and apparent digestibility were not significantly different although there were significant differences (P < 0·05) in the amount of nitrogen excreted as urine, which was greatest on T23 and least on T33, and milk which was least on T23 and greatest on T33. Mean gross energy (GE) intake increased by 17 MJ/day from T23 to T33 but the differences were non-significant. Faecal energy output on T23 was significantly lower (P < 0·05) than the other treatments whilst urine energy on T23 was significantly higher (P < 0·05) compared with T33. Methane energy losses were not significantly different. There were no significant differences between treatments in either GE digestibility or metabolizability, digestible or metabolizable energy (ME) intakes or in the partition of ME to heat, tissue or milk. The calculated ME concentrations of the maize silages were not significantly different with an overall mean of 12·3 MJ/kg VCDM estimated at maintenance intake, or 0·63 MJ/MJ GE. Changes in maize silage composition resulted in a doubling of the ratio of digested starch to digested NDF (0·66, 0·94, 1·10 and 1·21) for treatments T23 to T38 respectively. Despite this large change in digested nutrients no differences in the efficiency of energy utilization were detected.

Differences in insulin binding affinity and in concentrations of insulin receptor, were found in a variety of tissues taken, at slaughter, from mature steers (701 (s.d. 23) kg) and growing lambs (47 (s.d. 2·1) kg). In both species, liver had lower insulin binding affinity than skeletal muscles m. pectineus m. longissimus dorsi and m. rectus capitis (all P < 0·001) and subcutaneous, omental and perirenal adipose depots (all P < 0·001). Site-specific differences in affinity for insulin existed between adipose depots (subcutaneous < omental, P < 0·05; subcutaneous < perirenal, P < 0·001) and between tissue-types (subcutaneous fat < m. pectineus skeletal muscle, P < 0·05; m. rectus capitis < perirenal fat, P < 0·05) in steers. In lambs also, receptor affinity for insulin differed between tissue-type (m. longissimus dorsi < perirenal fat, P < 0·05; m. rectus capitis < subcutaneous fat, P < 0·05 and m. rectus capitis < perirenal fat, P < 0·001) but lambs did not show the adipose depot-specific differences in insulin affinity observed in steers. Insulin receptor concentration differed between adipose depots (subcutaneous < omental, P < 0·05; subcutaneous < perirenal, P < 0·01) and between tissue-type (m. pectineus < perirenal fat P < 0·05) in steers and perirenal and subcutaneous adipose depots of lambs had higher receptor concentrations than m. longissimus dorsi and m. pectineusP < 0·001). This is the first study to demonstrate, in any species, differences in insulin receptor binding affinity and receptor concentration in a wide range of tissues (liver, skeletal muscles and adipose depots) from the same individual. Such differences in meat-producing animals could, through effects on tissue sensitivity and/or responsiveness to insulin, influence nutrient partitioning to tissues and affect overall rates of lipid storage and net protein synthesis.

To mimic the abnormal patterns of follicular growth in the early post-partum period, heifers were injected with 15 mg oestradiol and 37•5 mg progesterone every 12 h for 7 days starting on day 15 of the oestrous cycle. Control and treated animals (no. = 8 per group) were monitored by daily ultrasonography and plasma hormone measurements. Five treated animals had quiescent ovaries for 11 days during which period oestradiol concentrations exceeded 30 pg/ml. After this, the first post-treatment follicular wave produced a normal ovulatory follicle. The other three heifers had quiescent ovaries for 17 days during exposure to high oestradiol values but this was followed by the formation of persistent follicles. The prolonged exposure to oestradiol probably disrupted normal LH surges in the latter animals. Growth rates and internal diameters for normal, ovulatory and prolonged persistent follicles were similar for the first 6 days after emergence, but the persistent follicles grew larger (P < 0·05) than normal follicles over the next 20 days. Luteinization of a subsequent persistent follicle was observed in one heifer. For 2 to 3 days prior to follicular growth, FSH concentrations were similar in controls, and heifers with ovulatory or persistent follicles (P > 0·05). When follicles first emerged and for the next 4 days, oestradiol concentrations were greater in follicles which later persisted (P < 0·05). For the second half of the life-span of persistent follicles, oestradiol concentrations were basal, thus the structure remained for many days after endocrine function had declined. These observations allow new interpretation of previously confusing findings in subfertile cattle presented to veterinarians.

To evaluate the effect of crop maturity on digestion of maize silage in the rumen and post-ruminal digestive tract, four multiparous Holstein-Friesian cows fitted with a simple cannula in the proximal duodenum and a rumen cannula were offered four diets in a 4 ✕ 4 Latin-square design. Forage maize (cv. Hudson) was harvested and ensiled at target dry matter (DM) contents of 230, 280, 330 and 380 g per kg fresh weight (FW) to provide a range of starch contents. The mean values for volatile-corrected DM (VCDM) and starch content of the four maize silages as given were 221, 277, 308 and 372 g/kg FW and 173, 257, 328 and 382 g/kg VCDM respectively. Grass silage (GS) containing 250 g VCDM per kg FW was produced from the primary growth of a perennial ryegrass sward. The diets were 8·7 kg DM per day of a dairy concentrate supplement with one of four forage treatments offered ad libitum. The forage treatments were a 3 : 1 DM ratio of maize silage with GS, designated as T23, T28, T33 and T38. Each period lasted 6 weeks with rumen and duodenal samples being taken over 3 days in week 4 and faeces being collected in respiration chambers over 6 days in either week 5 or 6. Milk yield tended to increase with advancing maturity (30·5, 31·8, 32·5 and 32·3 kg/day) but individual treatment differences were not significant. DM intake increased from 19·62 to 21·30 kg/day (P < 0·05) but there were no significant effects on digestibility in the rumen, post-ruminal tract or total tract. Digestibility of neutral detergent fibre in the rumen declined with increasing starch content in the maize silage (P < 0·05) but total digestibility was not significantly affected. Starch intake increased from 3·11 to 5·04 kg/day (P < 0·001), duodenal flow from 0·40 to 0·89 kg/day (P < 0·01) and the amounts digested in the rumen and post-ruminal tract respectively from 2·72 and 0·34 kg/day to 4·16 and 0·71 kg/ day (P < 0·01). However the only significant effect on starch digestibility was a small fall in total digestibility from a mean of 0·981 for T23, T28 and T33 to 0·966 for T38. There were no treatment effects on nitrogen digestion. The molar proportions of acetic acid and n-caproic acid decreased and that of n-butyric acid increased with advancing maturity. It is concluded that the changes in composition of maize silage with increasing maturity result in large increases in the contribution of starch to DM digested in the rumen but only small differences in rumen fermentation. Post-ruminal starch digestion doubles but this is due to the increased starch concentration of the silage rather than major changes in digestion and the amount is small compared with that likely to result from feeding maize grain.

Two experiments were conducted with 32 Charolais cross steers (experiment 1) and 36 Holstein-Friesian and Welsh Black steers (experiment 2) to examine the effects of dietary n-3 polyunsaturated fatty acids (PUFA ) and breed on meat quality. Diets were comprised of grass silage and a concentrate (60 : 40 on a dry-matter basis). Lipid in the concentrate provided 30 g/kg diet dry matter derived from either linseed, fish oil or linseed/fish oil (experiment 1); and linseed or linseed/fish oil (experiment 2). These n-3 PUFA sources were compared with Megalac, a saturated fatty acid control, in both experiments. Diets were offered for 120 days (experiment 1) and 90 days (experiment 2). Measurements of meat quality included fatty acid composition, lipid oxidation and colour during retail display (i.e. shelf life parameters) and eating quality assessed by a trained taste panel. The samples examined were sirloin (longissimus) steaks and minced beef burgers produced from the forequarter muscles infraspinatus, supraspinatus and triceps brachii. The fatty acid results showed that linseed increased the proportion of 18 : 3 n-3 (a -linolenic acid) in neutral lipid of the burgers and approximately doubled it in the phospholipid. Increased synthesis of 20 : 4 n-3 and 20 : 5 n-3 also occurred, raising their levels in the phospholipid. Fish oil doubled the proportions of 20 : 5 n-3 and 22 : 6 n-3, with the linseed/fish oil results intermediate between linseed and fish oil. The Welsh Blacks in experiment 2 had higher proportions of 18 : 3 n-3 in neutral lipid and higher proportions of 18 : 3 n-3, 20 : 5 n-3 and 22 : 5 n-3 in phospholipid. This showed a clear genetic effect on fatty acid composition. The fish oil diet in experiment 1 greatly increased lipid oxidation during retail display in both overwrapped loin steaks and burgers packed in a modified atmosphere. Values for lipid oxidation in the burgers were much higher than in the steaks due to the intimate mixing of phospholipid fatty acids and prooxidants. Lipid oxidation was also greater in the linseed/fish oil samples than controls in both experiments but was similar in linseed and controls. Colour oxidation also proceeded more rapidly in the fish oil samples in experiment 1 and tended to be faster in the linseed/fish oil groups in both experiments. Eating quality was affected by diet in experiment 1 — the fish oil samples eliciting higher scores for ‘fishy’ and ‘rancid’ than controls and having lower ‘overall liking’ scores. Steaks from animals given the linseed diet (with high 18 : 3 n-3 proportions) had the highest ‘overall liking’ scores in experiment 1 but the cattle given linseed for the shorter time in experiment 2 were not different from controls. Despite their different PUFA profile in muscle, Welsh Blacks had similar eating quality scores to Holstein-Friesians which deposited more neutral lipid (marbling fat) in muscle.

Fifty-five multiparous Holstein-Friesian cows were used in a 20-week continuous design study to determine the effect of maize silage maturity on food intake and milk production. Forage maize (cv. Hudson) was harvested and ensiled at target dry matter (DM) contents of 230 (T23), 280 (T28), 330 (T33) and 380 (T38) g per kg fresh weight (FW). The mean values for volatile-corrected DM (VCDM), starch, neutral-detergent fibre (NDF), crude protein and predicted metabolizable energy (ME) content of the four maize silages were 226, 290, 302 and 390 g/kg FW, 114, 274, 309 and 354 g/kg VCDM, 574, 447, 431 and 448 g/kg VCDM, 96, 80, 74 and 75 g/kg VCDM and 10·3, 11·5, 11·6 and 11·2 MJ/kg DM, respectively. Grass silage containing 296 g VCDM per kg FW was produced from the primary growth of a perennial ryegrass sward. At week 3 of lactation cows were allocated to one of five forage treatments offered ad libitum. The forage treatments were either grass silage alone (TGS) or a 3 : 1 DM ratio of maize and grass silage designated as T23, T28, T33 and T38. All cows also received 8·7 kg DM per day of a dairy concentrate. Forage VCDM intake for TGS was lower (P < 0·001) than for T23 to T38. Increasing maize silage DM content from 226 (T23) to 290 (T28) g/kg increased (P < 0·05) forage VCDM intake from 10·9 to 13·3 kg/day but a further increase to 390 (T38) g/kg tended to reduce VCDM intake. When compared with TGS, the inclusion of maize silage increased milk yield from 28·0 kg/day to 29·4, 32·7, 33·0 and 30·8 kg/day for T23 to T38, respectively, the increases being significant for T28 to T38. However, milk yield was reduced (P < 0·05) when the DM content of the maize silage increased from 302 to 390 g/kg. Increasing maize silage DM content from T23 to T33 reduced (P < 0·05) milk fat content from 45·8 to 41·8 g/kg, which was also lower (P < 0·05) than for TGS. The inclusion of maize silage increased fat yield with a significant difference (P < 0·05) between TGS and T28. The inclusion of maize silage increased milk protein content (P < 0·05) and protein yield (P < 0·001) when compared with TGS. While increasing maize silage maturity did not affect (P > 0·05) milk protein content, protein yield was higher (P < 0·05) for the two intermediate DM contents. There were no treatment effects on body condition score. It is concluded that the changes in composition of maize silage with increasing maturity, which are associated with increased starch and reduced NDF content, resulted in large increases in food intake and yield of milk and protein as crops matured from T23 to T33. However, when crop maturity increased further to T38 there was a tendency for DM intake and yield of milk and protein to decline.