High quality grass silage (10·5 MJ metabolizable energy per kg dry matter (DM)) was offered ad libitum to three groups of autumn-calving dairy cattle, each group containing eight cows and eight heifers. In a 20-week period commencing at week 3 post partum each group received, on average, 1260 kg fresh weight of a concentrate containing 180 g crude protein per kg. Animals in treatment F each received a flat-rate of 9 kg concentrates per day throughout. In treatment D, a declining rate of 11, 10, 9, 8 and 7 kg/day was given in successive 4-week periods. Animals in treatment Y were each offered a fixed rate of concentrates (range 7 to 12 kg/day) based on their milk yield at 2 weeks post partum with a mean intake of 9 kg/day for the group. For treatments F, D and Y respectively, the mean daily milk yields were, 26·2, 26·7 and 26·9 kg for cows, and 19·5, 19·1 and 18·8 kg for heifers; mean live-weight gains were, 0·28, 0·30 and 0·22 kg/day for cows, and 0·41, 0·54 and 0·38 kg/day for heifers; and intakes of silage were, 10·1, 10·6 and 10·7 kg DM per day for cows, and 7·8, 7·7 and 7·3 kg DM per day for heifers. The differences between treatments were not significant but there were significant differences between cows and heifers. No significant differences were found between treatments in milk composition although heifers produced milk with significantly higher milk protein concentration (P < 0·05) and significantly greater milk lactose concentration (P < 0·01) than did cows. During the residual period (4 weeks indoors and 16 weeks grazing) all animals were treated as a single group and there were no significant differences in performance. The 305-day milk yields were not significantly different between treatments and averaged 6587 kg for cows, and 5124 kg for heifers.

Data from 5270 lactation records of 1380 cows sired by 132 bulls and recorded from 1962 to 1977 were analysed. Statistical analyses, using least squares and maximum likelihood methods, showed significant effects for genetic group, age of cow, month and year of calving, and lactation length. Overall mean milk yield was 2780 kg (CV = 0·31) with mean lactation length of 281 days. Maximum production occurred in the fifth lactation (104 or 105 months of age at calving) with a yield of 1·3 times that of the first lactation. Repeatability estimated by intraclass correlation was 0·40 (s.e. 0·03). Heritability estimated from paternal half-sib correlation was 0·16 (s.e. 0·06). Overall results were very similar to those obtained from research with European breeds in temperate areas.

The diurnal cycle of chromium excretion was estimated over the last 24 h of a 13-day period in which nine single- and nine double-suckled cows were dosed twice daily (10.00 and 16.00 h) with shredded Cr2O3 paper. All faecal passages voided were sampled and analysed for chromium. Rectal samples were also taken at 10.00 and 16.00 h during this period. Sources of variation in the patterns of excretion that could be attributed to cow live weight, daily milk yield or total weight of the calf or calves being reared were also investigated.

Mean faecal Cr concentrations followed a cyclic pattern which was significantly described by a sinusoidal equation.

The estimated fundamental period (0·1334 rad/h) did not differ significantly from the theoretical value (2π/48 = 0·1309 rad/h). Fitting the model for each cow explained from 0·61 to 0·99 of the variation in faecal Cr concentration. Differences between suckling treatments in predicted faecal Cr content at discrete 2-h intervals over the 24-h period were not significant. Equations for heavier cows had lower constant terms, consistent with lower faecal Cr contents expected as a consequence of higher intakes. Differences in cow milk production and total calf live weight being reared were related to the pattern of Cr excretion (P < 0·05) but the reasons for these effects were not readily apparent. Mean Cr concentration in rectal samples was significantly correlated (r = 0·916) with mean 24-h faecal Cr content predicted from the model.

A study of 1514 lactations that occurred between 1977 and 1982 in 790 Friesian, Ayrshire and Holstein crossbred cows was undertaken. One thousand and eighty-four of these lactations were used to consider the association between the occurrence of clinical mastitis and changes in milk yield, and to illustrate a technique that enables the previous lactation history of a cow to be used for estimating changes associated with the disease.

The lactation curves were described using the model y(n) = anbe−cn from which values for peak yield, persistency, rate of decline at week 25, and recorded and extrapolated 305-day yield were calculated. A significant correlation between successive lactations of the same animal was observed for each of these variables. Pairs of successive lactations free from clinical mastitis were then compared by regression analysis with lactations in which the preceding lactation was free from the disease whilst the second lactation of the pair was infected.

Significant reductions in peak yield, recorded and extrapolated 305-day yield were found when mastitis occurred before the week of peak yield. A reduction in recorded 305-day yield was also observed when the disease occurred between peak and 10 weeks after peak. Mastitis later in the lactation had no significant effect.

The mean reduction in recorded 305-day yield of 540 kg when mastitis occurred before peak for a cow with a mean yield of 4830 kg, was higher than previous estimates. No evidence of recovery was observed in subsequent lactations that were free of clinical infection, indicating that once a cow has contracted mastitis it may not achieve its full milk-yield potential in the next lactation.

In a 25-week experiment beginning at week 3 post partum, grass silages of 10·5 (H) and 8·9 (L) MJ metabolizable energy per kg dry matter (DM) were offered ad libitum to two groups of 24 autumn-calving dairy cows. Within each silage-quality group, two patterns of concentrate allocation were compared, a flat-rate (F) and a variable rate (V). All four treatment groups, HF, HV, LF and LV, received on average 1575 kg fresh weight per cow of a concentrate containing 170 g crude protein per kg during the 25 weeks. The cows on treatment F were all individually given 9 kg concentrate per day throughout. Individuals on the V treatments received different levels of concentrate, based initially on their 14-day milk yield and then reduced by 1 kg/day at 10, 15 and 20 weeks. For treatments HF, HV, LF and LV respectively, mean adjusted daily milk yields were, 24·4, 24·1, 21·6 and 22·1 kg; intakes of silage DM, 9·1, 8·7, 7·6 and 7·6 kg/day, and live-weight gains, 0·39, 0·31, 0·28 and 0·22 kg/day. The effects of silage quality were significant in each case, but the effects of pattern of concentrate allocation were not. Cows given the H silage produced milk with significantly greater lactose and solids-not-fat concentrations. During the residual period (2 weeks indoors and 14 weeks grazing) no significant differences in milk yield were observed. The 305-day yields of 6215, 6096, 5786 and 5824 kg for treatments HF, HV, LF and LV respectively, reflected the differences obtained during the indoor feeding period.

One hundred and sixty Friesian heifers were divided into four groups on the basis of live weight and age. All four groups received a production ration of 15 kg maize silage, 0·5 kg straw and either 1·5 or 0·5 kg concentrates according to their mean live weight. This ration supplied only 38 mg (3-carotene per animal per day.

Two groups of heifers received a daily supplement of 300 mg β-carotene per head. The other two groups acted as controls and received a daily supplement of 60 000 i.u. vitamin A (18 mg retinol). All heifers received an adequate supply of vitamin A.

Supplementation with 300 mg β-carotene per day significantly increased mean plasma concentrations from 3·52 mg/1 at housing to 5·58 mg/1 at first insemination (P < 0·001). Mean plasma concentrations in the control heifers declined from 3·31 mg/1 at housing to 2·42 mg/1 at first insemination and to 2·13 mg/1 50 days later. Of the 40 smaller controls half had concentrations below 1·00 mg/1 50 days after first insemination.

Supplementation with β-carotene did not affect reproductive performance or growth rate in heifers receiving a ration based upon maize silage.

In two experiments cows with access to self-feed grass silage were offered concentrates either twice daily in the milking parlour at a fixed level (controls) or in addition given free-access to a concentrate dispenser sited in the self-feed area (dispenser). A time-lapse mechanism on the dispenser limited successive 1 kg feeds to a minimum of 10 min in experiment 1 and 5 min in experiment 2. The ‘dispenser’ cows had significantly greater total concentrate intakes than had the controls (10·4 v. 7·1 kg/day in experiment 1, 13·4 v. 7·3 kg/day in experiment 2), but there was a large variation in intake between individuals. Access to the dispenser increased milk yields only slightly, reduced milk fat concentration and increased milk protein concentration and live-weight gain. Following turnout to grass in the spring, there was evidence that the cows that had been on the dispenser treatment showed a faster rate of decline in milk yield than did the controls, and this was supported by lower lactation yields in the dispenser group.

Comparative slaughter was used to assess the body composition of Shorthorn-Hereford (SH), Africander cross (A×), Brahman cross (B×), and late castrated Brahman cross (B×(late)) steers of the F, generation with respect to their yield of carcass, gross carcass composition and offal composition. Animals were slaughtered at pre-determined weights of 315, 355, 399, 449 and 505 kg.

The B× animals had the highest carcass yield (expressed either as dressed carcass weight at the same fasted body weight or at the same empty body weight), while the A×, B×(late) and SH animals had similar carcass yield. Within a breed, rate of growth affected carcass yield, with faster growing animals having the lower carcass yield, particularly with respect to fasted body weight.

The breeds were different in carcass composition but this was dependent on both size and growth rate. Brahman cross animals had a lower proportion of bone than A× and SH animals, particularly at the higher body weights. Faster growing animals tended to contain more muscle and bone and less fat, with the exception of the SH animals.

The breeds were also significantly different in the composition of the offal components. A× were notable for high head weights and low tail weights, B× having high blood weights and low total gut tissue weights, and Bx(late) having high hide weights and low abdominal fat weights.

Rate of growth had some effect on offal composition, the general trend being that the faster growing animals were characterized by a lower proportion of heart, blood and pancreas. However there was also evidence that the rate of growth differentially affected the offal composition with respect to breeds. This effect mainly arose because the faster growing B×(late) animals had lower weights of abdominal fat. Within the other breeds, the opposite trend was observed.

The purpose of the experiment was to investigate the possibility of using concentrations of hormones and metabolites in plasma of potential breeding bulls early in life as indirect selection criteria for butterfat production. Sixteen Red Danish bull calves were included in the experiment, 10 were offspring of parents selected for high butterfat production for two or three generations, and six were from parents selected for low butterfat yield. The average estimated relative breeding values of the calves in the two groups were 111 and 91.

At 3·5 and 7 months of age blood samples were collected every 6 h during 2 days of ad libitum feeding, 5 days of fasting and 2 days of refeeding. The samples were analysed for glucose, urea, free fatty acids, insulin and thyroxine. At 3·5 months plasma concentrations of free fatty acids were significantly correlated with breeding value under all feeding conditions examined. The increase in plasma glucose during refeeding at both ages was positively related to breeding value. Plasma insulin during the 1st day of fasting was positively correlated with genetic merit at 3·5 months of age and negatively correlated at 7 months. Plasma thyroxine was negatively correlated with breeding value at both ages, but the correlation was only significant at 7 months. Multiple regression analyses showed that a large part of the variation in breeding value for butterfat production could be described by plasma levels of hormones and metabolites when more than one variable was included in the model. With six variables in the model 0·67 and 0·73 of the variation could be accounted for at 3·5 and 7 months of age respectively.

The results of the experiment have to be considered with caution because only one sire was used per group, the parents were preselected, and the number of animals was small. The results, however, do indicate that plasma levels of hormones and metabolites in the early life of potential breeding bulls, measured after suitable physiological challenges, may be useful as selection criteria for butterfat production of their offspring.

The response to avoparcin in cattle diets was examined in two trials. In trial 1 compound diets containing 0, 15, 30 or 60 mg/kg avoparcin were given to 32 British Friesian bulls from 231 kg body weight to slaughter at a mean body weight of 422 kg. In trial 2 diets containing 0, 15, 30 or 45 mg/kg avoparcin and composed of equal portions of dry matter (DM) from grass silage and compound food were given to 64 British Friesian steers over a 12-week period from 258 kg body weight to 340 kg body weight.

There was a significant growth response of 120 g per head daily in trial 1 and 80 g per head daily in trial 2 to inclusion of 15 mg/kg avoparcin in the diet compared to the control diet without avoparcin. Food conversion efficiency of diets with 15 mg/kg avoparcin was improved by a reduction of 0·52 and 0·61 kg DM per kg live-weight gain respectively in the two trials. There was no further growth response or improvement in food conversion with higher levels of avoparcin with the diets used, the type of cattle employed and the management which applied in these trials. These findings are in good agreement with those previously published.

Fourteen growing Belgian White Blue bulls were assigned to three groups: five controls (C); five bulls implanted with 140 mg trenbolone acetate and 36 mg Zeranol (TBA-Z); and four bulls implanted with 140 mg trenbolone acetate and 20 mg oestradiol-17β (TBA-E2). Testosterone (T) and luteinizing hormone (LH) levels in blood plasma were determined at day 0, 30 and 60. Mean plasma LH concentrations measured by repeated sampling over a 10-h period were similar at day 0, 30 and 60 in the three groups. At days 30 and 60, T levels were significantly lowered in treated bulls: namely 2·0 (s.d. 0·7) μg/1 v. 2·7 (s.d. 0·5) μg/1; 0·7 (s.d. 0·1) μg/1 v. 1·0 (s.d. 0·3) μg/1; 0·5 (s.d. 0·1) μg/l v. 0·4 (s.d. 0·2) μg/1 in the C, TBA-Z and TBA-E2 groups respectively. Moreover, anabolic compounds completely abolished pulsatile liberation of LH and T.

In control bulls intravenous injection of 0·5 ng/kg body weight of LH releasing hormone (LHRH) caused the release of a large quantity of LH (10 to 13 times the basal level after 10 min) followed by an increase in plasma T levels. On the other hand, LH and T responses to LHRH were reduced by TBA-E2 and TBA-Z treatments. A delay in LH response to LHRH was apparent 6 days after anabolic treatment. However, the total amount of LH liberated during the test was increased. The second effect was a quantitative reduction at days 20, 30 and 60 in LH and T secretion after LHRH. The modification of the hormonal pattern was quicker and more pronounced in TBA-E2 than in TBA-Z animals. Correlation was negative (r = −0·68; P < 0·05) between the mean daily gain during the experimental period and the total quantity of T liberated by the testis after LHRH stimulation at day 60. It was concluded that administration of trenbolone acetate plus Zeranol or trenbolone acetate plus oestradiol-17β in pubertal bulls reduced the LH and T responses to LHRH and abolished the pulsatile LH and T secretions.

Ten crossbred (Karan Swiss) cows were induced to calve about 1 month prior to expected term using either 25 mg dexamethasone alone (Group B) or 25 mg dexamethasone in combination with 25 mg vetoestrol (Group C). Another five animals served as controls (Group A). The average time interval from injection to calving was not significantly influenced by the two treatments used, and was 52·2 ± 4·07 h and 49·0 ± 1·55 h for groups B and C respectively. The mean gestation lengths for animals in groups A, B and C were 283·60 ± 2·77, 255·20 ± 1·93 and 255·20 ± 2·3 days respectively. The calves born from cows induced to calve early were significantly lighter at birth compared to controls (P < 0·05). The average live-weight gain over the first 12 weeks among calves was not significantly influenced by treatment averaging 2·58 ± 0·07, 2·81 ± 0·16 and 2·20 ± 0·16 kg/week for groups A, B and C respectively. Foetal membranes had not been voided by 24 h in the animals induced to calve early and hence required manual intervention. The length of the service period, number of services per conception and the milk yield of the cows induced to calve was not significantly different from their previous records (P > 0·05).

Two experiments were conducted to investigate the effect of the composition and particle size of the basal diet on the outflow of chromium-treated fish meal from the rumen of lactating British Friesian dairy cows, using Cr-concentrations in faeces. A 4 × 4 Latin square design was used and the cows were fed at twice the estimated energy requirements for maintenance in two equal meals.

Fractional outflow rates per h were, 0·079, 0·088, 0·086 and 0·064 for the 1·00 hay: 0·00 concentrate, 0·75 hay: 0·25 concentrate, 0·50 hay: 0·50 concentrate and 0·25 hay: 0·75 concentrate respectively. The difference between 0·75 and 0·50 concentrate was significant (P < 0·05).

Grinding of long dried grass through 40 or 20 mm screens had no significant effect on the outflow of Cr-treated fish meal from the rumen, however fine grinding (5 mm) and pelleting significantly reduced the outflow from rumen (P < 0·05). Fractional outflow rates per h were 0·080, 0·086, 0·088 and 0·047 for the long, 40, 20 mm and the 5 mm and pelleted diets respectively.

Post-weaning growth, dry-matter intake, carcass characteristics, chemical composition of the 9th to 11th rib section and food conversion efficiency were evaluated for Simmental bulls (15) and heifers (18) and Hereford bulls (17) and heifers (14) from approx. 240 days of age to 470 days of age. Within each breed × sex sub-class, animals were assigned to one of three energy intake levels: (1) ad libitum, (2) 795 kJ metabolizable energy (ME) per kg0·75 per day and (3) 544 kj ME per kg0·75 per day.

Simmentals tended to exhibit higher post-weaning growth rate and consumed more dry matter than Herefords. At ad libitum intakes, efficiency estimates (gain/food) were greater initially but decreased more rapidly for Herefords than for Simmentals. No differences were observed in efficiency estimates between Herefords and Simmentals fed at 795 kJ ME per kg0·75 per day and both breeds fed at this level improved in efficiency as time on test increased.

Bulls tended to have greater growth rate, and consume more dry matter than heifers. At ad libitum food intake, bulls were more efficient than heifers and the decrease in efficiency of the two sexes was parallel. Heifers fed at 795 kJ ME per kg0·75 per day had a constant efficiency throughout the test while bulls improved in efficiency.

Grass silage was offered ad libitum to twelve 4-month-old British Friesian steers in an incomplete Latin-square experiment. The silage was given either alone or supplemented isonitrogenously with 50 g fish meal or 63 g groundnut meal per kg silage dry matter.

Both protein supplements significantly increased the intakes of dry matter and organic matter by an amount about equivalent to the (calculated) contribution of the supplement (P < 0·05); they also increased the intakes of digestible organic matter and nitrogen (P < 0·001) but with no significant difference between supplements. Protein supplementation had no effect on the intake of indigestible organic matter.

The digestibility coefficients of dry matter and of organic matter were significantly increased by supplementation (P < 0·05) as were the digestibility coefficients of gross energy and of nitrogen (P < 0·001). Nitrogen retention was also increased from 1·4 to 8·2 g/day (P < 0·001), with no significant difference between supplements.

Eating qualities of beef from entire and castrate male animals were compared using taste panel, objective texture and chemical measurements and a consumer panel. The eating quality of roast m. longissimus dorsi, casseroled m. supraspinatus, minced m. gastrocnemius and grilled m. psoas major from bull beef, slaughtered at 400 days was different (by triangular tests) from that of twin steer beef. The differences (attributed to flavour, texture and juiciness) were not substantiated using descriptive scaling tests when the only significant difference was that roast m. longissimus dorsi from bulls was slightly drier than that from steers. Tenderness, juiciness and flavour of roast m. longissimus dorsi from 71 bulls and 84 steers raised semi-intensively to 390 to 510 kg and slaughtered commercially were assessed using descriptive category scales and the instrumental toughness values. There was no significant difference in organoleptic qualities and the distributions of tenderness and juiciness within these populations were similar. Bull beef contained more connective tissue and had less intramuscular fat. Fatness was poorly related to tenderness (r = 0·3) and unrelated to juiciness or flavour. A consumer panel of 606 assessors showed that bull beef was not as pale as steer beef and found no difference in fatness of the cuts, flavour or juiciness. Fore-rib roasts of bull beef were marginally less tender than steer fore rib.

Body-composition data from 73 non-pregnant, non-lactating cows of five genotypes were used to calculate the composition of empty body-weight change in mature cattle. The composition of empty body-weight change was shown to be dependent on empty body weight, containing more fat and less water, protein and ash at higher empty body weights. There were no differences between the genotypes. Between 300 and 600 kg empty body weight the protein concentration in empty body-weight change ranged from 125 to 40 g/kg, whilst application of standard energy values for fat and protein gave equivalent figures for body energy of 22·5 to 32·7 MJ/kg.

The relative importance of the breed of lamb and the breed of dam in determining the copper status of the lamb until 24 weeks of age was investigated by transferring embryos within and reciprocally between Scottish Blackface and Welsh Mountain ewes. A diet low in Cu (2·4 mg/kg dry matter (DM) was fed both to the ewes from mating onward and subsequently to their lambs.

At birth, lambs with Welsh dams had greater concentrations of Cu in their livers than lambs with Blackface dams. This difference, although reduced, still remained at 9 weeks of age (weaning), when lambs with Welsh dams also had greater concentrations of Cu in plasma.

By 24 weeks of age, Welsh lambs, irrespective of their dams' breed, had greater concentrations of Cu in both liver and plasma than Blackface lambs, although the average Cu concentration in the liver was below 10 mg/kg DM in both breeds.

Results are also given for concentrations of Cu in kidney, brain and milk.

The experiment suggests the importance of maternal breed in determining the susceptibility, both of the foetus and of the young lamb to problems associated with Cu deficiency.

The relative importance of the breed of dam and the breed of lamb in determining the copper status of the lamb was investigated by transferring embryos reciprocally between Scottish Blackface and Welsh Mountain ewes. A diet moderately high in Cu (8 mg/kg dry matter (DM)) was fed both to the ewes from mating onward and subsequently to their lambs.

At birth, 9 and 24 weeks of age the concentration of Cu in the liver of lambs was the same for the two maternal breeds but within breed groups there was correspondence between full sibs when they were born to the same dam.

By 9 weeks and at 24 weeks of age Welsh lambs, irrespective of their dam's breed, had greater concentrations of Cu in liver than Blackface lambs. The average concentration at 9 weeks was 190 and 130 mg/kg DM respectively for the two breeds of lamb.

Results are also given for concentrations of Cu in plasma, kidney, brain, milk and faeces.

The results differ from those found in the previous paper under a regime of low dietary Cu where the maternal breed affected concentration of Cu in the liver of lambs up to 9 weeks of age.

Four central performance tests of growth in Hereford bulls from about 10 to 19 months of age on pasture were conducted in New Zealand. From the 100 bulls performance tested 63 were representatively sampled, including bulls with high and low performance test rankings, and progeny tested in dairy herds. Crossbred progeny were purchased from the dairy herds at 3 to 4 months of age, assembled in one location and reared together on pasture for 14 to 15 months prior to slaughter. Regressions of progeny growth and carcass traits on a number of different performance traits for growth of their sires were in almost all cases not statistically significant. The effective heritability, from offspring-sire regression, was 0·07 (s.e. 0·05) for final live weight and 009 (s.e. 0·06) for post weaning gain from about 200 to 550 days of age. It is concluded that central performance tests, as presently conducted in New Zealand, are of limited value for ranking breeding values of bulls for growth. Possible reasons for these results are discussed. It is suggested that pre-test environmental effects and age at the start of the central test are critical factors.