1. For four consecutive years, each one of four herds of 13 cows and calves grazed land stocked and fertilized at one of the following combinations of rates (ha/cow, kg N/ha): 0·61, 82; 0·51, 82; 0·51,203 and 0·40, 203.

2. The Devon and Devon × British Friesian cows present in each herd reared calves by Devon bulls. Calving occurred indoors over the period February to April, the cows having been housed in early December.

3. Live-weight gains of calves to weaning in mid-October did not differ between herds in any year. Live-weight increase of cows over the grazing season was similar and substantial in all herds. On average pure-bred calves were 25 kg lighter at weaning than the cross-bred calves.

4. The main difference between treatments was in quantity of grass conserved and it was only in the herd kept at 0·51 ha/cow, 203 kg N/ha that enough was made to supply all the energy needs of the herd for a 150-day winter.

5. Gross margins/ha were greatest at the higher rate of nitrogen application but no further improvement was evident at the maximum stocking rate. The importance of maximizing output/animal is discussed.

Forty-one Texel and Texel-Oxford sires were selected over 5 years (1978-82) on high and low adjusted 100-day weight from 174 ram lambs artificially reared from birth and performance tested. The correlated responses to selection were measured in 1103 crossbred progeny, out of an experimental group of crossbred ewes, the progeny being naturally reared in field conditions. Hierarchical analysis of variance was performed, fitting the usual fixed effects and interactions. Co-heritabilities (rAh2h2; rA is the genetic correlation between traits with heritabilities h12 and h22) were estimated from offspring-parent regression and from the realized responses to selection. The selection differentials achieved (1·70 standard deviations in 100-day weight between high- and low-weight sires) were lower than expected, due to mating difficulties, mortality and other requirements for the stock. The co-heritabilities for growth traits were generally positive but small (mean 0·08; s.e. 0·08). Though not statistically significant, lambs slaughtered at a fixed weight from the high-weight rams were slaughtered earlier with lighter and leaner carcasses, as expected. Similarly, lambs slaughtered according to fat cover from high-weight rams were slaughtered later with heavier slaughter and carcass weights. Generally, the co-heritabilities for carcass traits were not significantly different from zero for either slaughter group. On the basis of these results, selection on ram 100-day weight with artificial rearing may not offer any advantage over natural rearing in the improvement of lamb growth and carcass traits.

Efficient reproductive performance in the pig breeding herd depends on many different factors including the behaviour and semen production characteristics of the boar. The latter are difficult to measure under on-farm conditions but results are accumulating from experimental and A.I. units (e.g. Du Mesnil du Buisson, Paquignon and Courot,1978; Fent, Wettermann and Johnson, 1983). The preliminary results presented here investigated semen production traits in a large commercial A. I. stud.

Mineral requirements of pregnant dairy goats are still not well defined; therefore, we investigated the net Ca, P, Mg, Na and K requirements for pregnancy and for maintenance during pregnancy in two separate experiments. Experiment 1 was performed to estimate the net Ca, P, Mg, Na and K requirements in goats carrying single or twin fetuses from 50 to 140 days of pregnancy (DOP). The net mineral requirements for pregnancy were determined by measuring mineral deposition in gravid uterus and mammary gland after comparative slaughter. In total, 57 dairy goats of two breeds (Oberhasli or Saanen), in their third or fourth parturition, were randomly assigned to groups based on litter size (single or twin) and day of slaughter (50, 80, 110 and 140 DOP) in a fully factorial design. Net mineral accretion for pregnancy did not differ by goat breed. The total daily Ca, P, Mg, Na and K requirements for pregnancy were greatest in goats carrying twins (P<0.05), and the requirements increased as pregnancy progressed. Experiment 2 was performed to estimate net Ca, P, Mg, Na and K requirements for dairy goat maintenance during pregnancy. In total, 58 dairy goats (Oberhasli and Saanen) carrying twin fetuses were assigned to groups based on slaughter day (80, 110 and 140 DOP) and feed restriction (ad libitum, 20% and 40% feed restriction) in a randomized block design. The net Ca, P and Mg requirements for maintenance did not vary by breed or over the course of pregnancy. The daily net requirements of Ca, P and Mg for maintenance were 60.4, 31.1 and 2.42 mg/kg live BW (LBW), respectively. The daily net Na requirement for maintenance was greater in Saanen goats (11.8 mg/kg LBW) than in Oberhasli goats (8.96 mg/kg LBW; P<0.05). Daily net K requirements increased as pregnancy progressed from 8.73 to 15.4 mg/kg LBW (P<0.01). The findings of this study will guide design of diets with adequate mineral content for pregnant goats throughout their pregnancy.

This study examined the comminution of fresh herbage, subsequent nutrient release, and the characteristics of swallowed boli from three physically and chemically contrasting forages during ingestive mastication by dairy cows. The extent and pattern of nutrient release will determine their availability to rumen microflora, and potentially influence their efficiency of use. The forages evaluated were perennial ryegrass (ryegrass, Lolium perenne L., cv Alto AR37), lucerne (Medicago sativa L., cv Torlesse) and chicory (Cichorium intybus L., cv Choice). Experimental design was a 3×3 cross-over with three forages and three consecutive 1-day measurement periods, conducted twice. Six non-lactating, pregnant, multiparous Holstein-Friesian×Jersey cows (Bos taurus) were used, with the first cross-over applied to three mature (10.1±0.61 years old; BW 631±64 kg) cows, and the second to three young (4.8±0.02 years; BW 505±19 kg) cows. Fresh cut forage was offered to the cows following partial rumen evacuation. Swallowed boli were collected directly at the cardia at the commencement, middle and end of the first feeding bout of the first meal of the day. Forage species did not affect the fresh weight of ingested boli (mean 169 g, P=0.605) but the proportion of saliva in boli varied between forage. Boli of chicory contained the greatest amount of herbage material and least amount of saliva, whereas ryegrass boli were the opposite. Boli fresh weight tended to increase as time in the meal progressed, but the age of the cow was not shown to affect any boli characteristics or nutrient release. Particle size reduction was affected by forage, with 31%, 38% and 35% of chicory, lucerne and ryegrass herbage reduced to <2 mm. There was little evidence of relationship between comminution and any physical or chemical characteristic of the forage, except in ryegrass where extent of comminution was moderately correlated with herbage strength. Proportional release of herbage soluble carbohydrate exceeded that of N during mastication. Differences in loss of N were moderately correlated with the amount of N in the herbage (R2=0.53) but herbage comminution was not strongly correlated with release of either N or carbohydrate. These findings illustrate the complex animal×forage interactions that occur during mastication, and that it is not possible to infer nutrient loss from herbage based on herbage characteristics as the driver for this differ between species.

This work was designed to study the effects of carcass maturity on meat quality characteristics and intramuscular connective tissue of beef semitendinosus muscle from Chinese native Yellow steers. Chemical determinations, histological and mechanical measurements were performed on the raw and cooked meat at 4 days post mortem. In raw meat, intramuscular fat, collagen solubility, mechanical strength and transition temperature of intramuscular connective tissue increased (P < 0.05) with carcass maturity before body maturation, whilst moisture, total collagen, fibre diameter decreased after body maturation. Warner-Bratzlar shear force (WBSF) of cooked meat increased with maturity before body maturation due to the muscle atrophy, and thus the decline of moisture content and the increase of cooking losses. After body maturation, the increase of WBSF was neutralised by the increase of intramuscular fat, the decrease of total collagen and the elongation of sarcomere length.

Dobruja Finewool ewes were mated to two rams of each of the Clun Forest, Hampshire, Suffolk and Oxford Down breeds as well as to rams of their own breed. The crossbred and purebred lambs were compared in terms of growth, food consumption and carcass attributes. The crossbred lambs of Hampshire, Suffolk and Oxford Down breeding were superior to the purebred control lambs on all counts while Clun Forest crossbred lambs were superior to controls only in carcass attributes and the time taken to reach slaughter weight but not in efficiency of conversion.

Four silages were prepared from whole crop maize, each receiving additives of 21 1 formic acid per t fresh crop, and 0, 14, 27 or 53 g formaldehyde per kg crude protein in the crop. These silages, together with 19·6 g urea per kg dry matter, were offered ad libitum for 83 days to 60 British Friesian steer calves, initially 99 kg live weight, either alone or with groundnut or fish meal to raise the dietary crude protein content by 27 g/kg dry matter.

Formaldehyde treatment restricted silage fermentation, increased silage and dry-matter intake and live-weight gain, but reduced digestibility, so digestible organic matter and digestible energy intakes were unaffected. Much of the increase in live-weight gain appeared to be due to an increase in gut fill, as carcass weight was not significantly affected by formaldehyde treatment. There was no improvement in the utilization of dietary nitrogen, but there was some evidence that formaldehyde treatment may have increased the proportion of muscle in the carcass.

Supplementation with protein improved intake, nitrogen retention, feed conversion ratio, live-weight gain and carcass weight. The improvement in intake and food conversion ratio occurred mainly on the control silage, there being little effect on the formaldehyde-treated silages. Fish meal supplementation increased the digestibility of organic matter, cellulose and energy, and was more effective in improving food conversion ratio than groundnut meal. There were no significant differences between diets in the proportion of dietary nitrogen retained.

It was concluded that the scope for the use of formaldehyde, when ensiling maize for use in diets for young calves, appears to be limited.

Previous research in our laboratory has shown that lactating rats given low protein diets will readily mobilise approximately 20% of body protein to sustain lactational performance. However in such females lactational performance falls markedly around day 6 of lactation and remains at this low level for the remainder of lactation. The objective of this study was therefore to investigate whether this decline in lactational performance coincided with the exhaustion of labile protein reserves, and secondly whether such protein depleted females could reestablish effective lactation in mid lactation when given an increased supply of dietary protein.

Sixty six multiparous Sprague-Dawley rats were mated individually with a proven male breeder, mating being confirmed through the presence of vaginal plugs, then transferred to solid bottomed plastic cages for the remainder of the experiment.

A temporary tremor condition in adolescent pigs is described which shows similarities with a tremor condition known to occur in young piglets. Growth and carcass traits were on average superior in affected pigs compared with unaffected litter-mates, paternal half-sibs and genetically unrelated pigs. Females were over-represented among the affected pigs which were born in large litters.

The concentrations of maternal immunoglobulin in 2-day-old lambs born to Scottish Blackface ewes which had been mated when 6 to 7 mo old were significantly lower than in lambs born to these ewes a year later. But the mortality rates were almost identical. The concentrations in lambs born to the same ewes in successive years were significantly more highly correlated than the concentrations in lambs born to older females in successive years, examined in a previous study.

1. Sixty-four Blackface wether lambs, weaned some 8 days previously from the hill were divided into two similar groups. One group of lambs was implanted with 15 mg. hexoestrol.

2. The treated lambs had gained an average of 2·32 lb., and 3·88 lb. live-weight more than the control group, after 4 and 7 weeks respectively.

3. The mean carcass weight of 23 hexoestrol-implanted lambs was 1·5 lb. greater than that of the same number of untreated lambs.

4. Carcass grading provided no evidence of a deterioration in quality as the result of hexoestrol implantation.

5. Light lambs responded at least as well as heavy lambs to the hormone.

An experiment was conducted with 72 male British Friesian calves between 5 and 11 weeks of age. The major treatments were the inclusion of 0, 20 or 40% wheat straw or 20, 40 or 60% lucerne in a complete pelleted diet. The roughage was either ground or chaffed. A methane inhibitor was included in the diets given to 36 of the calves. The weight gains of the calves were greater with diets containing lucerne than with those containing wheat straw. Grinding increased the intake of wheat straw but depressed intake of lucerne. The apparent digestibility of dry matter and acid detergent fibre, which was greater for the diets containing lucerne than for the diets containing wheat straw, was reduced by grinding both roughages.

Inclusion of the methane inhibitor in the diets increased the feed intakes and weight gains of the calves given the all-concentrate diet and the diets containing wheat straw, but not those given the diets containing lucerne.

Effects of alternative pen rearing system, stocking density, breed-type and their interactions on post-weaning rabbit performance were investigated in a replicated experiment. Californian purebred and terminal crossbred weanlings (no. = 502) were randomized amongst four pen treatments: CSD = conventional wire pen (61 × 76 × 46 cm) stocked with five rabbits; PSD = iron framed, wire-fitted, pen (76 × 244 × 46 cm) stocked with 20 rabbits; PDD = pen stocked with 40 rabbits, and PTD = pen stocked with 60 rabbits. Pen traits measured were average daily food intake (Fl), food efficiency (FE), survival rate (SR), and final weight uniformity (CV). Individual traits were initial (IW) and final (FW) weights and average daily gain (ADG) over 6 weeks.

In CSD v. PSD pen trait comparisons, FI was increased (P < 0·05), and numerically poorer FE and greater CV were detected (P > 0·05) in CSD; however, SR means were similar. Non-significant differences were observed in the PSD v. (PDD + PTD)/2 contrast (P > 0·05). For PDD v. PTD, pen FE was numerically better in the former but CV was greater (P > 0·05). Individual FW and ADG were increased (P < 0·05) in PSD v. (PDD + PTD)/2 groups; no other significant contrast differences were observed. Breed-type (B) × pen treatment (P) interaction was not significant (P > 0·05) for IW, ADG and FW; and individual sire/B × P interaction accounted for proportionately less than 0·05 of the total random variation. These results suggest the commercial potential of large pen rearing of rabbits.

The present study was carried out on the pure Bauscat (Bau), pure New Zealand (NZW) and pure Californian (Cal) strains of rabbit. Overall reproductive performance for overdue does of the three breeds was determined and compared with that of does delivering at the normal time. Overdue does of the Bau and NZW breeds had a significantly (P < 0·05) higher annual mean number of pups weaned than overdue Cal does. There was a high incidence of pup mortality in post-mature litters, and the causes of this high mortality were crushing of the skull followed by subsequent stillborn-birth difficulties and intra-uterine death in all three breeds. Obliteration of the anterior fontanelle of pups from post-mature litters occurred in 71%, 75% and 69 % of the deaths diagnosed at birth in the Bau, NZW and Cal breeds, respectively. Induction of parturition with either PGF2α or oxytocin reduced pup mortality in overdue does. The birth-to-remating interval was significantly (P < 0·01) lower in overdue does in which parturition was induced with PGF2∞ but significantly longer when parturition was induced with oxytocin.

A procedure has recently been developed for estimating economic values which employs a profit function implying that animals with mean values for variates in the profit function give the most profit. However, the proposed index selects extreme animals, a paradox which is explained by showing that the index is appropriate for only part of the profit function. More appropriate selection indices are developed and illustrated graphically.