One hundred first lactation Friesian dairy heifers were used to investigate the effect of level of nutrition n i late pregnancy and for a limited period around the time of insemination on reproductive performance. The heifers were housed throughout the period of the trial in cubicle yards and all individuals were given controlled amounts of food.

Fifty animals were offered a ‘high’ (H) level of feeding in late pregnancy (for 10 weeks before calving) and 50 were offered a ‘low’ (L) level. After calving, the heifers were re-randomized with half of each pre-calving group being offered either the H or L level of feeding in early lactation (weeks 6 to 18), thus forming four subgroups of 25 heifers: HH, HL, LH and LL. The level of feeding in late pregnancy for all groups increased towards calving. The high plane heifers consumed 83·6 MJ metabolizable energy (ME) per day on average compared with 64·6 MJ ME per day for the low plane heifers, a proportional mean difference of 0·29 (P < 0·001). After calving, heifers consumed an average of 86 MJ ME per day in week 1 rising to 126 MJ ME per day by week 5. Between weeks 6 to 18 of lactation, the high plane group consumed an average of 146·8 MJ ME per day compared with 119·8 MJ ME per day for the low plane group, a proportional mean difference of 0·23 (P < 0001).

There were no significant effects of feeding treatments on milk yield. Fat yield in weeks 6 to 18 was increased by the high level of feeding in lactation (P < 0001), while protein yields in weeks 1 to 5 and n i weeks 6 to 18 were increased by high plane feeding in pregnancy (P < 0·05) and lactation (P < 0·05), respectively. Heifers receiving the high level of feeding in late pregnancy gained significantly (P < 0·001) more weight than those on the lower level of feeding. All groups lost similar amounts of weight during the first 5 weeks after calving, but there were marked differences in the rate of live-weight gain between weeks 6 to 11 of lactation (P < 0·05 to P < 0·001). In particular, the HL group had the lowest rate of live-weight gain, and this was significantly lower than that of the HH group (P < 0·01).

First ovulation occurred significantly earlier in heifers receiving the high level of feeding in pregnancy P ( < 0·01), but there was no effect of treatment on ovulation detection rate, time to first oestrus, time of first insemination or the proportion of wrongly-timed inseminations. Heifers receiving the high level of feeding in lactation had a successful pregnancy rate to first insemination of 0·42 compared with 0·63 for those on the lower level of feeding (P < 0·05), with the greatest difference observed between the HL group (0·72) compared with the HH group (0·35) (P < 0·01). Embryo loss rate was low in the HL group (008) compared with that in the HH group (0·26; P < 0·l). The net result was that the HH group had a median interval from calving to successful pregnancy of 95 days with an interquartile range of 82 days, whereas the figures for the HL group were 75 and 23 days (P < 0·001). Live-weight change at artificial insemination (AI) and level and change in milk yield at AI had independent effects on reproductive performance and as a consequence net energy output showed the strongest relationship with days to successful pregnancy. Heifers with the highest net energy outputs per day at AI had the longest intervals to successful pregnancy (r = 0·408; P < 0·001).

One hundred first lactation Friesian dairy heifers were used to investigate the effect of level of feeding n i late pregnancy (83·6 or 64·6 MJ metabolizable energy (ME) per head daily and around the time of first artificial insemination (AI) (weeks 6 to 18 of lactation: 146·8 or 119·8 MJ ME per head daily) on reproductive performance.

Heifers receiving the high level of feeding in lactation had a successful pregnancy rate to first AI of 0·42 compared with 0·63 for heifers receiving the lower level of feeding. Heifers receiving the higher level of feeding in late pregnancy followed by the lower level in lactation had a pregnancy rate of 0·72 o t first AI resulting in a median interval from calving to pregnancy of 75 days compared with figures of 0·35 and 95 days respectively, for heifers receiving the higher levels of feeding throughout the experiment (P < 0·001).

Blood samples were taken from all heifers 2 weeks before and on weeks 1, 5, 9, 13 and 18 after calving, and were analysed for 13 components. Of the blood components measured, only p"-hydroxy-butyrate concentrations, particularly at week 9, were affected by the nutritional treatments imposed and consistently related to fertility (P < 0·01 to P < 0·001).

Milk yield and live-weight change, individually and as the components of net energy output, showed the strongest relationships with reproductive performance (P < 0·01 to P < 0·001). The three variables which together accounted for the highest proportion (0·30) of the variation in days to successful pregnancy were net energy output at AI, (3-hydroxy-butyrate at week 9, and mean tail score in weeks 10 o t 13. These enabled the calving to successful pregnancy interval for an individual or 100 first lactation heifers to be predicted with a 95% confidence interval of ±58 days or ±8·6 days, respectively.

Silages were made from the primary growth of perennial ryegrass (Lolium perenne) or red clover (Trifolium pratense) and were given ad libitum to 52 British Friesian cows, together with 70 kg dry matter per day of a barley/ground maize/soya bean supplement in 2 years. Twenty of the cows were used in both years, providing a total of 72 observations. Three treatments were imposed during weeks 3 t o 20 of lactation: red clover silage, (RC/RC); red clover silage, weeks 3 to 10, grass silage weeks 12 to 20 (RC/PRG); grass silage (PRG/PRG).

Apparent digestibility of the gross energy assessed in lactation weeks 14 and 15 was slightly lower for red clover than for perennial ryegrass (0·683, 0·706 and 0·701 for treatments RC/RC, RC/PRG and PRG/PRG respectively). There was no effect of previous treatment on the digestibility of perennial ryegrass diets (RC/PRG v. PRG/PRG). Cows given red clover silage consumed proportionately 1·22 of the dry matter and 1·09 of the digestible energy ingested by those given perennial ryegrass. The intake of perennial ryegrass in mid lactation was similar, irrespective of early lactation treatment.

During weeks 3 to 20, cows given red clover yielded 1·9 kg more milk than did those given perennial ryegrass (P < 0·01). However, this milk had a significantly lower concentration of fat (P < 0·01; 37·2 and 41·2 g/kg for treatment RC/RC and PRG/PRG respectively). In mid lactation the cows that had received red clover silage in early lactation (RC/PRG) had the lowest yield of milk, milk fat, protein and lactose and the difference between this treatment and PRG/PRG was significant for milk and milk fat yields (P < 0·05).

Red clover silage rather than perennial ryegrass silage of similar digestibility resulted in higher silage intake and higher yields of milk, milk protein and lactose. However, the strategic use of red clover silage to increase yield in early lactation did not induce positive residual effects in mid lactation; rather, there was evidence of a negative effect on milk and milk-fat yield.

Four concentrate mixtures were given with grass silage to 52 cows in early lactation in an 8-week randomized block production trial. A further eight cows were used to measure apparent digestibilities of the total diets in a double 4 × 4 Latin-square trial.

The concentrates contained varied proportions of barley, soya bean meal (soya) and formaldehyde-treated soya bean meal (treated soya) together with fixed proportions of wheatfeed and molasses. Crude protein (CP) concentrations in the concentrate mixtures and sources of supplementary protein were 133 g/kg air-dry concentrate, soya (A); 130 g/kg, treated soya (B); 187 g/kg, soya (C); 169 g/kg, soya plus treated soya (D). In the production trial, 9 kg concentrates were given daily together with silage ad libitum, whilst in the digestibility trial the daily ration was 7·6 kg concentrates and 6·6 kg silage dry matter (DM). The silage contained 462 g DM per kg and 140 g CP per kg DM with an in vitro digestibility of DM of 0·7.

The digestibilities of DM, organic matter and energy showed similar trends. Cows given treatments A and B had significantly lower digestibilities of energy than did those given treatments C and D.

Nitrogen digestibility was highest for cows given treatment C and lowest for those given treatments A and B. Silage DM intake and live-weight change were unaffected by treatment during weeks 1 to 8, all treatment groups being in positive live-weight balance in this period.

Milk yields during weeks 1 to 8 were 18·8 (A), 19·6 (B), 20·3 (C) and 20·7 (D) kg/day. Yields for cows given treatments C and D were significantly higher than those for cows given treatment A. There were no differences between treatments for any constituent of milk, but protein concentration in milk tended to be lower for cows given treatment D. During weeks 9 to 20, there were no significant residual effects of treatment upon milk yield or composition.

Parallel regression analysis of milk yield and yields of milk constituents upon CP concentration in the concentrate indicated significant effects of CP concentration on yield of milk, milk fat, protein and lactose during weeks 1 to 8. When examined during weeks 1 to 20 the responses to increased CP concentration were non-significant. The analysis showed a significant positive milk-yield response to formaldehyde treatment during weeks 1 to 8 and 1 to 20. The response in lactose yield was also significant during weeks 1 to 8 and 1 to 20. There was a trend, though not significant, towards an increased milk-fat yield during weeks 1 to 8 for the formaldehyde treatment, whilst protein yield was unaffected.

In two experiments the effect of giving concentrates to dairy cows from a fully-controlled out-of-parlour dispenser was compared with giving concentrates twice daily in the milking parlour. In experiment 1, 22 cows were used in a cross-over design during the first 19 weeks of lactation. In experiment 2, 34 cows were used in a continuous trial during the first 18 weeks of lactation. Weeks 1 to 3 of each experiment were used as a standardization period during which all cows were given equal amounts of concentrates twice a day during milking. At the end of this period cows were paired and assigned to receive concentrates either in the milking parlour (group P) or to receive 1·0 kg concentrates per day in the milking parlour and the remainder from an out-of-parlour dispenser (group O). Within pairs, between treatments, cows were offered the same amount of concentrates and allowed access to ad libitum silage. Means for milk yield, fat and solids-not-fat concentrations during experiment 1 were 25·1 v. 23·9 kg/day (P < 0·01), 36·5 v. 38·1 g/kg, 89·9 v. 89·1 g/kg (P < 0·001), and for experiment 2 were 27·1 v. 25·4 kg/day (P < 0·01), 39·8 v. 42·6 g/kg, and 90·9 v. 90·9 g/kg, for groups O and P respectively. Mean concentrate intakes during experiment 1 were 8·3 v. 8·4 kg/day (P < 0·01) and during experiment 2 were 8·9 v. 8·6 kg/day (P < 0·01) for groups O and P respectively. In both experiments, group O had more positive changes in weight and body condition score (P < 0·05). It is concluded that the use of the dispenser improved milk yield, weight and condition-score changes, though milk fat concentration was decreased compared to that of parlour-fed cows.

Post-weaning metabolizable energy intake, growth of empty-body chemical components and efficiencies of energy utilization were evaluated for Hereford intact males (17) and females (16) and Simmental intact males (15) and females (16) during a 212-day feeding period. Within each breed × sex subclass, animals were assigned to one of three levels of metabolizable energy (ME) intake: (1) 544 kJ/kg M0·75 per day, (2) 795 kJ/kg M0·75 per day, and (3) ad libitum. Body composition of each animal was estimated at the beginning and end of the feeding period by deuterium oxide dilution.

Protein and water gain of Hereford and Simmental cattle were similar at restricted levels of intake but were greater for Simmental than for Hereford cattle at ad libitum intakes. Similarly, rates of protein and water gain tended to increase more rapidly in response to increased energy intake by males than by females. Hereford males gained fat and energy slightly more rapidly than Hereford females, but Simmental males gained fat and energy at slower rates than Simmental females.

Males had higher maintenance requirements and tended to use ME with less efficiency for maintenance and gain than females. Hereford cattle had lower maintenance requirements and used ME with greater efficiency for both maintenance and gain than Simmental cattle.

Two experiments were conducted using British Friesian bull calves to determine the effects on growth, food intake and rumen volume of including 0, 150, 200 or 250 g ammonia-treated (35 g/kg dry matter (DM)) or untreated barley straw per kg pelleted concentrate based on cereal. All calves received once daily 440 g milk replacer powder reconstituted in 3 1 warm water, were weaned at 56 days of age and given one of the seven pelleted diets to appetite from 14 days of age. In experiment 1, the seven diets were allocated at random to 70 calves. Food intake was increased by the inclusion of straw but there was no effect on intake of the increased concentration of straw; daily DM intake from 14 to 77 days of age was 1·36 and 1·77 kg/day respectively for diets with or without straw. From 14 to 56 days of age intake of concentrate was increased by the addition of straw but was negatively correlated with the concentration of straw in the diet. After weaning inclusion of straw, whilst increasing total intake, tended to depress intake of cereal. Treatment with ammonia increased the nitrogen concentration in the straw but had no effect on the digestibility or amount of diet consumed. After adjustment was made for gut fill, the increases in weight between 4 and 84 days of age of calves given 150, 200 or 250 g straw per kg food were 6·6, 1·2 and 1·0 kg respectively greater than those that occurred when there was no straw in the diet. DM digestibility of all diets was above 0·67 but the mean digestibility of acid detergent fibre was low (0·19). The pH and ammonia concentration of rumen liquor were low and below the optimum for cellulose digestion. In experiment 2, rumen volume was measured in vivo in a group of 24 calves given the same diets as in experiment 1. Rumen volume was increased two fold at 42 days of age by the addition of straw to the diet (5·6 v. 2·6 1, P < 0·001), by 87 days of age the difference was increased to 7·11, (19·0 v. 11·9 1, P < 0·01). When all calves were given the same diet from 91 days of age, there was no effect of previous treatment on intake or rumen volume at 147 days of age.

The effect on animal performance of the inclusion in the diet of avoparcin at one or more of the following levels 0, 150, 300 and 450 mg per head daily and 200 mg per head daily monensin was studied i n a series of four trials. Finishing cattle of 428 (s.e. 3·9) kg live weight were used in three trials and yearling heifers (218 (s.e. 4·9) kg live weight) in the fourth. All animals received grass silage ad libitum with 0·5 to 6·0 kg per head daily of a cereal-based supplement. Relative to the control diets with no additive, proportionate increases in live-weight gain of between 0·07 and 0·38 were obtained with the inclusion of avoparcin at 150 mg per head daily in the diet with a small depression in silage dry-matter intake. The effects at higher levels of inclusion of avoparcin and of monensin were more variable. Alteration in the proportion of propionate to acetate in the rumen fluid of the animals was observed only at the highest levels of additive inclusion. There was no effect of additive treatment on carcass weight or dressing proportion.

The variation in yield of carcass of Shorthorn-Hereford (SH), Africander x SH (Ax), Brahman x SH (Bx) and late-castrated Brahman x SH (Bx(late)) steers of the F, generation was examined in relationship to rate of growth and other expressions of composition.

On a fasted body-weight basis, yield of carcass was shown to be related to rate of growth. Of the non-dressed-carcass parts of the body, yield of carcass was particularly related to the proportion of gut contents. When this was taken into account, the relationship between yield of carcass and rate of growth was diminished but not eliminated, and breed differences in yield of carcass still remained.

Relationships between yield of carcass (relative to the empty body), carcass composition and offal composition are complex, due to the fact that each of these three shape vectors are related to size and rate of growth. Nevertheless, these shape vectors were shown to be related to each other independently of size. However, there was some confounding between the effect of rate of growth on a given shape vector and the effect of the other shape vector, particularly with respect to the relationship between yield of carcass and carcass composition. Nevertheless, it could be said that the proportion of the variation in a particular shape vector that was associated with variation in rate of growth, is explained more simply in terms of variation in another shape.

Within breed, animals with a high yield of carcass had a high ratio of muscle to bone plus fascia and tendons in the dressed carcass.

The large difference in yield of carcass between breeds.could be accounted for by differences in offal composition, but not by differences in carcass composition. Breed differences in carcass composition at the same size were accounted for by either yield of carcass or offal composition. However, breed differences in the relationship of carcass composition to size were not accounted for by these shape vectors. The effect of yield of carcass on carcass composition was itself accounted for by offal composition.

The effect of passive immunization against testosterone on reproductive performance was investigated in 180 mature Scottish Blackface ewes in different levels of body condition at mating. Ewes were fed to achieve a wide range of condition (scores 1·5 to 3·0) by 2 weeks before a synchronized mating. During the week before mating, 90 ewes were each injected with 32 ml of a neat anti-testosterone antiserum (1: 96 000 initial titre) and 90 ewes were untreated. At about 55 days after mating, 50 immunized and 50 control ewes were slaughtered and the numbers of corpora lutea and embryos present were recorded. The proportion of immunized ewes that conceived during two periods of mating was in excess of 0·9 in all condition categories. By contrast, untreated ewes in the low condition category (score =£ 2·00) had significantly lower conception rates than ewes in higher condition categories. Immunized ewes with condition scores of 2·50 or less at mating had significantly higher ovulation rates, litter sizes and lambing rates compared with control ewes, while immunized ewes with scores of 2·75 or higher were not significantly different from control ewes in these measurements. There was no effect of immunization on embryo mortality rate, lamb sex ratio, lamb birth weight, or lamb survival rate in the 1st week after birth.

Relationships between estimates of some factors affecting growth hormone (GH) and prolactin (PRL) secretion and rates of deposition of fat, protein and ash and rate of gain were investigated in Suffolk ram lambs. Factors affecting secretion were determined from measurements made by radioimmunoassay on blood samples collected at 15-min intervals during a 6-h period at a body weight of 43 to 58 kg. Depositional traits were estimated over the period of growth from 32 to 73 kg. The endocrine secretory measurements were adjusted statistically for weight at blood sampling. The only single endocrine secretory measurement that significantly correlated with a growth or depositional trait was frequency of GH peaks which was negatively related to rate of ash accretion. Multiple regression analysis was used to estimate the association between endocrine secretory measurements and rates of gain and accretion. R2 values were 0·43, 0·29, 0·42 and 0·70 for average daily gain and accretion rate of protein, fat and ash, respectively. Models with minimal error mean squares contained linear, quadratic and/or crossproduct terms for the independent variables, thus suggesting nonlinear relationships of the hormones in the mediation of rate and pattern of growth. These results emphasize the value of assay of multiple samples from each animal, the subsequent estimation of secretory characteristics and the use of expanded statistical models to determine the relationship present in the system under investigation.

Two groups of six heifers of mean age 284 days and mean body weight 233 kg were offered respectively, a barley-beef (BB) diet and a diet based on dried grass and sugar beet pulp (DG) at a rate calculated to give a live-weight gain of 0·5 kg/day. Three heifers from each group were fed twice daily, and the remaining three were fed through an out-of-parlour concentrate dispenser, and, during the period of blood sampling, hourly. Following a period of adaptation, blood samples were taken hourly during 24 h and the plasma analysed for insulin, prolactin and growth hormone (GH). The experiment was repeated 28 days later using the same heifers offered the same diets except that the twice-daily fed heifers were fed hourly and vice versa.

Comparing the heifers fed the BB diet and those fed the DG diet, insulin in plasma was higher (7·11 v. 3·54 mU/1, P < 0·001) and GH lower (2·48 v. 3·41 uxg/l, P < 0·05) in heifers fed the BB diet. There were no overall significant differences between the two diets for prolactin or between the two frequencies of feeding for all three hormones.

The residual variation among and within heifers was used to estimate the standard error of a treatment mean for different numbers of hourly samples on different numbers of heifers. Little was to be gained by taking in a day more than eight hourly-samples for insulin and more than 12 hourlysamples for GH and prolactin. Precision was most improved by increasing the number of heifers sampled. Feeding the heifers more than twice daily did not improve precision significantly.

Nineteen pluriparous buffaloes of Nili-Ravi breed which calved during the months of October and November 1983 were studied for the effects of sucking stimulus on the uterine involution, post-partum ovarian functions and fertility. On the day of calving, buffaloes were assigned to either a limited-suckling (LS) or non-suckling (NS) group. Changes in reproductive organs were monitored by rectal palpations at weekly intervals. Buffaloes were observed for oestrus twice daily (04.00 and 18.00 h) with the help of a teaser bull, and were artificially inseminated at the first post-partum and each subsequent oestrus. LS buffaloes had a shorter period to uterine involution (20 days) than NS buffaloes (28 days). Intervals to regression of the corpora lutea of pregnancy and to resumption of post-partum follicular development did not differ in the two groups. LS buffaloes had longer intervals to first post-partum oestrus and conception (54 and 88 days respectively) than NS buffaloes (39 and 68 days respectively). However, the difference in services per conception of LS and NS buffaloes was non-significant (2-05 v. 1·62). These limited data reveal that the suckling stimulus has a negative effect on the post-partum resumption of oestrous activity, and that conception is delayed. Further studies are indicated to verify these observations in a larger sample size and during all seasons of the year.

Fifty-six Landrace ♂ x Yorkshire ♀ gilts were divided at 140 days of age into four groups in a 2 x 2 factorial design whereby they were exposed continually (BE) or not exposed (NE) to a mature boar and were or were not blood sampled twice weekly for progesterone determinations.

There was no effect of BE on the age at the first or second ovulation. Since detection of oestrus was only 70·80% accurate, BE apparently delayed the onset of first and second oestrus by 16 days (p = 0·06). Blood sampling advanced first oestrus by 15 days (F = 0·07) and second oestrus by 32 days (P = 0·001).

The results suggest that gilts are unlikely to be responsive to boar exposure at 140 days of age, that observations of oestrus alone may be a misleading end-point of the effect of boar exposure and that the use of blood sampling for the measurement of progesterone as an index of ovarian activity may attenuate the response to stimuli intended to advance puberty in the gilt.

Groups of five Yorkshire ♂ x Landrace ♀ gilts were either exposed (BE) or not exposed (NE) to a mature boar commencing at 140, 147, 154 or 161 days of age. Each group of BE gilts was slaughtered 10 days after initial boar exposure, for examination of the reproductive tract, with one of the four NE groups killed at a corresponding age.

NE gilts remained prepubertal throughout. Boar exposure induced ovulation in one gilt at 140 days, two gilts at 147 days, two gilts at 154 days and one gilt at 161 days. Boar exposure also increased uterine weight (P < 0·001). There were no effects of age either on the number of gilts ovulating or on uterine weight. There was a significant positive effect of body weight on uterine weight which was greater in BE gilts than in NE gilts. These results suggest that body weight may be a determinant of the response to boar exposure by gilts between 140 and 170 days of age.

Field data from four breeds (Charolais, Hereford, South Devon and Welsh Black) comprising a total of 145, 68, 262 and 197 records respectively and obtained from 30, 24, 38 and 25 herds were used. Station data from two breeds (Charolais and Hereford) comprising 268 and 687 records respectively, from cattle originating from 27 and 44 herds respectively were also used. The data were analysed to identify environmental factors which significantly affected bull performance traits. In performance traits, herd of origin, in field and station data, accounted on average for 0·50 and 0·18 respectively of the total variance. Year, season and dam's age accounted for 0·02, 0·03 and 0·02 respectively of the total variance, the last being higher in pre-weaning than in post-weaning traits.