New methods of design and analysis for mixed grazing experiments are proposed and compared with previously reported designs. In general, with previous designs the effects of mixed grazing per se were confounded with other factors. The concepts of equality of grazing pressure and of livestock equivalents are examined and criticized when used as starting points for mixed grazing experiments. Two year's results of a mixed grazing experiment with cattle and sheep are analysed and provide evidence that mixed grazing is beneficial to both species in terms of production per animal. A simple economic analysis shows how the price ratio between the value per unit weight gain of the two species can be used to decide on the area of financial benefit from mixed- as opposed to single-species enterprises.

Effects on cow reproductive performance, of cow age, parous state, body weight and body-weight change over the breeding season were examined using 6490 annual records from indigenous cows in Botswana.

Calving percentage rose from 69% at 2·5 yr of age to a maximum of 82% at 6 to 7 yr and declined in cows over 8 yr of age. Heifers and previously non-parous cows had a calving percentage of 85%; 8, 18 and 30% higher respectively than parous cows that had calved at the beginning, middle and end of the previous calving season. Cows weighing less than 300 kg at the beginning of the mating season achieved a 50% calving. This rose steadily to 85% as body weight increased to 430 kg.

Cows that lost weight over the mating period achieved a 67% calving, while gains of 20 kg raised this to 76%. Increased weight gains thereafter had little effect on calving percentage. In all cases, as percentages increased, days to conception decreased in a similar manner.

Under these range conditions in Botswana, animals least likely to achieve high calving percentages were young cows; cows which calved previously at the end or middle of the calving season; cows less than 310 kg in weight; and cows gaining less than 20 kg body weight during the mating season.

Measurements of the live weight and body condition of 105 Scottish Blackface, North Country Cheviot and South Country Cheviot male sheep (rams) per year were made at three locations over a period of 2 years.

A distinct cyclical pattern of change in live weight and body condition throughout the year was apparent in all rams. Maximum values recorded in the autumn were followed by rapid and substantial losses throughout the mating period, with recovery of both weight and condition during the spring and summer months. The amplitude of the annual live-weight curve was of the order of 20 kg (22%) and that of body condition was more than 1 unit.

The patterns of annual change in live weight and of inferred change in body composition of rams are compared with those of ewes, and some of the probable effects on production are considered.

1. Young adult and adult British Friesian female cattle (heifers and cows) which were lactating were individually fed on diets of grass silage ad libitum with supplements of dried grass, dried grass/barley or barley/groundnut in two randomized block experiments.

2. In Experiment I, equal quantities of dry matter (DM) as dried grass in the form of a wafer (W), cob (C) or pellet (P) were given with the silage during weeks 8 to 18 of lactation, to three groups of 12 heifers. Silage DM intakes were respectively 14·2, 14·3 and 15·8 ± 0·43 g/kg live weight per day (P<0·05). Milk yields were 14·0, 15·6, 16·7 ± 0·35 kg/day (P< 0·001). Milk composition and live-weight change did not differ significantly.

3. In Experiment II, five treatment groups of heifers and cows were offered silage with equal amounts of a supplement of either dried grass pellets (treatment 1) or dried grass/barley in the ratios of 2: 1 (treatment 2), 1: 2 (treatment 3), or a barley/groundnut supplement (treatment 4). In treatment 5 the cattle received the same supplement as in treatment 4, but at a 10% higher level. Silage DM intakes for treatments 1 to 5 during lactation weeks 6 to 22 were 8·64, 8·94, 7·96, 6·96, 7·63 kg/day (1, 2>4, P<0·01; 2>5, P<0·05). The intake of digestible organic matter, milk yields and live-weight changes over the whole experimental period were not influenced significantly by treatments 1 to 4, but in treatment 5 the milk was significantly higher in fat, protein and energy content than in treatments 1 to 4. Blood composition was normal and did not differ markedly between treatments.

Incubation with rumen liquor gave a lower rate of release of ammonia and a higher dehydrogenase activity with urea phosphate (UP) than with urea.

Four concentrate diets containing 13 % crude protein, 27% of which was supplied by urea or three different forms of UP, were each given to eight Awassi lambs. With twice-daily feeding (but not five-times daily feeding), a beneficial effect of UP over urea was observed, expressed in lower blood ammonia and urea levels. There was no effect on the pH of rumen liquor.

In a N-balance experiment with 24 lambs, four diets were examined: a basal diet containing 9·5% crude protein and three other diets in which the crude protein content was raised to 13% by addition of soya bean meal, urea or UP. The diets were given twice daily. Urea phosphate and the soya bean meal gave a significant increase in N retention whereas the urea treatment did not. However, the difference in N retention between the UP and urea treatments was not significant. Total volatile fatty acid concentrations in the rumen did not differ significantly between treatments but the ratio of acetic to propionic acids was significantly lower with the urea diet.

1. Young adult and adult British Friesian female cattle (heifers and cows) which were lactating were individually fed ad libitum on ryegrass silage of high (HS) or low (LS) digestibility with one of two levels of a supplement of pellets of dried grass (H or L) in a 2 × 2 factorial experiment with three heifer and seven cow replicates.

2. The percentages of digestible organic matters in the dry matter (DM) in vitro were respectively 64·4, 57·5 and 69·0 for forages HS, LS and and the dried grass. The HS crop, however, was significantly lower in DM content, and after ensiling with formic acid additive had a higher lactic and total acid content than the LS crop.

3. The dry-matter intake of the less acid silage LS was greater than that of HS (P<0·05) although the dry-matter digestibility of the LS diets was on average 6 units lower than the HS diets. The intakes of digestible dry matter (DDM) and digestible organic matter were greater (P<0·05) in mid lactation when HS was fed. DM and DDM intakes were significantly increased by the higher level of feeding of the dried grass supplement.

4. The yield, composition and energy content of milk did not differ between silages but the yield and protein content of the milk increased significantly at the higher level of supplement feeding. The milk yields were respectively 19·35, 17·54, 19·49 and 17·97 ± 0·505 kg/head per day for treatments HSH, HSL, LSH and LSL on these all-grass diets over lactation weeks 4 to 20. Live-weight loss was greater (P<0·01) on the LS diets. Blood composition was normal and did not differ markedly between treatments.

1. Some criticisms of the classical approach to constructing a selection index are advanced. This approach (the economic model) is contrasted with an alternative one (the biological model) which is derived from the concept of the biological efficiency of production of lean tissues. The selection objective which is proposed from the biological model is the improvement of lean tissue feed conversion. The most important single means of achieving this is increasing the lean tissue growth rate.

2. The approaches were compared in three studies: (a) the effects of errors in economic and genetic parameters of the economic index; (b) phenotypic relationships between biological objectives and other measures of performance; (c) a theoretical model based on the utilization of metabolizable energy.

3. In a fixed situation the results were similar for both models, but the main advantage of the biological model is that it gives good indications of what happens, and what selection policies should be, in different situations. In addition, lean tissue feed conversion and lean tissue growth rate are closely related to concepts widely applied in biology, and their use as selection objectives should be helpful in enabling workers in many disciplines to make use of each other's knowledge.

Dissection data for 643 steer carcasses of 15 breed-type × feeding system groups were used to examine the distribution of intermuscular fat (IF) and subcutaneous fat (SF) depots between standardized commercial joints.

The increase in weight of IF and SF in each joint relative to the corresponding depot weight in the side was examined using the allometric equation. Pooled within-group growth coefficients for both IF and SF were lowest in the distal limb joints increasing inwards to the joints of the rib and loin regions. They were highest for the thin flank joint.

Group means for weight of IF and SF in each joint were adjusted to equal total IF and SF weight respectively using the pooled growth coefficients. Statistically significant but relatively unimportant differences were recorded between groups in the adjusted means for all joints tested. The largest differences occurred for the top piece and were 0·39 and 0·40 kg (in one side) for IF and SF respectively. The stability of regression equations between groups for predicting the percentages of IF and SF in the side from the respective percentage in each joint was also examined. Joints which gave the least precise predictions of IF (shin and leg) and SF (shin, leg and clod and sticking) had the most unstable prediction equations. The equations for the other joints differed little between groups.

Ten Landrace × (Landrace × Large White) young female pigs (gilts) were allocated to each of three growth rate treatments so that they attained 73 kg live weight at 135, 160 or 190 days of age. At 73 kg live weight the gilts were introduced to a vasectomized boar for 30 min each day, and were subsequently mated at the second oestrous period. The interval from boar introduction to puberty was 15·2 and 19·0 days respectively for gilts having first boar contact at 190 and 160 days of age, these intervals being significantly shorter (P<0·05) than the 34·3 days for the 135-day group. However, the mean ages at puberty of the 135- and 160-day groups (169·4 and 178·2 days respectively) were not significantly different but these gilts were significantly younger at puberty than the 190-day group (205·3 days). There were no significant differences between treatments for gilt live weight at puberty or first litter size.

A Piétrain boar was placed on each of six farms where the terminal sire was a Large White and the breeding females were either Large Whites or Large White × Landrace. Cooperators were requested to obtain 10 litters by each boar and record their performance to slaughter at 64 kg live weight. Farrowing rate to first service was relatively higher for sows mated with Large White boars but not significantly so. Pietrain-cross piglets were heavier at weaning (7·5%) but breed of boar did not influence other litter traits or age of progeny at slaughter. Pietrain crosses had higher carcass yields (2·4%), shorter carcasses (2·5%) and larger eye muscles in cross-section (10·6%) and in commercial evaluations relatively more were placed in the highest grade.

Two castrated male pigs from each of 620 litters were fed ad libitum to 90 kg market weight at three stations. The pigs represented 20 three-breed crosses produced by mating Yorkshire, Landrace, Lacombe, Hampshire and Duroc sires to Landrace-Yorkshire, Hampshire-Landrace, Large Black-Lacombe, Large Black-Landrace, Duroc-Lacombe and Duroc-Yorkshire dams. The data on feed conversion, average daily gain, age at slaughter, backfat thickness and area of loin eye muscle were analysed by least-squares.

Within breed cross of dam, pigs sired by Hampshire were consistently superior in feed conversion, carcass quality and in 3 crosses out of 5 had the fastest growth rate during the fattening period. They were, however, the oldest at 90 kg live weight. Pigs sired by Duroc ranked second in carcass quality and growth rate, whereas those sired by Landrace had the slowest growth rate. The pigs produced by Hampshire-Landrace sows were superior in carcass quality but inferior in feed conversion and growth to those from sows of the other five crosses.

In descending order, the four highest ranking crosses based on an index combining average daily gain, backfat thickness and feed efficiency were Hampshire × (Landrace-Yorkshire), Hampshire × (Duroc-Lacombe), Duroc × (Landrace-Yorkshire) and Hampshire × (Large Black-Landrace).

Carcasses of Piétrain-cross pigs slaughtered at 64 kg live weight and purchased by retail butchers were accompanied by questionnaires aimed at obtaining an appraisal of them relative to the butchers' normal purchase. Consumer reaction to loin chops from Pietrain crosses and contemporaries sired by the Large White was determined by panel—, household- and shop-testing respectively. Retail butchers showed a strong preference for Pietrain-cross carcasses on lean content but not shape and few considered that the muscle tissue had defects. In panel— and household tests participants showed a strong preference for Pietrain-cross chops on their appearance but broad equality for the two types of chops on organoleptic properties. In shop tests a preference was shown for Piétrain-cross chops over Large Whitecross chops and those normally stocked by the shop.

1. The true availability of Cu in animal excreta and pasture dressed with excreta was assessed in three experiments from the responses in plasma Cu concentration of initially hypocupraemic ewes repleted with diets containing different Cu sources.

2. Herbage from a sward treated with Cu-rich pig slurry contained a larger proportion of available Cu than untreated herbage (0·058 v. 0·047; P<0·05, Experiment 1). Herbage Cu content was also increased from 7·3 to a maximum of 10·2 mg Cu/kg DM by slurry application.

3. Availability of Cu in dried pig slurry (DPS) and Cu sulphate was similar and lowered from 0·068 to 0·040 in both sources by increasing the sulphur content of the diet from 1 g/kg in Experiment 3 to 3 g/kg in Experiment 2. Availability of Cu in dried poultry waste (DPW) was greater than that in DPS (P < 0·05).

4. Treatment with ethylene diamine tetra-acetic acid extracted 64·3 % and 78·3% of the Cu in DPW and DPS, respectively.

5. The Cu toxicity hazard associated with the recycling of animal excreta of high Cu content is discussed.

Animal Production, Volume 20, part 2, pp. 249–255

Evaluation of crossbred sows for the production of pigs for slaughter

M. H. Fahmy, W. B. Holtmann and T. M. Macintyre

In Table 3, some of the rankings shown in parentheses are erroneous. The rankings shown should be ignored and recalculated from the breed mean values.

Seventy-six pigs provided with indwelling venous catheters were exposed for 40 min to a temperature of 40°C and 100% relative humidity. Plasma 17-OHCS levels were determined during the period of stress and up to 24 hr thereafter. The results obtained were assessed in relation to backfat thickness, and eye-muscle area and appearance (Göfö value) in groups of 10 animals showing maximum and minimum values for these parameters. In all the animals the heat and humidity stress brought about an increase in the plasma levels of 17-OHCS. Significant differences were more often found in the induced 17-OHCS levels in those animals which appeared to be leaner on the basis of backfat thickness and eye-muscle area and produced poorer quality meat than in those with less lean of better quality. These results support the notion that there is increased activity of the adrenals of leaner types of pig which produce meat of poor quality.

The optimum design of genetic controls is considered with respect to several factors, such as a fixed total expenditure, differing costs for males and females, different plans for retaining parents and choosing replacements, the value of keeping spares and the effects of mortality and infertility among individuals in the control.

The effects of mortality and infertility are important for these will tend to reduce the annual effective size and lower the optimum age for replacement of parents. Keeping individuals to a fixed age, without spares, will usually be preferable in practice to the lifetime retention of parents with spares, since spares will be at the expense of other breeding animals. It is shown that with the same total expenditure, the annual effective size of a control may be substantially increased by the appropriate choices among the various factors studied and methods are given for finding the optimum design.

Expressions are given for the variance of estimates of breed differences for direct and indirect comparisons among foreign breeds, using either purebreds or crossbreds. These expressions allow for planned genetic relationships among the groups tested.

Ventilation rates of 0·14, 0·42 and 0·71 m3/min per pig (2·3, 6·9 and 11·5 air changes per hour) were compared at weight ranges from 42 to 65 kg and from 69 to 88 kg and at optimum ambient temperature and at 8°C above optimal. A total of 96 pigs was used, housed so that gases from manure decomposition were present. Growth rate and food conversion were not affected by ventilation rates, but food intake was significantly lower at the lowest ventilation rate compared with the other two rates at the hotter temperature only. The odours and gases at the lowest ventilation rate were such that attendants strongly objected to them.

A total of 177 sows representing five two-breed crosses were used in a 2×2 factorial experiment to study the effects of post-weaning stress (changing environment and group housing) and feeding regime (flushing by feeding ad libitum until mating) on the weaning-oestrus interval and other reproductive traits up to 30 days of pregnancy.

The group which was stressed had about 10% (P<0·05) fewer reproductive failures than those not stressed, while little difference was found between the two feeding regimes. About 61% of the flushed sows returned to oestrus within 7 days after weaning, 9% higher than for those not flushed. The stress treatment had little effect on the weaning-oestrus interval. Neither treatment affected ovarian and follicular-fluid weights, percentage of follicles of different sizes, ovulation rate nor number of viable embryos. The flushed group, however, had 9% lower embryo survival than the group not flushed. A positive relation was found between the number of days on ad libitum feeding and ovulation rate and embryonic mortality.

Differences among breeds were significant for all the traits, except weaning-oestrus interval, weight of follicular fluids, percentage of large follicles, ovulation and survival rates. The weaning-oestrus interval was not significantly correlated with any of the reproductive traits studied.

An experiment was conducted to study the post-weaning response of young pigs to a flavouring substance (Firanor No. 3) designed to be incorporated into the sow's milk if added to her diet during lactation. During the first 3 weeks after weaning the average feed intake and growth rate of all pigs were 0·755 kg/day and 0·385 kg/day respectively. The average feed intake and growth rate of pigs weaned from sows given a flavoured diet during lactation and subsequently offered a flavoured weaner diet were 0·818 kg/day and 0·450 kg/day respectively, each significantly greater than the corresponding results for pigs which had no previous experience of the flavouring or which had access to flavoured feed in only one period.