In two experiments prepubertal gilts were injected with a combination of 400 international units pregnant mare's serum gonadotrophin and 200 international units human chorionic gonadotrophin. The gilts were housed either in contact with or isolated from mature boars. Data were obtained of ovarian activity determined immediately after gonadotrophin treatment and at the anticipated time of the second oestrus.

All treated gilts ovulated in response to the treatment and 83% displayed oestrus. Ovulation rate varied both within and between experiments, in experiment 1 the range being 7 to 19 corpora lutea and in experiment 2, between 5 to >30 corpora lutea. Four distinct types of behaviour were observed at the time of the second cycle: ovulation associated with oestrus; ovulation without oestrus; oestrus but no ovulation; and a return to a prepubertal state with no oestrus or ovulation. The presence of boars enhanced the maintenance of cyclic activity. Overall, more gilts displayed a second oestrus (33/39 v. 19/41, X2 = 11·2, P<0·001), and more had a second ovulation (32/39 v. 24/41, X2=4·2, P<0·05) when boars were run with the gilts.

1. The primary growth and first regrowth of perennial ryegrass were preserved either without additive (NA), or with a mixture consisting of equal volumes of formic acid and formalin at 10·0 and 13·01/t fresh crop for primary growth and regrowth herbage respectively (35 g formaldehyde per kg crude protein) (FF). The silages were given ad libitum to 40 lactating British Friesian heifers and cows, with a supplement of either pelleted ground maize (104 g crude protein per kg dry matter) (LP) or pelleted ground maize and soya bean meal (254 g crude protein per kg dry matter) (HP), at 6·1 and 7·1 kg per head per day for heifers and cows respectively. The primary growth silage was given from weeks 4 to 14 and the regrowth from weeks 15 to 22 of lactation. The silages were supplemented with urea so that the dietary supply of rumen degradable protein exceeded 7·8g/MJ metabolizable energy.

2. Silage FF had lower concentrations of both fermentation acids and ammonia-nitrogen than silage NA. The digestibility of the dry matter, energy and crude protein of the diet containing silage FF was significantly less than that of diets containing silage NA when cows were given primary growth material (P < 0·001). But silage treatment had no significant effect on the digestibility of cellulose. When cows were given regrowth silage, silage treatment had no significant effect on the digestibility of dry matter, energy and cellulose, but formic acid/formaldehyde reduced the digestibility of crude protein (P < 0·01). The inclusion of soya bean meal in the supplement significantly increased the digestibility of crude protein, dry matter and energy, but when cows were given the primary growth silage the effect on the digestibility of dry matter and energy was only apparent with silage NA.

3. Cows and heifers given silage FF from primary growth consumed 160g/kg more dry matter than those given silage NA (P < 0·01). This effect was not apparent when the animals were given regrowth silage. The effect of formic acid/formaldehyde on the intake of digestible energy was not significant in either period on the trial, but the inclusion of soya bean meal in the pellet significantly increased the intake of digestible energy (P < 0·01).

4. Cows and heifers given silage FF from primary growth produced 90g/kg more milk and 50g/kg more solids-corrected milk than those given silage NA, but the differences were not significant and these trends were not apparent when regrowth silage was given. An increase in the crude protein content of supplement increased the milk (P < 0·01) and protein yield (P < 0·05) of cows, but not heifers, when they were given primary growth silage. The effect was less when milk output was expressed in terms of solids-corrected milk since milk fat content tended to fall when cows were given the HP supplement. Treatments had no significant effect on live-weight change.

5. It is suggested that the increases in milk output were mediated via changes in the supply of energy rather than of protein.

A randomized block experiment was used to assess the effects of wilting of herbage prior to ensiling. Three silages, each a composite of three harvests taken over the season, were prepared by ensiling herbage as unwilted, medium-wilted or high-wilted material with mean dry-matter contents in the resulting silages of 192, 254 and 455g/kg respectively. The silages were ensiled in bunker silos using the same harvesting machinery and with formic acid applied at the rate of 2 81/t of herbage. The silages were offered to 81 January- and February-calving cows from the 8th day post partum until going to pasture on 27 April, with a mean period on treatmen t of 92 days. In addition, all animals received a fixed concentrate allowance of 7·6 kg/day. Wilting increased silage dry-matter intake, the mean intakes being 9·2, 9·4 and 10·0kg/day for the unwilted, medium-wilted and high-wilted material respectively, but resulted in a significant depression in milk yield, with the yields obtained during the final 14 days on treatment being 23·6, 21 -8 and 21·5kg/day respectively. Milk composition, live weight, body condition, total ration digestibility and nitrogen-balance data are also presented.

Nineteen prepubertal gilts were injected with a combination of 400 international units pregnant mare's serum gonadotrophin and 200 international units human chorionic gonadotrophin. Blood was sampled throughout the ensuing oestrous cycle and assayed for progesterone and oestradiol-17β.

Eighteen gilts had vulval development consistent with oestrus within 5 days and had ovulated by day 12. Oestradiol levels in the plasma were elevated between days 2 and 6, and progesterone concentration increased between days 6 and 10 due to the establishment of functional corpora lutea. Progesterone concentration in the luteal phase was related to ovulation rate (r = 0·72, P<0·001).

Three types of cyclic activity followed the luteal phase and a characteristic hormone profile was established for each. Five gilts exhibited a second ovulation accompanied by signs of oestrus. They had a second peak of oestradiol around days 24 to 26 and a subsequent rise in progesterone concentration. Four gilts displayed vulval development at this time but did not ovulate. A peak of oestradiol was detected. The remaining gilts did not display oestrus, nor did they ovulate. Oestradiol and progesterone concentrations remained basal in these gilts. The ovaries of prepubertal gilts treated with this combination of gonadotrophins produce normal patterns and levels of oestradiol and progesterone. Cyclic activity is not always maintained, probably due to differences in the maturity of the hypothalamic-pituitary-ovarian axis.

Results are reported from four trials in which neonatal calves were given either whole milk or milk substitute containing the lactoperoxidase system.

Trial 1 was a pilot trial conducted in Sweden in which calves given whole milk with the lactoperoxidase system gained significantly more weight than controls (P < 0·05). Trials 2, 3 and 4 were carried out in successive years at the National Institute for Research in Dairying, using large numbers of newborn, female Friesian calves. In trial 2 a significant positive effect of the lactoperoxidase system with whole milk on live-weight gain was established by 3 weeks of age (P < 0·05) and sustained until weaning at 5 weeks. There was no significant effect of the lactoperoxidase system for the milk substitute treatment. In trial 3 the whole milk comparison from trial 2 was repeated. There was a significant positive effect of the lactoperoxidase system on the live-weight change after 2 weeks of age only (P < 0·05). In trial 4 two different methods of activating the lactoperoxidase system were compared for calves given whole milk. There was no effect of either method on the live-weight gain of the calves. However, as the levels of scouring were extremely low for all calves, a comparison of the two methods of activating the lactoperoxidase system was not justified. The combined results from trials 2, 3 and 4 confirmed that the lactoperoxidase system significantly increased the live-weight gain of calves given whole milk, despite the fact that the overall level of mortality and incidence of scouring was low in these trials.

Most farms that were feeding complete diets to dairy cows in the east midlands lost barley to starlings during the 1978/79 winter and more outdoor than indoor feeding sites were infested. The maximum total loss recorded on any one farm was 11 -881, this being 9% of the 1321 of barley presented to the cattle. The presentation of ground barley, rather than rolled barley, reduced the quantity of grain removed by starlings but the proofing of buildings i n which cattle are fed complete diets is suggested as the most effective means of preventing this food loss.

Twenty-seven mature boars were housed in individual pens for 9 weeks under one of the following social conditions: isolated from female pigs; near sexually non-receptive female pigs; and near sexually receptive female pigs. The sexual behaviour of the boars during the 9-week treatment period was observed weekly in standard 15- min tests. The sum of the individual courting behaviour activities and the total time spent ejaculating were significantly greater for the boars housed near either sexually receptive or sexually non-receptive females than for those boars isolated from female pigs (P<0·01 and P<0·05, respectively). Although the boars housed near sexually receptive and sexually non-receptive females achieved 43 and 38% more copulations, respectively, than those isolated from females, the difference was significant only for the latter comparison (P<005). There was no consistent difference in testosterone concentration over a 12-h period between boars housed near sexually-receptive females and those isolated from females.

Thirty-six pigs were weaned at 21 days of age and were given diets supplemented with either dicalcium phosphate (DCP) or defluorinated rock phosphate (DFP) from 4 weeks of age until slaughter at 50 kg live weight. From 4 to 9 weeks of age the diets contained either skim milk powder (SKIM) or soya bean meal (SOY) as the main protein supplement. The dietary treatments were arranged in a 2 × 2 factorial design. From 9 weeks of age until slaughter, SOY was the only protein supplement used. Four 7-day measurements of phosphorus, calcium and nitrogen balance were made on each pig. Faecal endogenous P was estimated in two pigs per treatment by the 32P dilution method.

There were no significant effects of P supplement on performance or on apparent absorption, true absorption or retention of P. The apparent absorption and retention of Ca were both 0·07 lower with DFP than with DCP in the period from 9 weeks of age to slaughter (P< 0·001).

From 4 to 9 weeks of age there was no effect of protein supplement on performance. From 9 weeks of age to slaughter, when all pigs were given SOY, those which had received SKIM in the previous period grew slightly faster (P<0·05); their growth-rate overall, from 4 weeks of age to slaughter, was also significantly better (P <0·05).

Pigs given SKIM showed a higher apparent absorption of P (P < 0·001) and higher apparent absorption (P<0·01) and retention (P<0·001) of both Ca and N from 4 to 9 weeks of age. Again, there were carry-over effects in the period from 9 weeks of age to slaughter, although the trends observed in the first period were reversed; pigs previously given SKIM showed significantly lower apparent absorption and retention of both P and Ca, and apparent absorption of N, than those previously given SOY.

There were no significant effects of dietary treatments on the ash, Ca or P content of the fourth metacarpal.

1. Two experiments were conducted to examine the effects of a cereal-based supplement and herbage mass on the intake and performance by Border Leicester × Scottish Blackface ewes nursing twin lambs in early lactation.

2. In one experiment 16 ewes, individually penned, were given one of four amounts of supplement (0, 320, 640 and 960 g organic matter per ewe per day) and offered ad libitum freshly-cut perennial ryegrass herbage (organic-matter digestibility 82%). Intake of herbage and total organic matter digestibility declined linearly with increasing intake of supplement (0·84 g organic matter of herbage per g organic matter of supplement and 0·50 percentage units per 100 g organic matter of supplement respectively).

3. In the second experiment three amounts of supplement (0, 480 and 960 g organic matter per ewe per day) were offered individually to groups of seven ewes grazing a perennial ryegrass sward of high digestibility, maintained at herbage masses of either 500 or 750 kg organic matter per ha. A further group of seven unsupplemented ewes were grazed on the same sward maintained at 1500 kg organic matter per ha. Intakes of herbage and digestible organic matter by ewes, and lamb live-weight gain, were all significantly greater and ewe live-weight loss significantly less at herbage masses of 750 and 1500 tha n at 500 kg organic matter per ha (P <0·05). The mean decline in herbage intake was 0·93g organic matter per g organic matter supplement consumed. Amount of supplement had no significant effect on lamb live-weight gain at either weight of herbage nor on ewe live-weight loss at the 750 kg organic matter per ha herbage mass. At 500 kg organic matter per ha herbage mass, intake of digestible organic matter was significantly greater and ewe live-weight loss was significantly less for 960 than for 0 and 480 g organic matter per day amounts of supplement (P <0·05).

Three experiments were carried out to investigate the effect of different forage types on the performance of male British Friesian calves up to 6 months of age. Unwilted and wilted silages were compared in all experiments, and in experiment 1 hay was also compared with the two silages. All the forages were compared at different levels of concentrate supplementation ranging, in different experiments, from none to ad libitum.

Calves fed wilted silage consumed 490, 90 and 200g/kg more forage dry matter respectively than those fed unwilted silage in the three experiments but this extra intake was generally not reflected in an increased rate of gain. Hay which was of lower digestibility than silage gave significantly lower live-weight gain. Quantities of silage consumed at an early age were small, with a mean daily intake over the first five weeks of 0·13 kg dry matter. Concentrate reduced silage dry-matter intake by 0·49 kg/kg concentrate dry matter consumed. Estimated mean concentrate intake required to achieve a daily gain of 0·75 kg in 1- to 6-month-old calves with silage offered ad libitum was 0·83 kg dry matter.

In an experiment on the occurrence of lactational oestrus, 92 multiparous Camborough sows and their litters were grouped in multi-accommodation pens at either 10, 15, 20 or 25 days post partum. The sows were fed ad libitum on a proprietary diet containing 160g crude protein per kg. A boar was introduced to the group the day following grouping. Weaning took place at 42 days post partum.

All sows except one showed oestrus in the period from grouping to weaning. Lactational oestrus occurred on average 10·9, 9·2, 12·2 and 7·3 (s.e. of difference 1·3) days after grouping (P < 0·05), and 21·0, 24·6, 32·2 and 32·8 (s.e. of difference 1·4) days following farrowing (P < 0·001) for the grouping treatments at 10, 15, 20 and 25 days. Subsequent farrowing rates were 48, 61, 78 and 45% and the number of pigs born 9·2, 9·5, 12·2 and 10·6 (s.e. of difference 1·3), respectively.

Piglet mortality in the suckling litters was higher on the day 10 treatment than either the day 20 or day 25 treatment. This led to a significantly lower litter weight for the day 10 treatment compared with any of the other treatments.

The heat losses of 24 individually housed pigs (initial body weights 20·0 to 31·8 kg) were measured for periods of 7 days at environmental temperatures of 10, 20 and 30°C. Within each environmental temperature three levels of air movement, 3, 33 and 56cm/s, were applied for a 2- or 3-day period either in an increasing or decreasing order.

Heat loss was dependent on the environmental temperature and level of air movement to which the animals were exposed. The decrease in total thermal insulation at the highest air movement was equivalent to reducing the air-ambient insulation to almost zero. In terms of its thermal effect a 5cm/s increase in wind-speed was equivalent to a 1°C decrease in temperature.

The lower critical temperature increased with increase in air movement from 19° at 3cm/s to 25° and 30°C at 33 and 56cm/s, respectively. Between air movement rates of 33 and 56cm/s, a 1°C decrease in critical temperature resulted from a 5·3cm/s decrease in air movement.

The effect of increasing air movement from 3 to 56cm/s was to increase the animal's maintenance energy requirements from 706 to 881 kJ/kg0·75 per day at 10°C, from 490 to 715 at 20°C and from 517 to 625 at 30°C.

Two groups of 15 ewes in store body condition were either given a maintenance level of feeding or a twice-maintenance level (flushed) during the course of one oestrous cycle. Five ewes from each feeding level were slaughtered at 0, 18 or 48 h after the onset of the oestrus at the end of the treatment period and measurements were made of the luteinizing hormone content of their pituitary, the luteinizing hormone concentration in their blood plasma, their ovulation rates, and ovarian follicle numbers and sizes.

‘Flushed’ ewes had a significantly higher ovulation rate (260, s.e. 0·24 v. 1·80, s.e. 0·20; P <0·05), although there was no significant difference in either pituitary luteinizing hormone content or plasma luteinizing hormone concentrations at oestrus.

Analysis of the patterns of ovarian follicle distribution suggest that flushing ewes for one oestrous cycle might increase ovulation rate by preventing the late atresia of large follicles in the last 30 h before ovulation.

The reproductive performance of does of New Zealand White (N) and Californian (C) strains of rabbit was compared with that of the two reciprocal crosses, C × N and N × C (sire × dam). Both types of crossbred doe showed a reproductive performance superior to the purebred strains, having both a higher conception rate and mean litter size at birth. C × N, N × C, N and C does reared on average 6·6, 7·4, 5·0 and 4·9 pups to weaning age respectively. Expressed in terms of an estimated annual production of weanlings the N × C does produced nearly twice as many progeny to 4 weeks of age as the purebreds N and C (37 pups cf. 21 and 19 pups respectively). Total losses prior to weaning were approximately 25% in all breeds, largely from stillbirths, and subsequent chilling and/or starvation in the nest (36% and 38% of diagnosed deaths respectively). Other contributory factors are discussed.

Thirty-six British Friesian castrated male cattle (steers) were included in an experiment to measure the response in live-weight gain and body composition to feeding barley-based diets containing increasing levels of formaldehyde-treated soya bean meal. The response was measured between 100 kg and 350 kg or 450 kg live weight. The basal diet of pelleted whole barley and 10% ground oat straw contained 16·6g to 38·5 g nitrogen per kg dry matter. There were no overall differences in live-weight gain or in feed intake. Between 100 kg and 250 kg live weight, live-weight gain increased significantly from 1 08 to 1·24 kg/day when the lowest and highest nitrogen diets respectively were fed (P<0·05). Animals given the highest nitrogen diets also consumed significantly more feed (P<0·05). Conversely, in the subsequent growth period between 250kg and 350kg live weight, live-weight gain decreased from 109 to 0·89 kg/day when the highest nitrogen diet was fed. There were no significant differences in feed intake.

Groups of four animals per treatment were slaughtered at 365 kg and 465 kg fasted live weight. When animals were fed 23·7 g nitrogen per kg dry matter and slaughtered at 365 kg fasted live weight there was significantly more omental fat (P<0·05) and the fat depth at the 12th rib was greater than in animals fed the higher levels of nitrogen. The differences in omental fat weight between the 23·7 g nitrogen and 16·6g nitrogen per kg dry matter diets were not significant. The proportion of crude protein (nitrogen × 6·25) in the boneless 9-10-1 lth rib of animals fed 23·7 g nitrogen per kg dry matter was the lowest of all diets and significantly less than the two highest nitrogen diets (P<0·05). When similar animals were slaughtered at 465kg there was a non-significant trend for omental fat weight and fat depth at the 12th rib to decrease as the nitrogen content of the diet increased.

Twenty-four pigs were weaned at 21 days of age and given restricted feed allowances for the subsequent 8 days. Eight suckled pigs served as control and gained 320 g daily, of which approximately 40 g were lipid and 40 g protein. Pigs were slaughtered at 2-day intervals, physically dissected into non-carcass, carcass fatty tissue and carcass muscle plus bone, and these fractions were then analysed for water, protein and lipid. On average, weaned pigs made small positive body-weight gains. In comparison with suckled pigs, weaned pigs contained more water and less lipid but the same protein, and more non-carcass and less carcass fatty tissue but similar carcass muscle plus bone. Losses of lipid were offset by gains of water and associated with an increase in the percentage water content of carcass fatty tissue. At zero weight gain, pigs lost 43 g carcass fatty tissue, gained 37 g non-carcass, lost 56 g lipid and gained 53 g water, while carcass muscle plus bon e and protein gains were themselves not significantly different from zero. No change in carcass fatty tissue weight was associated with counterbalancing losses of lipid (18 g) and gains of water (15 g) and protein (3g). Lipid catabolism to support anabolism of essential body tissues commenced in the weaned pigs when weight gains fell below 193 g/day; this was about two-thirds of the gains achieved by the suckled control pigs. Plasma free fatty acid concentrations indicated that maximum lipid catabolism to occur on the 2nd day after weaning, and to reduce thereafter as body fat stores were progressively depleted.

A simple and general procedure for calculating the equilibrium improvement lag in a livestock dissemination system is presented. The lag is conveniently measured in terms of the number of years of genetic change that it represents, and depends on the age and on the genetic superiority of the parents used in each step of the dissemination system. The total lag is the sum of the lags in all steps, weighting each step by the proportion of genes going through it.

The effects of reducing the feed intake of 12 winter-calving (Hereford male × British Friesian female) cows to the maintenance level for 6 weeks from week 10 of lactation were investigated during two consecutive lactation periods. Initially, six cows were in their first and six in their third lactation. In each year the period of ‘underfeeding’ was preceded by a period of ‘adequate feeding’ (maintenance plus milk production requirements) and succeeded by a period of ‘refeeding’ (2 × maintenance). Changes in body water, estimated by the dilution of tritiated water and deuterium oxide at the end of each feeding period, were used to calculate changes in body tissue. Milk yield during the period of ‘adequate feeding’ indicated that individual cows differed markedly in milk production potential. During ‘underfeeding’ milk yield was related to lactation potential. Cows of higher potential tended to maintain higher yields than those of lower potential but in doing so they incurred higher body-weight losses. The ‘refeeding’ period did not result in significant increases in milk yield. The weight losses during ‘underfeeding’ consisted mainly of fat but some cows apparently mobilized relatively large amounts of protein. More fat per unit body weight loss was mobilized by the heifers than by the cows, which, on the other hand appeared to mobilize relatively more protein. On ‘refeeding’, only a few cows were able to achieve complete tissue repletion.

Twenty-four Large White × (Landrace × Large White) gilts were allocated to one of four treatments such that one gilt from each of the litters was on each treatment. Three of the treatments involved 30-min daily contact with a boar, the boar being either (1) 2 years of age, (2) 11 months of age, or (3) 6·5 months of age, at the start of the trial. The fourth group were controls, receiving no boar stimulation.

The experiment began at a gilt age of 165 days and continued until puberty was detected. The gilts were slaughtered 5 days after puberty was reached.

The results indicate no significant difference for age at puberty between gilts exposed to the 2-year- or 11-month-old boars (182·0 v. 181·6 days respectively), although both were significantly younger at puberty than gilts exposed to the 6·5-month-old boars or having no boar contact (P<001) (206·0 v. 203·0 days respectively).

Twenty-five Greyface wether lambs were allocated at approximately 40 kg live weight to be slaughtered, to be untreated controls, or to be implanted with 57·5 mg trenbolone acetate plus 8·1 mg oestradiol-17β (treatment To8), 60mg trenbolone acetate plus lOmg oestradiol-17β (treatment To10) or 70mg trenbolone acetate plus 12 mg zeranol (treatment TZ). The control and treated lambs were slaughtered after 63 days. Effects on live-weight gain were small and not significant. On average, hormonal treatments resulted in: (a) significant increases in dressing percentage, gain in carcass weight and carcass protein, kidney weight (g/kg live weight), depth of thorax and in the activity of liver tyrosine amino transferase; and (b) variable reductions in hind leg length, concentration of plasma urea and (g/kg live weight) kidney fat, mesenteric fat and fleece. Significant differences recorded between treatments included the conversion of food into carcass protein (treatments To8 and TO10 v. TZ) and mesenteric fat (g/kg live weight) and fat cover at the 12th rib (treatment To8v To10).