To investigate the effect of dietary fat and metabolizable energy (ME) on milk protein concentration, an experiment was carried out using 12 multiparous early-lactation Holstein-Friesian dairy cows. Three diets were offered in a complete Latin-square change-over design, based on ad libitum access to grass silage. One of three concentrates was offered at a rate of 12 kg/day, each formulated to supply one of two levels of ME (12·1 and 13·6 MJ/kg dry matter (DM)) and one of two levels of fat (31 and a mean of 88 g acid hydrolysis ether extract per kg DM): low energy, high fat (LEHF); low energy, low fat (LELF); and high energy, high fat (HEHF). The concentration of milk protein was significantly higher from animals offered the LELF concentrate (32·5 v. a mean of 31·2 (s.e.d. 0·45) g/kg, P < 0·05), because of lower milk yields (31·0 v. a mean of 33·4 (s.e.d. 0·63) kg/day, P < 0·05). Animals offered the HEHF concentrate produced the highest yields of milk protein but their milk had the lowest concentrations of fat (32·5,34·4 and 31·9 g/kg for LEHF, LELF and HEHF respectively; s.e.d 1·07; P < 0·05 for difference between LELF and HEHF). Silage DM intake was significantly increased by animals offered the LEHF concentrate (9·1, 8·6 and 8·7 (s.e.d. 0·19) kg/day, P < 0·05 for differences between LEHF and the other two concentrates). Urinary purine derivative excretion, used as an index ofmicrobial protein supply, was highest from animals offered the LELF and HEHF concentrates, which both supplied similar amounts of fermentable ME. It is hypothesized that increased de novo synthesis offatty acids on the low fat diet reduced the availability of glucose for lactose synthesis, leading to reduced milk yields and hence increased milk protein concentrations.

The potential of milk allantoin as an index ofmicrobial protein supply was evaluated in two experiments conducted with 12 multiparous Holstein-Friesian dairy cows that examined the effects of altering the supply of metabolizable energy (ME) and fermentable metabolizable energy (FME). In the first experiment, late lactation cows received a 14·3 kg dry matter (DM) per day basal diet consisting of (g/kg DM) chopped barley straw (415), soya-bean meal (322), molassed sugar-beet pulp (197), molasses (33), urea (17) and a vitamin and mineral supplement (17) for a 21-day co-variance period. During four 16-day periods, six treatments were allocated randomly to cows, consisting of potato starch (1, 2 or 3 kg DM per day) or fat supplements (0·64, 1·27 or 1·91 kg DM per day). In the second experiment, early lactation cows received 40 kg/day (fresh weight, (FW)) of silage (307 g/kg toluene-corrected dry matter, 149 g/kg DM crude protein and 11·6 MJ/kg ME). During three 21-day periods, four treatments were evaluated consisting of supplements of either 4·1 (LI) or 8·1 (12) kg fresh weight per day of a low fat concentrate (acid hydrolysis ether extract (AHEE) 45 g/kg DM) or 3·8 (HI) or 7·5 (H2) kg fresh weight per day of a high fat concentrate (AHEE 110 g/kg DM). Both experiments showed individual cow milk allantoin concentration or excretion to be poorly correlated with urinary purine derivative excretion or calculated microbial protein supply. Use of treatment mean (TM) values dramatically improved these relationships. For pooled TM (no. = 10) values from both experiments, close relationships existed between milk allantoin excretion and concentration with milk yield (r values 0·991 and 0·883, respectively). Auto-correlation with milk yield appeared to account for milk allantoin excretion and concentration being highly correlated with urinary purine derivative excretion (r values 0·908 and 0·934, respectively) and calculated microbial protein supply (r values 0·938 and 0·945, respectively). Current experimental data indicates that measurement of milk allantoin is not a reliable indicator of microbial protein supply for individual cows.

Food can be used in an automatic milking system (AMS) to encourage frequent attendance to, and modify behaviour in, an AMS. An AMS was designed such that a cow had to pass from a bedded area through the AMS to enter the feeding area. A visit resulted in milking if the interval since the last milking was greater than 4 h.

Fourteen Holstein-Friesian dairy cows were allowed to attend voluntarily an AMS for 15 h/day for three 8-day periods. In period 1 the cows were given forage in the feeding area and concentrates in the bedded area but in period 2 this was reversed. Period 3 repeated period 1. The cows were also divided into two groups of seven, only one of which was given 1 kg of concentrates when milked in each period in a cross-over design.

Visits per cow per day increased when the cows were given forage in the feeding area (6·0 v. 4·1 (s.e.d. 0·08) P < 0·05) but milkings per cow per day were only slightly different (2·6 v. 2·4 (s.e.d. = 0·02) P = 0·052). Feeding forage in the feeding area modified forage-eating behaviour by reducing the number of bouts (4·9 v. 7·6 bouts per cow per day, P < 0·05) and total forage eating time (209 v. 289 min per cow per day (s.e.d. = 33·6), P < 0·05). The cows also tended to spend less time lying (529 v. 620 min per cow per day (s.e.d. = 43·2) P = 0·051).

There was no effect of feeding/not feeding concentrates in the milking stall on visits per cow per day or milkings per cow per day. However, feeding tended to create more shuffling behaviour during the automatic teat cup attachment process (3·4 v. 6·7 shuffling bouts per milking (s.e.d. 2·07) P = 0·053) but there were no effects on the levels of kicking, successful teat cup attachment rate, vocalization, elimination, hesitations in mounting a step or poor rear leg positions. The cows tended to adjust to a more accessible stance during both the automatic attachment process (from 17% of milkings exhibiting poor leg positions at the start of attachment, to 10% at the end, P < 0·01) and over the course of the experiment (from 26% to 10%, P < 0·02). There was a trend for cows who were not fed to milk out quicker than those who were fed for all milkings per day combined (733 s v. 811 (s.e.d. 43·3) s P = 0·074) but there were no other effects on yield, milk flow rate from the udder or time taken to milk out for all milkings through the day combined or just the first milking of the day.

Feeding concentrates in the feeding area can be used as an alternative to feeding forage in the feeding area, but there is no need to feed concentrates in the milking stall. Feeding cows while they were being milked did not improve their behaviour or milking characteristics.

Haemorrhagic lesions, heel erosions and changes in foot conformation have been associated with husbandry, underfoot conditions and nutrition of dairy cows.

These characteristics were monitored in 40 heifers in a 2 × 2 factorial design starting in the last trimester of pregnancy and continuing until 12 weeks post partum. Primary treatments were housing in straw yards or cubicles and secondary treatments were alternative complete diets given during lactation which differed in concentrate: forage ratio. A scoring system was developed for each of the foot lesions to allow statistical analysis of results. Locomotion scoring was carried out weekly.

White line haemorrhages, sole haemorrhages and heel erosions were all present before calving. White line haemorrhages were exacerbated by housing in cubicle yards and alleviated by housing in straw yards (P < 0·001) with an interaction between diet and housing around calving (P < 0·05). Sole haemorrhages were exacerbated both by housing in cubicle yards (P < 0·01) and the high concentrate diet (P < 0·01) with an interaction between diet and housing around calving (P < 0·05). Heel erosions were exacerbated (P < 0·05) by housing in straw yards but not affected by diet. Sole haemorrhage and heel erosion scores generally increased during early lactation (P < 0·001) independent of the treatments. There was evidence that these foot lesions were not caused by laminitis. There was a higher incidence of lameness for heifers given the high concentrate diet but no correlation between locomotion score and the type of lesion or lesion score.

Two experiments were conducted with dairy cows to examine the effects of including white clover in perennial ryegrass swards and of offering the cows a choice between tall and short mixed perennial ryegrass/white clover swards. In the first experiment, cows grazed a perennial ryegrass sward (treatment Prg); a mixed sward of perennial ryegrass and white clover (treatment WC); treatment Prg during the night and treatment WC during the day (treatment Prg night/WC day); or they were offered a choice between Prg and WC (treatment Prg/WC). Cows in treatment WC produced more milk than cows in treatment Prg, with cows in Prg night/WC day and Prg/WC intermediate. The milk fat content of cows in treatment Prg was greater than in the other three treatments. When cows were offered both mixed grass/clover and pure grass swards (treatments Prg night/WC day and Prg/WC) they exhibited a partial preference for the WC sward and grazed it to a lower herbage height than the pure grass sward. In the second experiment, cows were offered a WC sward at 6 or 3·5 cm sward surface height, or a choice between pastures at the two heights. Cows offered only the tall sward produced most milk, and those offered only the short sward produced the least. Milk fat content was reduced for cows offered only the tall sward. Cows offered a choice of the tall or short swards spent longer grazing in total than the cows offered only tall or only short swards but there was no difference in the time spent grazing the tall and short swards.

The objective of this study was to evaluate the influence of calving season on the interactions among reproductive disorders prior to conception and their effect on subsequent reproductive performance in dairy cows. Data from 3170 lactations of Holstein-Friesian cows that subsequently conceived were analysed by means of path analysis techniques. The cows were from nine commercial dairy herds in north-eastern Spain. Lactation incidence rates for retained placenta, metritis, ovarian cysts and repeat breeding (more than four artificial inseminations per conception) were 6·4, 3·7, 5·4 and 7·9%, respectively, and there were no differences between warm (May to September) and cool (October to April) calving seasons. However, our data show that calving season influenced the interrelationships among reproductive traits. Lactation number was not related to any of the path model variables for cows calving in cool seasons and retained placenta did not directly influence ovarian cysts or repeat breeding. In contrast, older cows that calved during warm seasons showed an increased risk of experiencing retained placenta, ovarian cysts and more days open; retained placenta was a direct risk factor for ovarian cysts and repeat breeding. Our data indicated that a cool season decreased interactions among reproductive disorders of dairy cows. Cows that calved in a cool environment could more effectively cope with reproductive disorders prior to conception and this fact was mainly observed in older cows.

Energy and nitrogen balances were carried out with four multi-porous Holstein/Friesian cows offered four diets in a Latin-square experiment to evaluate urea-treated whole-crop wheat as a partial grass silage replacement for lactating dairy cows. Grass silage (GS) was produced from the primary growth of a perennial ryegrass sward. Spring wheat (cv. Axona) was harvested at 603 g dry matter (DM) per kg and preserved with 20 (WCW-20) or 40 (WCW-40)kg urea per t DM. The diets were 6 kg DM of a dairy concentrate daily with one of four forage treatments offered ad libitum. The forage treatments were GS alone, a 2:1 DM ratio of GS with WCW-40 (2:1 40), or a 1:2 DM ratio of GS with WCW-20 (1:2 20) or WCW-40 (1:2 40). Each period lasted 4 weeks with energy and nitrogen balances being carried out in respiration chambers over 6 days in the last week. Replacement of GS by diets containing WCW resulted in significant increases in DM intake (P < 0·01). Changes in milk yield and composition were small and non-significant but yields of milk fat and protein were higher on WCW diets than on GS diets (P< 0·05). With increasing proportions of WCW in the diet there were significant linear falls in apparent digestibility of DM (P < 0·001), organic matter (F < 0·001), neutral-detergent fibre (F < 0·01), acid-detergent fibre (F < 0·01), starch (F < 0·001) and nitrogen (P < 0·01). Gross energy intakes (P < 0·01) and faecal (P < 0·001), methane (P < 0·05) and milk (P < 0·05) energy outputs were higher with the WCW diets than with GS but urine energy and heat losses were unaffected. In consequence there were no significant differences among the diets in digestible or metabolizable energy (ME) intakes. However dietary ME concentrations (MJ ME per kg corrected DM) fell with increasing WCW inclusion from 11·54 on GS to a mean of 9·96 on the 1:2 diets (P < 0·001). It was calculated that the ME concentration of the WCW was only 8·1 MJ/kg corrected DM at maintenance intake, considerably lower than values used conventionally. There were no significant diet effects on the partition of ME or on the partial efficiency of ME utilization for milk production (k1). The increasing inclusion of WCW increased N losses in urine (P < 0·05) and faeces (F < 0·01) with no net effect on N digested or retained though there was a small increase in milk N output (P < 0·01). It is concluded that low digestibility is the major cause of the small milk response to the partial substitution of urea-treated WCW for grass silage with no evidence of a reduction in the efficiency of utilization of ME.

Fifty-five multiparous Holstein-Friesian cows were used to evaluate the short- and long-term effects of varying the crude protein (CP) content of concentrates offered at a low level (5 kg/day) along with ad libitum access to a high quality grass silage. Three dietary treatment groups in lactation weeks 4 to 22 received concentrates containing either 156 (L), 247 (M) or 338 (H) g CP per kg dry matter; from weeks 13 to 21, half of the L animals changed over to the H concentrate and vice versa so that there were five treatment groups (LL, LH, MM, HL and HH). Feeding M or H compared with L increased silage voluntary intakes (P <0·05) and the yields of milk (P <0·05), fat (P < 0·05) and protein (P < 0·01). Milk protein concentration increased with level of concentrate CP (P < 0·05). Pattern of concentrate CP supply (comparison ofLH, MM and HL) had no significant effect on intake or yields of milk and milk solids across the experiment (weeks 4 to 21), though cows gained less weight on treatment HL than on LH (P <0·05) or MM. Intake, milk and component yields were all markedly affected by a change in concentrate CP at week 13; there were positive effects of additional CP (LL v. LH) and negative effects of reduced CP (HH v. HL) on silage intake (P <0·05), as well as milk yield (P < 0·001), milk protein yield (P < 0·001) and milk protein concentration (P < 0·001). Responses to increased concentrate CP were of a similar magnitude in early and midlactation; extra concentrate CP can recover depressed yields and concentrations of milk protein in established lactation. Production responses to concentrate CP involved a concomitant increase in silage voluntary intake.

Two experiments were carried out with Holstein Friesian early lactation cows of high genetic merit to evaluate the effects on intake and milk production when the animals were offered a concentrate supplement either within a complete diet (CD) or separately from grass silage (separate feeding, SF) through a computerized out-of-parlour feeder system. This system offered the daily allowance of concentrates in four × 6h time windows and the cows could choose to have several accesses to concentrate within each time window. In experiment 1 22 first lactation cows were used in a two-treatment change-over design with 10-week periods, while in experiment 2 48 animals (28 in lactation 1 and 20 in lactation 2 or over) were used in a continuous design with an average of 80 days on experiment. In both experiments the diets on the CD treatment were offered ad libitum with a concentrate proportion of 0·61 in total dry-matter (DM) intake while on the SF treatment grass silage was offered ad libitum and the allowance of concentrate was made equal to the mean concentrate intake of the CD treatment during the previous week. All the animals in experiment 2 were turned out to pasture on 5 April for 120 days to examine the residual treatment effects. Twelve mid to late lactation cows and eight rumen-fistulated beef steers were also used to evaluate the effects of the two feeding methods on nutrient utilization and rumen fermentation, respectively. In the latter two trials, the concentrate on the SF treatment was also offered four times daily but in a conventional trough-feeding arrangement.

In experiment 1 both silage and total DM intakes were similar between the two treatments. However, in experiment 2 silage DM intake was significantly increased fP < 0·002) and total DM intake tended to be higher (P > 0·05) with the SF treatment. Feeding the complete diet tended to increase milk yield in both experiments (P = 0·057 in experiment 1), but significantly reduced both the concentration and yield of fat in experiment 2 (P < 0·05). There were no significant treatment effects on the concentration of protein in either experiment, nevertheless in experiment 1 the yield of protein was significantly increased (P < 0·05) with the CD treatment. When the animals in experiment 2 were turned out to pasture, there were no significant residual effects of the indoor feeding treatment on milk production, or yield of fat or protein. However, the concentrations of fat and protein in milk, obtained during the first 60 days on pasture, were significantly higher for the cows offered the concentrate separate from silage during the indoor feeding treatment. The nutrient utilization and rumen fermentation trials indicated no significant difference between the CD and SF treatments in either whole tract apparent digestibility of nutrients (DM, organic matter, energy or nitrogen (N)) or rumen fermentation characteristics (pH, ammonia-N concentration, total volatile fatty acids (VFAs), or molar proportion of each individual VFA in the rumen liquor). It is concluded that feeding the concentrate within a complete diet rather than separately from the silage had no significant effects on total DM intake, milk production, nutrient digestion or rumen fermentation.

Cattle breeds of African, European and Indian origins are being evaluated at Rockhampton for their suitability for beef production in northern Australia. In the current study, Belmont Adaptaur (HS), Belmont Red (AX) and Belmont BX (BX) dams were mated to produce straightbreds and crossbred progeny by Brahman (B), Boran (Bo) and Tuli (Tu) sires. B dams were mated to produce straightbreds and crossbred progeny by AX, BX, Bo, Charolais (Ch), HS and Tu sires. This paper reports values for heterosis for some crosses and live weights on pasture for some straightbred and crossbred genotypes at birth, at weaning and at 18 months.

Heterosis for birth weights was greatest for taurine dam breed × indicine sire breed, generally negative for the reciprocal cross and markedly less for Tu-sired than for B- or Bo-sired progeny. Heterosis was not estimated for Bo and Tu crosses at weaning or at 18 months. At these ages, heterosis for growth includes a component related to resistance to environmental stresses. Thus, heterosis was then greater for B crossbreds derived from the less resistant HS than from the more resistant AX.

There were significant differences between genotypes in live weights at each age. Progeny by B sires from taurine dams had higher live weights than progeny by Bo or Tu sires. Evidence is presented that strongly indicates that the difference in growth rates between the B- and Bo-sired progeny arose entirely from differences in mature live weights of the B and Bo, not from differences in efficiency of growth of their crossbred progeny. Similarly, live weights of progeny by taurine sires from B dams ranked according to the mature live weights of the sire breeds. Thus, the Ch- and Tu-sired progeny had the highest and lowest live weights at all ages respectively. Comparative growth potentials of the indicine sire breeds were estimated by comparing 18-month live weights of progeny from HS dams. Relative to Bo = 100, growth potential of B = 205. Similarly, growth potentials of the taurine sire breeds were estimated from progeny from B dams. Relative to Tu = 100, the estimates were HS = 104, AX = 111 and Ch = 117. Crossbred progeny by B and Bo sires were generally significantly heavier at all ages than the corresponding straightbreds. However, Tu-sired progeny had similar birth weights too, but generally higher weaning and 18-month live weights than, the corresponding straightbreds. Relatively low birth weight and low heterosis for birth weight identify the Tu as a potentially useful sire breed when an increase in birth weight of crossbreds is undesirable.

Within each dam breed, no straightbred could match the growth rate of the best crossbred. At 18 months this advantage was proportionately 0·21, 0·09, 0·05 and 0·16 over that of the straightbred HS, AX, BX and B respectively. Live weight of every crossbred based on B dams exceeded that of the straightbred B, the most populous breed in northern Australia. Thus, increases in growth rates could be achieved by crossbreeding irrespective of the base breed. Live weights at 18 month for progeny of Bo, Tu and AX sires from B dams, all of which exceeded those of the straightbred B, suggest that the African breeds can be used to complement the B in crossbreeding programmes in northern Australia.

The effects of adrenergic challenge (in order to evaluate the adipose tissue lipolytic potential) and time of challenge relative to feeding on the response curve of plasma non-esterified fatty acids (NEFA) in four underfed or overfed non-lactating non-pregnant cows were studied. Basal NEFA and NEFA response to isoproterenol (ISO; 4 nmol/kg body weight) were higher when challenged before than after feeding and higher in underfed than overfed cows. Interaction between feeding level and time of challenge was significant (P < 0·001) for the rising part of NEFA response. Pooled NEFA response curves from several trials (no. = 63 challenges) were analysed in order to obtain a simplified procedure for the prediction of the NEFA response. High correlations were found between the response area or maximal NEFA response and NEFA response at 15 min (r = 0·95 and 0·98, respectively). This simplified procedure was applied on pooled data from 84 challenges in order to evaluate the effects of energy balance, physiological status, body condition score (BCS) and time of challenge relative to feeding. Energy balance had a significant effect on basal plasma NEFA and NEFA response at 15 min after ISO challenge (–7·6 and –14·2 μmol/l when the daily energy balance increased by 1 MJ, respectively). Time of ISO injection relative to feeding had a greater effect on stimulated NEFA than on basal NEFA (308 v. 239 μmol/l). There was a significant effect of BCS (41 μmol/l per unit of BCS) on the basal plasma NEFA level. The NEFA response at 15 min after ISO challenge was lower (387 μmol/l) in lactating cows than in dry cows. The NEFA response to ISO at 15 min could provide an efficient method of studying the adipose tissue lipolytic potential of cattle in vivo.

Data comprised information on herd life from two different sources: actual lifespan and type data. The optimum way of predicting breeding values (BVs) for herd life from both these sources is a multivariate best linear unbiased predictor (BLUP) analysis of lifespan and the linear type traits most closely related to it. To reduce computing requirements, we suggest a bivariate BLUP analysis, where the direct information is lifespan, measured in lactations and the indirect information is a phenotypic index of type traits weighted by their economic values. Such an index is shown to be almost as efficient as using the individual traits.

Genetic correlations between functional lifespan and the linear type traits were estimated, and based on these foot angle (rg = 0·22) udder depth (rg = 0·24) and teat length (rg = -0·44) were chosen to predict herd life. Breeding values for herd life were predicted in a BLUP analysis for around 500 000 heifers. The traits were lifespan and the phenotype index offoot angle, udder depth and teat length. For bulls with a minimum of 10 daughters BVs ranged from -0·9 lactations to +1·0 lactations, indicating a difference of approximately one lactation between the daughters of extreme bulls. For sires with at least 50 daughter records for lifespan, type information contributed little to the accuracy of herd life BVs.

The effects of concentrate energy source on feeding behaviour and energy utilization, when offered with grass silages of differing intake characteristics, were studied in lactating dairy cows. A total of five silages, which differed in fermentation and intake characteristics, were prepared. Silages A, B and D and silages C and E were harvested from primary regrowths and secondary regrowths respectively of predominantly perennial ryegrass swards. Herbage was ensiled either pre-wilted or unwilted and either untreated or treated with a bacterial inoculant or formic acid based additives. Five concentrates (0s, 25s, 50s, 75s and 100s) were formulated to contain similar concentrations of crude protein, effective rumen degradable protein and metabolizable energy (ME) but using different carbohydrate sources to achieve a wide range of starch concentrations. The silages were offered ad libitum, supplemented with 10 kg concentrates per head per day. In experiment 1, a partially balanced change-over design experiment involving 50 lactating dairy cows was undertaken to examine the effects of concentrate energy source on silage feeding behaviour. Silages A, B, C, D and E were each supplemented with concentrates Os, 25s, 50s, 75s and 100s. Concentrate energy source did not alter (P > 0·05) silage feeding behaviour. The number of meals per day decreased (P < 0·01) as silage dry-matter concentration increased. Experiment 2, a completely randomized experiment involving 18 lactating dairy cows, was undertaken to examine the effects of concentrate energy source on energy utilization with cows offered silages B, C and D. These were supplemented with 10 kg/day of concentrates Os, 50s and 100s. Concentrate energy source had little effect (P > 0·05) on ME intake, energy output or on the efficiency of utilization of ME for lactation (k1). In experiment 3, the effect of concentrate energy source on silage preference was examined in a factorial design experiment involving 12 lactating dairy cows. Silages B, C and D were supplemented with concentrates Os, 50s and 100s. Concentrate energy source did not alter (P > 0·05) silage preference. It is concluded that with silages of differing fermentation and intake characteristics but of similar digestibility, concentrate energy source had no effect on feeding behaviour, silage preference or energy utilization. Furthermore there was no evidence of concentrate energy source by silage type interactions on silage feeding behaviour and preference, or energy utilization.

Cattle breeds of African, European and Indian origins are being evaluated at Rockhampton for their suitability for beef production in northern Australia. In the current study, Belmont Adaptaur (HS), Belmont Red (AX) and Belmont BX (BX) dams were mated to produce straightbreds, and crossbred progeny by Brahman (B), Boron (Bo) and Tuli (Tu) sires. B dams were mated to produce straightbreds, and crossbred progeny by AX, BX, Bo, Charolais (Ch), HS and Tu sires. All animals were reared together in the presence of cattle ticks and gastrointestinal nematodes (‘worms’). Over a 10-month period, half of each genotype was treated every 3 weeks to control ticks and worms. The resistance of each genotype to these parasites was estimated from direct counts of maturing female ticks (‘tick counts’) and from a combination of worm eggs in fresh faeces (‘worm egg counts’) and response to treatment to control the parasites.

The ranking of the sire breeds for tick resistance was B, Bo > BX > AX, HS, Tu > Ch and for worm resistance was B > Bo, BX > AX, Ch, HS, Tu. Only the B × BX and B × Bo could match the resistance of the B to ticks and worms combined.

All genotypes responded to treatment to control parasites but at the low to moderate levels of infestation recorded throughout the study the response of the more resistant genotypes was too low to warrant the cost of treatment. However, the ranking of the genotypes for live-weight gains changed with parasite challenge. Progeny by B and by Bo bulls from each of the dam breeds had higher live-weight gains than the corresponding straightbreds irrespective of the level of parasite challenge but gains of Tu-sired progeny exceeded those of the corresponding straightbreds only at lower levels of parasite challenge. The difference in resistance between the B and the more resistant F2s was small and even at twice the parasite challenge experienced throughout the study, the Fts would still be expected to outgain the B. For those genotypes for which it was measured, heterosis was consistently significant for live-weight gains and for tick counts but not for worm egg counts. Heterosis for live-weight gain was consistently higher for control than for treated groups. Potential roles of the different breeds for crossbreeding is discussed in relation to the effects of different levels of parasite challenge on growth rates of their progeny.

The effect of pregnancy on the fat and protein contents of milk was studied on a 414-lactation sample. One hundred and forty-nine lactations of non-pregnant cows managed under identical conditions served as controls. The difference between individual fat or protein contents of each pregnant animal and the mean corresponding values in controls was computed weekly from the week of conception. The effect of pregnancy on fat and protein concentrations began to be significant from the 20th week of pregnancy, regardless of the week of conception. It was higher in the Friesian breed than in Holstein or Montbeliarde cows. In Holstein and Montbeliarde cows, the effect of pregnancy was higher in high producing multiparous cows (+2·8 and +2·9 g/kg for fat and protein concentrations, respectively, at the 29th pregnancy week) than in primiparous or low producing multiparous cows (+2·0 and +1·4 g/kg, for fat and protein concentration, respectively). In each of these three lactation groups (Friesian, high producing multiparous Holstein and Montbeliarde cows, other Holstein and Montbeliarde cows) the following linear model

was fitted, where Y is the difference between fat or protein concentration of pregnant and non pregnant cows at a given stage (week), Pw is the pregnancy week, and a and b are parameters. This increase in milk fat and protein concentrations in late pregnancy cannot compensate the concomitant decrease in milk yield, so that fat and protein yield decreased in the same manner as milk yield during pregnancy (-77 glday and -68 glday at the 29th week of pregnancy, for fat and protein yield, respectively).

The metabolic response of dairy cows to high as opposed to low altitude conditions (2000 m v. 400 m above sea level) was determined. In the first experiment, four cows were subjected to a series of measurements before, during and after transport from lowland to high altitude pasture. During transport, cortisol, l-lactate and non-esterified fatty acids were significantly elevated but decreased within 1 to 3 days to initial levels. After transport, β-hydroxybutyrate and the thyroid hormones immediately increased and returned within 3 weeks to initial levels. Plasma urea increased during transport and subsequently was at an intermediate level due to the different diet. There were no direct carry-over effects of transport on metabolic traits during pasturing.

In the second experiment, three groups of six different dairy cows were either grazed in one of two consecutive years or kept inside (2nd year only). Lowland sojourn lasted for 4 weeks, and high altitude period for 8 weeks. At the end of high altitude sojourn, both outside and inside groups were found still to have significantly higher plasma cortisol values than at lowland. Thyroid hormones and ketosis related metabolites sharply increased at the start of the alpine period and were elevated for 1 to 3 weeks thereafter. According to the hormonal and metabolic profiles, the permanently housed cows did not benefit from the less adverse climatic conditions and the lower physical strain. Plasma urea closely reflected dietary changes in the ratio of nitrogen to fermentable organic matter. Plasma protein, albumin, creatinine, and liver enzyme activities were not affected by transport or high altitude sojourn in both experiments. The results indicate that the metabolic response to transport and high altitude conditions can be mostly explained by the efforts to cover the additional energy requirements. Overall the data suggest a wide but nevertheless limited ability of early-lactating cows to adapt to high altitude conditions.

The effect of underfeeding and ref eeding on digestion was studied in Bos taurus and Bos indicus cows. Eight nonlactating cows, four B. taurus and four B. indicus (live weight 156 kg and 207 kg respectively) were first given a forage-based diet at a level above energy maintenance requirements for 4 weeks (3·65 and 4·66 kg dry matter (DM) per day respectively for B. taurus and B. indicus). They were then restricted at a low level of intake for 2 months (1·83 and 2·33 kg DM per day respectively for B. taurus and B. indicus) and finally refed at the first level for 2 months. Digestion measurements were made before the underfeeding period, at 3 and 8 weeks of underfeeding and at 3 and 8 weeks ofref eeding. Organic matter apparent digestibility decreased with underfeeding and increased with refeeding (0·637, 0·591, 0·652, 0·692 and 0·669 in B. taurus and 0·674, 0·560, 0·580, 0·698 and 0·692 in B. indicus, respectively 1 week before, 3 and 8 weeks after underfeeding, and 3 and 8 weeks after refeeding). This lower apparent digestibility at low level of intake was not expected either by ruminal particle retention time, which increased when intake decreased, or by measurements ofmicrobial activity: DM degradability measured in situ and ruminal particle size did not vary with level of intake. An effect of the length of underfeeding and refeeding was seen: the apparent digestibility tended to increase after several weeks of undernutrition and was higher after refeeding than before underfeeding. No difference was observed between the two genotypes.

Bovine blood neutrophil oxidative burst activity, the total leukocyte count and its differentiation, as well as progesterone, glucose and cortisol levels were studied on 10 cows from 1 week prior to calving until 8 weeks after parturition.

From day –7 before parturition a decrease in the metabolic oxidative burst activity of neutrophils was observed, reaching the lowest value 3 days after calving (0·28 (s.e. 0·06) nmol/l H2O2 per min 106 neutrophils) (P <0·01). Thereafter, values increased with a maximum of activity 26 days after parturition (0·57 (s.e. 0·05) nmol/H202 per min per 106 neutrophils). At the end of the experiment the neutrophils H2O2-productionwas comparable to values observed on day–7.

The maximum total leukocyte count was observed on the day of parturition (8, 108 (s.e. 370) leukocytes per /A blood) (P <0·01) returning to normal levels about 3 weeks after calving. Lymphocytes and neutrophils showed a trend analogous to that of the total leukocytes. Eosinophils and monocytes did not change during the entire period. With the rapid increase of circulating neutrophils observed on the calving day, a marked left shift was observed with a maximum number of immature neutrophils (48·6%) observed on day +3 (1477 (s.e. 242) immature neutrophils per fjl blood) (P <0·01), reaching normal values about 4 weeks after parturition.

A significant increase (F < 0·01) of plasma glucose was found on the day of parturition (91·4 (s.e. 6·8) mg per 100 ml plasma), while the levels of cortisol reached their maximum 3 days after calving (22·05 (s.e. 8·46) nglml plasma).

Progesterone levels averaged 4·07 (s.e. 1·21) jigll 7 days before calving, declining precipitously to 0·06 (s.e. 0·45) Hg/l 3 days after calving (F < 0·01), remaining very low for a period of about 3 weeks. Minimum and maximum anoestrus post-partum were 22 and 57 days, respectively.

Despite great hormonal variation observed in the peripartum period, no significant correlation was found between measured hormones and the oxidative burst activity of neutrophils.

A comparison was made between fattening systems with Belgian Blue bulls of the double-muscle type, in order to assess the reponse in terms of compensatory growth when the bulls were grazed at a high stocking rate. Two groups of eight bulls were grazed on Lolium perenne and Trifolium repens pasture during an initial period of 135 days (period I). One group grazed at a stocking rate of six animals per ha allowing for normal growth at pasture (NGP); the other group grazed at stocking rate of 10 animals per ha (low growth at pasture, LGP). Both groups were then finished indoors (period II) with a concentrate based on dried sugar-beet pulp. Eight control bulls were also fattened indoors on the concentrate diet during periods I and II (CG). The bulls were slaughtered according to similar finishing fattening state. Live-weight gains were 1·47, 1·10 and 0·52 kg/day (P < 0·002) during period I in CG, NGP and LGP groups respectively. Corresponding live-weight gains during period II were 1·22, 1·37 and 1·50 kg/day (P > 0·05). The LGP group had lower food conversion ratios, slaughter weights (P < 0·05) and dressing proportions (P < 0·01). The meat from the grazed bulls had lower cooking losses (P < 0·05) and tended to have lower drip losses (P > 0·05) and higher tenderness (P > 0·05). It also had a higher cholesterol (P < 0·05) content. Large differences were observed in the fatty acid composition according to fat location (subcutaneous, intermuscular or intramuscular). The proportions of mono and polyunsaturated acids were increased in the fats of the animals previously grazed (P > 0·05, P < 0·05).

One of the sources of variation in the in vitro gas production (GP) technique is the inoculum source that is used and this could be greatly affected by the diet that is given to the donor animal. To study the effect of the host diet on the gas production profiles of grass hay and high temperature dried grass, two cows were offered either a silage: barley diet (80:20 dry-matter (DM) basis; GSB) or barley straw (ad libitum; STR). An adaptation period of 3 weeks was used and each animal experienced each diet type twice. Rumen fluid and solids were collected at the end of each 3-week period and used to inoculate the substrate cultures. The volume of gas produced (mllg DM) was 379 and 289 for GSB and STR respectively; gas yield (mllg organic matter degraded) was 442 and 411. The maximum fractional rates of degradation (per h) were 0·067 and 0·061 and the time (h) taken to reach these rates were 5·3 and 12·6. None of these differences was significant. There were also no significant differences in the concentration of total volatile fatty acids (VFA) in the final incubation media, or in the molar proportions of individual VFA. These results suggest that the fermentation stoichiometry was not affected by donor animal diet and, while microbial activity from STR was lower, this did not significantly affect the GP profile. The difference in microbial activity between the two diets was perhaps minimized by taking the sample of rumen contents before the morning meal.