Annual surveys of fertilizer practice have been conducted since 1942. Since 1985, nitrogen application rates to grass have progressively declined and phosphorus application has been reduced since the mid 1970s. Increasing environmental issues and the present interest in organic farming and low input systems indicate that these trends will continue. Present overall fertilizer use for grazing on dairy farms is about 170 kg N, 10 kg P and 20 kg К per ha. Higher rates are used for intensive silage production, 200 kg N, 15 kg P and 50 kg К per ha. In contrast, recommended applications are 340 kg N, 18 kg P and 25 kg К per ha for grazing and 380 kg N, 40 kg P and 260 kg К per ha for intensive silage. Herbage yield is controlled by the amount and timing of nitrogen fertilizer applications. The major mineral content depends on herbage maturity within the growth cycle; both phosphorus and potassium contents fall with declining crude protein concentrations.

Nitrogen fertilizer generally increases both magnesium and sodium concentration whilst potassium application decreases both. The overall effect of combined applications is to minimize changes. In the critical spring and autumn periods, herbage dry-matter intakes may be as important as magnesium content and availability when assessing the risk of hypomagnesaemia in the grazing cow.

Fertilizers, including phosphorus, even in the long term, have little effect on the calcium and phosphorus contents of herbage. Nitrogen and phosphorus concentrations are significantly ocrrelated in grazed herbage, silage and hay. If environmental or economic policies were to result in a reduction in the crude protein content of grazed herbage from ca. 250 to ca. 200 g/kg dry matter, the phosphorus intake of a cow giving 30 kg milk per day would fall by 0·5 g/kg dry-matter intake. This, together with any desirable additional magnesium, should preferably be given as an oral mineral supplement rather than by attempting to modify the mineral content of herbage.

Two experiments were carried out to investigate the effect of restricted suckling and milking regimes on milk yield, milk composition and calf growth. Experiment 1 was carried out in temperate conditions in the United Kingdom and experiment 2 under tropical conditions in Mexico. In experiment 1 a Latin rectangle (change-over) design with 3-week periods was used with eight Holstein Friesian cows suckling their Simmental-sired calves. Saleable milk yield (SMY), sucked milk (CSM), milk composition and calf performance were studied. The treatments were: once a day milking (a.m.) with suckling immediately after (1χAM); once a day milking (a.m.) with suckling p.m. (1χPM); twice daily milking with suckling after a.m. milking (2χAM); twice daily milking with suckling after each milking (2χ2χ). The cows were offered maize silage ad libitum and 4·3 kg dry matter (DM) per day of rapeseed meal plus minerals and vitamins. The calves had ad libitum access to concentrates (165 g crude protein (CP) per kg DM) and wheat straw. In experiment 2, 11 B. indicus χ B. taurus cows, suckling their Brahman-sired calves were used in an experiment with the same treatments and experimental design. Cows were offered star grass (Cynodon nlemfuensis) hay ad libitum and 4.0 kg DM per day of concentrate (117 g CP per kg DM). The calves had ad libitum access to concentrate (151 g CP/kg DM), star grass hay and Ramon leaves. For 1χAM, 1χPM, 2χAM and 2χ2χ respectively in experiment 1, the total milk yields (TMY = SMY + CSM) were 17.9, 18.0, 16.7 and 19.5 kg/day (s.e.d. 1.11) and SMY represented 0.70, 0.45, 0.77 and 0.53 of TMY. Corresponding results for experiment 2 were 6.0, 6.2, 7.0 and 7.1 kg/day (s.e.d. 0.32) and 0.69, 0.45, 0.78 and 0.61. Effects of treatment on milk yield and composition were consistent with the feedback inhibitor of lactation theory. It was concluded that different milking and restricted suckling patterns can be used to manipulate saleable milk production and calf growth. Holstein Friesian dairy cattle in a restricted suckling system without the calf presence at milking, behaved similarly to zebu-crossbred cows by reducing milk let down at milking.

In a lifetime study of spring-born cattle in a 20-month beef system the effects of production factors on carcass characteristics were examined using 302 serially slaughtered animals born in three consecutive years. A multifactorial design was used with three animal factors — maturity (early maturing Hereford crosses v. late maturing Charolais crosses), sex (heifer v. steer) and method of rearing (suckled calves v. bucket-reared calves). After an initial rearing period, feeding treatments were imposed during the subsequent winter period, followed by the imposition of two sward heights (low 6 to 8 cm and high 8 to 10 cm) during the subsequent grazing season. An initial representative group of 16 cattle was slaughtered at the start of the grazing season and most of the remaining cattle were subsequently slaughtered off grass at three randomly allocated slaughter times, on average 67, 110 and 154 days post turn-out. Interactions between the main production factors were not significant with the exception of slaughter date with winter feeding levels for fat in rib joint and weight of saleable meat, and slaughter date and sex for live weight, carcass weight and weight of saleable meat. Breed type, sex and method of rearing affected the weight of saleable meat off grass by 14·7, 14·8 and 5·6 kg respectively. The influence of the winter feeding treatments on the weight of saleable meat was small by the time the final group were slaughtered. Sward height had a transient effect on weight, condition and carcass composition, the effects becoming less evident as the grazing season progressed. The effect of delaying slaughter had the largest and most significant influence on carcass composition of all the production factors studied, although changes in body composition between slaughter dates were relatively slow.

Three experiments were undertaken to assess the Zimbabwean donkey. In the first study, 191 male and 144 female working donkeys from Matopos, Nkayi and Matobo districts were weighed. Age, sex and coat colour were recorded and heart girth, umbilical girth, body length and height were measured. There were no differences (P > 0⋅05) in live weight, 142 and 141 kg, heart girth 115 and 115 cm, body length 89 and 90 cm and height 105 and 105 cm between males and females. This suggests that draught potential might be similar between the sexes. Heart girth was the best single predictor of live weight: live weight (kg) = heart girth (cm)2⋅83/4786 (R2 = 0⋅86). Donkeys were similar in size to others in Africa. In the second study, the voluntary dry-matter intake (DMI) of a poor quality hay was measured for 35 days in nine male (mean live weight 150 kg) and nine female donkeys (142 kg) allocated to one of three treatment groups: water available ad libitum, or given every 48 h, or every 72 h. There were significant differences in daily water (P < 0.001) and DMIs (P < 0.05): 8.5, 4.9 and 5.1l and 3.1, 2.8 and 2.7 kg for the three treatment groups, respectively. However even with restricted access to water, donkeys maintained a relatively high DMI. In the third experiment a 3 Х 3 Latin square was designed with three teams of four male donkeys each, either working (5 h/day) I no access to food (5 h/day); not working/no access to food (5 h/day) or not working/access to food 24 h/day, for 63 days. For working and non-working donkeys, there were no significant differences (P > 0.05) in DMI, DM apparent digestibility and mean retention time (MRT) of hay. Time of access to food did not influence DMI. The apparent lack of response was attributed primarily to the poor quality of the hay.

With a view to comparing previous findings from experimental journeys, with observations during commercial transport of sheep, hormonal and other physiological data were gathered during three long journeys (866 to 1178 km), all of which involved a sea crossing (1 h 45 min to 8 h 55 min). One was a commercial journey from the United Kingdom to continental Europe and the other two, which were simulated commercial journeys under the control of the investigators, were from a Scottish island to Cambridge. In all journeys there was a break in lairage (duration 13 to 24 h). The stocking rate on the commercial journey (0·17 m2 per sheep for shorn sheep of 35 to 37 kg body weight) was less generous than previously used in experimental journeys. In all journeys there was an apparent increase in plasma concentration of cortisol soon after loading and commencement of travel, with subsequent decline. Transient increases in beta-endorphin and prolactin were also observed but changes in creatine kinase were not obvious. Haematocrit showed slight evidence o f a decline during the journeys. These findings are generally similar to those obtained in experimental journeys and there was no evidence of a hormonal response to sea conditions during the ferry crossings. When transport was resumed after a period of rest with food and water off the vehicle, the physiological responses were less marked than they had been during the first stage of the journey. Under the circumstances observed, long journeys of the type commonly practised commercially probably do not of themselves pose a major welfare challenge.

This study examined whether work applied at different stages of lactation had any effect on reproduction of cows under two feeding regimes. Twenty-four F1 crossbred dairy cows (12 Friesian × Boran and 12 Simmental × Boran) were allocated one of two diets (H + 3: natural pasture hay + 3 kg concentrate per day; and H + 5: natural pasture hay + 5 kg concentrate per day) and one of three work treatments — starting 45 days (D45), 90 days (D90) and 135 days (D135) post partum — using a principal component analysis score based on milk yield, live weight, calving interval and parity. Cows pulled sledges for 50 days (pull = 108 N per 100 kg live weight). Over the experimental period of 315 days, cows on diet H + 5 travelled a similar distance and produced amounts of fat-corrected milk (FCM) similar to those of cows on diet H + 3. Total intake of dry matter per kg live weight 0·75 was higher for cows on diet H + 5 than for cows on diet H + 3 and was similar across work times. Hay dry-matter intake was greater for the H + 3 group than for the H + 5 group at 180 days post partum and thereafter. Cows on diet H + 5 lost less weight in early lactation and gained more in mid and late lactation than cows on diet H + 3. During the work period, live-weight change was similar across diets but it was different between work treatments D45 and D135. The interval from calving to conception decreased by 63 and 101 days when start of work was delayed from D45 to D90 and from D45 to D 135, respectively. Output/input ratios of metabolizable energy equivalents were 0·35 for H + 3 and 0·37 for H + 5 diet, and 0·34, 0·37 and 0·40 for work times D45, D90 and D135, respectively. These results indicate that work started in early lactation significantly increased days to conception and decreased overall productivity of lactating working cows. Farmers must weigh the relative importance and cost of delayed ploughing against those of delayed oestrus or against the cost of borrowing draught power.

Compared with small groups, housing in large groups offers the pig more total available space, resulting potentially in an increased degree of control over its (micro) environment. For the producer, large groups require fewer pen divisions and offer more possibilities for the sharing of resources such as feeders and drinkers. However, whilst large groups may offer benefits to higher ranking animals in the group, there may be serious disadvantages for those further down the social hierarchy, who also need to compete for access to resources. This study investigated the interactive effects on welfare of food availability (one single space hopper per 20 or per 10 pigs) and group size (20, 40 or 80 pigs per pen), at constant stocking density (0·55 m2 per pig) in part-slatted pens. Groups provided with two feeding spaces per 20 pigs were less active than groups with one feeding space per 20 pigs. The number of aggressive interactions per pig at the food trough was not affected by group size but decreased with number of feeder spaces per 20 pigs. The number of skin lesions increased with group size. Average daily gain in the first half of the finishing period was negatively influenced by group size and positively by number of feeding spaces. No effect on weight gain was found subsequently. Within-group variation in growth was not affected by group size or number of feeder spaces. No differences between treatments were found in the number of pigs removed for health reasons. Interactive effects of the two treatments were found on some behaviours but not on any of the performance variables measured. It is concluded that, from a welfare point of view, the number of pigs per feeder space should be lower than 20, although performance levels appear acceptable at 20 pigs per feeder. Further research will have to identify whether the effects of group size on general aggression is common to all finishing pig systems, or whether the presence of straw can serve as a mitigating factor.

This study was conducted to determine whether carotenoid pigments can act as biomarkers of grass feeding to trace lamb production systems. Three production systems were compared: G = grazing (72 lambs), S = stall-feeding (26 lambs), and GS = grazing period followed by a stall-feeding period (27 lambs). Presence of carotenoids in tissues was evaluated by plasma concentration and reflectance spectrum of subcutaneous caudal adipose tissue. Plasma carotenoid content was measured during the grazing period for G and GS lambs, at the end of the grazing period for GS lambs and at slaughter for G, S and GS lambs. Reflectance spectrum of adipose tissue was measured at slaughter for 38 G and 26 S lambs. We collected 135 G and 26 S blood samples. Carotenoids were detected in 97% of the G blood samples, whereas they were not detected in 93% of the S blood samples. Plasma carotenoid content of all the GS lambs decreased during the stall-feeding period. Mean reflectance spectra of adipose tissue of G and S lambs differed between 450 and 510 nm, which corresponds to light absorption by carotenoids. We performed a mathematical analysis of the spectrum in order to quantify absorbance in this zone and to propose an index that can be used in the meat industry to trace animal production systems. This method was less discriminating than plasma carotenoid analysis, as there was some overlapping in the frequency distribution of the traceability index for G and S lambs that concerned 19% of the lambs. Sensitivity of the two methods to bias and applicability to cattle are discussed.

The work performance of two teams of four donkeys (heavy, 680 kg and light, 460 kg) and one pair of Jersey crossbred oxen (646 kg) was compared when they ploughed 4 hi day on four types of soil (clay, redsoil, sandy soil and sandy clay) using two types of plough, a conventional ox plough (40 kg) and a lighter prototype, the ‘Walco’ plough (32 kg) on an experimental farm. Work parameters were also measured with farmers’ cattle and donkey teams ploughing on f arms in Matobo and Nkayi districts. Working speed, power and effective field capacity (ETC) were higher for the ox-team (1·03 m/s, 920 W and 14·5 h/ha for the conventional plough and 0·99 m/s, 745 W and 13·9 h/hafor the Walco plough) and the heavier donkey team (0·87 m/s, 689 W and 14·2 h/hafor the conventional plough and 0·87 m/s, 787 W and 17·3 h/hafor the Walco plough) than for the lighter donkey team (0·59 m/s, 461 W and 22·1 h/hafor the conventional plough and 0·64 m/s, 445 W and 23·4 h/hafor the Walco plough). Expressed as a proportion of live weight or metabolic live weight there were no significant differences in draught forces exerted between teams but power output per unit live weight was greater in the ox-team than in the light donkey team but similar to that in the heavy donkey team. The Walco plough required a lower force (742 N) to operate than the conventional plough (816 N) but apart from this did not have any marked advantages over the conventional plough. On-farm, team sizes of donkeys varied from three to seven animals (team weight 340 kg to 1007 kg) and cattle team sizes from two to four animals (team weights 558 to 1709 kg). Regardless of team number, the heavier teams tended to out-perform the lighter teams (speed range 0·63 to 1·08 m/s, power 395 to 1136 W, EFC 9·1 to 25 h/ha)) with one exception, a well trained team of two oxen (team weight 879 kg, speed 1·02 m/s, power 775 W, EFC 9·1 h/ha). Donkeys tended to plough at a slower pace than oxen, with a lower power output, although when weight differences between teams were equalized (four heavy donkeys compared with two oxen), then there was little to chose between the species. Results suggested that teams of three or more donkeys can effectively be used for ploughing on the soils tested. The results highlighted the importance that team live weight and training/experience have in determining work performance.

Performance, water intake and feeding behaviour of two groups of 30 (trial 1), 40 (trial 2) or 50 (trial 3) weaned pigs offered either pellets or meal of the same formulation were compared.

Average daily weight gains (ADG) were higher for pigs given pellets rather than meal in trials 2 (413 v. 363 g/day,

P < 0·001) and 3 (356 v. 324 g/day, P < 0·05). Mean daily water intake (DWI) was higher with meal than with pellets but only during trial 1 (2·31 v. 1·65 I/day, P < 0·01).

The occupation time (ОT) and the number of animals using the feeder simultaneously (N) were higher when pigs were given meal rather than pellets, whatever the animal density: trial 1: 82·6 v. 69·9% (P = 0·05) and 3·8 v. 2·3 (P < 0·01); trial 2: 90·9 v. 77·9% (P > 0·05) and 5·2 v. 3·1 (P < 0·01); trial 3: 96·2 v. 83·6% (P < 0·05) and 5·9 v. 3·8 (P < 0Ό1). When using pellets, ОT and N were always significantly lower during the night than during the day but when using meal in groups of 40 and 50, ОT during the night was almost as high as during the day.

The greater the group size, the lower were ADG (both diets) and DWI (only with meal) and the higher were ОT and N (both diets). Furthermore, significant linear and curvilinear regressions of DWI, ОT and N according to time were calculated.

In conclusion, pigs need more time to eat meal than to eat pellets. Thus the number of pigs per feeder has to be adapted to the food presentation. Too high a number of pigs per feeder impairs feeding behaviour and eventually welfare, by preventing preferential diurnal feeding activity and this may affect productivity.

Effects of heat load and of photoperiod on lactation performance were evaluated using milk test data of three Israeli Holstein herds over a period of 3 years, from 1994 to 1996. All together 2209 cows, with 28029 milk records, were included. Photoperiod effects were examined as associated with day length and daily changes in day length and heat load index was formulated as a function of the seasonal day and night ambient temperatures, to account for the heat load effect. The regression model included effects of cow, herd, year, lactation number and days in milk in addition to the seasonal effects. The dependent variables were milk yield and fat, protein and lactose concentrations. Milk yield was affected by both photoperiod and heat load, with the peak photoperiod effect in May and amplitude of 3·1 (s.d. 0·9) kg/day and negative heat load effect of-1-8 (s.d. 0·4) kg/day at its peak. Protein concentration was affected by photoperiod, with the peak effect in January (amplitude of 1·7 (s.e. 0·5) g/kg) but not by heat load (-0-2 (s.d. 0·6) glkg). Fat concentration was affected primarily by heat load (-3-4 (s.d. 0·7) g/kg), with a photoperiod effect which peaked in October (amplitude of 1·8 (s.d. 0·8) g/kg). Lactose concentration was affected by both environmental factors to a lesser extent (photoperiod amplitude of 0·6 (s.d. 0·2) g/kg and heat load effect of-0-03 (s.d. 0·16) g/kg). Comparison of the predicted seasonal effects on milk yield and composition with the annual fluctuation in the national herd showed a good match of the predicted effects with the national observations. It is concluded that while heat load relief may be beneficial, manipulation of the photoperiod may induce adverse effects on milk yield and composition.

A study was conducted to determine whether sheep form conditioned flavour aversions (CFAs) or preferences (CFPs) for food flavours associated, respectively, with excessive or appropriate concentrations of sulphur (S) and also whether the rate of formation and strength of CFAs and CFPs are dependent on the animal's initial S status or the level of administration of S. In experiment 1, 48 mature ewes were conditioned to associate a new food containing a novel flavour with an infusion of S delivered intra-ruminally, or the same food containing another novel flavour with an infusion of distilled water. The same flavours were then used in experiment 2. At the end of each conditioning period, the relative preference for the two flavoured foods was determined by measuring the amount of each food ingested during a two-choice, 20-min preference test. Experiment 1 consisted of two phases. In phase 1 each conditioning period lasted for 5 days and was repeated four times, whereas in phase 2 the conditioning period lasted for 8 days and was repeated three times.

In experiment 1 the sheep were initially in an S-adequate state. In experiment 2, the sheep were re-randomized to treatments and started in an S-depleted state. The conditioning periods also lasted for 8 days and were repeated three times. There was no evidence to support the hypothesis that sheep develop CFAs or CFPs to food flavours associated with S doses in phase 1 of experiment 1. In phase 2, however, sheep formed CFAs towards the food with the flavour they had come to associate with administration of high levels of S. Repeated exposure to the flavour associated with high levels of S led to stronger aversions and there was an interaction between the S dose level and conditioning periods, indicating that the rate of development of these CFAs was highest for the highest S dose levels. The differences between results of phase 1 and 2 were probably due to the different numbers of reinforcements and different intervals between specific flavour/dose associations.

In experiment 2 there was no evidence for the development of CFPs or CFAs to food flavours associated with S doses. The apparent indifference of the sheep to S was probably due to their responding more to their previous experience of the food flavours than to their S status. Spearman rank correlations on flavour preferences indicated that conditioned flavour responses formed in experiment 1 persisted in individual sheep when they were allocated at random into their new treatments in experiment 2 and influenced or masked the formation of new associations. This demonstration of ‘carry-over’ effects highlights the importance of considering an animal’s previous experience of flavours and their associations with post-ingestive consequences when coming to conclusions concerning current development of CFAs and CFPs. These results may also have more general implications for feeding studies in animals that are randomized into treatment groups without regard to their previous feeding experiences.

Economic values for average ad libitum food intake capacity (FIC) were estimated with two different linear-plateau models. One model based on a constant minimum fat to protein deposition ratio (Rmin). The other model relied on a constant minimum marginal ratio between fat and protein deposition (MR). Economic values were used to define aggregate genotypes where the driving variables of the growth models were considered as traits. The consequences of a possible implementation of such aggregate genotypes were evaluated with a comparison of the expected selection responses for the different traits.

Economic values for the traits under the two models indicated the same direction of selection and differed only slightly in their magnitude. For a FIC below its optimum, FIC had a positive and Rmin or MR a negative, economic value. In this situation the maximum protein deposition rate Pdmax had no influence on the production costs and therefore an economic value of zero. Selection emphasis is then mainly put on FIC which leads to an increase in average daily gain (ADG). If FIC is above its optimum, economic values for FIC were negative, positive for Pdmax and equal to zero for Rmin or MR. Practically no differences between the selection responses under the two growth models were observed.

The use of growth models to estimate economic values for FIC allowed to attribute a positive economic value to this trait if it is below its optimum. This is not possible when economic values are estimated with an economic production model.

A comparison was made of sow lying behaviour, piglet aggregation behaviour and performance in crates (no. = 10) and oval pens (no. = 8). Twenty-four hour time-lapse video tapes were made and a farrowing day defined for each sow by noting the 24-h period during which the sow gave birth (09:00 to 09:00 h). Each sow and litter, balanced for parity and time of year, was analysed from 12:00 to 20:00 h during the 24 h immediately following this day. The following analyses were conducted: (1) the number and type of lying behaviour; (2) each litter was scanned every 10 min and at each lying event the number of piglets within 0·3 m of the sow noted; two indices were then calculated, based on the mean of the 10-min scans and the mean for the lying events, for each sow expressed as a proportion of the total litter size. Any dead piglets were removed and cause of mortality established by post-mortem examination. Production data showed that there was no significant difference between litter size at birth and at weaning but overall level of mortality was higher in the pen compared with the crate due to crushing. The majority of crushing events occurred in the first 3 days after farrowing (crate 75%; oval pen 64%). The total number of lying events and related posture changes did not differ between systems; only ‘roll-over’ events (movement from lateral on one side to the other within 10 s) were higher in the oval pen. There was no difference in the proportion of aggregating piglets at the 10-min scans or the lying events. Increased crushing mortality in the pen does not appear to be due to the aggregation behaviour of piglets but to the increased number of sow roll-over behaviours.

In data collected for feeding behaviour analysis, feeding events are generally separated by many very short to very long intervals during which no feeding occurs. When feeding is clustered in bouts, a meal criterion (that is the longest non-feeding interval accepted as part of a meal) must be estimated before events can be grouped into meals. Until recently, three methods that estimate quantitative meal criteria were available. These methods consist of fitting a ‘broken-stick’ (two straight intersecting lines, both with a negative slope) to the frequency distribution (method 1), the loge-transformed cumulative frequency distribution (the log-survivorship curve; method 2) or the loge-transformed frequency distribution (method 3) of intervals between events. Recently, new methods have been proposed that fit either two (method 4) or three (method 5) Gaussians to the frequency distribution of loge-transformed interval length (log-normal models). We compare the estimates obtained with these five methods when applied to a data set of 79575 intervals between visits to food dispensers. These were recorded with 16 lactating cows during an average period of 156·6 (s.d. 51·5) days per cow. Meal criteria were estimated as 1·9, 6·0, 7·5, 32·4 and 49·1 min by methods 1 to 5, respectively. Estimated daily number of meals ranged from 5·7 to 12·1 per cow and estimated average meal size from 4·0 to 8·4 kg. The observed probabilities of cows initiating feeding in relation to time since feeding last showed best agreement with the predictions of the log-normal models. We conclude that the first three methods do not, while log-normal models do, have an adequate biological basis for a clear interpretation of the estimated meal criteria. Log-normal models are, therefore, the most promising for estimating meal criteria in cattle and probably in other species as well.

Resistance to naturally acquired gastro-intestinal (GI) nematode parasite infections (predominantly Haemonchus contortus) was studied in 166 Red Maasai, 230 Dorper and 294 crossbred (Red Maasai Х Dorper) ewes in the sub-humid coastal region of Kenya. Live weights (LWT), blood packed-cell volume (PCV) and faecal egg counts (PEC) were recorded at mating, 3 months post mating, 1 week before lambing and 1, 2 and 3 months post lambing for four separate lambings that took place between 1993 and 1996. The Red Maasai ewes were more resistant to GI nematode infections than Dorper ewes as shown by their significantly lower FEC and significantly higher PCV at most of the sampling times over the reproductive cycle. The breed difference for FEC was significant in the lactating ewes but not in the non-lactating ewes. At most sampling times, the crossbred ewes were as susceptible as the Dorper ewes in terms of both PCV and FEC, particularly at the 1 and 2 month post-lambing samplings. Resistance was also manifested by a lower proportion of ewes having to be treated with an anthelmintic and a lower mortality rate in the Red Maasai than the Dorper. The Red Maasai ewes were significantly lighter by about 1 to 2 kg than the Dorper ewes at all sampling times. There was a significant increase in FEC and decrease in PCV over the first 2 months of lactation in lactating ewes compared with non-lactating ewes. This peri-parturient increase in FEC occurred in both breeds and the crossbreds but was more marked in the susceptible Dorper ewes.

Three hundred and thirty (330) records from 363 lactations and 104 cows born between 1979 and 1991 from crossbreeding Holstein-Friesian (H) bulls with H, Ngaoundere Gudali (G) and Holstein × Gudali F1 (H1G1) cows, Montbeliard (M) bulls with G and Montbeliard × Gudali Fl (M1G1) cows and M1G1 bulls with M1G1 cows and raised in the Dairy Herd Unit of the Wakwa Animal and Veterinary Research Station in the sub-humid highlands of Cameroon were analysed to investigate the effects of genotype and environment on lactation and reproductive traits. Fixed effects of genotype season and year of calving parity and age of cow at calving were studied. Lactation milk yield (LMY), lactation length (LL), annualized milk production (AMP), calving interval (C1), dry period (DP) and age at first calving (AFC) were amongst the traits analysed. F1 crosses (H1G1, M1G1), backcrosses (¾ Holstein — ¼ Gudali; ¾ Montbeliard — ¼ Gudali) (H3G1, M3G1) and F2 crosses (MGF2) were compared. Results showed that H1G1 cows were proportionately 0·49 and 0·23 better than their corresponding backcross in LMY and AMP, respectively, while M1G1 cows were proportionately 0·12 and 0·24 inferior to M3G1 in these traits. M1G1 were proportionately superior to MGF2 in LMY (0·05), AMP (-0·04) and AFC (-0·14). M3G1 were superior (0·18 to 0·19) to MGF2 in LMY and AMP. H1G1 were consistently superior to M1G1 for most traits, suggesting that H1G1 may be better than M1G1 for dairy production.

This paper demonstrates how interactions between host genotype for resistance to an infectious disease and the epidemiology of that disease can have large influences on animal productivity and hence on breeding goals for domestic livestock. This is illustrated for the case of gastro-intestinal parasitism in lambs. A model of the parasite infection was developed to include between-animal variation (genetic, permanent and temporary environmental) for live-weight gain, food intake, larval establishment rate in the host, worm fecundity and worm mortality rate. Achieved live-weight gain was defined as the sum of potential live-weight gain under conditions of no parasite infection, a trait correlated with food intake and growth-rate reduction due to the infection. The reduction in growth-rate was calculated from cumulative larval challenge and cumulative worm mass in the lamb. Genetic parameters were then estimated for the output traits of observed live weight at 6 months of age, growth rate reduction and faecal egg count. Model parameters were chosen so that the output means and heritabilities for faecal egg count and live-weight gain mimicked field data for Scottish Blackface lambs and growth-rate reductions were proportionately 0·25 , on average. The model predicted a weak phenotypic correlation (mean = -0·10) between observed live weight and faecal egg count, the indicator of resistance but a stronger favourable (negative) genetic correlation between these traits (mean = -0·27). The severity, or epidemiology, of the disease greatly influenced the results - the genetic correlation between observed live weight and faecal egg count strengthened from -0·02 to -0·46 as the disease severity changed from mild to severe. Selection for reduced faecal egg count resulted in large correlated increases in live-weight gain, more than twice that predicted by quantitative genetic theory, due to the reductions in growth rate losses as the disease challenge to the animals decreased. Conversely, selection for increased live-weight gain resulted in reductions in faecal egg count close to expectations. This asymmetry of selection response emphasizes the epidemiological benefits obtainable from selection for resistance to infectious chronic diseases - such selection will result in improvements in both animal health and productivity not seen when selection is for improved productivity, alone. Breeding goals should be designed to take account of such effects.

The purpose of this study was to examine the importance of the genetic and maternal environmental factors influencing the 12-week weight (12WW) of Welsh Mountain lambs and to estimate genetic parameters for this trait. Records of 8880 Welsh Mountain lambs born between 1979 and 1995 were analysed. The records were from the nucleus flock of the CAMDA cooperative breeding group. In this flock selection of replacements had been based on a multi-trait index incorporating lamb growth and maternal ability as important objectives and 12WW as one of the selection criteria. Twelve models were examined, all including direct additive genetic variance and various combinations of genetic and environmental maternal effects. The most appropriate model was chosen based on log-likelihood ratio tests. It included appropriate fixed effects, and direct additive, maternal additive, maternal permanent environment and maternal common environment (litter) random effects that defined proportionally 0⋅21 (h2), 0⋅09 (m2), 0⋅06 (pe2) and 0⋅18 (ce2) of the phenotypic variance. Ignoring the additive maternal effect resulted in inflated estimates of direct heritability and ignoring the environmental effects associated with dam inflated the direct and maternal heritabilities. There was no correlation (P < 0⋅05) between the additive direct and additive maternal effects. Additive direct and maternal breeding values increased by 0⋅12 (s.e. 0⋅006) kg/year and 0Ό3 (s.e. 0⋅003) kg/year respectively. The results demonstrate the effective incorporation of selection index methodology in the context of a hill sheep flock and also the importance of several categories of maternal effects.

Genotype with nutrition interactions in carcass composition and meat quality traits were examined by testing pigs from four selection lines and a control line on isoenergetic diets, which differed in lysine: energy content. The selected lines resulted from seven generations of selection for high daily food intake, lean food conversion ratio (LFC) and lean growth rate on ad-libitum or restricted (LGS) feeding regimes in a Large White population. There were 128 pigs in the study, with 24 pigs per selection line and 32 pigs from a control line. During performance test, 30 to 90 kg, pigs were offered one of three isoenergetic diets, 14·0 MJ digestible energy (DE) per kg dry matter, which differed in ileal digestible lysine: digestible energy (A: 0·40 , C: 0·76 and E: 1·12 g lysine per MJ DE) on ad-libitum or restricted (0.75 g/g ad-libitum daily food intake) feeding regimes.

For the majority of performance test, carcass composition and meat quality traits there was no evidence of a genotype with diet or genotype with feeding regime interaction. The selection line with feeding regime interactions for average daily gain, daily food intake and rates of lean and subcutaneous fat deposition were primarily due to no feeding regime effect for the LFC selection line. Selection for high LFC had reduced ad-libitum daily food intake to such an extent that it was not significantly different from daily food intake on a restricted feeding regime, unlike other selection lines in the study. A selection line with feeding regime interaction was detected for muscle рH24h and muscle reflectance, which resulted from the LGS selection line. LGS pigs offered food ad libitum had higher muscle рH24h and lower muscle reflectance than LGS pigs given food at a restricted level, while there was no effect of feeding regime for the other selection lines.

The general absence of genotype with nutrition interactions for traits measured in the study indicated that the ranking of genotypes for performance test traits, carcass composition and meat quality traits will not be dependent on diet or feeding regime. Genotype specific nutritional inputs will also not be required for identification of pigs of high genetic merit, within a genotype. However, diet and feeding regime had significant effects on carcass composition and meat quality traits, such that the estimated mean value of a genotype will be dependent on the diet or feeding regime used to evaluate the genotype.