The impact of internal and external parasitism on productivity of farm animals is considered for cattle, sheep, pigs and poultry. The parasitic challenge experienced and the outcome of that challenge is a dynamic one in which environment, management practices, including housing or grazing management, nutritional status, the host's ability to develop effective immunity and the speed with which this can occur, play a significant role. Much of our assessment of the impact of infection comes from pathophysiological and nutritional studies with contrived infestations. A common feature of all infestations is reduced efficiency of food utilization through reduction in food intake, though in some cases increases in nutrient requirement are induced as a result of damage to or loss of host tissue. Assessment of the impact on productivity in the field is technically very difficult and must take account of fluctuating challenge, determined by environmental and management decisions, and the manager's objectives for the performance of a particular category of livestock. This review attempts to integrate the assessment of losses in productivity based on pathophysiological studies with those based on protection of groups of livestock in production systems by regular pesticide use. Throughout the review the limitations inherent in both approaches and in our knowledge of how parasites impair productivity of the host are emphasised.

Alternative index procedures for selection on non-linear profit are quadratic indices, desired gains indices, group or mate selection indices, or direct optimization of responses over multiple generations. In this study a multiple generation time horizon was considered and several linear, quadratic and desired gains indices were compared. Genetic and economic responses over multiple generations were calculated considering a quadratic profit function combining protein yield and days open.

Directly optimizing reponse over multiple generations was found to yield slightly higher economic responses (+ < l.5%) than stepwise (each generation) adjustment of a linear index. A constant linear index using base population averages and a quadratic index were found to be less efficient. The quadratic index was less efficient than the linear index when considering multiple generations. Desired gains indices allowed stabilization of base population average for days open, however, forcing considerable economic losses. Relative efficiencies of methods depended on the degree of non-linearity of the profit function.

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.

Three groups of 16 cattle each comprising three multiparous Jersey cross Holstein-Friesian cows, seven primiparous and six multiparous Holstein-Friesian cattle were offered, ad libitum, a silage-based complete diet with different concentrate ingredients following an initial 3-week covariate period. The relationship between these three diets and other parameters with lesions of the weight-bearing surface of the hoof was studied by scoring mobility weekly (locomotion score) and examining all the feet of all cows for visual lesions particularly those involving the horn of the foot. In addition hoof angle, hardness and growth and wear were also recorded. The mean locomotion score during the initial 3-week covariate period was a significant covariate for the subsequent locomotion score, milk yield, and live weight (P < 0·001). Furthermore weekly locomotion score also proved a significant covariate for weekly milk yield (P < 0·05). There were no significant differences between dietary treatment groups for locomotion score, overall lesion score (despite significantly fewer ulcers of the sole in one dietary group: P < 0·001) but a significant (P < 0·05) difference between cow ‘type’ and there was also a significant (P < 0·05) diet × breed interaction for locomotion score and milk yield. It was concluded first that initial mobility was an important factor in subsequent mobility of the cow and so experimental design; secondly that while nutrition and genotype interacted to influence mobility, visual lesions of the hoof and lameness, the mechanisms involved were far from clear; and thirdly that the simple lesion score used required some adjustment or correction factor(s) to ensure that more severe lesions were given a greater weight than a simple unitary increase.

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.

A total of 148 dairy cows in their first lactation and with a mean calving date of 6 December were used in a 4–year experiment. The experiment was designed to examine the effect of level and distribution of concentrate given during the winter period in addition to grass silage (ad libitum) and hay (4 kg/day) on total lactation performance. Each year the same five treatments were compared: three levels of concentrate supply during the winter period (H, M and L), and, for levels M and L, two different allocation patterns (standard (S) or flat rate (F)). Concentrate allocation was individually pre-determined according to expected milk production. During summer, all animals grazed together as a single group. During the experimental period (weeks 4 to 18 of lactation), concentrate and roughage intakes were 6·3, 5·0 and 3·6 kg dry matter (DM) per day and 9.;5, 9·6 and 10·0 kg DM per day in group HS, MS and LS respectively. Milk yield and protein concentration of group HS were higher than that of group MS (+1·3 kg I day and +1·0 g/kg) or LS (+3·0 kg/day and +1·7 g/kg). During winter, live-weight changes were +4, -26 and -39 kg for group HS, MS and LS respectively. Over the 40 weeks of lactation, the differences in milk production and concentrate supply were 193 kg and 196 kg DM between groups HS and MS, and 518 kg and 413 kg DM between groups HS and LS. There was no significant difference between groups S and F.

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.

First lactation production and linear type records of 72 559Holstein-Friesian cows, calving from 1982 to 1989, were analysed by multivariate restricted maximum likelihood, using a sire model. The data comprised offspring of 1066 randomly used sires, and 91 proven i.e. widely used bulls. All phenotypic correlations between the type traits and the yield traits were small, but moderate genetic correlations were obtained between milk, fat and protein yield and angularity (~—0·43) and between the yield traits and udder depth (~0·44), indicating that higher yielding heifers are more angular and have deeper udders. The heritabilities of the type traits were in line with previous analyses, but those for milk, fat and protein yield were rather high at 0·47, 0·52 and 0·45 respectively

Crossbreeding data involving Ghana Shorthorn, Sokoto Gudali and their Jersey F1s and backcrosses collected over a 16-year period were analysed to estimate additive and heterotic effects for milk production, reproduction and calf growth traits. Sokoto Gudali was significantly better than Ghana Shorthorn in all milk production traits. Calving interval and annualized milk production were better in Gudali than in the Shorthorn. The F1s had higher lactation milk yield, milked longer, produced their first calves earlier and had shorter dry periods and calving intervals than their corresponding purebreds. However, genotype was not significant for number of services per conception. Both F1s had higher average daily gain and weaning weight than their corresponding purebreds. Sokoto Gudali backcross (Jersey × F1) was significantly (P < 0·05) better than the F1 in lactation length. However, in Gudali crosses, there was no advantage in increasing the proportion of Jersey genes beyond 0·5 for milk production traits. Additive effects were significantly (at least P < 0·05) lower in the Shorthorn and the Gudali than in Jersey for milk production traits except proportion of butterfat. Heterosis estimates were significant (P < 0·01) for milk production traits for the Shorthorn but not for the Gudali. Heterotic effects were large and significant (at least P < 0·05) in improving annualized milk production in Shorthorn crosses, whilst none of the heterotic effects for reproductive traits was significant. At both 0 and 0·5 levels of Jersey inheritance, the Gudali was superior (P < 0·01) to the Shorthorn in birth weight, weaning weight and pre-weaning average daily gain. Heterotic effects for calf traits were positive and much larger in Gudali crosses than in Shorthorn crosses. In general, backcrosses were, at best, similar to the F1s implying that upgrading these indigenous breeds beyond 0·5 European inheritance may not be desirable.

High digestibility ryegrass was ensiled using either good methods including formic acid application (HDG) or poor methods without formic acid (HDP). Low digestibility ryegrass (LDG) and lucerne (LUC) were ensiled using similar methods to HDG. Digestible organic matter in the dry matter (DM) in vivo (DOMD) for HDG, HDP, LDG and LUC were 0·756, 0·774, 0·645 and 0·562 respectively. Silages were offered ad libitum to 40 HolsteinFriesian cows in two Latin-square design experiments during weeks 8 to 22 of lactation either alone (experiment 1) or with 3, 6, 9 or 12 kg concentrate DM per day (experiment 2). Relative intakes of silage given alone were respectively 1·00, 0·44, 0·98 and 0·79. Low intake of HDP could not be predicted from silage analysis. In experiment 2, DM intake increased by 0·11 kg and milk yield by 0·24 kg for each 0·010 change in grass silage DOMD. Intake of HDG, LDG and LUC declined linearly with increasing concentrate, on HDP the effect was non-linear and intake increased up to the 6 kg level.

In experiment 1, milk and protein yields were greatest on HDG, protein yield was higher on LDG than LUC and fat concentration higher on HDP and LUC. With supplementation milk yield was greatest on HDG up to the 6 kg level, at higher levels differences between silages were not significant. Fat concentration was highest on LDG and protein highest on HDG and lowest on LUC. On all silages giving the highest concentrate level reduced the concentration and yield of fat. Protein concentration increased up to the 9 kg level. Fat plus protein yields reached a maximum on HDG with 6 kg concentrate DM per day and with 9 kg on the remaining silages.

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.

Growth-promoters are banned by the European Community, but different hormonal cocktails are still illegally used. This experiment was therefore conducted to evaluate the effects of one of the most currently used cocktails on some hormonal parameters and spermatogenesis in finishing bulls in an attempt to provide a suitable screening technique for their illegal use. Sixteen double-muscled Belgian White Blue finishing bulls (mean ivcight: 535 (s.d. 37) kg) were blocked into control (C; no. = 7) and treated (Dex; no. = 9) groups. Animals were treated i.m. with the hormonal preparation (dexamethasone isonicotinate and phosphate, chlormadinone acetate and ethinyl oestradiol) on day 0, day 15 and day 30. Animals were slaughtered on day 45. Three h before each treatment and just prior to slaughter, jugular blood samples were collected to monitor the testosterone (T) response to an i.v. injection of gonadotropin releasing hormone (GnRH) (0·5 fig GnRH per kg body weight). Testicular tissue was also collected at slaughter. Plasma T and insulin-like growth factor-1 (IGF-1) concentrations were measured by radioimmunoassay. IGF-binding proteins (IGFBPs) were evaluated using Western ligand blotting. Daily weight gains were lower in the control group (1·29 (s.d. 0·13) kg for C v. 1·60 (s.d. 0·39) kg for Dex) but the difference ivas not significant. After treatment, spermatogonia, spermatocytes, spermatids and spermatozoa disappeared from the testis and seminiferous tubules consisted only of Sertoli cells; these observations suggest that treated animals were sterile. Moreover, plasma T concentrations in response to GnRH stimulation were suppressed fP < 0·001) in the Dex group between day 15 and day 45 (mean maximal responses: 5·4 to 7·9 μg/l in C group v. < 0·2 μg/l in Dex group at day 15, 30 and 45). Treatment did not show any prominent effect on plasma IGF-1 levels but increased IGFBPS band intensity. In conclusion, treatment with a cocktail containing dexamethasone esters, chlormadinone acetate and ethinyl oestradiol for a short period induced a number of changes in finishing bulls luhich might be possible to develop as a screening method for the identification of illegally treated animals.

One hundred and twenty spring-born steers, comprising 40 Friesians (FR), 40 Meuse-Rhine-lssel (MRI) × Friesians (MR), and 40 Belgian Blue × Friesians (BB) were reared together from 3 weeks of age to the start of their second winter. During the second winter there was a 3 (FR, MR and BB breed types) × 2 (3 kg and 6 kg supplementary concentrates per head daily with grass silage ad libitum) × 2 (96- and 220-day finishing periods) factorial arrangement of treatments (10 animals per subgroup). Carcass weights and grades were recorded after slaughter at the end of the second winter, and one side from each of 96 carcasses (eight per subgroup) was dissected into bone, muscle, intermuscular fat and subcutaneous fat. A sample of m. longissimus from the 10th rib was chemically analysed. Slaughter weights and carcass weights per day from arrival to slaughter were 796, 813 and 828 (s.e.d. 11·7) g and 419, 440 and 457 (s.e.d. 7·1) g for FR, MR and BB, respectively. Corresponding carcass weights were 314, 329 and 342 (s.e.d. 4·5) kg. BB had better conformation than both FR and MR. BB also had a lower carcass fat score, lower proportions of bone, intermuscular fat and subcutaneous fat, a higher proportion of muscle and muscle with higher proportion of moisture and a lower proportion of lipid than FR and MR. The higher level of concentrates increased side iveight by 8 kg, but the overall effects on carcass composition were small. The longer finishing period increased side weight by 25 kg and was associated with significantly reduced proportions of bone and muscle and an increased proportion of fat. Allometric regression coefficients for carcass weight on slaughter weight, and for bone, muscle and fat weights on side weight were 1·19, 0·39, 0·80 and 2·16, respectively. It is concluded that despite the better carcass conformation of MR, there was little difference in carcass and muscle composition between FR and MR. BB, in addition to having a higher growth rate and better carcass conformation than FR, also had more muscle in the carcass, more of the total muscle in the higher value joints and a lower proportion of lipid in the muscle. It was calculated that FR, MR and BB would have similar proportions of separable fat in the carcass at approximate carcass weights of 300, 320 and 400 kg, respectively.

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.

Overall efficiency of energy utilization (i.e. total net energy intake as a fraction of metabolizable energy intake) in cattle given food ad libitum was calculated from information included in the United Kingdom energy evaluation system as published by the Agricultural Research Council. For growing cattle (live weight 250 kg), overall efficiency was estimated for five levels of diet metabolizability (ranging from q = 0·45 to q = 0·65) for each of two diet types: coarse/long roughage and fine/pelleted diets. The overall efficiencies varied from 0·58 to 0·62 and were not systematically affected by diet type or diet metabolizability. For lactating cattle (live weight 600 kg), overall efficiency was also calculated for five diets with metabolizability ranging from 0·45 to 0·65. Calculations were made for cows at equilibrium intake (i.e. zero energy balance) and at milk production levels proportionately 0·30 higher or lower than those attained at equilibrium intake. Overall efficiencies varied from 0·60 to 0·63 and were not systematically affected by diet metabolizability.

It is concluded that, in practical cattle production systems with ad libitum feeding, the net energy content of food may be estimated at 0·6 of the metabolizable energy content (or 0·5 of the digestible energy content), irrespective of diet type, diet metabolizability or productive function.

The effect of inclusion of live yeast culture (YC, Saccharomyces cerevisiae plus growth medium) in a high concentrate diet given to buffalo (Bubalus bubalis) calves on the rumen microbial population and fermentation pattern and in sacco dry matter disappearance of dietary constituents was examined. Six rumen-fistulated buffalo calves of about 120 kg live iveight were divided into two equal groups. The control group was given a diet consisting of, on a dry-matter basis, 0·90 kg ivheat straw, 1 kg berseem (Trifolium alexandrinum) and ISO kg concentrate per day per calf and the yeast group the above diet plus 5 g YC which was put directly into the rumen via the fistula. After feeding this diet for 6 weeks (supplementation period), inclusion of YC was stopped and both groups were given the control diet for a period of 3 weeks to examine the performance of the YC group after withdrawal of YC. At week 4 of YC supplementation the pH was significantly increased (P < 0·01) and lactate concentration was decreased (P < 0·01) in the rumen fluid for up to 6 h post feeding. The number of total bacteria, total viable bacteria, cellulolytic bacteria, amylolytic bacteria and protozoa were increased proportionately by 0·554 (P < 002), 0·482 (P<0·01), 0·670 (P <0·01), 0·077 (P > 0·05) and 0·079 (P>0·05), respectively. The concentrations of total volatile fatty acids, particularly at 4 h post feeding (P < 0·01), acetate fP < 0·01) and propionate and the acetate to propionate ratio were higher in the YC compared with the control group. On YC inclusion, the concentration of ammonia-nitrogen was decreased while that of trichloracetic acid insoluble protein was marginally increased. All these differences in rumen variables started to disappear on YC withdrawal and values returned to control levels by the 3rd week after YC withdrawal. YC supplementation increased the in sacco dry-matter disappearance of various dietary components particularly after 3, 6 and 22 h incubation.

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.

Two experiments were conducted to determine whether female to female influences could reduce the duration of the post-partum anoestrous period in beef cows. In experiment 1, cows were housed from calving, either in individual stalls, which precluded physical contact with other cows (treatment I; no. = 19) or as a group, with a cow in oestrus introduced to the group twice per week (treatment G; no. = 18). The percentage of cows cycling by day 50 post partum was similar for both treatments, but at 91 days post partum was significantly higher (P <0·05) in the G than in the I cows (89% v. 58%).

In experiment 2, cows were housed in individual stalls from calving and exposed twice per week to either cervical mucus collected from cows in oestrus (treatment M; no. = 21) or distilled water (treatment W; no. = 24). The percentage of cows cycling by 70 days post partum was similar in both treatments but by 130 days there were significantly more (P <0·05) M cows cycling (86% v. 58%). In neither experiment were LH profiles at 22,43 or 64 days influenced by treatment.

The results indicate that cervical mucus of cows in oestrus contains pheromone(s) which can reduce the postpartum anoestrous period in beef cows with extended anoestrous periods.

The aim of this experiment was to determine whether there is any physiological basis for concerns that selection for fleece mass may decrease fitness by increasing the partitioning of nutrients to wool at the expense of other body functions.

Forty-five Merino rams (24 months old) were given food at an ad libitum and a maintenance level of nutrition. Animals were grouped into high, average or low clean fleece growth-rate categories on the basis of measurements made during the ad libitum feeding period. During ad libitum feeding, high producers grew proportionately 0·42 more clean fleece, and deposited proportionately 0·36 more energy and 0·42 more nitrogen (N) as greasy fleece than average producers. This was achieved by partitioning a higher proportion of N consumed to wool (0·08 v. 0·06), and not by increased energy or N retention. High producers adapted to the maintenance diet by decreasing clean wool growth rate proportionately by 0·32. There were no differences between high and average wool producers in clean wool growth rate or the percentage of N or energy intake partitioned to wool at the maintenance level of feeding. Although there were no differences in initial live mass between groups, low producers gained proportionately 0·45 more live mass during the experiment than average producers.

It was concluded that Merino rams of high clean-wool production potential are not more efficient, but partition more of the available nutrients to wool production at the cost of body tissue deposition.

Effects of time of supplementation on forage intake, nutrient apparent digestibility and rumen fermentation were studied with 12 mature castrated male sheep (wethers) offered grass hay from 16.30 h to 09.30 h and supplemented with a cereal-based concentrate given at either 09.30 or 16.00 h. Voluntary intake of hay organic matter (OM) was decreased by feeding the concentrate (P < 0·01). Offering concentrate at 09.30 h after hay was available, increased intake of hay and total OM compared with offering it at 16.00 h before hay was available (P < 0·05). Daily pattern of hay intake was not changed when concentrate was offered at 09.30 h compared with feeding hay alone, but concentrate given at 16.00 h resulted in a lower hay intake between 16.30 and 18.00 h. Sheep offered concentrate at 09.30 h had higher rumen ammonia levels than those offered concentrate at 16.00 h, but there were no differences in the apparent digestibility of the nutrients, rumen pH and molar proportions of the main volatile fatty acids. There were also no differences between groups in the blood plasma concentrations of 3-hydroxybutyrate (30HB), nonesterified fatty acids (NEFA) and glucose. It is concluded that feeding supplement after rather than before a period of intake of forage or a bout of grazing may offer a means of minimizing reduction of forage intake as a consequence of feeding concentrate.