Thirty-six male pigs weaned at 28 days of age were used to study the effects of methyl-3-(2- quinoxalinylmethylene) carbazate-N1, N4-dioxide (carbadox) in high- and low-protein diets on the performance of pigs growing between 7 and 32 kg live weight, and on carcass characteristics at the latter weight.

The inclusion of carbadox (55 mg/kg) in a high-protein diet containing 195 g crude protein per kg and 10·2 g lysine per kg had no effect on performance or on carcass characteristics. Pigs offered the high-protein diets grew more rapidly, had a lower food conversion ratio and were leaner at 32 kg live weight than those offered a lowprotein diet containing 146g crude protein per kg and 6·0 g lysine per kg. Supplementation of the low-protein diet with lysine (4·2 g/kg) had no effect on performance or carcass characteristics but the inclusion of carbadox in the low-protein diet increased growth performance and reduced carcass backfat measurements at 32 kg. However, the performance was inferior, and the backfat thickness greater, compared with the high-protein diets. On the other hand, supplementation of the low-protein diet with lysine plus carbadox raised growth performance and reduced carcass backfat measurements to the levels exhibited on the high protein diets.

Nineteen field trials were conducted in eight 1 uropean countries to examine the effects of tylosin, administered in the food at a level of 20mg/kg to healthy pigs under good management conditions. Average daily gain and food conversion ratio were improved by 33 g and 0·17 respectively over untreated control animals, with no change in average daily food consumption. These improvements in growth performance were similar in the grower and finisher phases, and the response to tylosin was not affected by sex, initial weight or year. Absolute responses in average daily gain and efficiency of food utilization were constant, whatever the level of performance in the controls.

Ewes with body condition scores of 2·6 (T) and 3·3 (F) on day 90 of pregnancy were allocated to one of two feeding regimes calculated either to maintain ewe body reserves (H) or to mobilize body reserves and produce a daily loss of 150 g in ewe body weight (L) during the last 8 weeks of pregnancy. Eight ewes with twin lambs from treatments TL, TH, FL and FH, and six ewes with single lambs from treatment TH, were grazed for the first 10 weeks of lactation at a mean daily herbage dry matter allowance of lOOg/kg live weight.

Feeding treatments applied during pregnancy produced differences in ewe live weights and body condition scores at lambing (68·6, 72·4, 76·7, 831 (s.e. 2·40) kg and 1·9, 2·9, 2·8, 31 (s.e. 011) for treatments TL, TH, FL and FH respectively) that persisted through lactation, but had no effect on herbage organic matter intake by ewes (mean 21 (s.e. 0·05) kg/day) milk yield (2·4 (s.e. 0·13) kg/day), lamb growth rate (mean 245 (s.e. 4·7) g/day) or herbage intake by lambs in weeks 7, 8 and 10 (mean 0·23, 0·28 and 0·36 (s.e. 0·007) kg/day).

Ewes with single lambs, when compared with ewes with twins, had similar intakes of herbage organic matter (mean 2·2 (s.e. 0·14) kg/day), produced 0·28 less milk (mean 1·7 (s.e. 010) kg/day) and increased in weight (mean 5·0 (s.e. 1·96) kg). Single lambs had significantly higher growth rates (322 (s.e. 13·1) g/day) overall but had similar intakes of herbage organic matter in weeks 7, 8 and 10 (means 0·25, 0·29 and 0·39 (s.e. 0·03) kg/day).

The range of ewe body condition and feeding in late pregnancy examined in this experiment had little subsequent effect on milk production by the ewes suckling twin lambs, given a plentiful supply of herbage.

Individually penned Finnish Landrace × Dorset Horn and Suffolk × Scottish Halfbred ewes were used to study the effects of supplementing diets based on ad libitum swedes. Supplementing a pregnancy diet of ad libitum swedes plus 225 g of hay with 454 g of a barley/soya bean meal supplement per day had no effect on swede intake or ewe performance in terms of the birth weight and survival of lambs born. Level of swede intake during late pregnancy was constant.

In early lactation, ewes offered ad libitum swedes plus 225 g hay per day were supplemented with 454 g of either barley or soya bean meal daily. Soya bean meal supplementation resulted in a 014 increase in swede intake to give a daily intake of 113g dry matter per kgM 0·7·5 and a total live-weight gain of 218kg in early lactation compared with a loss of 2·53 kg by barley-supplemented ewes. Lamb daily gain increased by 54g per day. The results are discussed in relation to trends towards the housing of ewes and current feeding practices for lactating ewes.

Progesterone, oestradiol-I7β and luleinizing hormone were measured by radioimmunoassay in plasma samples collected daily or on alternate days following insemination in six ‘repeat breeder’ buffaloes. The endocrine profiles in these animals demonstrated that a variety of temporary disturbances in behaviour of these circulating hormones resulted in reproductive failure.

Progesterone concentration was measured in milk samples collected twice or three times weekly from 157 suckling beef cows in three herds during the period from parturition until the resumption of ovarian cycles. The length of the post partum acyclic period varied between cows from 11 to 125 days. The length of the acyclic period did not differ between cows suckling one or two calves or between the two breeds of cow studied. There were significant negative correlations between the length of the acyclic period and 1. body weight at calving (r = −0·394; P<0·001) and 2. days from calving to the next longest day of the year (r=−0·782; P<0·001). Cows calving between February and April were acyclic significantly longer (83 days) than those calving between August and December (44 days; s.e. of difference = 3·5; P < 0·001). In one herd there was a significant negative correlation between the length of the acyclic period and order of calving both in spring (r=−0·379; P<0·05)- and autumn/winter (r=− 0·349; P < 0·05)-calving cows. Of the 40 spring-calving cows in the same herd, 17 were served naturally prior to any rise in milk progesterone concentrations and 11 of these conceived to this service.

The live-weight gain and efficiency of food utilization of purebred British Friesian steers and of crossbred steers out of British Friesian dams by Aberdeen-Angus, Charolais, Devon, Hereford, Lincoln Red, Simmental, South Devon and Sussex sires were examined in two beef production systems. One system was similar to the commercial 18-month grass/cereal system (16-month system) and the other to a commercial 2-year system (24-month system). The cattle were slaughtered at a standard level of fatness, determined by the use of the Scanogram ultrasonic machine.

The trial extended over 3 years and a total of 579 cattle were involved.

Data for the two production systems were analysed separately. Adjustment was made to equal age at the beginning of the test and to equal carcass subcutaneous fat concentration.

There were important differences between sire breeds in daily live-weight gain (P < 0.05), the order of performance for the different sire breeds being similar in the two systems. Charolais and Simmental crosses grew fastest, followed by South Devon crosses, and then by the purebred British Friesian and the other native breed crosses. Faster growing sire-breed crosses were generally heavier and older at slaughter; they ate more, and there was no obvious relationship between sire-breed means for growth rate and efficiency. The range in efficiency between sire breeds was 27 g and 17 g live-weight gain per kg digestible organic matter intake for the 16- and 24- month systems respectively. In both systems, Hereford crosses ranked highest and the purebred British Friesian among the lowest. Probability levels for sire breed differences were P < 0.1 (16 month) and P < 0.01 (24 month).

Carcass characteristics of purebred British Friesian steers and crossbred steers by eight sire breeds out of British Friesian dams, in 16-month and 24-month beef production systems, were compared. Sire breeds included Charolais, Simmental and the main traditional British beef breeds. A total of 579 cattle were involved.

The cattle were slaughtered at a fixed level of fatness and the carcasses evaluated using a standardized commercial cutting technique. Data were adjusted to equal carcass subcutaneous fat concentration.

Sire breed differences were similar in both feeding systems. Charolais crosses killed-out best and Aberdeen- Angus and Devon crosses poorest; the range was 25 g/kg live weight.

Significant differences were recorded between breeds in the proportion of saleable meat in the carcass (P<0·001): Charolais, Sussex and Aberdeen-Angus crosses had the highest values, on average being 15g/kg carcass weight better than purebred Friesians. Breed differences were detected in the proportion of total saleable meat occurring in the higher-priced joints, Simmental and Charolais crosses ranking highest, but the range across sire breeds was only 10 g/kg carcass weight. There were important differences between sire breeds in rate of meat weight gain that were related to mature size.

Purebred Friesians were less efficient than either Charolais or Hereford crosses in converting food into meat in the 24-month system. Friesians also had the lowest efficiency and Hereford crosses the highest efficiency in the 16-month system, although the differences were not statistically significant.

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.

Effects on animal health and productivity of offering diets composed wholly or partly of kale to Hereford × Friesian steers were examined in two growth trials and a digestibility trial. Rates of daily gain (kg), daily dry-matter intake (kg) and coefficients of dry-matter digestibility by 24 steers offered proportions of 0·50 or 0·75 kale with rolled barley or 100 kale were respectively 1·05, 7·5, 0·76; 0·72, 5·8, 0·72; and 0·48, 5·3, 0·70. Of 48 steers given 0·25 or 0·50 kale with rolled barley, fodderbeet or swede turnips, the food intakes and daily gains of those offered barley were greatest on the higher proportion of kale whereas with fodderbeet and turnips the food intakes and gains were higher (P<005 and P<0·01) respectively on the lower proportion of kale. Although daily intakes of S-methylcysteine sulphoxide were high, reaching 0·25 and 0·33 g per kg body weight in trials 1 and 2 respectively, and moderate changes in blood metabolism occurred, there were no cases of haemolytic anaemia. Steers given only kale produced the poorest daily live-weight gain and the results suggested that the inclusion of kale should be limited to 0·50 of the total diet.

The experiment assessed the effects on performance from calving to the 20th week of lactation of milking cows three times daily (3 × ) compared to milking twice daily (2 × ). After 20 weeks all cows were milked 2 ×. Each treatment consisted of 18 cows and 11 heifers. The mid-calving date was 21 September 1979.

Complete diets of the same composition were offered separately to each group in quantities equivalent to 1040 g/kg of their previous intake. The diet for the first 18 weeks of lactation was estimated to have an energy concentration within the range 11·0 to 11·3 MJ metabolizable energy per kg dry matter. After 18 weeks, the diet was reformulated to reduce the energy concentration to 10·3 MJ per kg dry matter. Total food intakes for the 20 weeks of treatment were 2352 kg dry matter (3 ×) and 2241 kg dry matter (2 ×). From 8 April 1980 the cows were turned out to grass to complete their lactations.

During the 20 weeks the mean daily milk yields of heifers were 19·3kg (3×) and 171kg (2×) (P<005). Cow yields were 28·4 (3×) and 23·9 kg (2×) (P< 0·001) during the same period. After 3× daily milking ceased, there were some positive carry-over effects on milk yield and food intake.

Lactation yields from heifers were 4881 (3 ×) and 4498 kg (2×), whilst for cows the equivalent yields were 6485 (3 ×) and 5694 kg (2 ×) (P<0·01). There were no significant differences in milk quality. At 20 weeks after calving the cows milked 3 × daily had gained less weight, but by 44 weeks from calving the weight gains were similar at 42 (3 ×) and 45 kg (2 ×).

One hundred and sixty Friesian heifers were allocated to two groups 8 or 9 weeks before artificial insemination and group-fed to gain live weight at 0·8 or 0·3 kg/day. Half the heifers of each group were moved to the other group 2 weeks before first insemination. All heifers received two intramuscular injections of prostaglandin (cloprostenol) 11 days apart, followed by inseminations at 72 and 96 h after the second injection.

The feeding regimes applied did not significantly affect the fertility of groups of heifers as measured by pregnancy rates to fixed-time or all inseminations. There were significant differences between pregnant and nonpregnant heifers within groups where changes in feeding levels were imposed (P<0·1 to P<0·01). Heifers whose growth rate was most severely checked, or whose body condition deteriorated relative to others in the group, were less fertile. For heifers changed from the low to the high plane of nutrition, those experiencing the greater increase in growth rate and body condition were more fertile than others.

No relationship was found between live-weight change, plasma glucose concentrations and fertility. In a second trial 158 Friesian heifers received two injections of cloprostenol 11 days apart, followed by inseminations at 72 and 96 h after the second injection. After the fixed-time inseminations the heifers were divided into two groups and were group-fed to gain live weight at 0·8 and 04 kg per head per day. Although the mean live-weight gain of the high group was significantly higher than that of the lower group (P<0·001), the overall pregnancy rates were not significantly different.

In three experiments the effects of giving Hereford × Friesian cows 61 to 64 MJ/day of metabolizable energy in the last 8 weeks of pregnancy, followed by either 49 to 56 (L) or 85 to 100 (H) MJ/day for the first 8 weeks of lactation, were determined. A further comparison was made in experiment 3, in which energy intakes were restricted to 46 and 64 MJ/day (M) in the two periods respectively. The L and M groups had a similar average weight loss of approximately 55 kg over winter whereas the H groups maintained their weight. The L and M treatments had a negligible effect on milk production at 3 weeks post calving but they caused a significant depression at 6 weeks in experiments 2 and 3. Milk energy and protein concentrations were reduced in all three experiments. Calf growth was similar on both treatments in experiment 1 but was 9 to 13% lower in experiments 2 and 3 for the L and M groups compared with the H group. Reproductive performance was not significantly affected. There was a substantial increase in milk production for all groups on turnout to grazing. This was greater for the L and M groups so that their summer milk production was almost equal to that of the H group. Cows from L and M groups gained more weight at pasture. By the end of the trials cows and calves from all treatments had similar weights except in experiment 3, when cows from the L and M treatments were still lighter than those from the H treatment.

Forty-eight Hereford × Friesian cows and their South Devon calves were paddock grazed at high or low stocking rates of 412 or 206 cows and calves per ha in experiment 1, and either paddock grazed or set stocked at high or low stocking rates of 4·12 or 2·74 cows and calves per ha in experiments 2 to 4.

There was no significant effect of grazing system on milk yield, milk composition or calf growth but in experiment 2 paddock-grazed cows gained more weight than those set stocked. Cows at low stocking rates gained more weight than those at high stocking rates and, in general, gave more milk. Calf growth rates were also higher at low stocking rates in experiments 1, 3 and 4 but not in experiment 2. Milk composition was not significantly affected by stocking rate. There were substantial increases in calf live-weight gain per ha at the high stocking rate but, because of a lower gain by cows, the differences in total live-weight gains per ha for cows and calves were much smaller.

The 305-day lactation milk yields and the numbers of inseminations required to obtain a pregnancy during a particular lactation were obtained from 1475 lactations of 808 daughters of eight bulls, whose Improved Contemporary Comparisons spanned two genetic standard deviations of milk yield. All lactations were completed before September 1978. Cattle requiring more than one insemination for a pregnancy produced 173 (standard error of difference = 55) kg more milk in 305 days than those requiring only one. There was no correlation between the Improved Contemporary Comparisons of the sire and either the difference in yield, or the proportion of animals needing one or those needing more than one insemination per pregnancy.