The objective was to determine the effects of avoparcin, bovine somatotropin (bST) and the additive effects of both avoparcin and bST on milk yield, milk composition, live-weight changes and reproduction parameters in post-partum dairy cows. Forty-eight autumn calving cows were allocated using a split-plot within randomized complete-block design to the following treatments: (i) control (2 ml saline plus 1 kg untreated concentrate per day); (ii) avoparcin (2 ml saline plus 1 kg concentrate containing 100 mg avoparin per day); (Hi) bST (25 mg bST in 2 ml saline plus 1 kg untreated concentrate per day); and (iv) avoparcin plus bST (25 mg bST in 2 ml saline plus 1 kg concentrate containing 100 mg avoparcin per day). All injections were given subcutaneously and treatment continued for 84 days beginning 55 (s.e. 4) days after calving. The cows were offered grass silage ad libitum supplemented with 7·2 kg cereal-based concentrates daily. Milk yield and milk composition were measured thrice and once weekly, respectively. The cows were weighed and body condition score was assessed every 2 weeks.

Mean daily milk yield of cows assigned to control was 20·1 (s.e. 1·5) kg, avoparcin, 21·5 (s.e. 1·5) kg, bST, 23·9 (s.e. 1·0) kg and avoparcin plus bST, 25·2 (s.e. 1·2) kg over the 84 days of the trial. bST increased milk yield proportionately by 0·18 compared with all cows not given bST (P < 0·01). Avoparcin did not significantly increase milk yield. There was no effect of any treatment on milk composition, body weight or body condition score. None of the experimental treatments had any effect on calving to first service interval, calving to conception interval, number of services per conception or overall conception rate.

These results show that in early lactation, avoparcin alone had no effect on production or reproduction parameters in dairy cows; bST alone increased milk yield but did not affect any other production or reproduction parameter. There was no significant additional increase in milk yield when avoparcin and bST were given in combination, compared with bST alone.

To identify the separate and combined effects of energy and crude protein (CP) from concentrates on responses to concentrate feeding, 42 multiparous Friesian cows were given fixed amounts of concentrates with primary growth grass silage (194 g CP per kg dry matter (DM)) ad libitum for weeks 4 to 22 of lactation. A basal treatment of 3 kg DM per day of a standard concentrate (197 g CP per kg DM) was compared with 6 kg DM per day of the same concentrate (doubling energy and CP intake), 6 kg DM per day of a low-protein concentrate (106 g CP per kg DM) (doubling energy intake alone), or 3 kg/day of a high-protein concentrate (383 g CP per kg DM) (doubling CP intake alone). Results are presented in terms of main effects as interactions were not significant except for energy apparent digestibility. Silage intake was reduced by energy but increased by CP; in consequence extra energy from concentrates increased digestible energy (DE) intake but reduced CP intake and concentration whereas extra CP from concentrates increased not only DE intake but also CP intake and concentration. The ratio of the responses to CP compared with the responses to energy were 1·7 for milk yield, 0·9 for fat yield, 3·2 for protein yield and 1·4 for lactose yield. Energy reduced milk protein concentration and tended to increase milk fat concentration whereas CP had the opposite effect. The efficiency of converting food nitrogen to milk nitrogen was unaffected by extra CP but was increased, from 0·195 to 0·229, by extra energy. The poor response in milk protein yield and the reduction in its concentration with extra energy reflected the lower CP intake due to the reduced silage consumption. The experiment emphasizes the importance of concentrate CP supply in stimulating silage intake and yields of all milk constituents for diets containing fairly small amounts of concentrates.

Thirty-six British Holstein-Friesian cows were offered 9 kg dry matter (DM) daily of one of 12 concentrates together with grass silage ad libitum in a cyclical change-over design experiment during lactation weeks 8 to 22. The carbohydrate source in the concentrates was either mainly starch, mainly digestible fibre or a 1:1 mixture. Each concentrate type was formulated to provide 120, 160, 200 or 240 g crude protein (CP) per kg DM and similar metabolizable energy concentration. Silage contained 142 g CP per kg DM, in vivo digestible organic matter was 0·690 kg/kg DM, pH 4·4 and ammonia-N 172·2 g/kg total nitrogen.

Silage intake increased as fibre replaced starch in the concentrate. Apparent digestibility of organic matter and energy were highest for starch-based concentrates, but there was no effect of carbohydrate source on yields of milk and milk solids. Milk protein concentration was depressed by feeding mixed or fibrous carbohydrates.

Silage intake increased on average by 0·13 kg DM per additional 10 g/kg CP in the concentrate. The digestibility of the diet was not affected by increasing CP except for nitrogen. Milk yield increased by 0·028 kg per additional g/kg CP in the concentrate and there were linear effects ofCP on yields of milk solids.

As CP increased, milk fat concentration tended to rise with starch but was depressed both overall and by offering mixed or fibrous carbohydrates. In contrast milk protein concentration increased with mixed and fibrous carbohydrates but not with starch.

It is concluded that when silage is given ad libitum with 9 kg/day concentrates, CP level has more effect than source of carbohydrate on milk production.

Designs testing clones in a closed nucleus, in which 1024 cows are tested each year, were compared for their additive genetic response to selection (genetic response) and their genetic superiority of female genotype(s) selected for commercial cloning (clonal response), using stochastic simulation. Clones were tested at the expense of dam or sire families, matings per dam (sire), or full-sibs per family. The reference design maximized the genetic response corrected for inbreeding in the absence of cloning. The trait considered was overall economic merit for milk production, which was simulated assuming an approximate infinitesimal model with both additive and dominant gene action. Bulls and cows eligible for breeding were selected on their animal model estimated additive genetic effect at either 15 or 27 months of age. Female genotypes eligible for commercial cloning were selected on their estimated total genetic effect at 27 months of age. All (fe)male full-sibs were available for selection. With only additive gene action, testing clones at the expense of sire families, matings per dam or full-sibs per family reduced genetic response, while it increased clonal response and inbreeding. Testing clones at the expense of dam families, however, added to both the genetic and clonal response without increasing inbreeding. When eight clones were tested at the expense of dam families, the genetic response and the final genetic level of commercially available cloned embryos were maximal. Accuracy of clonal selection equalled 0·83. With dominant gene action, however, testing two clones at the expense of dam families maximized the final genetic level of cloned embryos, irrespective of the level of inbreeding depression (accuracy of 0·72). Reliable commercial clone lines can be produced now and in future generations by testing clones at the expense of dam families.

Twenty-one 6-month-old Israeli Holstein heifers were used to determine the effect of three 6-month feeding regimes on growth, blood concentration of insulin, prolactin and insulin-like growth factor-1 (IGF-1), attainment of puberty and milk production during first lactation. Feeding regimes were as follows. (1) Restricted: the heifers were given food during months 1, 2 and 4, 5 of an experimental period, to support live-weight (LW) gain of 0·35 and 0·50 kg/day, respectively and during months 3 and 6 the heifers were given food to support compensatory growth. (2) Control: the heifers were given food to support LW gain of 1·0 kg/day. (3) Control + C: the heifers were given the same as the control, with a daily supplement of 0·05 mg/kg LW cimaterol (C) for 4 months. The total LW gain of the restricted heifers during the 6 months of the trial was significantly lower than that of the control heifers. Cimaterol improved growth rate only during the first 2 months of its application and its withdrawal was associated with severe LW gain retardation. The feeding regime employed in the restricted treatment was associated with a significant reduction in serum concentrations of insulin, prolactin and IGF-1 during the first restricted phase, followed by an elevation in the first compensatory phase. During the second restriction-compensation cycle, only the serum concentration of prolactin was significantly reduced. Cimaterol addition was also associated with a reduced blood concentration of the hormones. The animals in the restricted, control and control + C groups attained puberty at LW of 249·2, 277·6 and 304·9 kg (P <0·05), respectively. No effect of the treatments on milk yield was observed. The effect of the feeding regimes on skeletal growth and on metubolizable energy efficiency for growth is discussed.

Concentrations of growth hormone (GH), insulin-like growth factor (IGF-1), insulin and glucagon were determined in the plasma of growing bulls, steers and heifers (no. = 138 in total, German Simmental breed). The animals were offered either a high level or a low level of energy resulting in relatively high and low average daily gain. Trials were subdivided into two experimental series and started at approximately 3 months of age at an average live weight of 110 kg. The animals were slaughtered at different body weights from 200 to 510 kg (heifers) or 660 kg (bulls, steers). Blood samples (needle puncture) were collected at biweekly intervals. Frequent samples time-course analysis of GH were taken by catheter from nine animals in total. Concentrations of GH declined during growth in steers and heifers as well as in bulls in blood samples collected by means of a catheter. IGF-1 and insulin concentrations increased from the start of the trial onwards up to different ages among the groups. Concentrations of glucagon constantly decreased from the start of the trial until slaughter. Significant differences (P < 0·05) in concentrations ofGH, IGF-1 and insulin could be observed between sexes and levels of nutrition, with the highest GH and IGF-1 levels in bulls followed by steers and heifers. In contrast insulin values were highest in heifers followed by steers and bulls. A high level of nutrition increased concentrations of IGF-1 and insulin in all sexes.

Changes in live weight, body condition, milk production and composition were monitored for single- and twinsuckling cows in two experiments. In experiment 1, all cows were managed for 3 months before calving to achieve condition scores at calving 2·1 (low) and 3·1 (moderate). Subsequently, these animals were placed on a fixed level of energy intake (80 MJ metabolizable energy (ME) per day) for 16 weeks. Post-partum diets contained differing amounts of digestible undegradable protein (DUP), but similar amounts of effective rumen degradable protein (ERDP). In experiment 2, single- and twin-suckling cows were fed to achieve a condition score at calving of around 2·75. These animals were subsequently placed on two levels of energy intake (80 MJ and 130 MJ ME per day) during the first 16 weeks of lactation. The diets providing these energy intakes also contained differing amounts of DUP. Neither the level of DUP in the diet nor the level of feeding significantly altered the digestibility of the dry matter or organic matter in the dry matter of the experimental diets.

Body condition at calving had little effect on daily milk yield (9·5 kg) and composition (33·5 g/kg fat; 30-0 g/kg protein) in experiment 1. Cows with higher body condition scores at calving lost 13·5 kg more live weight and 0·26 units more body condition (P < 0·05) during the 1st month post partum but remained in better condition throughout the trial period than cows with lower body condition scores. Cows on 130 MJ ME per day produced higher (P < 0·001) daily yields of milk, milk fat and protein (+2·0 kg; +151 g; +85 g) and lost 57 kg less live weight and 0·52 units less body condition (P < 0·001) than cows on 80 MJ ME per day. Elevated dietary levels of DUP promoted (P < 0·05) daily milk yields (by 1·25 kg) and reduced live-weight and body condition-score loss during the 1st month post partum in both experiments. Twin-suckling cows produced the highest average daily yields of milk throughout the 16-week trial period in both experiments but yields were not significantly higher after early lactation in experiment 1. Cow body condition score at calving and the level of DUP in the post-partum diet of cows had no effect on the post-partum performance of calves. Twin calves had slower growth rates (P < 0·001) than single calves (0·65 and 1·07 kg/day respectively) in experiment 1. However, twin calves sucking cows on 130 MJ ME per day in experiment 2 grew similarly to single sucking calves from week 8 of lactation (0·8 kg/day).

Changes in certain blood metabolites, serum progesterone concentration and pregnancy rate, were monitored for single- and twin-suckling cows in two experiments. In experiment 1, cows were managed to achieve condition scores at calving of 2·1 (low) and 3·1 (moderate). Subsequently, these animals were placed on a fixed level of energy intake (80 MJ metabolizable energy (ME) per day) for 16 weeks. Post-partum diets contained differing amounts of digestible undegradable protein (DUP), but similar amounts of effective rumen degradable protein (ERDP). In experiment 2, all cows were fed to achieve a condition score at calving of around 2·75. These animals were subsequently placed on two levels of energy intake (80 MJ and 130 MJ ME per day) for 16 weeks. The diets providing these levels of energy intake also contained differing amounts of DUP. Pregnancies were established by embryo transfer following induced oestrus.

Cows in moderate body condition at calving subsequently had higher (P < 0·05) serum non-esterified fatty acid (NEFA) concentrations. Cows on 130 MJ ME per day had lower serum NEFA concentrations than cows on 80 MJ ME per day. Cows given higher DUP diets had higher (P <0 ·05) serum NEFA concentrations when in negative energy balance and lower serum NEFA concentrations when close to energy equilibrium than cows given lower DUP diets. Twin-suckling cows had higher (P < 0·05) serum NEFA concentrations than single-suckling cows, but only during the first 3 weeks post partum. Plasma glucose concentrations were below 3 mmol/lfor twin-suckling cows until week 7 post partum when they became similar to the values for single-suckling cows. Serum D-3-hydroxybutyrate concentrations mirrored those of plasma glucose. Serum urea-nitrogen concentrations were high for twin-suckling cows on 80 MJ ME per day and single-suckling cows on 130 MJ ME per day.

Neither body condition at calving nor post-partum energy intake significantly influenced the time taken for cows to overcome anovulation nor did they significantly influence the proportion of cows which eventually resumed normal oestrous cyclicity. DUP concentration in the post-partum diet had no overall effect on the various measures of fertility assessed but thin cows at calving subsequently placed on the high DUP diet took longer to ovulate (55 days; P < 0·05) and had the lowest pregnancy rate (0·30). The post-partum anovulatory period was longer (P < 0·01) by 27 days in experiment 1 and 12 days in experiment 2 for hvin-suckling cows compared with singlesuckling cows. A lower proportion (P < 0·001) of twin-suckling cows regained oestrous cyclicity and became pregnant in experiment 1. Fertility traits were improved when twin-suckling cows were in moderate body condition at calving and/or offered 130 MJ ME per day during the post-partum period.

A combined crossbred and purebred selection (CCPS) method, i.e. using crossbred and purebred information, was proposed to achieve genetic response in crossbred animals. Selection index theory was applied to establish a CCPS index. The CCPS was compared with pure-line selection (PLS) and crossbred selection (CS) methods. The genetic correlation between purebred and crossbred performance (rpc) and crossbred heritability (hc2) are crucial factors in the comparison. The CCPS is always better than PLS or CS when a fixed number of purebred progeny is tested. With a fixed total number of purebred and crossbred tested progeny, CCPS is only worse than PLS for very high values of rpc (>0·8). Superiority of CCPS over PLS increases and over CS decreases with decreasing rpc. The larger hc2 is, relative to purebred heritability (hc2 the more response CS and CCPS will achieve. The robustness of CCPS against inappropriate assumptions on rpc and hc2 values was investigated. The expected response is always an overestimate, and the actual response is smaller than the optimal response when rpc is assumed one but the true rpc is smaller. The difference between actual and optimal response increases as rpc decreases but it is small for large rpc values (e.g. <3% for rpc >0·7). The expected response is smaller than the actual response when rpc is large and hc2> hp2 Finally, the actual response to CCPS is larger than the optimal response to PLS for positive values for rpc. The main conclusions are: (1) CCPS method is optimal for obtaining genetic response in crossbreds; and (2) CCPS with inappropriate assumptions on rpc and hc2 values (e.g. recognizing crossbreds as purebreds) achieves more genetic response than PLS for common values of rpc and crossbred heritability.

A study was carried out to determine if sheep could be used as a model for predicting the intakes of silages by cattle. Fifty ewes and 45 cows were offered five grass silages unsupplemented in two parallel randomized-block experiments over a 4-week period. Each silage had been made using the same equipment over a range of cutting dates (May, July, August 1991). The silages differed in fermentation characteristics, with lactic acid concentrations varying from 15·3 to 90·7 g/kg dry matter, and ammonia-nitrogen concentrations from 77 to 198 g/kg nitrogen. When expressed on a metabolic live-weight basis, the mean intakes of silages by cows were 2·25 times those of the sheep, with the mean intakes being 35·1 and 79·1 g/kg M0·75 for the sheep and cows respectively. However, there was no significant correlation between recorded intakes during the 4th week of the study by the two species (y (cows) = 0·62× (sheep) + 58·40; r2 = 0·03). It was concluded that sheep were not a useful model system to predict the intakes of a range of grass silages of similar chop length by dairy cows.

Carcass composition was measured on 133 Blackface ram lambs from a flock divergently selected for predicted carcass lean proportion. Prediction equations for different carcass components were developed using combinations of live weight and ultrasonic backfat and muscle depth. Both carcass lean and carcass fat proportion were best predicted using only live weight and fat depth, and a genetic transformation of the equation predicting carcass lean proportion was highly correlated (genetic correlation = 0·97) with the index on which the sheep were selected. Weights of carcass tissues were more accurately predicted than proportions. Lean weight was best predicted using live weight and muscle depth, and the weights of different fat components were best estimated using live weight, muscle depth and fat depth.

The equations predicting carcass lean proportion, carcass fat proportion, lean mass and fat mass had heritabilities of 0·29, 0·27 0·20 and 0·23, respectively. Heritabilities for carcass lean and carcass fat proportions, and the subcutaneous and intermuscular fat components were 0·43, 0·48, 0·24 and 0·49, respectively. Genetic correlations of the equation predicting carcass lean proportion with lean and fat proportions were 0·52 (s.e. 0·21) and –0·45 (s.e. 0·22), respectively. The same correlations for the equation predicting carcass fat proportion were –0·47 (s.e. 0·22) and 0·57 (s.e. 0·21). The equations predicting carcass lean and fat proportions were strongly correlated with subcutaneous fat proportion but weakly genetically correlated with intermuscular fat proportion.

An investigation was conducted to determine the effect of mating at puberty or third oestrus or after pre-mating oestrogen and progestagen therapy, designed to mimic the changes that occur in plasma oestrogen and progesterone concentrations during the 1st, 2nd or 3rd oestrous cycles, on fertility in ewe lambs. Twenty-five ewe lambs were mated at puberty on mean date of 18 October and 21 were mated at third oestrus on 3 December. Of these, 28% and 81% of animals mated at puberty and third oestrus lambed, respectively (P < 0·05). A similar number of ewe lambs were mated within 24 h of ram introduction in the groups given one, two or three consecutive applications oestrogen and progestagen (25 μg oestradiol benzoate followed 48 h later by a progestagen pessary left in situ for days). Of the 43 corpora lutea, 21 were represented by viable embryos in the 37 animals holding to service after one application compared with 34 out of 46 corpora lutea in 40 animals given three applications (P < 0·05). Furthermore, embryo crown-rump length, embryo weight and amniotic sac width was greater (P < 0·05), on day of pregnancy, in animals given one compared with three applications of oestrogen and progestagen. These results demonstrate that fertility is improved in ewe lambs mated on third oestrus or after progestagen and oestrogen therapy designed to simulate three oestrous cycles.

The effects of altering the glucogenic potential of the diet of wether lambs (initial body weight 56·4 kg) offered an energy allowance of 0·25 that required for maintenance on body-weight loss, nitrogen retention and blood and rumen fluid parameters were examined. Whole barley was offered alone or substituted on an isoenergetic basis with 40 or 120 g of a blend of glucose precursors (polyhydric alcohols, propylene glycol, sodium propionate) absorbed on to palm kernel meal (acetona meal), to 36 lambs (no. = 12 per treatment) for 8 weeks. Substituting barley with 40 g acetona meal had a small but non-significant effect in decreasing body-weight loss and plasma aspartate amino transferase activity and in increasing plasma insulin concentration. Increasing the glucogenic potential of the diet by substituting barley with 120 g acetona meal decreased body-weight loss in the early phase of the study, decreased plasma concentrations of non-esterified fatty acids and increased the proportion of propionate in volatile fatty acids in rumen fluid, plasma aspartate amino transferase and gamma-glutamyl transferase activities and plasma insulin concentrations. Increasing the glucogenic potential of the diet did not affect nitrogen retention or plasma glucose concentration. It is concluded that increasing the glucogenic potential of the diet of lambs resulted in an increase in metabolic efficiency at the onset of negative energy balance which was mediated through a change in plasma insulin concentration. The absence of a significant difference in body-weight loss between the diets in the latter part of the study reflects the lack of sustained ketosis.

In 56 balance trials sows received diets in pregnancy containing (g/kg diet) either 24·7 nitrogen (N) (C) or 16·7 N (L) followed by diets in lactation containing (g/kg dietary dry matter) either 28·5 N and 8·4 lysine (C) or 32·8 N and 10·3 lysine (H). N and energy balance during lactation (day 4 to 25) were made during three successive parities (23, 17 and 16 sows in parities 1,2 and 3, respectively). Retention in piglets was calculated from their body composition at weaning.

Mean daily litter gain was 2·72 kg/day and was not affected by the dietary treatments. Mean body-weight loss of sows was 0·67 kg/day and was lower only in parity 2 on lactation treatment H compared with lactation treatment C. N retention was less negative on lactation treatment H than on lactation treatment C (significant in parity 1) and N retention was less negative on pregnancy treatment L than on pregnancy treatment C (significant in parity 3). Fat mobilization on lactation treatment H was higher than on lactation treatment C (significant in parities 2 and 3). The proportion of energy mobilized as protein to the total energy mobilization was significantly lower on lactation treatment H compared with lactation treatment C. Estimated daily N, lysine and Heal digestible lysine requirements for first parity lactating sows were 162 g, 48 g and 37 g respectively. For second parity sows 179 g, 54 g and 42 g and for third parity sows 185 g, 56 g and 43 g. N excretion during lactation was proportionately about 0·6 of ingested N. This resulted in an N excretion of about 2·3 kg N during a 25-day lactation period. After correction for differences in litter size, body weight of sows, daily litter gain and N mobilization increased with parity number.

Various procedures for estimating the economic values required to weight characteristics in multitrait selection have been proposed. Some, despite their theoretically sound foundations, are frequently misinterpreted. One such method involves the derivation of economic values based upon accepted economic theories of the firm, profit maximization, and the concepts of marginal economic behaviour. An amplified and more rigorous presentation of this method and its theoretical basis is presented that confirms the basic propriety of the method, clarifies the misinterpretations surrounding its application, and offers additional insights into the potential fallacy of less economically rigorous alternatives.

This study was conducted to determine the relationship between plasma concentrations of thyroxine (T4), triiodothyronine (T3) and body weight in young Majaheem male camels. Eighteen camels aged 6 to 7 months were divided equally into three groups (Gl, G2 and G3). All groups were given concentrate pellets (187 g crude protein per kg) at the rate of 15 g/kg body weight daily. In addition, each group was given one of the following roughages: lucerne hay to Gl, rhodes grass hay to G2 and ammonia-treated wheat straw to G3. Roughages, salt and water were measured and given ad libitum. Every 2 weeks all camels were weighed and blood samples were collected. Data were statistically analysed using a general linear model procedure. There was a positive correlation between T4 concentration and body weight. T4 was higher in camels given either hay or straw compared with those given rhodes grass hay, while there were no differences among the three groups in T3 and in body weight.

Ten crossbred boars were penned individually and offered either meal or pellets of identical composition to appetite from single space hopper feeders which also provided water. The hoppers were sited on raised steel mesh platforms 1·2 m × 0·87 m in size under which was placed a similar sized collecting tray. Spilled food was collected for 24 h once weekly for the 4-week experimental period. Live-weight gain tended to be lower on the meal diet compared with the pellets (882 v. 968 (s.e. 28·7); P = 0·07) while food conversion efficiency (g food per g growth) was worse on the meal diet (2·65 v. 241 (s.e. 0·059); P < 0·05). Food spillage is the most likely explanation for the difference in food conversion, however collectable spilled food was (g/g food offered) 0·0089 and 0·0026 respectively of meal and pellets offered. The value for the meal diet is about one-tenth of the expected value and suggests that direct collection of spillage from non-pelleted diets even over a wide area in front of the feeder is not an accurate technique.

The value of a parameter such as heritability (h2) or intra-dass correlation in best linear unbiased prediction (BLUP) with the animal model or a family selection index affects both the rate of response achieved and the rate of inbreeding. If in BLUP an estimate of h2 is used which is biased upwards above its actual value, the rate of inbreeding can be substantially reduced with little reduction in the rate of response. Further, by mating individuals from families in which many are selected to others from families with few selected (compensatory mating), rates of inbreeding can be further reduced without substantial effect on response.