Twelve Ayrshire cows in a 16-week changeover design experiment were offered 8 kg hay per day together with a daily supplement of either: A, 8 kg concentrates; B, 6 kg concentrates and 4·5 to 50 kg draff/syrup mixture; or C, 4 kg concentrates and 9·0 to 10·0 kg draff/syrup mixture. The concentrate and the draff/syrup mixture had dry-matter concentrations of 872 and 385g/kg, and contained 229 and 255 g crude protein per kg dry matter respectively. Total daily intakes of dry matter were 13·77, 13·80 and 13·81 kg per cow for treatments A, B and C respectively, and were not significantly different. The mean daily milk yields for treatments B and C were 18·2 and 18·5 kg per cow respectively, and were significantly higher than the yield of 17·3 kg per cow for treatment A. The solids-not-fat and lactose concentrations in the milk, and the mean live weights, were also significantly higher for treatment C than for treatment A. Based on the differences in milk yield and composition between treatments, it was estimated that the metabolizable energy value of the draff/syrup mixture was 12·2MJ/kg dry matter. It is concluded that the draff/syrup mixture was a safe and acceptable food for dairy cows when it replaced half of the concentrate dry matter.

In two trials, three groups of eight dairy cows were fed for 2 months before calving to achieve condition scores at calving of 1·5 to 2 (low), 2·5 to 3 (medium) and 3·5 to 4 (high). For 16 weeks after calving, all cows were given a complete diet composed of silage, malt distillers' grains, barley, swedes and soya bean meal (metabolizable energy 12·25 and 12·35 MJ/kg dry matter in trials 1 and 2 respectively).

In both trials, significant differences were found between groups in dry-matter intake after calving. Cows that had higher condition scores at calving ate less and reached maximum intake of dry matter later than cows with lower condition scores (high, medium and low condition-score cattle attained maximum intakes in 14·5, 12·7 and 9·3 weeks in trial 1, and in 141, 9·6 and 7·9 weeks in trial 2). In trial 1, no difference was found in milk yield but, in trial 2, cows that had lower condition scores at calving produced slightly more milk. In both trials, cows that had higher condition scores at calving lost more body weight and condition, over a longer period, and started to regain the losses later than cows with lower condition scores. The biological efficiencies of milk production (energy output/energy input) from 8 weeks before calving until 16 weeks after calving were 0·302, 0·299 and 0·295 in trial 1, and 0·312, 0·290 and 0·306 in trial 2, for the low, medium and high groups respectively.

It was concluded that cows with lower condition scores at calving produced more milk directly from food rather than via body fat, were in positive energy balance earlier in lactation and over the total period were biologically more efficient than cows with higher condition scores. There appears to be no benefit from feeding cows to achieve a condition score greater than 1·5 to 2 at calving if high-energy complete diets are offered in early lactation.

The breeding records of 2710 lactating cows, of the Africander (1208), Tswana (542) and Tuli (960) breeds, were analysed to examine the effects of breed and environment on reconception. The reconception rate of Africander cows (0·56) was significantly lower than that of Tswana and Tuli cows (0·80 and 0·81 respectively) (P<0·01). The environmental effects of ranch, calving year, calving period and age/parity all had significant effects on reconception (P<0·01). Interactions between breed and the other main effects were all significant.

The Africander is considered to be a breed of lower fertility than the other two Sanga breeds, the Tswana and Tuli, in Botswana. The results are discussed with respect to determining management interventions to improve cow reproductive performance.

In each of two trials, three groups of eight cows, with condition scores of 1-5 to 2, 2-5 to 3 and 3-5 to 4 at calving, were given a complete diet for the first 16 weeks of lactation. Food intake, milk yield, live weight and condition score were measured, and related to levels of plasma glucose and free fatty acids, serum insulin, prolactin and progesterone in weekly blood samples, in an attempt to explain differences in food intake.

In both trials, levels of plasma free fatty acids were high after calving for all cows and declined rapidly until week 8, after which they were fairly constant. Glucose and insulin levels increased after calving, producing curves similar to that for dry-matter intake in the first 8 weeks of lactation. Prolactin levels fluctuated too markedly to provide useful information. Progesterone levels increased until week 7 and then fluctuated at 3-week intervals coincident with oestrus. Dry-matter intake was negatively correlated with free fatty acid levels and positively correlated with insulin in trial 1, and with glucose and progesterone in both trials.

The response of post-pubertal entire male cattle (bulls) to implantation with trenbolone acetate and hexoestrol was studied in two experiments. In experiment 1, eight British Friesian bulls, weighing approximately 359 kg at the beginning of a 90-day experiment, were either sham-implanted or implanted with 45 mg hexoestrol, followed 21 days later with a further implantation of 300 mg trenbolone acetate. In experiment 2, 16 bulls (14 British Friesian and two Simmental < ♂ × (Hereford < 5 × Friesian ♀), weighing approximately 349 kg, were similarly untreated or implanted with 30 mg hexoestrol and 300 mg trenbolone acetate. Treatment with hexoestrol gave a small and non-significant increase in live-weight gain in both experiments. However, live-weight gain and efficiency of conversion of food into live-weight gain were significantly improved in both studies following implantation with trenbolone acetate (P < 0·05). Treated bulls had heavier carcasses and greater mean values for estimated carcass gain (P < 005 in experiment 2). Comparison of mean values for blood metabolites indicated significant differences in concentrations of plasma glucose, free fatty acids and cortisol, and serum total protein, growth hormone, insulin and prolactin. Mean values were significantly lower in treated animals for serum albumin in experiment 2 (P < 001) and for plasma urea in both experiments (P < 0·001; P < 0·05). Treatment with hexoestrol resulted in lower mean concentrations of plasma androgens. These were further reduced following treatment with trenbolone acetate (P < 0·01). The results suggest that the combination of trenbolone acetate plus hexoestrol may improve growth performance, by altering protein metabolism, in post-pubertal entire male cattle. The combination of trenbolone acetate plus hexoestrol appears to have more potent anabolic activity than the endogenous hormones of these animals.

Measurements of the median diameter of all teats were recorded within 2 days of calving on 892 cows from eight breeding lines. Teats with a median diameter of ≥35 mm were classed as bottle teats. Their incidence varied from zero in a Hereford line to 0-55 in a Sahiwal crossbred line. In all lines, except the Hereford line, bottle teats were the most important single cause of mortality, up to 2 months of age, of calves that were born alive. However, mortalities became disproportionately high only when all four teats were classed as bottle teats.

Of calves that survived to weaning, those born to cows with at least one bottle teat had heavier live weights at weaning than those born to cows without bottle teats. Consequently, more calves were selected for high growth rate as potential sires from cows with bottle teats than from cows without bottle teats. This, combined with the observation that bottle teats occurred only after at least two calvings, is likely to reduce progress towards elimination of the defect through culling. However, indirect culling of the defect through any effect on calf performance is completely ineffective and uneconomic, and it is recommended that cows be culled directly for the defect in the year in which it first appears.

Four steers from a group of eight British Friesian steers were implanted with 300 mg trenbolone acetate and 30 mg hexoestrol at the beginning of a 90-day trial period. The remainder were untreated. They were offered diets that varied in estimated content of metabolizable energy as follows (MJ/day): day 0 to 34 (period A), 100; day 35 to 60 (period B), 50; and day 61 to 90 (period C), 75 increasing to 110. Implanted steers gained significantly more live weight in periods A and C, and lost less in period B, than controls. Implanted steers had significantly elevated concentrations of plasma glucose in period A, and lower values for plasma urea and serum albumin throughout. Differences between control and implanted steers for the other blood constituents studied, including growth hormone, insulin and prolactin, were small and not significant. The main effects of changes in dietary energy intake on blood composition included significant increases in both groups of animals in the concentration of free fatty acids and growth hormone during underfeeding (period B). These concentrations decreased in period C, concomitant with significant increases in the concentrations of insulin and prolactin.

The calving rates, survival and growth of calves of Brahman (344), Bonsmara (454), Simmental (601) and Tuli (276) crossbred cows, and pure Tswana (405), were collected for a 7-year period, 1974–80. Calving and survival rates for calves were 0·90, 0·88, 0·87, 0·87 and 0·82; and 0·94, 0·93, 0·96, 0·94 and 0·93, for Simmental, Tuli, Brahman and Bonsmara crossbreds, and pure Tswana, respectively. These differences were not significant (P<0·05).

Calves produced by Simmental ♂ and Bonsmara ♂ crossbred cows were significantly heavier than those from Brahman ♂ and Tuli ♂ crossbred cows (P<0·01), but not from Tswana-sired calves. At weaning, calves from Simmental-cross cows weighed 214 kg, significantly heavier than those produced by any other cow type (P<0·01). Bonsmara- and Brahman-cross cows produced calves weighing 203 and 198kg respectively at weaning, which were also significantly heavier than the calves of Tswana and Tuli crossbred cows (P<0·01), which weighed 187 and 184 kg respectively.

Productivity estimates combining these three traits, and expressed as weight of calf weaned per cow per year, per kg cow weight and per kg metabolic weight of cow, demonstrate the advantages of three of the crossbred cow types over the pure Tswana. Recommendations for the further development of crossbreeding systems in Botswana are made on the basis of this finding.

Values for weight and age of beef bulls at stud have been used to describe growth beyond the point of inflexion of the growth curve. Using the concept of ‘metabolic age’ it was shown that the maturation rate in Aberdeen Angus and Friesian bulls was close to a reported interspecies mean value. Hereford and Charolais bulls both matured relatively rapidly. Variation between individuals within a breed was consistent with the hypothesis that it is possible to select for rapid growth rate without necessarily selecting for an increase in mature size.

A study of 468 lactations in two herds of British Friesian cows sampled weekly between 1976 and 1979 was undertaken to investigate seasonal variations in milk yield and to compare four models of the lactation curve: (i) logey(n)=loge a + b logen—cn; (ii) y(n) = anbe-cn; (iii) y(n)= ae-pn—ae-qn; and (iv) y(n) = a—p'n—ae-q‘n.

Model (i) was fitted by unweighted linear regression and the remainder by maximum likelihood. Average peak yield was 29 kg/day and 305-day yield was 5720 kg.

Model (ii) fitted the data slightly better on average than models (iii) and (iv), and all were better than model (i). Compared with model (i), model (ii) reduced the average residual mean square proportionally by 0-10 in cows and 004 in heifers (first calvers). Model (iv) described the initial rise in milk yield up to week 5 better than models (i) or (ii) but reached a maximum value slightly early. Models (i), (ii) and (iv) slightly underestimated and (iii) slightly overestimated maximum milk yield, but model (ii) provided the best estimate of the position of maximum yield.

Peak yields for heifers occurred on average at approximately 10 weeks post calving compared with 7 weeks for cows. Mean persistency of lactation, calculated as s= -(b+1) logec, did not vary from the second lactation onwards, whereas the average rate of decline p' in model (iv) increased with parity.

When milk yields were adjusted for stage of lactation, significant variations were found that were related to the week of recording but this seasonal variation in milk production was smaller than that found nationally in the United Kingdom.

Four groups of 12 beef heifers were each given either straw treated with 35 g sodium hydroxide per kg (TS) or untreated straw (US) and were either supplemented with 35 mg monensin per kg (Ms) or not supplemented (Ns). The diet consisted of approximately 0·40 of a concentrate mixture that contained 12·8 MJ metabolizable energy and 243 g crude protein per kg dry matter, and 0·60 straw. Feeding was ad libitum. The average initial weight of the heifers was 207·2 kg and the experiment lasted 86 days.

The average dry matter consumed was 2·3g/kg live weight. Average daily gain (±s.e.) was 505±31·6, 371±33·8, 380±26·2 and 257±32·7g/day for treatment groups TS-Ms, TS-Ns, US-Ms and US-Ns, respectively. These findings indicate that monensin may counteract some ill-effects of diets high in sodium hydroxide-treated straw and thus further research is warranted.

Two farm trials were made to investigate the response to a second implant with the anabolic agent zeranol. Seventy cattle were implanted at the start of the growing period, at 10 to 12 months of age, the remaining 49 cattle being left as controls. Five months later, at the beginning of the fattening period, some cattle from each of the treatments during the growing period were implanted. The response to implantation in both periods was significant on both farms (P<0·05). During the fattening period there was no significant difference in the performance of cattle implanted only at the start of the growing period and that of the control animals, which suggested that the response to the earlier implant was permanent. Although differences in performance during fattening for cattle implanted twice, compared with that for cattle implanted for the first time at the start of fattening, were not statistically significant, on both farms performance was lower for the cattle implanted twice. These results suggest that the response to zeranol in the fattening period may be reduced by approximately 0·30 for cattle previously implanted. Over the combined growing and fattening period, cattle implanted twice showed a significant response in comparison with cattle given only one implant (P < 0·05).

Three experimental diets (L, M and H) containing 135, 175 and 210 g crude protein per kg dry matter respectively were given to crossbred does in two experiments. Protein quality was constant throughout.

In experiment 1 a total of 18 does (six per diet) were given the diets during two successive reproductive cycles. Losses of nitrogen in faeces and urine were estimated for four successive 7-day periods in each 28-day lactation period. Litters were culled at birth to give ‘high’ and ‘low’ lactational loads with 8 and 4 pups respectively. Total 28-day milk yields on diets L, M and H were 3·89, 4·82 and 5·27 kg respectively with eight pups sucking, and 302, 400 and 400kg respectively with four pups. These differences in milk yield were directly reflected in the weights of the pups when weaned at 28 days of age. There was no effect of diet on milk composition, pup birth weight or litter size. Does given diet L did not always consume their allotted ration and this may have affected the results.

The proportion of digested nitrogen utilized for milk protein synthesis differed significantly between diets and lactational loads, and was at its maximum (0·72) when diet L was given to does with eight pups. Does suckling eight pups retained 005 of the nitrogen they digested in their body tissues and those with four pups 0·13; there were no differences between diets in this respect.

In experiment 2 the nitrogen retention of 18 does (six per diet) was measured during pregnancy. Nitrogen retention increased as pregnancy progressed, and overall 0·20 of digested nitrogen was retained for conceptus growth and doe body tissue accretion.

A trial was made on a farm using seven newly calved Jersey cows to compare the actual dry-matter intake with that predicted by three commonly used multiple-regression equations. Daily average milk yields during the first 9 weeks of lactation were recorded and peaked at 27·8 kg per cow (s.e. 1·35) in week 7 of lactation. The daily dry-matter intake recorded was 19·2 kg dry matter per cow (s.e. 0·77), compared with the multiple-regression equations, which gave estimated intakes of 13·3, 16·7 and 12·5 kg/day respectively. Prediction was improved by the use of fat-corrected milk, and by taking account of source effects, such as location and the management of the herd (18·5 kg dry matter per day). A further observation trial with the same herd after 250 days from the start of their lactation indicated that the equations still underestimated the intake potential of the Jersey cow at this later stage.

The grazing behaviour of bulls and steers was examined by observation and the use of vibra-recorders. Twenty-four-h grazing times were similar for both bulls and steers but grazing patterns differed, with bulls being more sensitive to environmental change and grazing more intermittently than steers.

Poultry litter collected from a commercial broiler house, bedded with wood shavings, was used. The material was screened and ground before it was ensiled either alone or with other agricultural by-products, namely chopped barley straw, a mixture of weeds and grapefruit peels. The digestible organic matter in the dry matter value in vitro (0·39) for litter was comparable with that for straw and weeds. Of the total nitrogen (36·3 g/kg dry matter), 0·19 was ammonia-nitrogen and 0·77 protein-nitrogen. Digestible energy and crude fibre in the litter were 7·19 MJ and 334 g/kg dry matter, respectively. Addition of poultry litter at ensiling resulted in significant increases in nitrogen and ash content of the original mixtures. Inclusion of sodium hydroxide in fermented and non-fermented mixtures elevated digestible organic matter in the dry matter values in vitro by 0·19 and 0·13, respectively; the crude fibre concentration was lowered. All initial mixtures were free of lactic acid and were positive for the pathogen Proteus when tested. Unlike crude fibre, fatty acid and free ammonia, which were increased after fermentation, digestible organic matter in the dry matter and pH values were decreased. Ensiling killed the pathogen Proteus in the majority of the silages tested. The silages had a pleasant aroma and colour, and were consumed by Chios sheep.

To compare the genetic group differences in live-weight gains, efficiency of food conversion (in terms of dry matter, total digestible nutrients, digestible crude protein, digestible energy and metabolizable energy) and physiological responses related to heat balance, a total of 24 male lambs (91 to 180 days old), four each of Malpura, Sonadi, and their crosses with Dorset and Suffolk breeds, were given a ration having a roughage to concentrate ratio of 250:750g/kg and metabolizable energy content of 100MJ/kg dry matter. Live-weight gain per day was higher and the food conversion ratio (the intakes of total digestible nutrients, digestible energy and metabolizable energy per kg gain) was lower in the crossbreds than in the native sheep. The crossbreds had higher respiratory rates (153 per min) than the natives (140 per min) but there was no significant difference in rectal temperature between purebreds and crossbreds. The crossbred lambs in the present experiment grew faster, consumed more food and utilized the food more efficiently than did the native lambs, despite the fact that they dissipated more energy as body heat. It was, therefore, concluded that the crossbreds performed better than the native breeds between 3 and 6 months of age, even though they were not permanently acclimatized to hot environmental conditions.

Thirty-four pairs of sucking piglets, derived from six sow pairs, within which piglets were cross-fostered shortly after birth, were allotted to either a creep-food treatment or a control (no creep food). Piglets were weaned at 6 weeks of age and all were given a grower diet to slaughter at 9 weeks of age. There were no differences in carcass composition determined on piglets killed at 6 and at 9 weeks. Creep-fed piglets were heavier than controls at 6 and 9 weeks of age, but not at 3 weeks. There were no distinct differences in any of the blood serum samples obtained at 1, 3, 5 and 6 weeks of age for protein and albumin analysis, and zinc sulphate turbidity assay. It was concluded that there was no positive immunological response to the early provision of supplementary nutrients, although there was a positive growth response to creep feeding between 3 weeks of age and weaning at 6 weeks.

The effect of monensin supplementation on suckling male dairy calves was studied on a commercial farm. Twenty-eight calves were given monensin supplements from the age of 1 week and compared with a similar group not given monensin. During a 52-day suckling period, the supplemented calves gained 0·12 faster, with little difference in the conversion ratio of metabolizable energy into live weight. During the subsequent 42 days, there was no difference in daily gain, but the supplemented animals were 0·064 more efficient in the conversion of metabolizable energy into live weight.

The mean daily water intakes of individually penned wether sheep were determined over consecutive 7-day periods. Increased intakes of dry matter and/or crude protein resulted in higher intakes of water. The drinking pattern throughout the day was directly related to the type of food offered and its distribution during the day.